1
The effect of quantitative feed restriction on growth performance, carcass characteristics and selected meat quality parameters in broiler chickens
By Siphelo Velele
A dissertation submitted in fulfillment of the requirements for a Master of Science
(Agriculture) degree in Animal Science Department of Livestock and Pasture Science
Faculty of Science and Agriculture
Alice, South Africa
5700
ii Declaration
I, Siphelo Velele, declare that this dissertation has not been submitted to any other University
and that it is my innovative work conducted under the supervision of Prof V. Muchenje. All
assistance towards the production of this work and all the references contained herein have been appropriately acknowledged and accredited.
Signature: _____ _______ Date: 26-10-2017……
Siphelo Velele
Signature: ____ ___ Date: ______26-10-2017____
iii General notes
The dissertation is presented in the format prescribed by the Department of Livestock and Pasture Science at the University Of Fort Hare. The structure of this dissertation is designed such that it has several chapters and is preceded by an introduction chapter, objectives, literature review, two different chapters and general discussion and conclusion chapter.
To the best of my efforts, references, language and style format employed in this dissertation comply with the requirements of the Department of Livestock and Pasture Science, housed in the Faculty of Science and Agriculture. Currently, a publishable manuscript is being prepared for submission to a journal.
Conference presentation (s):
Velele, S and Muchenje, V. The effect of quantitative feed restriction on growth performance,
internal organs and carcass characteristics of broiler chicken. Paper orally presented on the 49th
South African Society for Animal Science Congress in Stellenbosch, South Africa, 3-6 July 2016.
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Acknowledgements
I owe sincere thankfulness to His highness, Jehovah-Nissi, Jehovah-Jireh, Almighty, His Excellency God the Father, and the Holy Spirit. It is with great pleasure that I have to thank my one and only supervisor, Indoda yasemamfeneni, ulisa, ujambase, Prof V. Muchenje. I am so thankful for his guidance and expertise rendered throughout the duration of my studies.
To the administration office and technical services, Ms. N Moko, Ms. S Sokanyile, and Mr. D Pepe; thank you so much for your technical and moral support. My Hon., MSc and PhD colleagues ‘the data collection team’ who helped sharpened knives, boiled water, slaughter and analysed all meat samples. I don’t want to single out individuals but I believe they know themselves. God bless you!! Nangamso zicaka zenkosi. Mr. Mapfumo and John Ntilini, I would also like to thank you for helping me analyse my data. I am thankful to the poultry team for the exciting and outstanding exchange of ideas. Let me thank, Mr. Mapfumo, Mrs. Dzviti, Melody, Dr. A Chulayo, Mr. Ntilini, Mr. Mazizi, Mr Chika, Dr. Falowo and Chika Oyeagu for reviewing my work. Special thanks are given to my late parents and the entire Velele and Dyonase family. My brothers and sisters provided an indescribable and outstanding moral support. I also owe my girlfriend and friends, both at the university and at my hometown for their love and support. The Department of Livestock and Pasture, housed in the faculty of Science and Agriculture and University of Fort Hare community at large, thank you so much for this opportunity. Lastly, the National Research Foundation (NRF) for monetary support towards my studies. Again, I would like to thank the following teams; Prof V. Muchenje research group, Livestock and
Pasture Department, GMRDC and DST-NRF for their support towards a paper presented on 3-6
v Abstract
Growth performance, carcass characteristics, pH and meat colour in broiler chicken subjected to quantitative feed restriction
The study investigated the effects of quantitative feed restriction on growth performance, carcass characteristics, internal organs, breast muscle pH and meat colour in broiler chickens. A total of 90, un-sexed, day-old broiler chicks were procured from an accredited supplier and were used for the current trial. For the first 14 days, all birds were brooded in one house and subjected to a uniform day-to-day management. Water was supplied throughout the trial, whereas, feed was
only supplied ad libitum between days 1-14 and 29-35 days in feed restricted birds. Feed phases
included starter (1-14 days), grower (15-28) and finisher (29-35), respectively. On day 15, birds were randomly allocated to three treatments; each treatment was replicated three times with 10
birds per replicate. The first treatment (T1) group, which acted as control group, was ad libitum
feeding for the whole trial duration (1-35 days). For treatments 2 (T2) and 3(T3), 85% and 70% of the Cobb 500 broiler feed intake standards were applied for a period of 14 days (days 15-28), respectively. Average daily feed intake (ADFI) was determined daily and then average body weight (ABW) was determined weekly. Feed conversion ratio and average daily weight gain was thus computed for each experimental unit (replicate). On day 35, broiler birds were electrically stunned and slaughtered by a sharp knife and then hung for complete bleeding. Data collected included slaughter, carcass, breast, thigh, wing, drumstick, feet, head, spleen, heart, gizzard, intestines (small & large) and liver weights. Breast muscle was further used for the determination of colour (L*, b* and a*), initial (pHi) and ultimate breast pH (pHu) measurements. Although, quantitative feed restriction (T2 & T3) significantly affected growth performance in weeks 3 and 4, birds submitted to T2 performed similar (P>0.05) to control in the final stage, whilst birds in
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T3 was the poorest (P<0.05). Furthermore, birds subjected to T2 showed no differences of edible carcass portions to the control, however, T3 group showed lower (P<0.05) slaughter and wing weights. Breast ultimate pH values of birds under T2 were similar to control, but birds in T3 had significantly higher (P<0.05) values. Birds under T2 had less (P<0.05) reddish breast meat colour than control at 45 minutes. At 24 hours post-mortem, birds in T3 had lower (P<0.05) lightness values and birds submitted to T2 had higher (P<0.05) yellowness values. Liver weight was significantly lower in birds under T3 and higher (P<0.05) gizzard weights were found in birds subjected to T2. Birds under T2 performed similar to control and were able to compensate for the weight loss when high plane of feed was re-introduced. It can be concluded from the results that restricting 15 % of feed from Cobb 500 standard feed intake had moderately affected broiler performance. Moreover, restricting 15% of feed significantly reduced feed intake in broiler chicken.
Key words: Quantitative feed restriction, broiler chicken, Cobb 500, carcass characteristics, internal organs growth performance, pH and Colour
vii Table of contents
Declaration ... ii
General notes ... iii
Acknowledgements ... iv
Abstract ... v
List of abbreviations ... x
Chapter 1: Introduction ... 11
1.1 Background of the study ... 11
1.2 Problem statement ... 13
1.3 Justification ... 14
1.4 General objective ... 15
1.5 Hypothesis... 15
1.6 References ... 17
Chapter 2: Literature review ... 21
2.1 Introduction ... 21
2.2 Feed restriction ... 22
2.3 Feed restriction methods ... 22
2.3.1 Physical feed restriction ... 22
2.3.2 Skip a day restriction... 23
2.3.3 Diet dilution ... 23
2.3.4 Use of low protein or low energy diet ... 24
2.3.5 Chemical methods ... 24
2.4 Compensatory growth in broiler chicken ... 25
2.5 Genetic and sex effect ... 26
2.6 Meat quality attributes of broiler chicken ... 26
2.6.1 Meat quality ... 26
2.6.1.1 Meat colour ... 27
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2.6.1.3 The pH of broiler meat ... 28
2.6 References ... 30
Chapter 3: Effect of quantitative feed restriction on growth performance and carcass characteristics of broiler chickens ... 35
Abstract ... 35
3.1 Introduction ... 37
3.2 Materials and methods ... 39
3.2.1 Study site ... 39
3.2.2 Experimental treatments and diets ... 39
3.2.4 Growth performance ... 41
3.2.5 Slaughter procedure ... 42
3.2.6 Dressing percentage ... 42
3.3.1 Growth performance ... 44
3.3.2 Carcass characteristics ... 48
3.4 Conclusion and recommendations ... 51
3.5 References ... 52
Abstract ... 59
4.1 Introduction ... 61
4.2 Materials and methods ... 64
Animal management, housing, diets and treatments ... 64
4.2.1 Internal organs determination ... 65
4.2.2 Meat pH ... 65
4.2.3 Meat colour ... 65
4.2.4 Statistical analysis ... 66
4.3 Results and Discussion ... 67
4.5 References ... 75
Chapter 5: General discussion, conclusion and recommendation ... 81
5.1 General discussion ... 81
ix List of tables
Table 1: Feed specification of the three phase diets that was fed to
chickens……….…………28
Table 2: The effect of feed restriction on growth performance parameters in broiler chickens
(The data is expressed on weekly
bases)…...33
Table 3: The effect of quantitative feed restriction on carcass characteristics and body parts of broiler chicken………49
Table 4: Quantitative feed restriction on internal organs and breast muscle pH and colour of broilers………..49
x
List of abbreviations ADG Average daily gain
FCR Fed conversion ratio
ABW Average body weight
ADFI Average daily feed intake
pHu Ultimate pH
pHi Initial pH
CW Carcass weight
SW Slaughter weight
Dressing % Dressing percentage
L* Lightness of meat
b* Yellowness
a* Redness
T1 Treatment 1 (Control)
T2 Treatment 2 (85% of Cobb 500 standard daily feed intake)
11 Chapter 1: Introduction
1.1 Background of the study
Growth performance of broiler chicken has been increasing over the last 50 years (Sahraei, 2014). This can be justified by the fact that modern broiler chickens take less than 35 days to reach a market weight of 2 kg (Wilson, 2005). Gunasekar (2007) and Sahraei (2012) suggested that each year, an improvement of 40-50 g on mature weight was observed and according to Cresswell (2007) this could double in the near future. Wilson (2005) claims that this high growth rate is due to constant selection, nutritional improvements, and controlled environment. Sahraei (2014) added that this improved growth rate is due to early life rapid growth rate, which subsequently leads to higher growth performance latter stage. Thus, today broiler industry is supplied with flocks that reach market weight for slaughter in shortest possible time.
Unfortunately, high growth rates and high consumption rates result in undesirable selection responses. Fast growth has been generally associated with increased body fat deposition, high incidences of skeletal problems, metabolic disorders and high mortalities (Yu and Robinson,
1992; Lesson and Zubair, 1997; Scott, 2002; Rezaei et al., 2006). In a modern production
system, broiler chickens are allowed free access to feed and water, such that they consume energy beyond their maintenance requirements and deposit excess as fat (Fantana et al., 1992; Cuddington, 2004). Fat is an undesirable and uneconomical product associated with many problems. These include feed inefficiency, lameness, metabolic disorders, and difficulties in meat processing and meat rejection by consumers citing danger to health (Urdenta-Rincon and Leeson, 2002).
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Feed restriction has been employed to improve feed utilisation, trigger compensatory growth and reduce fat deposition in broiler chickens (Teimouri et al., 2005). This is achieved by reducing maintenance requirements of birds and provoking compensatory growth in grower and finisher phase. It can be defined as the phenomenon where birds are denied free access to nutrients that
are needed for growth and development (Khethani et al., 2009). Currently, it is used to address
metabolic disorders, skeletal problems, and deaths, but this is achieved through compensatory growth (Fisher, 1984; Sahraei, 2012). Compensatory growth is an enhanced growth rate during refeeding after a period of feed deprivation. According to Tolkamp et al. (2005), a temporary reduction in the basal metabolic rate of feed in restricted broilers occurs and results in less energy required for maintaining body weight.
When manipulating feed restriction regimes, it is important to measure traits such as live weight, carcass characteristics, and meat quality. According to INRA (2008), live weight in same aged broilers can affect meat quality properties and carcass composition. The differences in growth
rates can explain subsequent differences in post-mortem metabolism. Tougan et al. (2013) could
not agree more with INRA (2008) findings that showed heavier chickens had lower ultimate pH, high drip loss, redder breast meat, lower yield and lower intramuscular fat.
There is potential to reduce production costs, in particular, feed costs through growth curve manipulation, although not captured in the present study. High prices, scarcity and competition
of human and livestock for conventional energy and protein sources (Nji et al., 2002), have
resulted in smallholder broiler producers cutting costs. Smallholder broiler producers are
struggling with feed costs and this threatens the emerging businesses’ sustainability (Khethani et
al., 2007). Therefore, applying feed restriction on broiler birds which results to a period of slow
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benefit includes lean carcass, reduced feed intake, and reduced maintenance costs. Hence, the current study strives to determine the effect of quantitative feed restriction on growth performance, carcass characteristics and meat quality of broiler chicken.
1.2 Problem statement
In general, increased growth rate in modern broiler chicken caused by constant selection, feed manipulation, and environmental control has resulted in undesired responses such as increased carcass fat, high mortalities, high incidences of leg problems, ascites and metabolic disorders like sudden death syndrome (SDS) (Marks, 1979). These problems are commonly associated with broiler chickens that are fed ad libitum (Nir et al., 1996).
In particular, broiler chickens have a high capacity to consume feed with energy content that is 2 to 3 times more than energy required for maintenance (Boekholt et al., 1994). This being the case, it said to be one of the major contributors of high-fat deposition and can be modified by nutritional manipulation (Kessler, 1999). High-fat deposition further results into problems of
metabolic disease, poor meat quality, poor carcass quality and mortalities in ad libitum fed
broiler chickens.
Furthermore, the effects of early feed restriction are still inconclusive with some studies supporting reduction in feed intake reduced carcass fat and improve protein deposition (Nielsen
et al., 2003; Omosemi et al., 2014), whilst other studies contradict these findings (Zhan et al., 2007; Khethani et al., 2009). Similarly, the effects of feed restriction on carcass edible portion weights/yield are not conclusive.
14 1.3 Justification
Therefore, feed intake/unit weight gain can be restricted to increase the net profit of the producer and produce carcasses with lower fat content which realize healthy nutrition for human consumption. This can be achieved by restricting the quantity of feed the birds consume per day. In the proposed study, birds will be re-introduced to high plane of feed to compensate for the weight lost during feed restriction period and reached market weight at the same time as full-fed birds. There if potential to feed broiler chicken to optimise feed conversion ratio and daily gain without additional inputs. Feed restriction is more likely to reduce high growth rate related
Poultry production in South Africa can play a role in poverty alleviation and in the supply of quality protein to rural dwellers (Pedersen, 1998). Broiler production is a potential business for rural dwellers and to some extent, start-up business people. This is merely because of high demand for chicken meat, one can achieve fast profits over invested capital, it is relatively low input capital and general small production scale make it a potential business for rural dwellers in the developing world. Feed restriction has been used over the years to reduce growth rates and
also change the body composition (McMurtry et al., 1988). It is now known that high growth
rates in modern broilers are marked by rapid post-hatch growth. There is potential to control feed intake and growth curve by means of reducing feed intake. There is limited information on the use of quantitative feed restriction during middle age on growth performance, carcass characteristics and meat quality of broiler chicken. Feed restriction on time regime has failed to reduce feed intake in broiler chicken.
15 1.4 General objective
The main objective of the study was to find whether/not feed costs can be reduced without significant effect on performance and carcass characteristics and meat quality compared to birds fed ad libitum.
Specific objectives
To determine the effect of quantitative feed restriction on feed intake, live body weight,
average daily gain, feed conversion ratio, carcass weight, dressing percentage, thigh, wing, breast, drumstick, head and feet of broiler chicken
To determine the effect of quantitative feed restriction on gizzards, heart, livers, spleen,
intestines (both small and large), breast pH and colour of broiler chicken
1.5 Hypothesis Null hypothesis
Quantitative feed restriction has no effect on feed intake, live body weight, average daily
gain, feed conversion ratio, carcass weight, dressing percentage, thigh, wing, breast, drumstick, head and feet of broiler chicken
Quantitative feed restriction has no effect on gizzards, heart, livers, spleen, intestines
(both small and large), breast pH and colour of broiler chicken
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Quantitative feed restriction has an effect on feed intake, live body weight, average daily
gain, feed conversion ratio, carcass weight, dressing percentage, thigh, wing, breast, drumstick, head and feet of broiler chicken
Quantitative feed restriction has an effect on gizzards, heart, livers, spleen, intestines
17 1.6 References
Boekholt, H. A., P. H. Vandergrintein, P.H., Scherurs, V.V.A.M., Los, M.J.N and C. P. Leffering, C.P. 1994. Effect of dietary energy restriction on retention of protein, fat and
energy in broiler chickens. Britain Poultry Science, 35: 603–614.
Cabel, M.C. and Waldroup, P.W. 1990. Effect of different nutrient restriction programs
early in life on broiler performance and abdominal fat content. Poultry Science, 69: 652-660.
Cresswell, D. 2007. ”Feeding the broiler”. Asian Poultry Magazine, 1: 20-23. Retrieved from: http://www.epu.edu.krd/journal/documents/20160229_030555.pdf. [Accessed: 30 may 2016].
Cuddington, S. 2004. High energy diets affect broiler chicken welfare. http://www/facs.sk.ca/pdf/animal_care_award/articles_2004/cuddington_chickens.pdf. [Accessed: 12 June 2016].
Fantana, E.A., Weaver, B.A., Watkins Jr., B.A. and Denbow, D.M. 1993. Early feed restriction of broilers: effects on abnormal fat pad, liver and gizzard weights, fat deposition
and carcass composition. Poultry Science, 72: 243-250.
Fisher, C. 1984. Fat deposition in broilers. Pages 437-470 in: Fats in Animal nutrition. J. Wiseman, ed. Proc, Easter School in Agricultural Science, University of Nottingham (37th), Butterworth, London, UK.
Gunasekar, K.R. 2007. Formulating feeds for broiler performance. Avian technology and Animal Health. http://www.thepoultrysite.com/articles/560/formulating-feed-for
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Kessler, A. M. 1999. Food programs to optimize the deposition of meat and fat in broiler
carcasses. In: Ribeiro, A.M.L., Benerdi, M.L., Kesler, A.M (Eds.) Topics in animal
production 1 Porto Alegre Federal University of Grande Do Sol, pages 183-199.
Khetani, T.L., Nkukwana, T.T., Chimonyo, M. and Muchenje, V. 2009. Effect of feed
restriction on broiler performance. Tropical Animal Health Production, 41: 379-384.
Leeson, S. and Zubair, K. 1997. Nutrition of the broiler chicken around the period of
compensatory growth. Poultry Science, 76: 992-999.
Marks, H.L. 1979. Growth rate and feed intake of selected and non-selected broilers.
Growth, 43: 80-90.
McMurtry, J.P., Rosebrough, R.W., Plavnik, I. and Cartwright, A.I. 1988. Influence of early plane of nutrition on enzyme systems and subsequent tissue deposition. pp.: 329-341. In: Biomechanisms Regulating Growth and Development (G. L. Steffens and T. S. Rumsey,ed). Betsville Symposia on Agricultural Research, Klumer Academic Publishers, Dordrecht, the Netherlands.
Nielson, B.l., Litherland, M. and Noddegaard, F. 2003. Effect of qualitative and
quantitative feed restriction on the activity of broiler chickens. Applied Animal Behaviour
Science, 83: 309–323.
Nir, I., Nitsan, Z., Dunnington, E.A. and Siegel, P.B. 1996.Aspects of food intake in young
domestic fowl: Metabolic and genetic considerations. World Poultry Science Journal, 52:
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Omosebi, D.J., Adeyemi, O.A., Sogunle, M.O., Idowu, O.M.O. and Njoku, C.P. 2014. Effects of duration and level of feed restriction on performance and meat quality of broiler
chickens. Architecture of Zootechnology, 63: 611–621.
Poltowicz, K., Nowak, J and Wojtysiak, D, 2015. Effect of feed restriction on performance,
carcass composition and physicochemical properties of the M. pectoralis superficialis of
broiler chickens. Annals of Animal Sciences, 15: 1019-1029.
Rezaei, M., Teimouri, A., Pourreza, J., Syyahzadeh, H. and Waldroup, P.W. 2006. Effect of diet dilution in the starter period on performance and carcass characteristics of
broiler chicks. Journal of Central European Agriculture, 7: 63–70.
Sahraei, M. 2012. Feed restriction in broiler chicken production: A review. Global Veterinaria, 8: 449-458.
Sahraei, M. 2014. Effects of feed restriction on metabolic disorders in broiler chicken: A
review. Research Journal of Biological Sciences, 9:154-160.
Scott, T.A. 2002. Evaluation of lighting programs, diet density and short-term use of mash as compared to crumbled starter to reduce the incidence of sudden death syndrome in broiler
chicks to 34 days of age. Canadian Journal Animal Sciences, 82: 375-383.
Teimouri, A., Rezaei, M., Pourreza, J., Sayyahzadeh, H. and Wladroup, P.W. 2005. Effect of diet dilution in the starter period on performance and carcass characteristics of
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Tolkamp, B.J., Sandilands, V., Kyriazakis, I. 2005. Effects of qualitative feed restriction
during rearing on the performance of broiler breeders during rearing and lay. Poultry
Science, 84: 1286–1293.
Urdenta-Rincon, M. and Leeson, S. 2002. Quantitative and Qualitative feed restriction on
growth characteristics of male broiler chicken. Poultry Science, 81: 769-788.
Wilson, M. 2005. Production focus In; Balancing genetics, welfare and economics in broiler
production. 1: 1. Publication of Cobb-Vantress, Inc.
Yu, M.W. and Robinson, F.E. 1992. The application of short-term feed restriction to broiler
chicken production: A review. Journal of Applied Poultry Research, 1: 147-153.
Zhan, X.A., Wang, M., Ren, H., Zhao, R.Q., Li, J.X., and Tan, Z.L. 2007. Effects of early feed restriction on metabolic programming and compensatory growth in broiler chickens.
21 Chapter 2: Literature review
2.1 Introduction
The poultry industry in South Africa has progressed over the years from practicing a backyard form of production, where people keep small flocks and a few large producers, to a more mature, efficient and highly productive commercial production (SAPA, 2012). In 2012, broiler meat production was the largest sector of South African agriculture amounting to 17%, which is, 1.7% of the total gross value of agricultural products (DAFF, 2013). Consequently, South African broiler meat production accounts for 80% of the total poultry meat production in the country. It is produced throughout the country with North West, Western Cape, Mpumalanga and Kwazulu-Natal being the largest producers (DAFF, 2011).
Poultry production, particularly poultry meat has increased over the past years as a result of increased consumption rate of leaner meat. Human demand for poultry meat remains high due to population growth, better incomes (making chicken meat affordable) and urbanization (FAO, 2012). That being the case, scientists are tasked to sustain improved growth characteristics, carcass quality and meat quality of broiler chicken. Improved feed efficiency will result to enhanced quality carcasses and is likely to attract more consumers at the point of purchase. This could also reduce fat deposition because it is a poor meat quality indicator; by possessing more saturated fatty acids and high cholesterol levels that are associated with diabetes mellitus and cardiovascular diseases in Western Societies (Micha et al., 2010). According to Nielsen et al. (2003), feed restriction could help reduce feed intake, fat deposition, whilst improving carcass protein deposition and meat quality.
22 2.2 Feed restriction
Feed restriction is essentially denying broiler chickens a full access to feed/nutrients as required
by the body for growth and development (Khethani et al., 2009). Other studies describe feed
restriction as a management strategy that is used in industry to reduce feed intake, so as to control bird’s growth and subsequently, reduce incidences of metabolic diseases, skeletal problems, and fat deposition and improve feed utilisation through compensatory growth phenomenon (Zulkifli et al., 1993; Thompson et al., 2008; Benyi et al., 2010: Sahraei, 2012).
Balley et al. (1992) added that feed restriction in poultry production involves duration, stage and
amount of feed restriction to determine whether or not the birds will catch up during final stage.
2.3 Feed restriction methods
Generally, feed restriction is classified as either qualitative, that is diluting the nutrient content of the diet and quantitative feed restriction, which is limiting the amount of feed given to animals on a daily basis (Leeson and Zubair, 1997). These methods include skip-a-day feeding (limiting the level of feed consumption by in time) or reducing the time of illumination of feeding and physical feed restriction (Religious et al., 2001). Diet can also be diluted or supplied with low protein or low energy diets and/or restricted by chemical means (Zubair and Leeson, 1996). In this study, the focus was shifted to quantitative feed restriction, which is limiting the amount supplied to birds per day.
2.3.1 Physical feed restriction
Physical feed restriction is one of the most used procedures to control feed intake during starter, but, few studies focused on grower phases of the bird’s cycle. It is thought to provide
well-23
deserved, calculated amount of feed per bird that is normally enough to meet maintenance requirements (Plavnik and Hurwitz, 1989). Feed restriction method in general, has been extensively studied in broiler production; however, little has been done on feeding certain proportions without withdrawal or reduced illumination (Balley et al., 1992; Khethani et al., 2009; Sahraei, 2012).
It is also referred to as quantitative feed restriction and has been reported to reduce mortality and
culling (Fontana et al., 1992). However, improved feed efficiency (Deaton, 1995) and catch-up
growth can also be observed. Provided that severity of feed restriction was not severe and the period was more than 6 weeks (Plavnik and Hurwitz, 1988). The current study also takes into account the new developments in broiler chicken industry such as rearing period of around 35 days and the study should be studied in the relevant rearing period.
2.3.2 Skip a day restriction
This type of method is not well studied in broiler chickens as compared to others mentioned in this study. Skip-a-day is the technique for restricting early growth by essentially removing the
feed troughs to deprive birds feed (Dozier et al., 2002; Sahraei, 2012). Feed is normally removed
for 8-24 hours during starter phase feeding and is known to reduce early fast growth and meat yield in broiler chicken (Sahraei, 2012). Oyedeji and Atteh (2005), confirmed these findings in the study conducted and reported a skip-a-day method to reduce early life growth. In addition, improved carcass quality and reduction in sudden death syndrome was noted after skip-a-day feeding for 3 weeks.
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This is one of the qualitative methods and involves mixing of the diets with non-digestible ingredients like fibre, subsequently reducing the nutrient density (Sahraei, 2012). Reduced body fat deposition has been commonly reported in diet dilution or physical studies, although there are variations. In one experiment, rice hulls were used to retard early growth. Findings revealed a reduced growth rate when diluting 50 to 65% of rice hulls (Jones and Farrell, 1992). According to Sahraei (2012), this technique appeared to be successful although the birds consumed more feed, the adjustment was not enough to normalize nutrient intake, and growth rate was reduced.
2.3.4 Use of low protein or low energy diet
Low energy and/or low protein concentrations in diets are employed in broiler production to retard growth rate in the early life of broiler chicken. In normal circumstances, broiler chicken is fed diets containing 18%, 20%, and 22% crude protein, respectively, in the order of finish, grower and starter, and also 3200 kcal ME/kg diet (National Research Council, 1994). It was observed that, birds fed low nutrient contents tend to consume more feed in an attempt to meet
up with the body needs. In contrast, birds fed ad libitum with 9.4% crude protein from days 8 to
14, lower feed intakes were observed and their weight gains to be approximately 57% and 41%, accordingly (Plavnik and Hurwitz, 1990).
2.3.5 Chemical methods
Chemicals or pharmacological agents like physical methods can be employed in broiler production to reduce feed intake. Chemical method of restricting feed is known to possess an advantage over physical feed restriction as it allows minimal variation among flocks and this is due to its ability to distribute feed equally to all birds in a group (Sahraei, 2012). The inclusion of 1.5% glycolic acid as an anorectic agent between days 7 to 14 severely reduced feed intake in
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broiler chicken. It also reduced body weight by 22%, and an increment of up to 3% inclusion further reduced weights by 50% (Pînchasov and Jensen, 1989). Moreover, the use of 50 g per kg of calcium propionic acid to suppress appetite was found to complement weight gains obtained from a recommended program of quantitative feed restriction for female breeders in the ages
between 2 to 6 weeks of age (Savory et al., 1996).
2.4 Compensatory growth in broiler chicken
The growth compensation or catch-up growth is defined by Zhan et al. (2007) and Sahraei
(2012), as the abnormally vigorous growth rate in broiler chicken after they have been subjected to a period of low nutrient density or low amount of feed and followed by a sudden high nutrient density. Mechanisms involved in the process of compensatory growth have been well studied (Wilson and Osbourn, 1960; Pitts, 1986), and two hypotheses that are thought to govern, are peripheral control hypothesis and central control hypothesis (Zubair and Leeson, 1996). According to Pitts (1986), peripheral control hypothesis suggests that tissues where cell number or, DNA, determines the extent of growth that follows a period of under-nutrition or illness are said to control the body size. On the other side, central control hypothesis postulates that for a particular age there is a set body size and that this control is housed in central nervous system (Wilson and Osbourn, 1960).
Animals, in particular, broiler chicken, can possibly respond in four ways during compensatory growth. Broiler chickens, when subjected to re-feeding, can either result in reduced mature size; re-grow partially, completely or nothing at all. In turn, these four responses mentioned above depend on the duration, timing, severity, nature of feed restriction and condition of re-alimentation (Sahraei, 2012). Feed restriction, especially nutritional deprivation was reported by
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Pitts (1986) to affect the DNA size, but not the number, such that during re-feeding the broiler chicken would be capable of gaining the desired size with respect to age. According to Benscho (2000), the efficiency of growth decreased maintenance costs and in other cases increases digesta load.
2.5 Genetic and sex effect
Generally, male broiler chicken have greater growth rate, leaner body and possess more capacity to compensate growth compared to female broiler chicken (Plavnik and Hurwitz, 1991; Santoso
et al., 1993). Some authors reported that, male broiler chickens exhibit greater compensatory
growth following a period of undernutrition than female broilers (McMurty et al., 1988; Plavnik
and Hurwitz 1991). Although that is the case, one needs to be educated about the fact that genetics of an animal play a considerable role than sex of the bird in feed restricted broilers. Genetics affect the nutritional requirement of broiler chicken and therefore influence the bird’s response to feeding restriction. Havenstein et al. (1993) confirm the importance of genetics by observing that genetic potential rather than nutrition affects the body composition of broiler chicken.
2.6 Meat quality attributes of broiler chicken 2.6.1 Meat quality
Meat quality, according to FAO (2014), is defined as the compositional quality (lean to fat ratio) and the sensory factors including firmness, juiciness, tenderness, visual appearance, smell, and flavour. As perceived by the consumers, the nutritional quality of meat is objecting, however,
27
determined by a combination of the sensory, chemical and lean carcass (better fat or muscular portions).
Meat quality can be further described on whether one is a producer, at abattoir, processor,
wholesaler or consumer. Bogosavljevic-Boskovic et al. (2010) added that aspects such as carcass
conformation, good sensory, aesthetic and nutritional characteristics must be assessed when evaluating for meat quality. Notable progress has been made in producing broilers with high growth rate, however, few studies have successfully reduced carcass fat. Furthermore, disincorporation of meat quality parameters subsequently resulted in meat muscle abnormalities
such as ‘Dark, Firm and Dry’ and pale, soft and exudative muscles (Souza et al., 2011).
2.6.1.1 Meat colour
Colour is an important physical property that influences the consumer’s purchasing decision for poultry products and assessment of product quality (Fletcher, 2002). It is determined in terms of the Hunter colorimetric coordinates with b*, a*, and L* (Kannan et al., 2001). Simela (2005) describes coordinate b* to represents yellowness and ranges from -60 (blue) to +60 (yellow), a* refer to how red is the meat and ranges from -60 (green) to +60 (red), lastly, coordinate L* stand for lightness and ranges from 0 (all light absorbed) to 100 (all light reflected).
Meat colour is very important so much that consumers get their first impression of the colour and is dependent on myoglobin. Myoglobin (consisting of a protein portion and non-protein porphyrin ring with a central iron atom) is a water-soluble protein that stores oxygen for aerobic metabolism in the muscle. Moreover, the defining factors of meat including the oxidative state of the iron (a vital player in meat colour), antioxidants present in the muscle, composition and
28 2.6.1.2 Factors affecting meat colour
A number of factors affect meat colour, some of which are ultimate pH, cooling rate,
Intramuscular fat, moisture content, muscle fibre and myoglobin (Muchenje et al., 2008). Colour
in fresh and processed poultry products is affected by sex, age, genotype, nutrition, pre- and post-slaughter handling and associated conditions especially time and temperature of live animals, packaging and processed products. These conditions can also affect processing variables associated with those products like ingredient selection and utilisation. It also includes processing technologies used and meat condition before processing (Kropf, 2008). Colour causes immediate positive or negative psychological responses in consumers and can subsequently have implications on economic gains of the poultry industry.
2.6.1.3 The pH of broiler meat
Colour of meat is affected by a variety of factors ranging from genetics to feed. To a large extent, meat quality is further influenced by ultimate pH. That is the rate and extent at which the muscle
pH declines after slaughter (Van Laack et al., 2000; Muchenje et al., 2009).
Post-mortem pH fluctuations contribute enormously to poultry meat quality. The increase or decrease of the ultimate pH of meat is dependent on lactic acid and glycogen levels in the muscle. The meat will either be pale, soft and exudative (PSE) or dark, firm and dry (DFD) (Zhang et al., 2010) It is, therefore, key in controlling the functional qualities of meat that has rapid pH decline and those are linked to quality defects like PSE (pale, soft and exudative)
syndrome (Castellini et al., 2008). This pH affects meat colour dramatically and a proven
29
Souza et al. (2011), postulates that the ultimate pH was found to directly affect the capacity of
myoglobin in expressing the red colour and the stability to bind water in the meat. Normal muscle pH at slaughter is approximately 7, however, glycolysis exhausts pH in the muscle and the pH ultimately declines to 5.8-5.4 over 24 hour period after slaughter (Heinz and Hautzinger, 2007). The glycolytic enzyme activity and glycogen reserves present determine the post-mortem
muscle pH decline and ultimate pH respectively (Fanatico et al., 2007).
Considering the glycolytic process (measurement of pH decrease 1 h p.m.), pH1-value provides the best information. Highly accelerated (pH1<5.6) as well as accelerated pH-decline (pH1 5.6-5.8) are related to a light meat colour and a poor juice retention, which in the majority of cases is the same for pH1-values ranging from 5.8 to 6.0 concerning exudative meat composition (Conley et al., 2001).
30 2.6 References
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Dozier, W.A., Lien, R.J., Hess, J.B., Bilgili, S.F., Gordon, R.W., Laster, C.P. and Vieira, S.L. 2002. Effects of Early Skip-a-Day feed removal on broiler performance live performance
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Leeson, S. and K. Zubair, 1997. Nutrition of the broiler chicken around the period of
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Marusich, W. L., DeRitter, E., Ogrinz, E. F., Keating, J., Mitrovic, M. and Bunnell, R. H. 1975. Effect of supplemental vitamin E in control of rancidity in poultry meat. Poultry Science. 54:831–844.
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and Bonsmara steers raised on natural pasture. Animal. 2: 1700-1706.
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quantitative feed restriction on the activity of broiler chickens. Applied Animal Behaviour
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Plavnik, I. and S. Hurwitz, 1989. Effect of dietary protein, energy and feed pelleting on the
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feed efficiency and body composition. Poultry Science, 67: 1407-1413.
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development of table fowl. Animal Production Sciences, 14: 219-230.
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34
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quality of broilers reared under different production systems. Brazilian Journal of Poultry
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35
Chapter 3: effect of quantitative feed restriction on growth performance and carcass characteristics of broiler chickens
Abstract
The objective of the study was to determine the effects of quantitative feed restriction on growth performance and carcass characteristics of broiler chickens. A total of 90 birds at 15 day old were randomly allocated to three treatments of 30 birds each with each treatment composed of 10 birds. In the first treatment (T1), birds were fed ad libitum throughout the experiment, and both treatments 2 (T2) and 3 (T3) was supplied with 85% and 70% of Cobb 500 standard daily feed intake, respectively. Birds in feed restriction treatments were kept for two weeks (day
15-28) and then fed ad libitum for the remaining week (day 29-35). Feed intake was determined
daily and body weight was obtained weekly, then feed conversion efficiency and average daily gain was computed. On day 35, 24 broilers were randomly picked from each treatment (total of 72 birds) for slaughter. Birds were sacrificed to determine slaughter weight, carcass weight, carcass edible portion weights, head, and feet. Results revealed that birds submitted to T3 feed restriction during the weeks 3 & 4 showed lower (P<0.05) body weight, average daily gain and feed conversion ratio than control. Birds under T2 showed lower (P<0.05) body weight in week 4, but, all other measurements were similar (P>0.05) to control. During re-alimentation, birds in T2 feed restriction consumed significantly lower (P<0.05) feed, although achieved similar final body weight with control. There was significantly lower final weight, feed conversion ratio and average daily gain in birds under T3. Furthermore, birds under T3 during final stage showed no compensatory growth evidence. Quantitative feed restriction (T2) had no effect (P>0.05) on carcass characteristics, however, birds in T3 had significantly lower slaughter and wing weights than control. It can be deduced from the results that moderate feed restriction was effective and
36
moderately affects growth performance and carcass characteristics. However, severe feed restriction has proven to retard compensatory growth and may detrimentally affect bird’s performance.
Key words: Feed restriction, broiler production, small-scale producers, growth performance and carcass characteristics
37 3.1 Introduction
Growth performance of broiler chickens has been increased intensely over the last 30 years. Owing to a controlled environment, nutritional improvements and genetic progress, broiler chickens nowadays take 33 days to reach slaughter weight of 2 kg (Boyle, 2005; Wilson, 2005). As a result, response indicators due to increased growth rates can be observed in growth patterns, carcass structure, and composition of broiler chickens. Further responses can be observed on digestion, central nervous functions, metabolism, endocrine, behaviour and immune function of
broiler chickens (Khajavi et al., 2003; Dawkins and Layton, 2012).
However, there are negative effects associated with this abnormally increased growth rate, which is principally caused by high feed intake capacity. These amongst others include, high mortalities as a result of Sudden death syndrome (Govaerts et al., 2000), ascites (Kalmar et al., 2013;
Wideman et al., 2013), cardiovascular disorders, high incidences of other metabolic disorders,
skeletal problems and high fat deposition (Leeson et al., 1991; Zubair and Leeson, 1999). Heavy
weight due to increased growth rate exerts pressure on fragile bones of legs and hips. This leads
to limb abnormalities, which in turn reduces the bird’s ability to move (Caplen et al., 2012).
Feed and feeding manipulation could affect the growth pattern and thus reduce the challenges associated with increased growth rates. In particular, apply feed restriction to reduce this ability
of broiler chickens to consume feed with energy content surpassing maintenance (Boekholt et
al., 1994). Feed restriction can be defined as a conventional strategy applied in modern broiler
breeder industry. It is known to reduce carcass fat deposition, improve reproduction efficiency
38
used, however, failed to successfully reduce feed intakes (Leeson et al., 1991; Ryan et al., 1993;
Zubair and Leeson, 1999; Khethani et al., 2009).
Feed restriction suppresses growth during restriction period and weight lost during this period
can be compensated by greater future intakes (Govaerts et al., 2000). It is vital to also point out
that there are negative effects associated with severe feed restriction or when inappropriately employed. These include, among others chronic hunger, feeding frustration, increased aggression and over-drinking of water (Savory et al., 1993). Nevertheless, more positive and neutral than
negative reports regarding the use of feed restriction have been published (Leeson et al., 1991;
Govaerts et al., 2000; Khethani et al., 2009; Sahraei, 2012).
Carcass characteristics are very important parameters to consider when evaluating alternative feeding programmes (Ledin, 1984a). Feed restriction on broiler birds does not affect carcass weight and carcass portion yields (Zubair and Lesson, 1994). It also resulted in increased sizes or weights of digestive organs (liver, gizzard, pancreas and crop) (Zubair and Lesson, 1994). Moreover, internal organs such as heart are also affected by feed restriction and re-alimentation. According to Ledin (1984b), this excludes the kidney and this can be noted by the bigger stomach.
Feed restriction is essentially employed to reduce cost (Proudfoot et al., 1983), reduce feed wastage by improving live weights, average daily gain, feed conversion efficiency, and feed intake. In this study quantitative feed restriction was used to attempt to discourage rapid feed intakes at 15 days of age. With that being said, the present study was carried out to determine the effect of quantitative feed restriction during the middle phase (15-28 days) on growth performance and carcass characteristics.
39 3.2 Materials and methods
3.2.1 Study site
The study was conducted at the University of Fort Hare, Alice campus in the Province of the Eastern Cape, South Africa. The study site is situated 520 m above sea level and is located 32.48 ° S and 26.53 ° E with an annual average rainfall of approximately 480 mm during summer in most times. The annual average temperature of the area is 18.7 °C and the area is appreciably flat with a few steep slopes.
Ethical consideration
Ethical clearance for the current study was applied for and obtained from the University Ethical clearance Committee. The ethical clearance reference number of the present study is MUC281SVEL01.
3.2.2 Experimental treatments and diets
The experiment was composed of 3 experimental treatments, the control, and two test treatments. The first treatment was T1 or control (where birds were fed ad libitum) and birds were fed throughout the cycle (1-35 days). Treatment 2 (T2) birds were fed 85% of Cobb 500 broiler feed intake standard and this amount was given from day 15 to 28. Treatment 3 (T3) birds were given 70% of Cobb 500 broiler feed intake standard and supplied for days 15 to 28. The rest of the
other days not mentioned for T2 and T3, the feed was supplied ad libitum (days 29-35). All
experimental birds were supplied with the same commercial feed; that is the starter (1-14 days), grower (15-28 days), and finisher (29-35 days). Refer to table 1 below for the feed compositions used in the current study.
40
Table 1: Feed specification of the three phase diets that was fed to chickens throughout the experiment
Nutrients g/kg (minimum) Starter Grower Finisher Protein 190 170 160 Total Lysine 12 9 9 Total methionine 5 4 4 Moisture 120 120 120 Fat 25 25 25 Fibre 50 70 70 Calcium 12 12 12 Phosphorus 6 5 5 (Source: Epol Manufacturers)
41 3.2.3 Animal housing and management
A total of 90, unsexed day-old broiler chicks (Cobb 500) were procured from an accredited supplier based in Berlin, Eastern Cape of South Africa. They were all placed in the brooding house, given water and feed immediately. All chicks were kept in one house and subjected to same routine management until day 14. On day 15 birds were randomly allocated to three treatments, namely; T1, T2, and T3.
A non-conventional, low cost poultry house consisting of three compartments was used for the experiment. All three treatments were represented in each division that had homogenous environmental conditions. The house compartments were each subdivided into three sections that were treated as an experimental unit. Each treatment received 30 birds with three replicates. All
the replicates were in groups of ten birds. Water was provided ad libitum during times of feed
restriction across all treatments. The light was also provided throughout the experiment and infrared lights were also offered during the first two weeks of chick arrival.
3.2.4 Growth performance
Three treatments consisted of three replicated each with 10 birds, making a total of 30 per treatment. A group of 10 birds in the experiment was regarded as the experimental unit. Feed was supplied to the birds every day (morning and evening) and measured according to the treatments. Every week feed intake was determined and birds weighed individually using a weighing scale but an average per pen was made. Average daily feed intake (ADFI), live body
42
weight (LW), feed conversion ratio (FCR) and average daily gain (ADG) of the birds on pen basis were recorded every week from week 3 to week 5.
ADG = (Week2 – Week1)/number of days in between the two weeks
Feed conversion ratio (FCR) was obtained by dividing average feed intake by the average daily weight
Average feed intake (ADFI) was deduced by subtracting supplied feed from the remainder before the second feeding time.
FCR = Total feed intake/ Total weight gained or average daily feed intake/weight gained
3.2.5 Slaughter procedure
At the end of the experimental period (day 36), eight birds in each experimental unit/pen were weighed for slaughter weight. This includes those groups that were regarded as replicates. All the birds were then stunned and slaughtered by a sharp knife for complete bleeding and feathers were plucked. Head, shanks, and viscera were removed and then hanged to remove excess water from the carcass.
3.2.6 Carcass characteristics
Immediately after hanging the carcass to remove excess water, carcass weight was determined using a weighing scale. The carcass weight excluded internal organs and dressing percentage was calculated thereafter: Dressing percentage = Carcass weight/Live body weight × 100. Whole carcasses were further expurgated into commercial carcass portions such as thigh, drumstick, breast and wing (Barbut, 2002).
43 3.2.7 Statistical analysis
Quantitative data for Average feed intake (ADFI), average body weight (ABW), average daily gain (ADG), feed conversion ratio (FCR), slaughter weight (SW), carcass weight (CW), dressing percentage (Dressing %), Thigh, wing, drumstick, breast, feet and head weights were analysed using a one-way analysis of variance using proc GLM of SAS (2003). The Fisher’s least significant difference method was employed to separate the means for weeks 3, 4 and 5. The mean were considered to be different at 5% significant level.
Yij = µ + Ti + Eij, where:
Yij = response variables (ADFI, LW, ADG, FCR, SW, CW, dressing %, thigh, wing, drumstick,
breast, feet and head)
µ = overall mean for the measurable variables
Ti = ith effect of feed restriction level (T1, T2 and T3)
44 3.3 Results and Discussion
3.3.1 Growth performance
The effect of quantitative feed restriction on growth performance was studied in the present study (Table 2). Birds in T2 had average body weight, average daily gain and feed conversion ratio similar (P>0.05) to control (T1) in week 3. Average daily feed intake during feed restriction (week 3) was significantly (P<0.05) different among all treatments, with birds in T3 having the lowest and control (T1) as the highest. Average body weight and average daily gain in week 3 were significantly lower (P<0.05) in birds subjected to T3, although feed conversion ratio was
higher (P<0.05). Results of the present study agree to those of Santoso et al. (1993), indicating
that lower feed intake, body weight and higher conversion ratio was found in birds fed 25% or
50% ad libitum as compared to control. The author also found significantly heavier bird weights
in birds fed 50% ad libitum for 3 days than control.
Lower body weight and average daily gain in this situation can be linked to lower feed intake. This could be due to the fact that restricted feeding stunts growth by restricting the amount of nutrients required for growth and development. Also by providing insufficient nutrients required by the birds for growth, this impairs weight gain, subsequently lower body weight. Our argument can be supported by Washburn and Bondari (1978) that body weight gain in broiler chicken can be inhibited by feed restriction. Poor feed efficiency in T3 birds can be linked to feed restriction stress in the first week of feed restriction.
In the second phase of feed restriction (Week 4), average daily feed intake followed similar pattern with week 3; that is, birds in control group (T1) had the highest (P<0.05) feed intake, followed by (T2), then (T3). As previously alluded in week 3, birds in (T2) had similar average
45
daily gain and feed conversion ratio, except average body weight, which was significantly lower (P<0.05) compared to control. Lower body weights during feed restriction were also found in other studies (Urdaneta-Rincon and Leeson, 2002; Jalal and Zakaria, 2012). Lower body weight can be explained by extended feed restriction period from day 15 to 28, which might have been slightly severe and leaving birds unable to withstand further feed restriction stress. Yu and Robinson (1992), explains that the longer is the under-nutrition period, the more difficult it is to recover from feed restriction. The recommended period for moderate feed restriction was 7 days, whilst, other studies suggest a maximum feed restriction duration of up to 14 days.
Inversely to T2, birds in T3 had significantly lower average daily gain and body weight during feed restriction in week 4. This was previously explained in week 3, stating that feed restriction impairs average daily gain and thus reduces live weight of broiler chicken (Washburn and Bondari, 1978). These results are also consistent with (Urdaneta-Rincon and Leeson, 2002 and Jalal and Zakaria, 2012). Poor feed efficiency in week 4, is consistent to that of week 3 and was
higher (P<0.05) than that of control. These results were previously reported by (Santoso et al.,
1993; Camacho et al., 2004; Jalal and Zakaria, 2012; Omosebi et al., 2014). High conversion ratios in both week 3 and 4 during feed restriction could be attributed to higher metabolic rate and the fact that most of the nutrients could be directed body functions other than converted to muscle.
During the re-alimentation period in week 5, birds subjected to T2 had significantly lower (P<0.05) average daily feed intake but similar (P>0.05) final weight compared to control (T1).
These results were also in line by those observed in other studies (Santoso et al., 1993; Dawood
and Mohammed, 2015). These could be due to slightly improved feed efficiency and average daily gain exhibited by birds in T2 that is similar (P>0.05) to control (T1) in the final stage.
46
Lippens et al. (2000) also claimed that the increased feed efficiency in feed restricted birds is caused by lowered maintenance requirements. As already stated, these birds tend to have smaller body weight prior finish stage, hence, require less to reach market weight relating age. These results could strongly suggest that feed restriction as a managerial programme promises an opportunity to reduce feed production costs and improve feed efficiency. There is evidence of partial compensatory growth in birds subjected to T2 feed restriction.
Quantitative feed restriction (T3) during re-alimentation period, significantly increased T3 bird’s feed intake to be equal to that of control (T1). This increased feed intake was also noted by Hassanabadi and Moghaddam (2006) and Sahraei and Shariatmadari (2007) in feed restricted birds. According to Naser Maheri-Sis et al. (2011), this is as a result of hypertrophy of the
gastrointestinal tract when birds are re-introduced to ad libitum feeding again. Although that is
the case, final body weight, feed conversion efficiency and average daily gain was significantly
lower compared to control (T1). These results were consistent with other studies (Khethani et al.,
2009; Jalal and Zakaria, 2012; Omosebi et al., 2014; Dawood and Mohammed, 2015).
This failure to produce similar final weight by T3 could be attributed to severity and longevity of feed restriction or rather re-alimentation period was shorter. Moreover, lower final weights could be due to metabolic programming, whereby, malnutrition leads to adult obesity (muscle is heavier than fat). It can be noted however, that T3 birds had improved feed efficiency which can be linked to reduced maintenance requirements because restricted birds tend to have smaller live
weights, and small bodied animals require small amounts of feed (Lippens et al., 2000;
47
Table 2: The effect of feed restriction on growth performance parameters in broiler chickens (The data is expressed on weekly bases)
Treatments 1 2 3
Growth parameters (g) Week 3
ADFI 530.07a ± 2.36 476.57b ± 2.36 435.23c ± 2.36 ABW 833.87a ± 28.99 778.07ab ± 28.99 745.13b ± 28.99 FCR 1.57b ± 0.02 1.63ab ± 0.02 1.71a ± 0.02 ADG 51.98a ± 4.12 43.27ab ± 4.12 38.55b ± 4.12 Week 4 ADFI 948.23a ± 2.36 809.40b ± 2.36 666.90c ± 2.36 ABW 1615.20a ± 28.99 1402.20b ± 28.99 1288.40c ± 28.99 FCR 1.70b ± 0.05 1.73b ± 0.06 1.93a ± 0.06 ADG 230.74a ± 4.12 200.31ab ± 4.12 184.06b ± 4.12 ADFI ABW FCR ADG Week 5 1220.67a ± 2.36 2086.53a ± 28.99 1.72a ± 0.04 298.08a ± 4.12 1213.23b ± 2.36 2072.27a ± 28.99 1.70a ± 0.02 296.04a ± 4.12 1219.67ab ± 2.36 1870.53b ± 28.99 1.53b ± 0.09 267.22b ± 4.12
Means with different superscripts in the same row are significantly different (P<0.05). Average
feed intake (ADFI), average body weight (ABW), average daily gain (ADG), feed conversion
ratio (FCR). Treatment 1 = control/ ad libitum, Treatment 2 = 85% of Cobb 500 standard daily
