This study reports on the development of a stochastic dynamic model to simulate a pastoral sheep enterprise. The event driven model was constructed using the iconic simulation package, Extend™. Events corresponded to the shifting of animals from one paddock to another. Each paddock was represented as a single entity with inherent attributes such as grazing area, sward characteristics and pasture production potential. The rotation sequence for grazing was determined by always allocating the flock of ewes, flock replacements or lambs to the paddock with the greatest pasture mass. Herbage mass was divided into three fractions: leaf, stem and dead. Pasture growth and senescence rates for individual paddocks were calculated from pasture leaf mass. A Micherlich-type function was used to relate leaf mass to total pasture growth. Senescence was assumed to increase linearly with herbage mass.
In pasture-based dairy systems over 81% of N is excreted in the paddocks, indicative that lower than 20% of urine N excreted is collected in the milking parlor . Understanding the daily pattern of UN excretion and how to fit it with the permanence of cows in the pasture or facilities, a potential strategy to reduce the urine N excreted into the pasture could be a combination between animal nutrition strategies and modification in the animals’ management during the day. The objective of this study was to evaluate whether changes in timing of herbage allocation and herbage mass (low (L) or medium (M) modify the daily pattern of UN concentration, rumen NH 3 and grazing behavior of
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Figure 3-2 Herbage mass pre-grazing (kg DM/ha) in: A) the pasture treatments grazed every two (dashed lines) and every four weeks (solid lines) throughout the first (December, 2011 to April, 2012) and second (August, 2012 to May, 2013) growing seasons, and in B) chicory (white), plantain (black), and the herb-clover mix (grey) pastures when grazing at two (2w) or four week (4w) frequencies in the first (2011-2012) and second (2012-2013) growing seasons. Vertical bars represent the standard error of the mean (SEM). Values noted with a, b, c are significantly (P<0.05) different in each growing season. ......................................... 72
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The previous herbage allowance and post-grazing herbage mass significantly affected herbage quality in this trial. However, this was dependent on pasture type, with lucerne quality being more affected by previous herbage allowance than perennial ryegrass. The regrowth from the post-grazing herbage mass in the perennial ryegrass treatment were of similar quality and there was no difference in ME values from the different previous herbage allowance rates. This result from this trial are different to earlier work where Mayne, et al., (1988) stated digestibility was increased as a consequence of increased grazing intensity. Mayne, et al., (1988) reported the regrowth mass containing higher proportions of grass leaf and a lower proportion of grass stem and dead material than regrowth from low grazing intensity pastures (Hoogendoorn et al., 1992; Michell et al., 1987). The reason for the different results in this study may be due to the increase in herbage growth rates and herbage mass of perennial ryegrass treatments at previous allowances above 40kg DM/cow/day. The increased herbage mass meant they rejected the dead material at the base of the sward and only grazing the green leaf in the top horizons, increasing the quality of diet consumed. This was similar to Michell, et al., (1987) who found that digestibility between perennial ryegrass regrowth from different post-grazing herbage mass had similar digestibility due to larger green leaf mass, despite large differences in the dead material present. They also stated that the cows would reject dead material and sacrifice intake to maintain diet quality. If the growth rates from the previous trial and the pre-grazed herbage mass had been similar, the increase in dead material (>40 kg DM/cow/day previous herbage allowance) would have not been diluted by an increase in green leaf mass and the quality of their diet would have been reduced.
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As mentioned previously high quality is associated with high digestible energy and protein which support the metabolisable energy and protein requirements of the grazing livestock. The quality of herbage offered to grazing dairy animals has a major effect on milk production and animal performance over the length of the milking season. The regrowth length of the pasture before the next grazing (rotational grazing) affects the pasture quality through changes in herbage composition and digestibility. Rotation length can be altered to manage the regrowth interval. If there is surplus feed, the round can be sped up by increasing the pasture allowance. However, increasing pasture allowance may result in higher post-grazing residuals. Alternatively, stocking rate could be increased to restrict allowance, to reduce post-grazing residuals. If low stocking rates do not allow, mowing could be used as management practise to maintain desired residuals and increase pasture allowance to utilise the pasture surplus without adverse effects on pasture quality. An increase in the regrowth length, results in increased herbage accumulation and therefore greater pasture masses. Swards with high herbage mass can reduce feeding value and dry matter intake of grazing dairy cows (O'Donovan & Delaby, 2008). This is largely influenced by organic matter digestibility of grass leaf and stem which is reduced with increased regrowth age due to a higher proportion senescent material in the grazing sward (Hoogendoorn, Holmes, & Chu, 1992; Korte et al., 1984). Holmes et al. (1992) found higher digestibility in pastures with low herbage mass (L HM; 2.86 t DM/ha) compared with high herbage mass (H HM; 4.79 t DM/ha) swards.
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The timing of turnout is an important factor affecting the grazing management of dairy cows. How- ever, its consequences are not well known in the short grazing season of northern Europe. Thus, the effect of the turnout date of dairy cows to pasture on sward regrowth, herbage mass production and milk production was studied in two experiments, 1) a grazing trial with 16 Holstein-Friesian dairy cows and 2) a plot trial where the treatments simulated the grazing trial. The treatments were early turnout (1 June) and normal turnout (6 June). Early turnout decreased the annual herbage mass (HM) production in the plot trial (P = 0.005), but due to a higher average organic matter (OM) digestibility (P < 0.001) the difference in digestible OM yield was not significant (P = 0.14). Similarly, early turnout decreased the mean pre-grazing HM in the grazing trial. The differences in HM quantity and quality between early and normal turnout occurred mainly in late June and early July and thereafter levelled out. Average post-grazing sward heights were lower for early turnout, indicating better HM utilization. There were no differences in yields of milk, milk fat or milk protein (P > 0.05). Although early turnout had no effect on milk yields it meant easier management of pastures.
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Kitessa (1992) reported that when a ‘Russell’ lupin stand was grazed at the full bloom stage (27/11/90) stock grazed to a residual of 270 kg DM/ha and the subsequent regrowth was 6690 kg DM/ha (Table 2.3). In comparison when grazed at the green pod (17/12/90) and dry pod (21/01/91) growth stage the grazing residual was 960 and 1920 kg DM/ha respectively with regrowth of 2818 and 362 kg DM/ha respectively. Although the amount of residual herbage mass remaining for regrowth was the smallest for lupins grazed at full bloom, the highest autumn regrowth was obtained from these lupins. Therefore, it was the time of grazing rather than the amount of residual herbage mass left that determined the amount of autumn regrowth obtained from ‘Russell’ lupin. Kitessa (1992) suggested that this probably related to the accumulation of nutrient reserves in the root system. The residual herbage mass did effect the quality of the regrowth, the combination of early grazing time at full bloom and the subsequent low grazing residual result in a favourable regrowth of high quality for an autumn grazing (flushing ewes). He concluded that, although annual DM yield was higher for lupins grazed at dry pod, grazing at full bloom increases the scope of incorporation of ‘Russell’ lupins in the New Zealand farming system.
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Chapter 5 demonstrated a marked effect of varying N fertiliser application on the physical presentation and chemical composition of non-legume swards, particularly ryegrass. The greater herbage mass of more highly fertilised ryegrass has been shown to promote greater DMI and feeding rate of cows when compared to cows grazing swards receiving less N fertiliser (Delagarde et al., 1997). Therefore, it was postulated that increasing rates of fertiliser N to other forage species would also increase DMI of cows, but that there would also be increased partitioning of dietary N to urine. Simulation modelling (Chapter 7), using sward chemical and physical data gathered in the N fertiliser study (Chapter 5) was used to explore implications of feeding diets of herbage grown under increasing rates of fertiliser N application (0 – 500 kg N/ha/y) to dairy cows. The greater herbage mass, larger leaves, weaker herbage tissue of the more highly fertilised plantain and ryegrass swards was predicted to increase daily DMI and intake rates of dairy cows. Whereas predicted DMI of cows grazing chicory would be improved at fertiliser rates of 200 compared to 0 kg N/ha/y, predicted DMI declined when rates exceeded 200 kg N/ha/y. Similarly, predicted DMI decreased for cows grazing fertilised compared to unfertilised swards of lucerne. The decreases in DMI predicted in heavily fertilised chicory or fertilised lucerne swards may have been associated with high soluble CP (CPS) content of herbage, which would have led to the greater ruminal ammonia concentrations. In the model, this increased rumen ammonia would likely have reduced incentive for grazing and thus DMI (Gregorini et al., 2013a). Overall, the predicted MS production of cows was associated with DMI (R 2 = 0.63) and N intake (R 2 = 0.88), and although the additional DM
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Species plots were unreplicated, and effects were evaluated by analysis of variance using general linear models (GLM ® Statistical Analysis Systems (SAS» in a completely randomised design with individual animals as the experimental units. The implications of this procedure are considered in Section 3.4. Comparisons were made of least squares means of lamb liveweights, using initial weight as a covariate, lamb FEe, pasture larval densities (L:Jkg herbage DM), pasture larval populations (L�a), pasture herbage mass (kg DMlha), tracer lamb nematode burdens, lamb faecal output (g DMlday), and estimated lamb OMI (g DM/day), transforming when necessary to normalise data as determined by the random scattcr pattcrn observed when residual vs predicted values were plotted. Thus lamb FEC were square-root transformed and tracer lamb nematode burdens were 10gIO transformed to normalise data prior to analysis.
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A dynamic simulation model is being developed with the objective of studying a variety of management questions in beef suckler systems of the Salado Region. Preliminary results of a particular study with the model are presented to illustrate the potential use of the model. The simulation adjusts the state of each paddock daily, based on the climate, the state of the paddock at the start of the day and grazing during that day. Pasture growth, senescence and decay are driven by daily net radiation, air temperature and soil moisture. Similarly, each animal's state is updated daily in response to its initial state, animal' s potential, energy intake and management rules. Herbage intake is calculated from herbage mass and green/dead ratio and is affected by the quality and quantity of the hay offered. Management strategies are specified using decision rules entered by the user. Animals are grouped into herds, and paddocks are grouped into blocks and most management rules are specified at herd or block level. These rules are checked every day and can trigger a variety of management actions: sell cows; wean cows; feed hay; move a herd to a new paddock; mate a herd; close paddocks; release paddocks; make hay; assign cows to herds. There are also rules to reassign paddocks to the different herds. Those actions represent the most important control points that a manager can use to operate the farm. Simulating performance at the level of individual animals and paddocks, but specifying management rules at the herd and block levels allows simulations of farms of different sizes and the representation of multiple alternatives for grazing management. Because management rules are not embedded in the code, but are specified through a user interface, a wide range of management strategies can be simulated and compared. The model was used to study the possible impact of changes to the mating period in a winter calving herd. As a base for the comparisons, a simulated farm was created that approximately imitates the management and general structure of the experimental cow-calf farm of INTA-Balcarce (Reserva 6) ("A"). The effect of delaying the breeding season 1 5 ("B") and 30 ("C") days was analysed. In B and C, the date for weaning and culling were delayed by the same amount of time (Table 4. 1 ). Table 4.1: Dates for mating, calving, weaning and culling for the three alternatives.
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RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1 4. 1 Grazing conditions and level of feeding . . . . . . . . . . . . . . . . . 6 1 4.2 Botanical composition and nutritive value of the grazed herbage and silage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
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The Plantain and Chicory mixes had a higher feeding value than the Pasture mix during early spring to autumn. Both Plantain and Chicory mixes produced heavier (P<0.05) lambs, higher (P<0.05) live weight gains (LWG) and carcass weights compared to the Pasture mix in all periods. Total apparent carcass weight production per ha were 407, 748 and 709 kg/ha in year one and 474, 607 and 642 kg/ha in year two in the Pasture mix, Plantain mix and Chicory mix, respectively. Both Plantain and Chicory mixes had lower (P<0.05) feed conversion ratios (FCR) and higher (P<0.05) herbage utilization efficiencies (EHU%) compared to the Pasture mix.
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2007 and 2008. The sward was mown to a residual height of 8 cm. A subsample of approximately 400 g of the total herbage was taken from the first and third cut in both years (23 May and 15 August in 2007, 26 May and 22 August in 2008), separated into individual species and dried in a forced draught oven at 80C to constant dry weight. The two grass species, perennial ryegrass and festulolium, were pooled. All unsown species were combined, but not analysed for mineral concentrations. The samples were ground in a Christy hammermill (Tekemas, Rødovre, Denmark) to pass a 0Æ8-mm sieve. Subsamples were digested with nitric acid (69–70%) and hydrogen peroxide (30%) in a ModBlock at 95C following the EPA (Environmental Protection Agency, USA) method 3050B (related to EPA 6020) (Husted et al., 2004). Calcium (Ca), phosphorus (P), magnesium (Mg), potassium (K), sodium (Na), sulphur (S), copper (Cu), iron (Fe), manganese (Mn), zinc (Zn), molybdenum (Mo), chromium (Cr), boron (B) and aluminium (Al) concentrations were analysed by Inductively Coupled Plasma Optical Emission Spec- troscopy (Perkin Elmer Optima 4300 DV ICP-OES; Perkin Elmer Life and Analytical Sciences, Inc., Boston, MA, USA) using instrumental settings as described by Hansen et al. (2009). Total nitrogen (N) was analysed with an ANCA-SL Elemental Analyser coupled to a 20- 20 Tracermass Mass Spectrometer (SerCon Ltd., Crewe, UK). The aluminium concentration was used solely as a quality control for the sample and was not included in the statistical analysis. Aluminium results obtained in the current study were within the common range for higher plants (data not shown; Kabata-Pendias and Pendias, 2000).
) when clipped 4 times per year compared to 740 g kg -1 for a single clipping per year. In addition, the same authors reported that NDF concentration increased from 705 to 729 g kg -1 as the last harvest of the season was delayed from Sept. to Nov. Consistent with previous reports, these responses can be explained due to plant aging and transitioning from vegetative to reproductive stages, as forage quality of switchgrass typically decreases with maturity (Burns et al., 1997; Griffin and Jung, 1983; Sanderson and Wolf, 1995; Mitchell et al., 2001; Twidwell et al., 1998) and also due to lower leaf:stem ratio (Fig. 2.3 Chapter 2) and greater NDF concentration in the stem component than leaf (Hans-Joachim and Vogel, 1992). Griffin et al. (1980) and Van Soest (1965) suggested that when the levels of NDF exceed 50 to 60%, this may result in limited herbage intake. Anderson and Matches (1983) recommended that clipping or grazing ‘Pathfinder’ switchgrass at juvenile stage may increase voluntary intake since matured ‘Pathfinder’ switchgrass always contained over 65% NDF, and occasionally over 80% NDF, and intake by livestock grazing may be limited by distension. This may be applicable to our study with the higher DF treatments (Fig. 3.3).
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The latter two estimates were calculated for lactating cows, and the one given in the L.I.C. ( 1 99 1 ) publication does not specify if the estimate takes into account different maintenance feed requirements of cows during lactation and the dry period, as well as their relative contribution (i.e. days in milk and days dry) in each lactation cycle. From Table 2.8 (Section 2.4. 1 .3) lactating and non-lactating grazing cows required for maintenance purposes about 1 .08 and 0.9 1 MJ MEIJLW0·75/day, respectively. Assuming a lactation length of 262 days as typical of the New Zealand pasture-based dairy system (Ahlborn & Dempfle, 1 992), a MID of 1 1 MJ ME/kg herbage DM (Hutton, 197 1 ) and a range in cow live weight between 350 and 550 kg, the maintenance cost of an extra 1 00 k g live weight/cow can be assessed as shown in the following table:
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Overall, both Effective microorganism (EM) solutions and urea had little influence on breaking the parasite lifecycle when applied in the field. For pasture larval contamination, lamb FEC, LW and DMI, there were no significant difference. This may reflect the design of the field study which the two days rotation provided an opportunity for half of the eggs to hatch. In vitro results suggested urea has a very potent effect on egg development with 98 % reduction. In the field, urea may have inadvertently encouraged Nematodirus development, which may either be from increased irrigation of 12 h, or the amount of urea that penetrated the faecal mass, may not have being sufficient when dealing with faeces of different moisture or different surface area as well as pH, which was not measured in the field. In addition, in vitro laboratory results, with plastic bag and field study shows little development in egg hatching. Although the disparity is not clearly understood between the field and the in vitro results, the possibility of an artificial high ammonia concentration was ruled out. Overall, urea may provide an opportunity to break the parasite lifecycle, but further investigations are needed in the field.
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