TAKE HOME MESSAGES
• An extensive metabolism of dietary unsaturated fa y acids in the rumen results in the lipid material leaving the rumen consis ng primarily of free fa y acids that are highly saturated.
• Fat is typically the most variable component in milk, and is aff ected by many physiological and environmen-tal factors.
• Fat supplements are commonly fed to increase dietary energy density and support milk produc on.
• Not all fa y acids are the same: know what fa y ac-ids are in the supplement and what form they are in; interac ons with other dietary components are key in determining response.
• Always consider poten al eff ects of fat supplements on DMI, milk produc on, and milk composi on. • Further work is required to characterize the sources
of varia on in response to fat supplementa on.
INTRODUCTION
Milk components and not milk volume typically drive pro-ducer milk prices. Recent evidence has increased our un-derstanding of factors aff ec ng milk component synthesis in the mammary gland that should allow the development of nutri onal management systems that allow strategic changes in milk composi on. Lock and Shingfi eld (2004) provide a comprehensive review
of the impact of nutri on on milk fat and protein. Importantly, diets that allow for an improvement in milk fat output would poten ally be economically advantageous. Equally, low (or reduced) milk fat percentage and yield is also an important economic issue to dairy farms. The emphasis of the current paper is to provide a general over-view of lipid metabolism in the dairy cow along with a discussion
on the poten al use of fat supplements in dairy ca le ons. Focus will include biological processes and quan ve changes during the metabolism of fa y acids (FA) in the rumen and the eff ect this has on FA availability to the dairy cow. Informa on will be provided on the impact of fat supplementa on on cow performance and the specifi c eff ects of fat supplements with diff erent FA profi les on feed intake, milk produc on, and milk composi on. Ob-viously, our knowledge of FA metabolism and u liza on is rapidly advancing and the opportunity and challenge is to eff ec vely apply this knowledge in the feeding and management of dairy cows.
LIPID METABOLISM IN THE RUMEN
As well as being derived from specifi c fat supplements, FA in the dairy cow’s diet are also present in forages and concentrates. The FA composi on of some typical feed-stuff s is shown in Table 1. Each fat source is composed of a diff erent mix of individual FA. Generally, most cereal grains and seeds contain a high concentra on of linoleic acid (18:2 n-6), whereas linolenic acid (18:3 n-3) is typi-cally the predominant FA in forage sources. For example, corn, co onseed, saffl ower, sunfl ower, and soybean oils are high in linoleic acid, whereas linseed is high in linolenic acid. Fish oil contains eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), two very long chain n-3 FA. Unsaturated FA are toxic to many rumen bacteria, thus an extensive metabolism of dietary lipids occurs in the rumen
The Skinny on Fat Supplements in Dairy Rations:
Options, Challenges, and Opportunities
Adam L. Lock
Department of Animal Science
Michigan State University
[email protected]
Table 1. Fa y acid composi on of typical feedstuff s (data from CPM feed library) Fa y acid (g/100 g fa y acids) Feed name C14:0 Myris c C16:0 Palmi c C18:0 Stearic C18:1 Oleic C18:2 Linoleic C18:3 Linolenic Corn silage 0.46 17.83 2.42 19.24 47.74 8.25 Alfalfa silage 0.66 18.81 3.35 2.05 15.91 38.71 Grass hay 0.43 16.44 1.33 2.53 23.38 49.90 Corn grain 2.33 13.21 1.99 24.09 55.70 1.62 Soybean oil 0.11 10.83 3.89 22.82 53.75 8.23
Corn dis llers 0.14 14.05 2.39 24.57 56.11 1.68
that has a major impact on the profi le of FA available for absorp on and ssue u liza on (Palmquist et al., 2005). The two major processes that occur are hydrolysis of ester linkages in lipids found in feedstuff s and the
on (BH) of unsaturated FA (Figure 1). BH of unsaturated FA results in the conversion of unsaturated FA to saturated FA, mainly stearic acid (18:0), through a series of BH inter-mediates (conjugated 18:2 and trans 18:1 FA). The major substrates are linoleic and linolenic acids and the rate of rumen BH is in the range of 70 to 95% and 85 to 100%, respec vely (Jenkins et al., 2008); thus stearic acid is the predominant FA available for absorp on by the dairy cow under typical feeding situa ons (Bauman and Lock, 2006). A series of recent in vitro studies concluded that BH occurs to enable rumen bacteria to survive the bacteriosta c ef-fects of polyunsaturated FA (PUFA), and that the toxicity of PUFA is probably mediated via metabolic eff ects rather than disrup on of membrane integrity. Furthermore, it appears that the degree of toxicity of diff erent PUFA varies for individual ruminal bacteria species; all the main spe-cies that comprise the ruminal celluloly c bacteria appear vulnerable to inhibi on by PUFA (Maia et al., 2007, 2010).
Improvements in analy cal techniques have revealed an impressive complexity in the pa ern of FA that are produced during rumen BH and subsequently incorpo-rated into milk fat. The established major pathways of BH describe the forma on of trans-11 18:1 and cis-9,
trans-11 CLA, but do not account for the FA intermediates
arising from minor pathways of rumen BH (Palmquist et al., 2005). This is an area of increasing interest because of the recogni on that some of these BH intermediates have specifi c and potent eff ects on ruminant metabolism and human health. For example, both trans-11 18:1 and
cis-9, trans-11 CLA present in milk fat have been shown to
have an carcinogenic and an atherogenic proper es in animal models of human health (Lock et al., 2009), while the role of trans-10, cis-12 CLA as a regulator of milk fat synthesis is well established (Bauman et al., 2011).
Fat supplements are o en used as a means to increase the energy density of the diet and many of these are re-ferred to as inert. In this case inertness simply means that the fat or FA supplement has minimal eff ects on rumen fermenta on. Although deemed inert at the level used, they can s ll be hydrolyzed, if a triglyceride, or biohydro-genated, if unsaturated (Figure 1). O en, calcium (Ca) salts of palm FA or canola are referred to as ‘protected.’ However, these are not protected from ruminal BH, but rather are considered to be ruminally inert with regard to their eff ects on the microbial popula on (Palmquist, 2006). Finally, it is important to remember that the forages
in the basal diet also make a signifi cant contribu on to the supply of dietary FA and substrates available for milk fat synthesis. In spite of the low lipid content of forages, grass silage for example, can account for propor onately 0.58 (Lock and Garnsworthy, 2002) and 0.67 (Off er et al., 1999) of total FA intake.
USE OF SUPPLEMENTAL FAT
Lipids in milk are primarily in the form of triacylglycerides (98%) with phospholipids and sterols accoun ng for 1.0 and 0.5% of total lipids, respec vely. Bovine milk is ex-tremely complex and contains about 400 FA, a large pro-por on of which are derived from lipid metabolism in the rumen (Jensen, 2002). Substrates for de novo synthesis are derived from ruminal fi ber diges on and dietary lipids supply preformed FA for direct incorpora on into milk fat. Microbial synthesis of branched and odd-chained number FA in the rumen and absorp on of BH intermediates also contribute to the diversity of FA secreted in milk fat. Under typical condi ons, about half of the FA in milk are synthe-sized de novo, 40 to 45% originate from FA in the diet, and less than 10% are derived from mobiliza on of adipose ssue (Palmquist and Jenkins, 1980). However, nutri on can substan ally alter the balance between mammary de novo FA synthesis and uptake of preformed FA.
The addi on of supplemental fat to the diet to increase dietary energy content can have variable eff ects on the concentration and yield of milk components. This is evident in a recent meta-analysis examining the eff ect of fat supplementa on to diets of dairy cows (Rabiee et al., 2012). In general milk produc on and milk fat % and yield increased, DMI and milk protein % decreased, and milk protein yield was not aff ected by fat
supplementa-Figure 1. Lipid metabolism in the rumen. Also shown are the predominant fat types in common feedstuff s (TG = triglycer-ides, GL = glycolipids and FA = fa y acids).
on. There was a wide range of responses (~5 standard devia ons) for all variables, indica ng varied and marked biological eff ect of the diff erent fats (Rabiee et al., 2012). Therefore, when considering the use of fat supplements, careful considera on should be given to the type of FA present and the form in which these occur. For example, Ca-salts of free FA and prilled saturated free FA are two common types of fat supplements used in the dairy indus-try, and they diff er in fat content and FA profi le. Calcium-salt supplements typically contain 80 to 85% FA of which approximately 50% are saturated and 50% unsaturated. By comparison prilled saturated free FA contain approxi-mately 99% FA which are approxiapproxi-mately 90% saturated, 10% unsaturated. A summary of the FA profi le of some commonly used fat supplements is provided in Table 2.
Changes in response to diff erent fat supplements are dependent on FA inclusion rate, degree of unsatura on, and physical form of the supplemental fat. For example, saturated FA aff ect sa ety less than unsaturated FA pos-sibly because they are less readily oxidized in the liver and less s mulatory to gut pep de secre on (Allen et al., 2009). Feeding fat supplements o en reduces milk fat content as a result of nega ve eff ects of addi onal unsaturated FA in the diet resul ng in changes in ruminal BH. As stated previously, unsaturated FA that have the poten al to aff ect the growth of some groups of rumen bacteria (Maia et al., 2007). On the other hand, saturated FA (e.g. palmi c [C16:0] and stearic acids) are considered to be inert in the rumen.
Total milk fat yield as well as fat percentage is o en in-creased when saturated FA supplements are fed. Chris-tensen et al. (1994) compared the eff ects of abomasal infusion of saturated long chain FA and unsaturated long chain FA (high oleic canola oil, soybean oil, and sunfl ower oil) and found that saturated FA infusion increased milk fat yield as compared to the unsaturated FA treatments. These fi ndings are similar to those of Relling and Reynolds (2007) who reported an increase in milk fat percentage and yield as a result of feeding saturated FA compared to a polyun-saturated (Ca-salts of soybean FA) and monounpolyun-saturated (Ca-salts of palm FA dis llate) fat treatments; furthermore the saturated FA treatment increased milk fat compared to the non-fat supplemented control treatment (Table 3).
There is limited evidence indica ng that specifi c satu-rated FA are more or less eff ec ve at increasing milk fat. Steele and coworkers in the 1960s performed a series of studies using rela vely pure sources of palmi c, oleic, and stearic acids, and their fi ndings suggest that palmi c acid supplementa on induces a higher milk fat response
(concentra on and yield) as compared to oleic and stearic acids supplementa on (Figure 2). More recent work from Enjalbert et al. (1998) suggests that the uptake effi ciency of the mammary gland is higher for palmi c acid than for oleic and stearic acids. In a recent study we found that feeding an 85% palmi c acid fat supplement (2% dietary DM) improved milk fat concentra on and yield by 8% as well as effi ciency of feed conversion into milk compared to a non-fat supplemented diet (Lock et al., 2011). There is mechanis c data to support the concept that individual FA can impact milk fat synthesis diff erently. Hansen and
Table 2. Fa y acid composi on of common fat supplements (data from our laboratory)
Fa y acid, g/100 g Tallow Ca-salt PFAD1 Saturated free FA C16:0-enriched C14:0 3.0 2.0 2.7 1.6 C16:0 24.4 51.0 36.9 89.7 C18:0 17.9 4.0 45.8 1.0 C18:1 (n-9) 41.6 36.0 4.2 5.9 C18:2 (n-6) 1.1 7.0 0.4 1.3
1Palm fa y acid dis llate.
Table 3. The eff ect of rumen-inert fats containing mostly satur-ated fa y acids (SFA), mostly monounsatursatur-ated fa y acids (MUFA), or mostly polyunsaturated fa y acids (PUFA) on DMI, milk yield and milk fat synthesis in midlacta on dairy cows (Adapted from Relling and Reynolds, 2007)
Diet
P1
Control SFA MUFA PUFA
DMI, kg/d 23.8 23.1 22.1 22.0 0.12
Milk, kg/d 36.9 37.3 35.8 34.8 0.44
Fat, % 3.37 3.86 3.32 2.61 0.03
Fat, g/d 1,249 1,436 1,184 911 0.02
1Probability comparing the diff erence between saturated and
unsatur-ated fat supplements (SFA vs. MUFA and PUFA).
Figure 2. Eff ect of palmitc (C16:0) and stearic (C18:0) acid supplementa on on milk fat concentra on and yield com-pared to non-fat supplemented control diets. (Steele and Moore, 1968; Steele, 1969)
Knudsen (1987) u lized an in vitro system and reported that palmi c acid s mulated de novo FA synthesis and in-corpora on into triglycerides whereas other FA were either neutral or inhibitory (Figure 3). In addi on, there were only minor diff erences in the esterifi ca on effi ciency into triglycerides of various FA, except for palmi c acid, which was a be er substrate than the other FA tested (Figure 3).
In addi on, the composi on of the basal diet is an impor-tant determinant of produc on responses to fat supple-ments. For example, par al subs tu on of corn silage with another forage such as alfalfa has been shown to negate the nega ve eff ect of tallow on milk fat yield (Table 4). In high producing dairy cows an interac on was observed between forgage to concentrate ra o and response to supplemental saturated FA (Weiss and Pinos-Rodriguez, 2009). In high-forage diets increased energy intake from supplemental saturated FA was directed mostly to body reserves, whereas in low-forage diets the increased energy intake from the supplemental saturated FA was directed mostly to milk produc on. Using lower producing cows Grum et al. (1996) compared diets at 2 diff erent forage to concentrate ra os either without or with added satu-rated FA. At both forage:concentrate levels supplemental saturated FA increased milk fat concentra on and yield (Table 5). Interes ngly, saturated FA supplementa on had opposing eff ects on DMI when supplemented in the low or high forage:concentrate diets (Table 5). Clearly, further work is required to characterize the impact of diff erent FA on produc on responses across diff erent diet types and
dif-ferent levels of produc on. Finally, van Knegsel et al. (2007) fed either high lipogenic or high glucogenic diets with the same concentrate to forage ra o (40:60). Addi onal FA in the lipogenic diet were provided by supplemental Ca-salts of palm FA dis llate and palm oil. Cows fed the lipogenic diet par oned more energy to milk than cows fed the glucogenic diet and had a higher milk fat yield (Table 6). No diff erences were found for energy retained as body protein, but energy mobilized from body fat tended to be higher in cows fed the lipogenic diet (van Knegsel et al., 2007).
SUMMARY
There are a wide range of FA supplements available for lac-ta ng dairy ca le. Just as we recognize that not all protein
Figure 3. Eff ect of palmitc (C16:0), stearic (C18:0), and oleic (C18:1) acid on lipid biosynthesis in dispersed ruminant mammary gland epithelial cells. (Re-drawn from Hansen and Knudsen, 1987)
Table 4. Eff ect of feeding tallow on rumen fermenta on and milk fat synthesis in dairy cows fed diets based upon corn silage or alfalfa silage with, or without tallow
on (Adapted from One et al., 2004)
Treatment1 CS CST AST Milk, kg/d 44.9 44.3 43.6 Fat, % 3.12 2.68 3.32 Fat, kg/d 1.38 1.17 1.45 trans-10 18:1, % 0.75 2.15 0.78
1CS = 50% corn silage + 50% conc; CST = 50% corn silage + 50% conc
+ 2% tallow; AST = 25% corn silage + 25% alfalfa silage + 50% conc + 2% tallow.
Table 5. Produc on responses of dairy cows fed increased energy from saturated fa y acids or concentrate (Adapted from Grum et al., 1996)
Variable Treatment 1 SEM LC LC + F HC HC + F NDF, % DM 32.8 33.6 27.5 28.4 FA, % DM 2.8 5.7 2.5 5.1 DMI, kg/d4 19.2 20.7 20.2 19.4 0.4 Milk, kg/d 27.3 29.4 28.3 27.8 1.1 Fat, %2, 3, 5 3.52 3.83 2.98 3.33 0.11 Fat, kg/d2, 3, 5 0.96 1.11 0.83 0.91 0.06 4% FCM, kg/d3, 5 25.3 28.5 23.7 24.8 1.4 Protein, kg/d 0.85 0.87 0.92 0.88 0.05
1LC: low (45%) concentrate and no supplemental fat; LC + F: low
concentrate plus 3% DM supplemental fat; HC: high (70%) con-centrate and no supplemental fat; HC + F: high concon-centrate plus 3% DM supplemental fat. Diets LC + F and HC were isoenerge c (1.7 Mcal/kg).
2Signifi cant eff ect of fat supplementa on. 3Signifi cant eff ect of concentrate.
4Signifi cant eff ect of interac on between fat supplementa on
and concentrate.
5Signifi cant eff ect of the comparison of equal energy density
supplements are the same it is important to remember that not all fat supplements are the same. The key is to know what FA are present in the supplement, par cularly FA chain length and their degree of unsatura on. Once this informa on is known it is important to consider the possible eff ects of these FA on DMI, rumen metabolism, small intes nal diges bility, milk component synthesis in the mammary gland, and the yield of milk and milk components. Interac ons with other dietary components and the level of milk produc on are poten ally important in determining the response to various fat supplements. Further work is required to characterize the sources of varia on in response to fat supplementa on.
Previously presented at the California Animal NutriƟ on
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