Reproduction in Domestic Animals

Reprod Dom Anim 43 (Supp. 2), 23–30 (2008); doi: 10.1111/j.1439-0531.2008.01139.xISSN 0936-6768Long Chain Fatty Acids of Diet as Factors Influencing Reproduction in CattleJEP Santos 1 , TR Bilby 2 , WW Thatcher 1 , CR Staples 1 and FT Silvestre 11 Department of Animal Sciences, University of Florida, Gainesville, FL; 2 Department of Animal Sciences, University of Arizona, Tucson, AZ, USAContentsCattle are fed moderate amounts of long chain fatty acids (FA)with the objective to enhance lactation and growth; however,recent interest on lipid feeding to cows has focused onreproduction, immunity and health. Increasing the caloricdensity of the ration by fat feeding has generally improvedmeasures of cow reproduction, but when milk yield and bodyweight losses were increased by fat supplementation, positiveeffects on reproduction were not always observed. Feeding fathas influenced reproduction by altering the size of thedominant follicle, hastening the interval to first postpartumovulation in beef cows, increasing progesterone concentrationsduring the luteal phase of the oestrous cycle, modulatinguterine prostaglandin (PG) synthesis, and improving oocyteand embryo quality and developmental competence. Some ofthese effects were altered by the type of FA fed. Thepolyunsaturated FA of the n-6 and n-3 families seem to havethe most remarkable effects on reproductive responses ofcattle, but it is not completely clear whether these effects aremediated only by them or by other potential intermediatesproduced during rumen biohydrogenation. Generally, feedingfat sources rich in n-6 FA during late gestation and earlylactation enhanced follicle growth, uterine PG secretion,embryo quality and pregnancy in cows. Similarly, feedingn-3 FA during lactation suppressed uterine PG release, andimproved embryo quality and maintenance of pregnancy.Future research ought to focus on methods to improve thedelivery of specific FA and adequately powered studies shouldbe designed to critically evaluate their effects on establishmentand maintenance of pregnancy in cattle.IntroductionRuminant diets are supplemented with fat primarily toincrease energy concentration and to enhance animalperformance. Dairy and beef cattle diets, without anysupplemental fat, contain approximately 2% long-chainfatty acids (LCFA) of vegetable origin that are predominantlypolyunsaturated. Because of the high energydensity, fats are usually incorporated into cattle rationsto improve production, growth and reproduction.During early lactation, when lactating cows undergo aperiod of nutrient deficit, it was initially thought thatincorporating supplemental fat to the diet wouldenhance energy intake and energy balance, which wasexpected to improve reproduction. Because early lactationcows mobilize large quantities of stored triacylglycerolsin adipose tissue, concentrations of fatty acids(FA) in blood are usually high during the first weeks oflactation (Drackley 1999). This has been suggested tocause an unbalance in substrate supply to the cow,which compromises appetite and overall energy intake(Drackley 1999). When fat is fed in early lactation, oftencows either consume less diet or production increases,therefore fat feeding early postpartum seldom altersenergy status even though a more energy dense ration isconsumed. Staples et al. (1998) indicated that feeding fatdid not alter the energy status of dairy cows andsuggested that reproductive responses were the result ofsupplying LCFA and altering substrate availability tothe cow rather than simply an energy effect.As with other nutrients, certain FA are essential formammals. In 1929, George O. Burr and his wife werethe first to describe the essentiality of FA in rats(Burr and Burr 1929, 1930). They observed that growingrats fed diets low in fat ceased growing and experiencedhealth problems and irregular ovulation, which werethen reversed after feeding fat sources rich in thepolyunsaturated FA C18:2 n-6 (linoleic acid) andC18:3 n-3 (a-linolenic acid) (Burr and Burr 1930).Therefore, the concept of essential FA was establishedand later understood that C18:2 n-6 and C18:3 n-3 couldnot be synthesized by mammalian cells because of lackof desaturase enzymes beyond the 9th C in the acylchain. Because of the essentiality of FA and the role ofspecific FA on reproductive processes, it is possible thatreproduction in cattle may be more influenced by thetype of fat fed than fat feeding per se. This is particularlyimportant and challenging as ruminants extensivelyhydrogenate polyunsaturated FA, thereby limiting thesupply of dietary unsaturated FA for absorption in thesmall intestine.Feeding Fat and Fatty Acids to CattleLipids are important molecules that serve as a source ofenergy and are critical components of the physical andfunctional structure of cells. Lipids present in cellmembranes such as FA in phospholipids play animportant role in regulating the properties and activitiesof cell membranes. Changes in chain length, degree ofunsaturation and position of the double bonds in theacyl chain of FA can have remarkable impacts on theirfunction and may play a role in reproduction in cattle(Staples et al. 1998; Mattos et al. 2000), although theexact mechanisms are still unclear. Potential mechanismsmay include improved dietary energy density(Ferguson et al. 1990), altered follicle development(Staples and Thatcher 2005), increased concentrationsof progesterone (Staples et al. 1998), suppressed luteolyticsignals around maternal recognition of pregnancy(Mattos et al. 2000), and improved embryo quality(Cerri et al. 2004).The use of fat in diets of dairy cattle usuallyincreases the energy density of the ration and improveslactation and reproduction, although improvements inreproduction occur in spite of provision of calories(Staples et al. 1998). These effects might be mediatedby the FA composition of the fat source; however, aÓ 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag