Reproduction in Domestic Animals

24 JEP Santos, TR Bilby, WW Thatcher, CR Staples and FT Silvestremajor impediment to the study of FA and reproductionin cattle is the inability to predict the delivery ofspecific lipids, particularly polyunsaturated FA to thesmall intestine for absorption, and the specific needs ofdifferent tissues for FA to modulate reproduction.Microbial activity in the rumen results in lipolysis oftriacylglycerols and biohydrogenation of unsaturatedFA which dramatically reduces the amount of polyunsaturatedFA reaching the small intestine forabsorption. In fact, Juchem (2007) demonstrated thatmore than 70% of the C18:2 n-6 and more than 85%of C18:3 n-3 fed to lactating cows were biohydrogenatedin the rumen when fed as unprotected oils oras Ca salts of long chain FA (Ca-LCFA), respectively.Therefore, if specific unsaturated FA are important forreproduction in cattle, it is critical that future researchwith lipids and reproduction aim to improve the extentof delivery of unsaturated FA for absorption. In spiteof the difficulties to deliver polyunsaturated FA toruminants, studies have generally indicated that thepolyunsaturated FA of the n-6 (linoleic acid) and n-3[a-linolenic acid; eicosapentaenoic (EPA), C20:5 n-3;docosahexaenoic (DHA), C22:6 n-3] families are themost beneficial to improving reproduction in cows.Fatty Acids and Postpartum Uterine HealthUterine health is an important risk factor for subsequentfertility in lactating dairy cows. During the process ofparturition, eicosanoids are produced in substantialamounts and play an important role in regulation andcontrol of parturition, and expulsion of the placenta anduterine contents through opening of the cervixand contractions of the uterus. Prostaglandin F 2a is animportant eicosanoid that regulates CL lifespan andmight influence retention of foetal membranes andsubsequent uterine health. Uterine synthesis of PGF 2ais regulated in part by substrate availability, andarachidonic acid (AA; C20:4 n-6) is the precursor forPGF 2a synthesis, so it is plausible to suggest thatincrements in AA content of endometrial tissue shouldenhance uterine PGF 2a secretion, which in turn mayinfluence uterine health.Burns et al. (2003) fed non-lactating beef cows n-3FA from fish meal and reduced the endometrialconcentration of AA and increased those of EPA andtotal n-3 FA. Similar effects have been observed withlactating dairy cows fed increasing amounts of fishmeal or Ca-LCFA enriched in fish oil (Bilby et al.2006b; Moussavi et al. 2007). Because of incorporationof n-6 and n-3 FA primarily in the phospholipidcomponent of endometrial tissue, it is possible thatchanges in FA content of the endometrial tissue mightmodulate endometrial secretion of PGF 2a in cows.Feeding approximately 2% of the ration as fish oil richin n-3 FA reduced the peripheral blood concentrationsof PGF 2a metabolite (PGFM) indicating reduceduterine secretion of PGF 2a (Mattos et al. 2004). Incontrast feeding supplemental fat pre-partum containingapproximately 30% of FA as C18:2 n-6 increaseduterine secretion of PGF 2a based on PGFM in blood(Cullens et al. 2004). Increased synthesis of PGF 2awhen cows were supplemented with n-6 FA pre-partummight enhance the potential for uterine and immunecells to secrete eicosanoids which may influencepostpartum uterine health and immuno-competenceof the cow. Collectively, these data indicate thatfeeding fat sources differing in FA profile during thetransition period can influence the natural release ofPGF 2a by the uterus of the cow.Three studies examined the effect of feeding fat prepartumon postpartum health of dairy cows (Cullenset al. 2004; Juchem 2007; Silvestre, unpublished data).When cows were supplemented with Ca-LCFA rich inn-6 FA pre-partum, incidence of postpartum diseasesincluding retained placenta, metritis and mastitis wasreduced (8.3% vs 42.9%) compared with cows not fedfat pre-partum (Cullens et al. 2004). Juchem (2007)supplemented the diet of 501 pre-partum dairy cowswith 2% Ca-LCFA of either palm oil or a blend ofC18:2 n-6 and trans-octadecenoic FA. Incidence ofretained placenta did not differ between treatments(6.6%). Risk of uterine disease was similar betweensources of FA, but cows fed the blend of C18:2 n-6and trans-octadecenoic FA had reduced the odds ofpuerperal metritis (8.8% vs 15.1%; adjusted oddsratio ¼ 0.53). Rate of uterine involution did not differ,and 91% of the cows had completed uterine involutionat the last ultrasonography on week 6 postpartum(Juchem 2007). In a similar attempt, Silvestre (unpublisheddata) fed 1167 pre-partum dairy cows 1.5% ofthe ration as Ca-LCFA of either palm oil or saffloweroil. Feeding a fat source rich in C18:2 n6 enhancedmeasures of innate immunity; however, incidences ofretained placenta (10.1%), metritis (17.4%), andpurulent cervical discharge (29%) did not differbetween treatments. These data suggest that, althoughfeeding fat sources rich in n-6 FA may enhanceimmune responses and have pro-inflammatory effects,its impacts on uterine health are subtle.Fatty Acids, Follicle Development andResumption of Postpartum CyclicityOne of the mechanisms by which fat feeding mightimprove fertility in cattle is by influencing folliclegrowth and ovulation (Lucy et al. 1993). Lucy et al.(1991) replaced corn with Ca-LCFA in the diet fed todairy cows beginning at parturition, and feedingCa-LCFA increased the number of medium (6–9 mm)sized follicles within 25 days postpartum, and that offollicles >15 mm in a synchronized oestrous cycle. Inaddition, diameter of the largest (18.2 vs 12.4 mm)follicle was greater in cows fed Ca-LCFA. When thisstudy was repeated with isocaloric diets, similar effectswere observed (Lucy et al. 1993). Staples and Thatcher(2005) summarized the effects of supplemental fats onthe size of the dominant follicle (Table 1). On average,dominant follicle diameter was 3.2 mm larger, whichrepresents a 23% increase in fat supplemented cows.Several studies have shown that dominant folliclediameter increased in cows fed diets enriched inpolyunsaturated FA compared with monounsaturatedFA, suggesting differential effects of FA on folliclegrowth (Staples et al. 2000; Bilby et al. 2006a). Folliclesfrom cows abomasally infused with yellow greaseÓ 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag