Reproduction in Domestic Animals

Factors Influencing Reproduction in Cattle 27Feeding n-3 FA can attenuate endometrial PGF 2aproduction. Feeding fish meal to dairy cows attenuatedthe decrease in plasma progesterone concentrations2 days after PGF 2a injection suggesting changes in CLregression because of fish oil FA (Burke et al. 1996).Mattos et al. (2002) demonstrated that FA from fishmeal reduced plasma PGFM concentrations comparedwith unsupplemented cows after an oestradiol ⁄ oxytocinchallenge. Dairy cows fed fish oil during the transitionperiod had greater EPA and DHA concentrations incaruncular tissues and reduced postpartum concentrationsof PGFM compared with cows fed olive oil(Mattos et al. 2004). Conversely, feeding fat sources richin n-6 FA increased plasma PGFM after an oxytocinchallenge (Robinson et al. 2002; Petit et al. 2004). Thussupplemental lipids can either inhibit or stimulate PGsecretion depending upon the specific FA.Incubation of bovine endometrial cells with AA stimulatedPGF 2a production compared with cells not supplementedwith FA. On the other hand, cellssupplemented with n-3 FA had reduced secretion ofPGF 2a (Mattos et al. 2003). The mechanism by which n-3FA inhibit PGF 2a secretion may involve decreasing theavailability of AA precursor, increasing the concentrationof FA that compete with AA for processing by PGHS-2,or inhibition of PGHS-2 (Mattos et al. 2000). Bilby et al.(2006b) concluded that n-3 FA supplementation tolactating dairy cows had little effect on the endometrialcomponents that regulate the PG cascade. Instead EPAand DHA exerted their regulatory effects as alternativesubstrates that reduced the lipid pools of AA. In supportof these conclusions, Burns et al. (2003) demonstratedthat feeding fish meal reduced the endometrial concentrationof AA and increased those of EPA and total n-3FA. Therefore, different FA can alter PGF 2a secretion byinfluencing FA availability in the endometrial tissue, andsupplying FA that inhibit PGF 2a release by the uterusmight improve the mechanism of embryo preservation,which may benefit embryonic survival in cattle.Fatty Acids and Fertility of CowsStudies evaluating the effects of supplemental fat onreproductive performance of beef cattle are limited. Toour knowledge, no controlled trials have been conductedwith adequate number of animals to evaluate thepotential for fat supplementation to impact establishmentand maintenance of pregnancy of beef cows. DeFries et al. (1998) observed a tendency (p = 0.09) forincreased pregnancy in Brahman cows fed 5.2% fatcompared with cows fed 3.7% fat in the diet; however,the number of cows used in this study was limited toonly 20 per treatment.Feeding fat to dairy cattle might improve pregnancyper AI (Table 3), although responses have not beenconsistent. When fat feeding increased postpartum bodyweight loss, primiparous cows fed fat had reducedpregnancy at first AI (Sklan et al. 1994). However,Ferguson et al. (1990) observed a 2.2-fold increased odds(odds ratio = 2.2) of becoming pregnant at first and allAI in lactating cows fed 0.5 kg ⁄ day of fat, which tended(p = 0.08) to enhance the proportion of pregnant cowsat the end of the study (93% vs 86.2%). In grazing cows,Table 3. Effect of fat supplementation on pregnancy at first postpartumAI in lactating dairy cowsReferenceCowsFatsource andamountPregnancy perAI, %ControlFerguson et al. (1990) 253 0.5 kg of saturated 42.6 59.1 *free FAMcNamara et al. (2003) 201 0.32 to 0.36 kg 35.5 51.1 *of FA fromCa-LCFASchingoethe153 Oilseeds 46.5 42.0and Casper (1991)Schneider et al. (1988) 181 0.5 kg of Ca-LCFA 43.1 60.5Scott et al. (1995) 443 0.45 kg of Ca-LCFA 49.3 45.7Sklan et al. (1991) 99 2.6% of ration 41.5 39.2as Ca-LCFASklan et al. (1994) 102 2.5 of ration asCa-LCFAPrimiparous 73.7 * 33.3Multiparous 42.1 33.3FA = fatty acid; Ca-LCFA = Ca salts of long chain fatty acids from palm oil.* Within a row, effect of supplemental fat (p < 0.05).supplementation with 0.35 kg of FA improved pregnancyafter the first postpartum AI, although theproportion of cows pregnant at the end of the study didnot differ (McNamara et al. 2003). Feeding Ca-LCFA ofpalm oil improved pregnancy of dairy cows (Schneideret al. 1988; Sklan et al. 1991), but the authors did notreport statistical significance. On the other hand, othersdid not observe improvements on fertility of dairy cowssupplemented with Ca-LCFA (Sklan et al. 1994; Scottet al. 1995) or oilseeds (Schingoethe and Casper 1991),which might be attributed to increased milk yield andbody weight losses (Sklan et al. 1991, 1994).Because the benefits of feeding fat may originate fromspecific FA (Staples et al. 1998; Staples and Thatcher2005), and absorption of unsaturated FA is limited inruminants because of microbial biohydrogenation in therumen (Juchem 2007), studies have evaluated whetherfeeding FA differing in the degree of saturation mightinfluence fertility of dairy cows (Table 4). When cowswere fed 0.75 kg of fat from flaxseed, a source rich inC18:3 n-3, or sunflower seed, a source rich in C18:2 n-6,pregnancy tended (p = 0.07) to be greater for cows fedn-3 FA (Ambrose et al. 2006). However, a similarresponse to flaxseed was not observed by others (Petitand Twagiramungu 2006; Fuentes et al. 2008). Similarly,feeding n-3 FA from fish oil as Ca-LCFA did notimprove pregnancy at first postpartum AI when comparedwith feeding beef tallow (Juchem 2007) or withCa-LCFA of palm oil (Silvestre, unpublished data),although pregnancy at second postpartum AI wasgreater for cows fed n-3 FA (Silvestre, unpublisheddata). Juchem (2007) evaluated the effect of feeding preandpostpartum cows Ca-LCFA of palm oil or a blendof C18:2 n-6 and trans-octadecenoic FA. Cows fedunsaturated FA were 1.5 times more likely to bepregnant at 27 or 41 days after AI compared with cowsfed palm oil. Improvements in pregnancy when cowswere fed Ca salts of a mix of C18:2 n-6 and transoctadecenoicFA were supported by increased fertilizationand embryo quality in non-superovulated lactatingdairy cows (Cerri et al. 2004).FatÓ 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag