Reproduction in Domestic Animals

Factors Influencing Reproduction in Cattle 25Table 1. Effect of supplemental fat on the diameter of the dominantovarian follicle of lactating dairy cows (from Staples and Thatcher2005)ReferenceFatsourceExperimental dietsControl (mm)Fat (mm)Ambrose et al. (2006) Rolled flaxseeds 14.1 16.9Beam and Butler (1997) Tallow, yellow grease 11.0 13.5Bilby et al. (2006a) Ca-LCFA or flaxseed oil 15.0 16.5Lucy et al. (1991) Ca-LCFA 12.4 18.2Lucy et al. (1993) Ca-LCFA 16.0 18.6Oldick et al. (1997) Yellow grease 16.9 20.9Robinson et al. (2002) Protected soybeans 13.3 16.9Staples et al. (2000) Soybean oil, fish oil 14.3 17.1Average 14.1 17.3Ca-LCFA = Ca salts of long chain fatty acids from palm oil or a blend of palmand soyabean oils.Control vs fat was P < 0.10 for each study.grew faster to a larger diameter than follicles fromcows infused with tallow (Oldick et al. 1997). Itappears that fat feeding, but more importantly typeof fat, stimulates follicle growth in cows. The impact oflarger ovarian follicles on fertility because of fatsupplementation has not been defined, but cowsexperiencing earlier postpartum ovulation have beenreported to have larger follicles (Beam and Butler1997). Therefore, it is possible that increasing thenumber and size of larger follicles by feeding fat canreduce the interval from calving to first postpartumovulation, which has been observed for postpartumbeef cows (Lammoglia et al. 1996, 1997; De Fries et al.1998).Although some studies have indicated that feeding fathastens follicle growth, which might influence resumptionof postpartum ovulation (Lammoglia et al. 1996,1997; De Fries et al. 1998), it is unclear whethersupplemental fats differing in FA profile have anydifferential effect on resumption of cyclicity. Juchem(2007) fed 699 multiparous cows either 400 g of FAfrom tallow or from Ca-LCFA containing palm and fishoils and observed no difference in proportion of cyclingcows at 65 days postpartum (83.2% vs 82.2%, respectively).Subsequently, dairy cows supplemented withCa-LCFA of palm oil or a blend of C18:2 n-6 and transoctadecenoicFA from 25 days pre-partum to 80 dayspostpartum experienced a similar mean interval to firstpostpartum ovulation (30.5 and 32.2 days, respectively;Juchem 2007). Recently, Silvestre (unpublished data) fedcows (n = 1055) either Ca-LCFA of palm oil or ofsafflower oil from 2 weeks pre-partum to 4 weekspostpartum, and then half of the cows in each transitiontreatment group were switched to either Ca-LCFA ofpalm oil or fish oil (264 ⁄ treatment). The proportions ofcyclic cows at 63 days postpartum were 84.2%, 79.5%,79.2% and 77.1% for cows fed palm oil ⁄ palm oil, palmoil ⁄ fish oil, safflower ⁄ palm oil, and safflower ⁄ fish oil,respectively, and they did not differ. Taken together,these data demonstrate that type of supplemental FA,whether more saturated or unsaturated does not influenceresumption of postpartum cyclicity in lactatingdairy cows.Fatty Acids and OestradiolOestradiol has stimulatory effects on uterine secretion ofPGF 2a (Knickerbocker et al. 1986), and can increase thesensitivity of the CL to PGF 2a (Howard et al. 1990)which may enhance regression of the CL. Thus loweredplasma oestradiol may help prevent pre-mature CLregression and early embryonic mortality. Oldick et al.(1997) reported that abomasal infusion of tallow oryellow grease reduced concentrations of plasma oestradiolon days 15 to 20 of a synchronized oestrous cyclecompared with cows infused with glucose, a responsethat also has been observed in beef cows supplementedwith lipids (Hightshoe et al. 1991). Also, oestradiolconcentration was reduced in the follicular fluid frombeef cows fed soybean oil (Ryan et al. 1992). Although areduction in follicular oestradiol caused by fat feedingmight potentially benefit CL lifespan, it may be detrimentalto expression of oestrus and uterine primingduring prooestrus.Fat and Luteal FunctionImproved fertility in cattle has been associated withincreased circulating concentrations of progesteroneduring the luteal phase before and after AI. Additionof fat to cattle diets has consistently shown to increaseplasma cholesterol and cholesterol content in follicularfluid and in the CL (Staples et al. 1998; Williams 1989;Ryan et al. 1992; Hawkins et al. 1995; Lammoglia et al.1996). Cholesterol serves as a precursor for the synthesisof progesterone by ovarian cells and both high and lowdensity lipoproteins deliver cholesterol to ovarian tissuesfor steroidogenesis (Grummer and Carroll 1991).Hypercholesterolemia may increase CL steroidogenesis;however, the increased plasma progesterone concentrationsin dairy and beef cows fed fat (Table 2) may beexplained possibly by reduced progesterone clearance,not by increased synthesis (Hawkins et al. 1995).Fatty Acids, Oocyte Quality and MembraneCompositionCompetence of the oocyte and embryo is related to FAcomposition; specifically, phospholipid content of thecellular membrane plays a vital role in developmentduring and after fertilization. The amount of lipid in theruminant oocyte is approximately 20-fold greater thanthat of the mouse (76 vs 4 ng) and consists (w ⁄ w) ofapproximately 50% triacylglycerol, 20% phospholipid,20% cholesterol and 10% free FA (McEvoy et al. 2000).Previous studies showed that C16:0 and C18:1 were themost abundant FA in the phospholipid fraction ofoocytes from cattle and may function as an energyreserve (Kim et al. 2001; Zeron et al. 2001). PolyunsaturatedFA comprised