Effects of polyunsaturated fatty acids and bovine somatotropin on endocrine function, embryo development and uterine-conceptus interactions in dairy cattle

A series of experiments were conducted to investigate mechanisms through which polyunsaturated fatty acids (PUFA) and bovine somatotropin (bST) increase fertility. The first study used nonlactating dairy cows to examine the effects of bST on components of the insulin-like growth factor (IGF) system. Exogenous bST decreased pregnancy rates. However, conceptus length and interferon-tau (IFN-tau) in uterine flushings were increased. The bST may have hyper-stimulated IGF-I and insulin concentrations, causing detrimental effects on conceptus viability.; The second experiment used the same estrous synchronization protocol and bST treatment as the first study; however, lactating dairy cows were used and effects of a diet supplemented with a fish oil enriched lipid (FO) were evaluated. Exogenous bST increased pregnancy rates, conceptus size, and IFN-tau in uterine flushings. The FO altered uterine gene expression, proteins, and plasma hormones in a manner that mimicked pregnancy. Furthermore, FO reduced the n-6:n-3 ratio and increased conjugated linoleic acid (CLA) concentrations in milk. Pregnancy altered endometrial expression of certain antiluteolytic associated genes and fatty acid composition, which may attenuate the luteolytic pulsatile secretion of prostaglandin F2 alpha (PGF2alpha) contributing to embryo survival.; In the last experiment, diets enriched in different omega fatty acids altered oocyte quality and follicular dynamics in lactating dairy cows. The C18:2 enriched diet reduced oocyte quality, as indicated by reduced in vitro embryo development, versus a C 18:1 cis enriched diet. Previously documented benefits of PUFA on reproductive responses reflect actions at alternative biological windows other than oocytes from follicles < 12 mm. Possible beneficial effects of PUFA on the periovulatory follicle and corpus luteum (CL) were evident by the increase in dominant follicle size and CL volume due to feeding PUFA.; In summary, bST had differential responses on fertility which were dependent on lactational status. The bST appears to increase pregnancy thru increased conceptus length and subsequent IFN-tau production in lactating dairy cows and by altering IGF gene expression in uterine endometrium. The FO altered endometrial responses and fatty acid distribution which may benefit pregnancy. Diets enriched in particular fatty acids may have different effects on oocyte quality and follicular dynamics in lactating dairy cows.