Effects of Dietary Polyunsaturated Fatty Acids on Rumen Biohydrogenation, Performance, and Reproduction in Dairy Cow

The objectives of this dissertation were to determine resynchronization strategies to optimize fertility in dairy cows, and to investigate the effects of feeding polyunsaturated fatty acids on rumen biohydrogenation, nutrient flow and digestibility, lactation performance, plasma hormones and metabolites, interferon-stimulated gene expression, and reproductive performance in dairy cows.;Chapter 1 introduces current management strategies for enhancing reproductive performance, and nutraceutical approaches aiming to improve production and reproduction in dairy cows.;Chapter 2 presents a literature review on the topics of establishment of pregnancy in cattle, pregnancy-associated glycoproteins, use of pregnancy-associated glycoproteins for indirect pregnancy diagnosis, fatty acids, metabolism of fatty acids in ruminants, rumen biohydrogenation, and the effects of feeding fatty acids on reproduction in dairy cows.;Chapter 3 evaluated the effects of early or late resynchronization based on different methods of pregnancy diagnosis on reproductive performance of dairy cows. The use of pregnancy-associated glycoproteins (PAG) enzyme-linked immunosorbent assay (ELISA) for early diagnosis of pregnancy had acceptable accuracy, but early resynchronization after nonpregnancy diagnosis with PAG ELISA did not improve the rate of pregnancy nor reduce days to pregnancy in cows continuously observed for estrus.;Chapter 4 describes the effects of supplementation of docosahexaenoic acid-enriched algae on reproduction and production performance in Holstein cows. Supplementation with algae resulted in increased concentrations of n-3 fatty acids in plasma phospholipids and milk fat, similar yield of energy-corrected milk, improved pregnancy per AI and reduced days to pregnancy compared with non-supplemented cows. Improvements in reproduction were associated with increased expression of interferon-stimulated gene, thereby suggesting advanced embryo development in cows fed docosahexaenoic acid.;Chapter 5 investigated the effects of feeding different types and sources of fatty acids on rumen unsaturated fatty acid biohydrogenation, fatty acid digestibility, and fatty acids profiles of plasma lipid fractions and milk fat in dairy cows. Feeding a blend of palm and soybean oils increased intake of unsaturated fatty acids, but only when fed as calcium salts was the delivery of unsaturated fatty acids to the intestine increased because of reduced rumen biohydrogenation. Feeding calcium salts containing more polyunsaturated fatty acids increased the incorporation of linoleic and alpha-linolenic acids into plasma lipid fractions and the secretion into milk fat. Although pelleting the calcium salts limited rumen biohydrogenation of unsaturated fatty acids, no improvements in transfer into milk fat were observed compared with the granular form likely because of the reduced digestibility.;Chapter 6 evaluated the effects of supplementation with different types and sources of fatty acids on rumen fermentation, digestibility of nutrients, animal performance, and plasma hormones and metabolites. Dietary treatments did not affect milk yield, 3.5% fat-corrected milk, energy-corrected milk, and feed efficiency. Milk fat content decreased and fat yield tended to decrease with feeding unsaturated fatty acids, but pelleting the calcium salts improved milk fat content. Feeding mostly unsaturated fatty acids as oil reduced organic matter and fiber digestion in the rumen compared with the same fatty acids fed as Ca salts; however, the same responses were not observed for total tract digestion. Oil increased fatty acid digestibility, and feeding Ca salts in a pellet form reduced post-ruminal FA digestion. Treatments did not affect N metabolism or volatile fatty acids concentrations. Plasma glucose concentration increased when feeding oil, whereas other metabolites and hormones did not differ among treatments.;Chapter 7 presents general conclusions and future directions on the topics addressed in this dissertation.