Objectives of the project: To evaluate the effects of a glucogenic supplement during the peripartum transition period on insulin, hepatic triglyceride accumulation, interval to first ovulation, and progesterone profile in dairy cows. To compare benefits of supplemental fats differing in fatty acid composition and fed prepartum on hepatic triglyceride accumulation, interval to first ovulation, progesterone profile, and uterine prostaglandin production in lactating dairy cows. To assess the differential and carry-over effects of glucogenic and fat supplements fed to peripartum dairy cows on steroidogenesis and fatty acids in ovarian follicles. To determine the carry-over effects of peripartum glucogenic or fat supplements on fertility in high producing dairy cows (modified in year 3 to Israel only). Added during year 3 of project: To assess the activity of genes related to hepatic lipid oxidation and gluconeogenesis following dietary supplementation (USA only). Background: High milk yields in dairy cattle are generally associated with poor reproductive performance. Low fertility results from negative energy balance (NEBAL) of early lactation that delays resumption of ovarian cycles and exerts other carryover effects. During NEBAL, ovulation of ovarian follicles is compromised by low availability of insulin and insulin-like growth factor-I (IGF-I), but fatty acid mobilization from body stores is augmented. Liver function during NEBAL is linked to the resumption of ovulation and fertility: 1) Accumulation of fatty acids by the liver and ketone production are associated with delayed first ovulation; 2) The liver is the main source of IGF-I. NEBAL will continue as a consequence of high milk yield, but dietary supplements are currently available to circumvent the effects on liver function. For this project, supplementation was begun prepartum prior to NEBAL in an effort to reduce detrimental effects on liver and ovarian function. Fats either high or low in unsaturated fatty acids were compared for their ability to reduce liver triglyceride accumulation. Secondarily, feeding specific fats during a period of high lipid turnover caused by NEBAL provides a novel approach for manipulating phospholipid pools in tissues including ovary and uterus. Increased insulin from propylene glycol (glucogenic) was anticipated to reduce lipolysis and increase IGF-I. The same supplements were utilized in both the USA and Israel, to compare effects across different diets and environments. Conclusions: High milk production and very good postpartum health was achieved by dietary supplementation. Peripartum PGLY supplementation had no significant effects on reproductive variables. Prepartum fat supplementation either did not improve metabolic profile and ovarian and uterine responses in early lactation (USA) or decreased intake when added to dry cow diets (Israel). Steroid production in ovarian follicles was greater in lactating dairy cows receiving supplemental fat (unsaturated), although in a field trail fertility to insemination was not improved.
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