RESUMEN
As lactating cows in severe negative energy balance have poor reproductive performance, the effect of dietary fat supplementation [fish oil, soybean oil] on PGFM secretion, ovarian function and blood metabolites is investigated. In this experiment, the effects of dietary polyunsaturated fatty acids on plasma metabolites, ovarian function and prostaglandin secretion of 20 primiparous Holstein cows was studied. The cows were randomly allocated to one of four groups that were fed either: 1] a control diet; 2] a diet with 3% [Feed dry matter basis] fish oil; 3] a diet with 3% soybean oil; or 4] a diet with 1.5% fish oil and 1.5% soybean oil. Groups were synchronized using the heat-synch method and were fed their respective diets for 35 days, allowing 14 days for dietary adaptation and 21 days for data collection. Concentration of plasma glucose, triglycerides and low density lipoprotein [LDL] cholesterol were not affected by the treatments, but plasma total cholesterol and high density lipoprotein [HDL] cholesterol concentrations were significantly higher in cows that consumed the oil-containing diets [p < 0.05].The number of follicles, corpus luteum size and plasma estradiol, progesterone and prostaglandin F[2a] metabolite [PGFM] concentrations were similar across all treatments. However, the size of the largest follicle was significantly greater in cows that consumed a diet containing fish oil or soybean oil [p < 0.05]. These results suggest that polyunsaturated fatty acids can influence both ovarian and uterine function in cows, but further studies are required to test their effects on dairy cow reproduction
RESUMEN
The objective of this study was to determine the effects of feeding different levels of monensin on feed intake, milk production and composition, and milk fatty acid profile in lactating Holstein cows. Four multiparous cows averaging 517 +/- 47 [SD] kg in body weight and 101 +/- 19.8 [SD] days in milk were housed individually in tie-stalls. The study was conducted as a 4 x 4 Latin square design for four periods [14-d for adaptation and 7-d for sampling]. Cows were offered four dietary treatments [0, 10, 20, or 30 mg of monensin/kg of DM] as total mixed ration, twice daily. Dry matter [DM] intake was similar among treatments. Monensin supplementation significantly increased [P<0.05] milk yield and 4% fat corrected milk [FCM]. Milk fat and protein percentages were not affected by monensin supplementation, but fat yield was increased. Monensin reducted the percentage of the short-chain and saturated fatty acids in milk fat, but had no effect on the percentages of medium- and long-chain fatty acids. Monensin supplementation increased [P<0.05] unsaturated fatty acids concentrations in milk fat. Based on the results of this study, feeding monensin was effective in inhibiting the biohydrogenation of unsaturated fatty acids in the rumen, and consequently increased the percentage of unsaturated fatty acids in milk fat, which improves the health characteristics of milk for human consumption