Uterine, Ovarian, and Production Responses of Lactating Dairy Cows to Increasing Dietary Concentrations of Menhaden Fish Meal

Abstract The primary objective was to determine whether the dietary polyunsaturated fatty acids, eicosapentaenoic (EPA, C20:5, n-3) and docosahexaenoic (DHA, C22:6, n-3), present in fish meal (FM) can attenuate uterine secretion of PGF 2α in response to a challenge with estradiol and oxytocin in lactating dairy cows. Cycling multiparous cows (n = 32) were fed diets containing 0 (0FM), 2.6 (2.6FM), 5.2 (5.2FM), or 7.8% menhaden FM (7.8FM). The diet consisting of 7.8FM also contained fish oil (0.28% of dietary dry matter) to increase intake of EPA and DHA. Average dry matter intake was 24.9 kg/d and unaffected by diet. Combined intakes of EPA and DHA averaged 0, 12.8, 24.1, and 54.0 g/d from the 0FM, 2.6FM, 5.2FM, and 7.8FM diets, respectively. At 30 to 34 d after initiation of dietary treatments, cows received an i.m. injection of 100 μ g of GnRH followed by i.m. administration of 25 and 15mg of PGF 2α after 7 and 8 d, respectively. Synchronous ovulation was induced by an injection of 3000 IU of human chorionic gonadotropin (hCG) given 24h later on d 9. Subsequent luteal phase increases in plasma progesterone concentrations did not differ (0.88ng/ml per day). At 15 d after hCG injection, cows were injected with estradiol-17 β (3mg, i.v.) at 0900h and oxytocin (100 IU, i.v.) at 1300h. Plasma PGF 2α metabolite concentrations after oxytocin injection were reduced in cows fed diets containing FM compared with those fed 0FM. Milk production (39.1 kg/d) and concentrations of fat, protein, or urea nitrogen in milk were not affected by diet. Feeding fish meal and fish oil containing eicosapentaenoic acid and docosahexaenoic acid reduced the proportion of n-6 fatty acids and increased that of n-3 fatty acids in milk in a dose-responsive manner.