The aim of this study was to investigate the effect of adding n-3 fatty acids (FA) and α-tocopherol (VE) to semen extender on freezing ability and FA composition of bull sperm. Semen was collected from 10 Iranian Holstein bulls and was pooled. In the first experiment, semen was divided into 12 groups including 4 levels of n-3 FA (0, 0.1, 1, 10 ng ml(-1) ) and 3 levels of VE (0, 0.1, 0.2 mmol). The treatment of 0.2 mmol VE and 10 ng ml(-1) n-3 FA had the best post-thawed sperm characteristics (P < 0.01). In the second experiment, lipid composition of the latest treatment and control (without FA and VE) was determined. Adding n-3 FA increased docosahexaenoic acid (DHA) percentage before freezing and after thawing. The ratio of n-3 to n-6 before freezing was higher (P < 0.05) in treated group than in control, and this ratio in the fresh sperm was greater than in the post-thawed sperm (P = 0.1). Results suggested that adding DHA accompanied with an antioxidant to an extender could improve cryosurvival of bull sperm via altering membrane lipid composition.

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In spite of the difficulties in delivering PUFA to ruminants, studies have generally indicated that the PUFA of the omega-6 (linoleic acid) and omega-3 [α-linolenic acid; eicosapentaenoic (EPA), C20:5 omega-3; docosahexaenoic (DHA), C22:6 omega-3] families are the most beneficial to improving reproduction in cows. The objectives were to determine if a diet enriched in α-linolenic acid (omega-3) or linoleic acid (omega-6) would influence milk production and composition, metabolic status, and reproductive performance in lactating dairy cows. High-yielding multiparous Holstein dairy cows (n = 120) with no overt clinical illnesses were blocked according to calving date and parity. Cows were assigned randomly to be fed 1) soybean whole roast (Soy, omega-6, n = 40) or 2) linseed (Lin, omega-3, n = 40) or 3) palm oil as a source of SFA (PO, n = 40) from calving until first heat after 40 d postpartum (dpp), and then half of the cows in each treatment group were switched to receive either Lin or SFA (PO) from first heat after d 40 to 120 dpp. Blood was collected from a subsample of cows. Blood was collected at 14 d intervals for 12 wk, starting on the day of calving. Results showed milk yield and DMI were not affected. Milk compositions were similar (P > 0.08) among diets, except concentration and yield of milk fat percentage, which was less in cows fed Lin (P < 0.05). Uterine involution in cows fed Soy occurred earlier (P < 0.05). Diets affected day to first estrus and day to first insemination in cows (P < 0.05). There were no differences among treatments for percent heat detection, percent pregnancy per first insemination, and percent conception per AI at estrus. Also, there is a trend of pregnancy by 120 d, which is 66.7% for the Lin group vs. 50.91% for the PO group (P < 0.08). Of the 4 pregnancy losses, 2 occurred in PO-PO group and 2 occurred in Soy-PO group, and none occurred in the other 4 treatments. In conclusion, our study showed feeding omega-6 fatty acids during 40 dpp could be a good treatment for early postpartum periods, and a shift to omega-3 fatty acids until 40 d after AI can be considered as a strategy for improving fertility in lactating dairy cows.

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