Research On Animal Production

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    The objective of this study was to compare first service conception rate before and after milking and changes in metabolite and hormones during four times realted to milking in lactating dairy cow. 300 High producing Holstein cows (> 30 Kg/d and BCS) were randomlly selected and assigned into two groups: 1- insemination before morning milking (0700 a.m, n = 150) and 2- insemination after morning milking (0900 a.m, n=150). Milking was performed at 8 a.m. All cows were synchronized with G7G-Ovsynch protocol started at d 30 postpartum. Blood samples collected from subsample of cows (n = 45 per group) and at four times (before milking, with milking, 1 h after milking and 2 h after milking) for measauring glucose, triglyceride, free fatty acids, albumin andcortisol concentrations. Results showed that Glucose, trigyceride, free fatty acids, abumin and cortiso concentrastions were affected by miking time (P<0.05) and significanty increased with milking compared to before milking (P<0.05) but significanty decreased 1 h after milking compared to milking and before milking. Conception rate at d 32 and 60 after AI were greater in cows inseminated after milking in comparsin with before milking. In conclusion results of the present study showed insemination of cows after milking compared to before miking resulted in increased fertility. 

Keywords: Cortisol, Dairy Cow, Free Fatty Acids, Milking Stress

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