A protocol for initiating oestrus and ovulation early post partum in dairy cows

The objective of the present study was to evaluate the efficacy of a prostaglandin F-2 alpha (PGF(2 alpha)) and progesterone (P-4) treatment in initiating oestrus and ovulation post partum (PP) in Holstein-Friesian cows. Using four herds, the treatment protocol consisted of a single intra-muscular injection of PGF(2 alpha) (Estrumate) between days 12 to 14 PP followed 48 h later by progesterone treatment via intra-vaginal CIDR insertion for a period of 7 days. Milk samples for progesterone determination were collected three times weekly from 7 to 65 days PP. The ovarian activity and reproductive performance of treated (T, no. = 153) animals and untreated control cows (C, no. = 315) were compared. Treatment was effective (P < 0.001) in reducing the mean interval to PP commencement of luteal activity from 29.62 (s.e. 0.82) days to 22.09 (s.e. 0.70) days. The mean interval to first PP oestrus in the T animals was significantly reduced (P < 0.001) from 55.62 (s.e. 1.58) days to 44.91 (s.e. 1.44) days and the incidence of silent ovulation in cycles between days 21 to 65 PP was reduced (P < 0.001)from 56.28% to 42.27%. In two herds under one management regime and with a similar block-calving pattern (no. = 280 animals), the treatment protocol was beneficial to the overall reproductive performance as there was a significant shortening in the mean interval to first PP service (75.82 (s.e. 1.93) v. 80.86 (s.e. 1.32) days) and in the interval to PP conception (83.07 (s.e. 2.49) v. 88.90 (s.e. 1.95) days), both P < 0.05.