A protocol for initiating oestrus and ovulation early post partum in dairycows

The objective of the present study was to evaluate the efficacy of a prosta glandin F-2 alpha (PGF(2 alpha)) and progesterone (P-4) treatment in initia ting oestrus and ovulation post partum (PP) in Holstein-Friesian cows. Usin g four herds, the treatment protocol consisted of a single intra-muscular i njection 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 per iod of 7 days. Milk samples for progesterone determination were collected t hree times weekly from 7 to 65 days PP. The ovarian activity and reproducti ve performance of treated (T, no. = 153) animals and untreated control cows (C, no. = 315) were compared. Treatment was effective (P < 0.001) in reduc ing 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 oestr us 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-cal ving 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. 88.9 0 (s.e. 1.95) days), both P < 0.05.