No abstract

The objective was to compare the reproductive efficacy of a Cosynch (GnRH-PGF 2a ( GnRH 'TAI), PG programme (one shot PGF 2a ) with artificial insemination (AI) on observed estrus and untreated control (AI on observed estrus) in subestrus (cycling but not detected in estrus by ]60 days postpartum) crossbred cows at smallholder farms. Ultrasonographic examinations were performed at AI, 7 d after AI and 28 d and 42 d after AI to determine the largest follicle, the new corpus luteum (CL) and to diagnose conception and pregnancy, respectively. Of the 69 enrollments in the estrus detection groups, 78.9% in PG programme and 54.8% in control were detected in estrus during the following two weeks (x2 04.57; P 00.04). Of the inseminated cows in all groups, 75.7% in Cosynch, 76.7% in PG programme and 82.4% in control were ovulated (x2 0 0.31; P 00.86). The size of the largest follicle at AI had a positive correlation with the resultant CL at d 7 (r 00.84, P00.001). The follicle in cows that subsequently became pregnant was larger (P00.01) than that in the non-pregnant cows (15.892.03 vs. 14.692.31), and this was smaller (P 00.001) in cows that experienced late embryonic mortality (12.391.03) than that with successfully maintained pregnancy (15.892.03) or have not conceived (15.692.67). In cows with an expected synchronisation response, the largest follicle size did not differ (P00.18) between cows that subsequently became pregnant or non-pregnant. The conception rates (Cosynch: 54.1%; PG programme: 63.3%; Control: 64.7%) were not different between the groups (x2 0 0.83; P00.37). The embryonic mortality was 12% in the cows during d 28 until d 42. The overall final pregnancy rate was 41.5% that did not differ (x2 0 1.56; P00.64) between the groups (Cosynch: 45.9%; PG programme: 44.7%; Control: 32.3%). Therefore, selective administration of PGF 2a to subestrus cows would be economically advantageous because of a saving in hormone injection costs, and veterinary supervision can lead to an increase in the estrus detection efficiency of the herd personnel.