Comparative efficacy of the synchrony programmes in subestrus crossbred cows at smallholder farms in Bangladesh

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The objective was to compare the reproductive efficacy of a Cosynch (GnRH-PGF2α− GnRH + TAI), PG programme (one shot PGF2α) 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 (χ2=4.57; P=0.04). Of the inseminated cows in all groups, 75.7% in Cosynch, 76.7% in PG programme and 82.4% in control were ovulated (χ2=0.31; P=0.86). The size of the largest follicle at AI had a positive correlation with the resultant CL at d 7 (r=0.84, P=0.001). The follicle in cows that subsequently became pregnant was larger (P=0.01) than that in the non-pregnant cows (15.8±2.03 vs. 14.6±2.31), and this was smaller (P=0.001) in cows that experienced late embryonic mortality (12.3±1.03) than that with successfully maintained pregnancy (15.8±2.03) or have not conceived (15.6±2.67). In cows with an expected synchronisation response, the largest follicle size did not differ (P=0.18) 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 (χ2=0.83; P=0.37). 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 (χ2=1.56; P=0.64) between the groups (Cosynch: 45.9%; PG programme: 44.7%; Control: 32.3%). Therefore, selective administration of PGF2α 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.