Effect of Season and Progesterone-Releasing Intravaginal Device Alone or with Pregnant Mare Serum Gonadotropin on Fertility Rates of Bunaji Cows

The effect of season and Progesterone-Releasing Intravaginal Device (PRID) alone or with Pregnant Mare Serum Gonadotropin (PMSG) on ovarian function of 106 Bunaji cows was investigated in two seasons. In the day season trial, 46 cows were randomly distributed into the following treatment groups: PRID alone (n = 16), PRID+PMSG (n = 15) and control (15). In the rainy season trial, 60 cows were randomly distributed into the following treatment groups: PRID alone (n = 20); PRID+PMSG (n = 20) and control (20). During the dry season, Bunaji cows treated with PRID alone had a significantly (p<0.05) lower estrus response than the cows administered with PRID+PMSG (37.5 vs 66.7%, respectively). During the rainy season, 65.0% of Bunaji cows treated with PRID+PMSG were found to be in estrus; this was not significantly higher than the value of 60.0% estrus rate recorded in Bunaji cows treated with PRID only. In PRID treated Bunaji cows, pregnancy rates of 25.0 and 45.0% was recorded during the dry and rainy season, respectively. Pregnancy rates in PRID+PMSG treated cows were 46.7 and 50.0% respectively. Pregnancy rate was generally lower in the dry season than in the rainy season in both PRID only, PRID+PMSG and control groups. However, the highest pregnancy rate of 50.0% was obtained in PRID+PMSG treated Bunaji cows during the rainy season. Conception rate in Bunaji cows treated with PRID only (66.7%) was lower than cows treated with PRID+PMSG (70%) during the dry season although not significantly. Similarly during the rainy season, Bunaji cows treated with PRID+PMSG had a higher conception rate than cows treated with PRID only (76.9 vs 75.0%, respectively). This study suggests that the rainy season enhances greater ovarian function in dairy cows in the Northern Guinea Savannah zone of Nigeria and that administration of PMSG may potentiate fertility rates.