[Effect of reducing dose of GnRH analogue used in heat-synch program on pregnancy rate and day open of dairy cows]

ABSTRACT

To reduce the cost of hormones used in Heat-synch protocol in dairy cows. Enpenimental study.144 Holstein cows, at 50 days postpartum. Cows randomly assigned into 3 groups [1] 40 cows; 7.5micro g luliberin, IM. [2] 45 cows; 15 micro g luliberin, IM. Seven days later in both groups, 150 micro g D-cloprostenol, IM 25 hours later Img Estradiol Benzoate was injected. Cows olserved for 48 hours and inseminated based on standing heat. Cows that did not display estrus were inseminated at 48 hours after estradiol injection. [3]Control group in=59, did not received any treatment and were inseminated 12 hours after displaying estrus. Pregnancy was diagnosed on day 42 after AI via rectal palpation.Days open and pregnancy rate were analyzed by One-way ANOVA and chi square tests, respectively.The number of days open did not differ among experimental groups [group one 104.17 +/- 7.76 days, group two 106.28 +/- 6.24 days and the third group 111.86 +/- 2.33 days [P>0.05]. Pregnancy rate to the first service was not different among groups [group one 47.5%, 19/40, group two 48.88%, 22/45, third group 32.20%, 19/59][P>0.05]. In conclusion, reducing the dose of GnRH analogue [Luliberin] to half of the full dose did not affect pregnancy rate and days open. Therefore the cost of Heat-synch program can be reduced by using half dose of Luliberin