Field trial of a planned breeding regimen for dairy cows, using gonadotrophin-releasing hormone and prostaglandin F-2 alpha

A planned breeding regimen, using gondadotrophin-releasing hormone (GnRH). prostaglandin F-2 alpha, and a second dose of GnRH, followed by a fixed tim e insemination, was evaluated in comparison with a negative control on eigh t commercial dairy farms in the south of England. Fertility data were colle cted from the 220 cows in the planned breeding group and from 220 matched c ontrol cows inseminated at observed oestrus. The planned regimen induced vi sible oestrus in the vast majority of the cows, and serving the cows at thi s oestrus reduced the calving to conception interval by 15 days, resulting in 12 per cent more cows being pregnant by 125 days after calving, and 6 pe r cent more by 150 days. The results from the individual farms suggested th at more benefit may be derived from using the regimen in herds with only av erage fertility indices. There was also evidence to suggest that the second GnRH injection was important, even in cows that came on heat and were serv ed before the fixed time insemination.