Effect of parity, season and FSH treatment on the calving interval of Ayrshire cows in the tropics

A total of 607 calving intervals on 99 Ayrshire cows with parities from 1 t o 10 and belonging to one dairy herd at Iringa in the southern highlands of Tanzania were analysed to study the effect of parity and season or month o f calving on the subsequent calving interval. In addition, 22 calving inter vals incorporating a superovulatory cycle were compared with those of 52 co ntrols that had calved around the same period. The average (mean +/- SEM) age at first calving was 985 +/- 16 days. The ef fect of parity on calving interval was highly significant (p < 0.001). Cows that calved in December, at the beginning of the rainy season, exhibited t he shortest calving interval (404 +/- 13), while those that calved in Septe mber/October, in the dry season, exhibited the longest average calving inte rval (466 +/- 20 days), although this difference was not significant. Prior treatment with follicle-stimulating hormone to induce superovulation, sign ificantly lengthened the average calving interval (579 +/- 28 vs 457 +/- 15 days; p < 0.001). It was concluded that both parity and FSH treatment affected the calving in terval. However, season (rainy vs dry) or month of calving did not influenc e this interval.