Season has important effects on reproduction in cows, although they may ovulate throughout the year. During winter, the effects of season delay puberty, prolong post-partum anoestrus and reduce fertility. There are seasonal differences in gonadotrophin secretion, pre-ovulatory follicular development and corpus luteum function. Furthermore, effects of season are more likely to be expressed when factors such as nutrition, age and lactation limit reproduction performance. Significant interactions occur between season and nutrition in the onset of puberty and the length of the post-partum anoestrous interval. In the pasture-based agricultural system in New Zealand, minimum feed supply occurs in winter when season depresses cow reproductive performance. A concentrated calving pattern is essential to improve feeding management and herd performance. To maintain a concentrated calving and high weaning percentage, calving date must be adjusted to reduce the effects of season and improve herd nutrition.

KL, Macmillan, MG Pearce, PJA Copeman, KA MacDonald, and R Kilgour

Proceedings of the New Zealand Society of Animal Production, Volume 45, , 35-38, 1985
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