Factors influencing conception rates to artificial breeding in New Zealand dairy herds: A review

K.L. Macmillan

Ruakura Animal Research Station, Hamilton

Proceedings of the New Zealand Society of Animal Production. 1979, 39: 129-137

Significant sire differences in fertility, as reflected by conception rate (CR), largely arise through differences in post-insemination sperm survival. These CR and survival differences cannot be reduced by doubling the sperm dose rate per insemination. CRs with sires of below average fertility are low when cows are inseminated in early oestrus. With semen from sires of above average fertility, CRs were similar when cows were inseminated in early versus late oestrus.

Significant CR differences between regions are not due to cow-fertility differences but rather arise from subtle differences in the attitude of the herd owners towards oestrus detection. A sire's average CR relative to the regional average CR is also influenced by these differences in attitude.

While herd differences in CR largely arise through differences in the owners abilities to identify oestrous cows, errors in diagnosis are less undesirable in terms of a herd's conception pattern than errors in identification or omission.

Changes in semen processing or herd management which result in improved CRs will tend to concentrate herd calving patterns and reduce the variation in calving interval but not the mean calving interval.

Keywords: NZSAPAB;