Presently, the milk yield of Holsteins in Hokkaido is increasing, but their conception rate at the first service is decreasing and the calving interval is increasing. To improve reproductive performance, the factors causing the above must be clarified. The objectives of this research were to investigate the effects of angularity on herd life and reproductive performance and to investigate the effects of lactation persistency on reproductive performance. [The Effects of Angularity on Herd Life and Reproductive Performance in Holsteins] The effects of angular body shape of Holsteins on herd life and reproductive performance were investigated. The cattle group with high angularity score showed a significantly longer herd life and higher parity, 305 day corrected milk yields, and peak milk yields. No variations because of differences in angularity were observed for the number of days from calving to first service, conception rate for calving to first service, number of days to reach peak milk yield, days open, and services per conception. Based on the above, it was clarified that differences in angularity scores affected the herd life, parity, 305 day corrected milk yields, and peak milk yields, but did not affect the reproductive performance and number of days to reach peak milk yield. Further, high angularity score was found to be associated with increased parity and subsequent increases in the 305 day corrected milk yield and peak milk yield. Therefore, the cattle group with high angularity scores was considered to have high parity, 305 day corrected milk yield, peak milk yield, and long herd life. Thus, the above findings suggest that if cattle with high angularity scores were selected, then it is possible to populate the herd with cattle that have high parity, 305 day corrected milk yields, and long herd life. [The Effects of Lactation Persistency on Reproductive Performance in Holsteins] The effects of lactation persistency on reproductive performance in Holsteins were investigated. The cattle group with high lactation persistency showed significantly low number of days for calving to first service and days open. Further, as the lactation persistency increased, the parity significantly decreases. No variations because of differences in the lactation persistency were observed in the conception rate for calving to first service, services per conception, or 305 day corrected milk yields. On the basis of the above findings, it was shown that differences in lactation persistency affected the number of days for calving to first service, days open, and parity, but do not affect the conception rate for calving to first service, services per conception, or 305 day corrected milk yields. The above findings suggest that selecting cattle with high lactation persistency can achieve the following 1) delaying the day until peak milk yield is reached post calving and reducing the post-calving negative energy balance 2) quick recovery of ovary functions and the uterus post calving and improving the number of days for calving to first service and days open 3) improving the conception rates for calving to first service, and services per conception. On the basis of the results of this research, it was clarified that differences in angularity scores affect the values of herd life, parity, 305 day corrected milk yields, and peak milk yields, but do not affect the reproductive performance and number of days until peak milk yield is reached. Accordingly, if cattle with high angularity scores are selected, then it is possible to populate the herd with cattle that have high parity, 305 day corrected milk yields, and long herd life. Further, differences in lactation persistency was found to affect the number of days for calving to first service, days open, and parity, but not the conception rate for calving to first service, services per conception, and 305 day corrected milk yields. The above findings suggest that selecting cattle with high lactation persistency can reduce the post-calving negative energy balance and improve reproductive performance.
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The Effects of Angularity and Lactation Persistency on Reproductive Performance in Holsteins
ホルスタイン種の鋭角性および泌乳持続性が繁殖成績に及ぼす影響
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