Rynia Isabella S C, House John K, Ingenhoff Luke
Livestock Veterinary Teaching and Research Unit, Sydney School of Veterinary Science, Faculty of Science, University of Sydney, Camden, NSW 2570, Australia.
Vet Sci. 2023 Sep 2;10(9):550. doi: 10.3390/vetsci10090550.
Monitoring 100-day in-calf rate (100DICR) is an integral part of the assessment of reproductive performance in year-round calving dairy herds. The objective of this study was to investigate the effect of month on 100DICR in year-round calving herds in New South Wales (NSW), Australia and determine whether a fluctuating 100DICR target is an appropriate alternative to a constant 100DICR target. The 100DICR is defined as the percentage of all current lactating cows over 100 days in milk (DIM) that conceive on or before 100 DIM. As dairy cows are typically dried off 7 months after conception, 100DICR was an approximate 7-month rolling average. Mean monthly 100DICRs were calculated with a generalised linear model for six NSW north coast herds located 15-140 km from the coast and four NSW south coast herds located less than 10 km from the coast, over a two-year period. The mean 100DICR was lowest in May at 28.62% (95%CI 28.31-28.93) and increased during winter and spring, peaking in December at 34.74% (95%CI 34.32-35.15). The observed trend was similar for north and south coast herds, although north coast herds experienced a greater change in 100DICR from the peak to a nadir of 27.58% (95%CI 27.18-27.98), a 7.15-point difference, compared to south coast herds with a nadir of 30.18% (95%CI 29.69-30.67), a 4.67-point difference between the peak and nadir. In conclusion, 100DICR is affected by month with the lowest 100DICRs observed in late autumn and the highest 100DICRs observed in late spring and early summer. Therefore, a fluctuating target 100DICR is an appropriate alternative to a constant target when assessing reproductive performance in year-round calving herds. While the district does not affect mean 100DICR per se, the district does affect the difference between peak and nadir 100DICR.
监测100日怀孕率（100DICR）是全年产犊奶牛群繁殖性能评估的一个重要组成部分。本研究的目的是调查月份对澳大利亚新南威尔士州（NSW）全年产犊牛群100DICR的影响，并确定波动的100DICR目标是否是恒定100DICR目标的合适替代方案。100DICR定义为所有泌乳超过100天（DIM）的当前泌乳奶牛在100 DIM及之前受孕的百分比。由于奶牛通常在受孕后7个月干奶，100DICR是一个大约7个月的滚动平均值。在两年期间，使用广义线性模型计算了新南威尔士州北海岸距离海岸15 - 140公里的六个牛群以及南海岸距离海岸不到10公里的四个牛群的月平均100DICR。100DICR的平均值在5月最低，为28.62%（95%CI 28.31 - 28.93），在冬季和春季增加，12月达到峰值，为34.74%（95%CI 34.32 - 35.15）。北海岸和南海岸牛群的观察趋势相似，尽管北海岸牛群的100DICR从峰值到最低点的变化更大，为27.58%（95%CI 27.18 - 27.98），相差7.15个百分点，而南海岸牛群的最低点为30.18%（95%CI 29.69 - 30.67），峰值与最低点相差4.67个百分点。总之，100DICR受月份影响，在深秋观察到最低的100DICR，在晚春和初夏观察到最高的100DICR。因此，在评估全年产犊牛群的繁殖性能时，波动的100DICR目标是恒定目标的合适替代方案。虽然地区本身不影响平均100DICR，但地区确实会影响100DICR峰值与最低点之间的差异。
