A population-based epidemiological study was conducted between 2007 and 2011 and involved 78 northern Australian commercial beef-breeding herds and in excess of 56 000 cattle concurrently monitored. Cow reproductive performance was described from the biannual assessment of fetal age and lactation status. Both novel and well established measures of performance were used within four broad country types and included the following: percentage of lactating cows pregnant within 4 months of calving; percentage of cows pregnant within an approximate 12-month reproductive cycle (annual pregnancy); fetal and calf loss between confirmed pregnancy and weaning; percentage of cows contributing a calf at weaning and percentage of non-pregnant females retained for re-mating. The results from the present study described the variation in reproductive performance of commercial beef herds across northern Australia and defined typical and achievable levels of performance. The results from the study suggest that a weaning rate of 66% is a more realistic target level of performance for the Northern Forest, while weaning rates of at least 75–80% are realistic for other country types. Female-cattle performance was much lower in the Northern Forest than in the other country types. In absolute terms, there were 15–20% fewer surviving mated cows contributing a calf at weaning in an annual production year and ~4% more missing pregnant cows, which was associated with the ~20% higher retention of non-pregnant cows for re-mating. The reproductive performance of herds varied substantially among and within country types, with a 20–30% variation in reproduction rates and 5–15% variation in fetal and calf loss for half of the herds in all regions. Further analyses were performed and identified the major causes of this variation and are reported in subsequent papers within this series. The results from the present study appear to suggest that substantial opportunities to increase the reproductive performance of northern beef herds exist, providing that the causes of this variation are able to be identified and alleviated.

中文翻译：

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澳大利亚北部牛群的繁殖性能。2. 受监测繁殖性能的描述性分析

2007 年至 2011 年期间进行了一项基于人群的流行病学研究，涉及 78 个澳大利亚北部商业肉牛养殖群，同时监测了超过 56 000 头牛。奶牛繁殖性能通过每两年一次的胎龄和泌乳状态评估来描述。在四个广泛的国家类型中使用了新的和完善的性能指标，包括以下内容：产犊后 4 个月内怀孕的泌乳母牛的百分比；在大约 12 个月的生殖周期内怀孕的奶牛百分比（每年怀孕）；确认怀孕和断奶之间的胎儿和小牛丢失；断奶时贡献一头小牛的母牛的百分比和保留用于重新交配的未怀孕母牛的百分比。本研究的结果描述了澳大利亚北部商业牛群繁殖性能的变化，并定义了典型和可实现的性能水平。研究结果表明，66% 的断奶率是北方森林更现实的性能目标水平，而至少 75-80% 的断奶率对于其他国家类型是现实的。北部森林的母牛表现远低于其他国家类型。从绝对值来看，每年生产年份断奶时幸存的交配母牛减少了 15-20%，丢失怀孕母牛的数量增加了约 4%，这与未怀孕母牛的保留率高约 20% 相关。 -交配。畜群的繁殖性能在国家类型之间和国家内部差异很大，在所有地区的一半牛群中，繁殖率有 20-30% 的变化，胎儿和小牛损失有 5-15% 的变化。进行了进一步的分析并确定了这种变化的主要原因，并在本系列的后续论文中进行了报告。本研究的结果似乎表明，存在提高北方牛群繁殖性能的大量机会，前提是能够确定和减轻这种变化的原因。