Measuring reproductive traits in tropical beef cattle breeds: Implications for genetic evaluation
thesisposted on 01.09.2020, 00:00 by Nicholas Corbet
Reproduction in beef cattle herds is a key driver of productivity and profitability of beef enterprises. Improving the efficiency of reproduction is necessary to keep pace with an increasing global demand for animal protein. Grazing lands across northern Australia, however, comprise large areas of relatively lowly productive land-types with hot, dry climates and unpredictable seasonal rainfall. The challenge for many north Australian beef enterprises is to improve reproduction in the tropically adapted beef breeds grazed extensively in these regions. Environmental factors influenced by climate and herd management practices account for a proportion of the variation in reproduction rate, but underlying genetic factors also explain individual animal differences. Industry-wide genetic improvement of herd reproductive performance has generally been slow, mainly due to perceptions of low heritability, late expression of the trait and difficulty in capturing the necessary joining and calving data. However, selection line experiments in research herds have demonstrated genetic improvement in pregnancy rates of 3% to 5% per annum in tropically adapted breeds. Likely contributors to the genetic differences seen in selected animals are the higher heritability of component traits of reproduction and genetic correlation of these component traits with reproductive performance. This study incorporates a series of experiments conducted across 9 years and reports moderate to high heritability of reproductive component traits. The traits studied included age at puberty and post-partum anoestrus in females; and scrotal circumference and percent morphologically normal sperm in males. In addition, the study reports moderate genetic correlation between these key component traits and lifetime reproduction. The estimated genetic parameters indicate that selection for genetic improvement of these attributes of reproduction, in conjunction with sound breeder-herd management, offers a sustainable solution to the challenge of improving reproductive efficiency in north Australian herds. The perceived challenge of data collection required for genetic evaluation, however, remains a barrier to the adoption of genetic improvement strategies by north Australian beef producers. With the aim of refining and automating data collection, the final two experiments report on the use of ultrasound scanning, on-animal devices and radio-frequency identification sequence through walk-over-weigh systems to autonomously record behavioural oestrus and predict time of conception in post-partum cows. Further detailed studies are required, but on-animal devices could potentially provide a suite of technologies to help reduce the challenge of recording and formatting data. Coupled with data handling software platforms, these technologies could provide beef producers with the necessary information on individual animals to more readily develop strategies for genetic improvement of reproductive efficiency.