Environmental variation effects fertility in tropical beef cattle

Abstract

The northern Australia beef cattle industry operates in harsh environmental conditions which consistently suppress female fertility. To better understand the environmental effect on cattle raised extensively in northern Australia, new environmental descriptors were defined for 54 commercial herds located across the region. Three fertility traits, based on the presence of a corpus luteum at 600 d of age, indicating puberty, (CL Presence, n = 25,176), heifer pregnancy (n = 20,989) and first lactation pregnancy (n = 10,072) were recorded. Temperature, humidity, and rainfall were obtained from publicly available data based on herd location. Being pubertal at 600 d (i.e. CL Presence) increased the likelihood of success at heifer pregnancy and first lactation pregnancy (P < 0.05), underscoring the importance of early puberty in reproductive success. A temperature humidity index (THI) of 65-70 had a significant (P < 0.05) negative effect on first lactation pregnancy rate, heifer pregnancy and puberty at 600 d of age. Area under the curve of daily THI was significant (P < 0.05) and reduced the likelihood of pregnancy at first lactation and puberty at 600 days. Deviation from long-term average rainfall was not significant (P < 0.05) for any trait. Average daily weight gain had a significant and positive relationship (P < 0.05) for heifer and first lactation pregnancy. The results indicate that chronic or cumulative heat load is more determinantal to reproductive performance than acute heat stress. The reason for the lack of a clear relationship between acute heat stress and reproductive performance is unclear but may be partially explained by peak THI and peak nutrition coinciding at the same time. Sufficient evidence was found to justify the use of average daily weight gain and chronic heat load as descriptors to define an environmental gradient.

Multi-breed genomic evaluation for tropical beef cattle when no pedigree information is available

“…Fifty-four collaborator beef cattle herds from across tropical Australia participated in data collection for the Northern Genomics project. The properties were located across Northern Australia, including South Western, Central, Western and Northern Queenslandand the Northern Territory of Australia, and the Pilbara region of Western Australia [ 38 ]. These regions are characterised by a wet season, and a dry season with little pasture growth.…”

“…These regions are characterised by a wet season, and a dry season with little pasture growth. Central and South Western Queensland regions tend to have good to high quality pasture, while Western Queensland and Western Australia regions are arid with low rainfall (350 mm or less per year) [ 38 ]. The 29,321 heifers enrolled included crossbred and approximately 8000 purebred heifers from at least 14 breeds, i.e.…”

“…To maximise genetic variation, the trait is actually measured when an estimated (by average live weight) 50% of the heifers are pubertal, i.e., at 1 to 2.5 years of age. Further details on the phenotypes are described in Copley et al [ 38 ].…”

Drinking Behaviour of Beef Cattle Subject to Water Medication in Various Environmental Conditions

“…In addition to evaporation, the temperature humidity index (THI, Supplementary Materials Table S2) was calculated according to Equation (3), as described in Copley et al [12]:…”

Proteomic applications for studies of bull fertility

“…The fertility index is determinant for profitability in all animal production models (NAYERI et al, 2017). It is influenced by numerous factors and variables (KENNY; BYRNE, 2018;LLAMAS-LUCENO et al, 2020;MORRELL, 2020;COPLEY et al, 2022), and should, therefore, be a permanent object of studies and research.…”