Factors associated with calf mortality in tropically adapted beef breeds managed in extensive Australian production systems

Abstract

Data from 9296 calves born to 2078 dams over 9 years across five sites were used to investigate factors associated with calf mortality for tropically adapted breeds (Brahman and Tropical Composite) recorded in extensive production systems, using multivariate logistic regression. The average calf mortality pre-weaning was 9.5% of calves born, varying from 1.5% to 41% across all sites and years. In total, 67% of calves that died did so within a week of their birth, with cause of death most frequently recorded as unknown. The major factors significantly (P < 0.05) associated with mortality for potentially large numbers of calves included the specific production environment represented by site-year, low calf birthweight (more so than high birthweight) and horn status at branding. Almost all calf deaths post-branding (assessed from n = 8348 calves) occurred in calves that were dehorned, totalling 2.1% of dehorned calves and 15.9% of all calf deaths recorded. Breed effects on calf mortality were primarily the result of breed differences in calf birthweight and, to a lesser extent, large teat size of cows; however, differences in other breed characteristics could be important. Twin births and calves assisted at birth had a very high risk of mortality, but <1% of calves were twins and few calves were assisted at birth. Conversely, it could not be established how many calves would have benefitted from assistance at birth. Cow age group and outcome from the previous season were also associated with current calf mortality; maiden or young cows (<4 years old) had increased calf losses overall. More mature cows with a previous outcome of calf loss were also more likely to have another calf loss in the subsequent year, and this should be considered for culling decisions. Closer attention to the management of younger cows is warranted to improve calf survival.

The Occurrence and Toxicity of Indospicine to Grazing Animals

“…Causes of a large proportion of both pre-and peri-natal losses in these extensive herds are unknown [54]. In a recent study of factors affecting calf mortality in this region, 67% of calves that died did so within a week of their birth, with cause of death most frequently recorded as unknown [55].…”

Dehydration as a risk factor for calf mortality in northern Australia

“…Although, foetal and calf mortality has been reported to be mostly associated with the nutrition, management and environment during gestation and around calving. These associations are as strong, if not stronger than associations with disease and animal factors (Bunter et al, 2013.…”

“…Tropically-adapted beef breeding herds are no exception, as during the period from positive pregnancy diagnosis to weaning, 67% (Bunter et al, 2013) or 43.8% (Holroyd, 1987) of mortality has been reported to occur during neonatal life 1 . Under frequent observations in extensively-managed Brahman and Brahman influenced herds, the majority of neonatal mortalities were unexplained (Bunter et al, 2013, Holroyd, 1987.…”

“…The causes responsible for the majority of occurring neonatal mortalities in northern Australia are not defined (Bunter et al, 2013, Holroyd, 1987. Although, foetal and calf mortality has been reported to be mostly associated with the nutrition, management and environment during gestation and around calving.…”

“…Interquartile ranges for incidence of foetal and calf mortality were between 5% and 14% . Bunter et al (2013)'s study focussed on tropically-adapted calf mortality and demonstrated that 67% of foetal and calf mortalities occur during neonatal life, i.e., within the week of birth.…”