Dehydration as a risk factor for calf mortality in northern Australia

Abstract

It is estimated that approximately one million calves die in Australia every year, with the majority unexplained. This thesis reviews losses associated with dehydration-mediated mortality during neonatal life, when there is highest risk of mortality, and reports three studies of neonatal calf dehydration.For 12 neonatal Brahman calves at Spyglass research site (northern forest land type, Queensland), variation in hydration status was investigated (Experiment 1). Change in live-weight from birth was used as the primary measure of hydration. Half of this cohort had low live weight gain between birth and day 3 of life (p = 0.01) compared to calves growing at 0.95±0.24 kg/day from birth. Low growth and associated reduced plasma protein (p = 0.04) in 6 calves indicated reduced colostrum, milk uptake and therefore reduced body fluid replenishment compared to other calves. This positions them at high risk of mortality under adverse environmental conditions. Urea space was tested as a measure of body water; however, percentage body water estimates were unrealistically elevated (> 80% of live weight) and therefore not representative of actual calf percentage body water.Descriptive analysis of risk factors for calf mortality was conducted for 478 and 378 tropically adapted newborn calves, respectively at Spyglass and Brian Pastures (southern forest land type, central Queensland) research sites (Experiment 2). The incidence risk of neonatal mortality in the southern forest of Queensland and northern forest of Queensland was 3.1% and 4.7%, respectively. Some risk factors and the percentage of calves exposed to high mortality risk included: dam body condition score ≤2 (8%), birth weight ≤28 kg (18%), low birth vigour (2%), large udder size (1%), at least two large teats (2%) and poor maternal protectiveness (5%). The low proportion of cows in poor body condition and good nutritional management limited the opportunity for dehydration-mediated neonatal mortality. There were no cases of prolonged heat stress around calving at the level previously associated with foetal and calf mortality. Experiment 2 indicates that low calf mortality may be achieved in any country type, provided that a low proportion of calves are exposed to high risk of mortality. A simple mechanistic model was developed to describe milk uptake volumes and ambient temperature (heat stress) impacts on neonatal hydration. This model provided clarification for the possible risk of dehydration mediated mortality across breeding herds of northern Australia.This thesis demonstrated variation in milk delivery, modelled that low milk delivery is associated with dehydration-mediated mortality and demonstrated that risk of mortality is low at a herd level when the risk factors associated with reduced milk delivery have low frequency.3

Parâmetros hematológicos de bezerros leiteiros mestiços do nascimento aos 15 dias de idade

“…Renaud et al (2018) identificaram que 12% dos bezerros alimentados exclusivamente com leite, apresentavam sinais clínicos de desidratação. Como demonstrado por Muller (2017), a baixa ingestão de leite está associada à mortalidade de bezerros mediada por desidratação, sendo este um importante aspecto a ser considerado no manejo dos neonatos.…”

Maternal Behavior in Beef Cattle: The Physiology, Assessment and Future Directions—A Review

“…However, as others have suggested [ 78 ], the unique patterns of seclusion behavior between individuals at the time of calving implicates that further work is needed to elucidate on the effects of interference and breed on cooperative milk provisioning. Failed milk delivery has also been identified by previous authors to be a crucial determinant to calf survival in extensive environments in northern Australia [ 14 , 15 , 17 ]. Whilst this is most likely a reflection of nutritional stressors in late gestation cows and heifers, it ultimately highlights that supply of milk, nutrients and immunity is a crucial aspect of successful mothering by the bovine cow.…”

“…Other recent work suggests that between 30–50% of calf losses may occur within a day to a week of calving, respectively, with stress and undernutrition of the pregnant cow being the major causative factors [ 14 ]. In these extensive northern Australian settings, dehydration of the calf appears to be major cause of death [ 15 , 16 ], likely due to failed milk delivery by the cow following nutritional deficiencies in late gestation and early lactation [ 17 , 18 ]. This reinforces the importance of achieving the adequate provision of nutrients to the newborn as part of successful mothering in the bovine.…”

Immediate prepartum supplementation accelerates progesterone decline, boosting passive immunity transfer in tropically adapted beef cattle

“…Calf mortality is an ongoing problem across the dry tropics, with most losses occurring within the first week after birth and for unexplained reasons (Bunter et al 2014). With the normally high temperatures during peak calving of tropical beef systems, any delay in milk delivery during the first 3 days after calving substantially increases the risk of dehydrationmediated calf mortality (Muller 2017). Pronounced deficits in metabolisable protein and energy and other nutrients during the prepartum period could be modulating colostrum yield and milk delivery, and a high incidence of calf mortality has been associated with poor cow nutrition and elevated environmental stress (McGowan et al 2014).…”