Reproductive performance of northern Australia beef herds. 6. Risk factors associated with reproductive losses between confirmed pregnancy and weaning

Abstract

Context High and variable fetal and calf loss in beef herds occurs across northern Australia. Reasons for the majority of these losses, a major cost to the industry, have remained unknown. Aims The research question was, which of the 58 region-, property-, management group-, and animal-level risk factors measured are associated with pregnant females failing to wean their calf? Methods An epidemiological study measured fetal and calf loss (consistently expressed as % points) between confirmed pregnancy and weaning and the major associated risk factors using a selected population from 55 commercial beef breeding herds representing 23 166 pregnancies in the mostly dry tropical environment of northern Australia. Key results Median fetal and calf loss was 9.5% with large variation. Achievable levels appeared to be <10% for Northern Forest herds, and <5% for Southern Forest, Central Forest and Northern Downs herds. The risk factors most strongly associated with fetal and calf loss were low-fertility country type interacting with phosphorus inadequacy (up to 10% increase), low body condition score interacting with phosphorus inadequacy (up to 8% increase), tall cows (up to 4% increase), and high temperature–humidity index around calving interacting with country type (up to 7% increase). These are nutritional and environmental risk factors and had the combined highest individual effect and frequency. Other risk factors associated with fetal and calf loss included first-lactation cows, which interacted with mustering around calving (up to 9% increase), having not reared a calf in the previous year interacting with cow age (up to 8% increase), low mustering efficiency (up to 9% increase), perceived predation by wild dogs (4–5% increase), high prevalence of Campylobacter fetus sp. venerealis antibodies (7% increase), recent infection with bovine viral diarrhoea virus (9% increase), and inadequate dry-season protein (4% increase). Conclusions The combined effects of environmental, nutritional and management risk factors on fetal and calf loss in northern Australia were large and additive and were much greater, collectively up to 30–40%, and more consistent than that due to either endemic infectious diseases or animal factors. Implications Opportunity for remedial action is high and, for the effect of non-infectious risk factors, should target milk delivery to neonatal calves.

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

“…The findings from the present study suggest a new hypothesis for the high rates of calf mortality and morbidity associated with poor pregnant cow nutrition in dry tropics beef production systems (Fordyce et al 2021), which opens the possibility for practical interventions to ameliorate the problem. As short-term improvements in nutrition can assist with the progesterone decline, the use of improved or spelled pasture and protein supplements around calving, together with group segregation, auto-drafters, and automated individual feeders, could be considered to develop cost-effective management strategies to improve milk delivery and reduce calf losses.…”

High frequency of delayed milk delivery to neonates in tropical beef herds

“…Before the specific mechanisms explaining neonatal mortality may be investigated in tropical beef calves, the risk factors for overall calf wastage in commercial herds must be considered. Herds exposed to poor pre‐partum nutrition consistently have increased calf wastage (Fordyce et al, 2022 ). In addition, high ambient heat load around calving is associated with increased calf wastage within three of the four major land types in tropical and subtropical Australia (Fordyce et al, 2022 ).…”

“…Herds exposed to poor pre‐partum nutrition consistently have increased calf wastage (Fordyce et al, 2022 ). In addition, high ambient heat load around calving is associated with increased calf wastage within three of the four major land types in tropical and subtropical Australia (Fordyce et al, 2022 ). Both poor pre‐partum nutrition for cows and high ambient heat loads around calving are risks that occur frequently across tropical and subtropical Australian herds.…”

“…While the primary risk factors for overall calf wastage provide useful context (Fordyce et al, 2022 ), the majority of neonatal mortalities in tropical beef herds remain unexplained (Bunter et al, 2013 ). The nutritional deficiencies associated with calf wastage are the same as those associated with reduced milk yields, especially deficiencies of energy (Banchero et al, 2015 ), protein (Cowan et al, 1980 ), phosphorus (Castells et al, 2014 ) and water (Murphy et al, 1983 ).…”

“…The nutritional deficiencies associated with calf wastage are the same as those associated with reduced milk yields, especially deficiencies of energy (Banchero et al, 2015 ), protein (Cowan et al, 1980 ), phosphorus (Castells et al, 2014 ) and water (Murphy et al, 1983 ). While high ambient heat loads around calving are associated with increased calf wastage (Fordyce et al, 2022 ), they are also associated with reduced milk yields (Brody, 1956 ; West et al, 2003 ). If neonatal calves do not receive milk, they die within three days at comfortable ambient temperature or within one day under hot conditions (Fordyce et al, 2015 ).…”