Physiological profiles to explain breed differences in lamb thermoregulation

By Holly Webb, ASAS/ASAP communications intern

Animal Production 2016 speaker highlight: Kate Plush

2nd-cross-lamb

Photo: The Australian Poll Dorset Association

In a recent study published in Animal Production Science, researchers from the Cooperative Research Centre for Sheep Industry Innovation, The University of Adelaide and South Australian Research and Development Institute (SARDI), have reported factors that could explain the differences in thermoregulation among breeds that differ in lamb survival.

Lamb mortality represents significant reproductive wastage and is an animal-welfare concern for sheep producers. Rapid adaptation from the uterine environment to self-thermoregulation is a vital ability for lamb survival. Survival is dependant on maintaining body temperature after birth and possessing energy reserves to continue maintenance.

Breed differences in resistance to cooling have previously been identified but why these differences exist is yet to be determined.

Researchers recorded rectal temperature at birth, cold resistance and cold recovery at 1 day of age in cross-bred (Poll Dorset Border Leicester and Poll Dorset Merino) and pure-bred (Border Leicester and Merino) lambs. To measure cold resistance, lambs were placed in a cooled bath and the time for rectal temperature to fall to 35°C was recorded. The time to restore rectal temperature after cold exposure was recorded as cold recovery.

The study found Border Leicester derived lambs were more cold resistant than Merino lambs and Poll Dorset Border Leicester had higher peak glucose concentrations than Poll Dorset Merino lambs. Pure-bred Border Leicester lambs took longer to reach peak glucose concentration but the eventual peak value was higher than in Merino lambs.

The cold resistance of both genotypes of lambs was significantly influenced by birth weight, although cross-bred lambs had greater cold resistance. Cold resistance was further shown to be influenced by lamb breed in both cross and pure-bred lambs. Additionally, the rectal temperature of lambs at birth was correlated with cold resistance.

The researchers conclude that variations in birth weight and glucose metabolism are associated with breed difference in thermogenesis of neonatal lambs, confirming the importance of carbohydrate metabolism during hypothermia. Breeds better able to resist cooling, in addition to an increased weight advantage, may be better able to generate and/or mobilise glucose when under cold stress.

Variation in physiological profiles may explain breed differences in neonatal lamb thermoregulation was published in Animal Production Science Volume 56 Number 4 2016.

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