EFFECT OF COLD EXPOSURE ON MILK PRODUCTION AND ENERGY BALANCE IN THE LACTATING EWE

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Abstract
The lactational performances of shorn ewes chronically exposed to a thermoneutral (21 ± 1 °C) or cold (0 ± 1 °C) environment were compared in two experiments. Heat production measured after 1, 21 and 41 days of cold exposure was increased by 20% (P < 0.05), 43% (P < 0.01) and 55% (P < 0.001), respectively, over thermoneutral control values. In both experiments, cold exposure increased milk fat concentration (P < 0.05). Milk protein and lactose concentrations were maintained in exp. 1 but tended to be increased in exp. 2 as a result of cold exposure. Milk obtained from the cold-exposed ewes was characterized by a relative decrease in short-chain fatty acid secretion (P < 0.01). Although milk composition was affected by cold stress, daily milk production was not significantly altered; as a consequence, total energy lost in the milk tended to be slightly higher for the cold-stressed ewes. The increased energy lost as heat and in the milk during cold exposure resulted in a net energy deficit throughout most of the experimental period. The present data suggest that the lactational performance of a ewe nursing a single lamb is not impaired by chronic exposure to an ambient temperature of 0 °C. Key words: Cold, milk production, milk composition, ewes, energy balance