title: Some effects of cold exposure on milk secretion in the goat
Creators: name: White, Janette Marie
Publisher: name: University of Glasgow
Year: 1984

description: The work described in this thesis was carried out in order to determine the effects of certain short-term changes in climatic conditions on mammary gland function, notably milk yield and composition in the goat. The technique involved transferring lactating British Saanen goats from an insulated byre to a precision climatic chamber where they were exposed for 2 or 3 days to a controlled cold environment. Whilst under this climatic stress the animals were fed and milked as in the byre. Milk yield and composition were determined over this period and certain plasma constituents were also monitored. In Chapter 3, Section 1, the effects of a range of environments on milk yield and composition are described. The thermoneutral environment (22°C) had a slight negative effect on milk yield after 3 days exposure but the mild cold (0°C +/- 1°C, still air) and the moderate cold (0°C +/- 1°C, wind speed 5.6 m/s) environments lead to a decline in milk yield to 86% and 81% of their previous yields respectively. The cold and wet environment (as for 'moderate' but with cold water sponged onto the animal's back) did not produce any significant effects on milk yield. All the test environments lead to small changes in the ionic composition of milk, but there was no suggestion of disruption of the mammary epithelium. Milk lactose concentration rose under all the test climatic conditions; there were no significant changes in milk citrate levels and milk fat content rose only in the mild cold conditions. The results of Section 2 show that the effects of the moderate cold environment on milk yield were most marked in mid lactation and that composition was most affected in early lactation. Section 3 examined the relationship of energy balance and the response of rate of milk secretion to the moderate cold environment. Food intake was restricted, thus lowering the calculated energy intake, and output of milk energy was determined by calculation. The results indicate that the response in terms of reduction in milk secretion was more closely related to stage of lactation than initial energy balance In Section 4 the response of denervated and intact mammary glands to moderate cold stress was found to be equal. Section 5 examined the concentration of intracellular metabolites in milk during exposure to cold environments. Phosphoenol pyruvate levels were found to decline during exposure of goats in mid-lactation to the moderate cold environment. Concentration of other metabolites was unaffected by the cold conditions. The results of plasma analysis shown in Section 6 indicate that plasma cortisol concentration was not affected by the cold environments but that the cold and wet conditions lead to increases in free fatty acid concentration. It is suggested that the animals exposed to the cold and wet conditions were the most stressed, but that this stress was not reflected in mammary gland function. In the final chapter, the response of the lactating goat to cold environments is discussed, in relation to effects on milk secretion.