Serum non-esterified fatty acids and plasma glycerol as indicators of fat mobilization in pregnant sheep subjected to cold stress

Fifteen pregnant ewes in an open barn were kept on a constant hay diet during the whole gestation period. The ewes were shorn as usually in fall and spring. The serum non-esterified fatty acids (NEFA) and the plasma glycerol (PG) content were followed during the gestation.The body weight, NEFA and PG values were rather constant during the first 2 months of gestation (NEFA: 430 ± 175 µeq./l serum, PG: 39 ± 19 µmol/1 plasma) indicating an adequate feeding during this period. NEFA and PG showed thereafter a parallel increase and reached maximal values at the first sampling after shearing which coincided with a marked drop in environmental temperature. NEFA was then 450 % and PG about 340 % of the normal values, indicating a strong increase in fat mobilization in this period. The shearing reduces the isolation property of the fur considerably, and the ewes have to produce extra heat to maintain the normal body temperature at low environmental temperatures. The metabolic rate after shearing was estimated to have been 2–4 times the basal rate at the temperatures in the barn. This strong increase in the metabolic rate was not compensated by an increased food intake, but resulted in increased fat mobilization.