Influence of a high ambient temperature on lipid metabolism in the growingpig

Because pigs are fatter when they are heat-stressed, it was hypothesized th at lipid metabolism is enhanced in heat-stressed pigs. To test this hypothe sis, an experiment was conducted to determine the influence of a high ambie nt; temperature on the level of plasma lipids, thyroid hormones, lipoprotei n lipase activity, and on the composition of very low density lipoproteins (VLDL) and chylomicrons in the growing pig. Twelve Large White x Landrace c astrated male pigs with an initial weight of 20 +/- 0.6 kg were allotted to one of the following treatments: 1) ambient temperature of 31 degreesC, wi th ad libitum access to feed or 2) ambient temperature of 20 degreesC and f ed the amount consumed by those kept at 31 degreesC until 35 kg BW. Ambient temperature did not affect piglet performance. Compared to that in pigs ke pt; at 20 degreesC, in pigs kept; at 31 degreesC the lipid content of backf at was 26% higher and the proportion of flare fat was increased by more tha n twofold (P < 0.001). Lipoprotein lipase activity was increased more than twofold in backfat and nearly twofold in leaf fat at 31 vs 20<degrees>C (P < 0.001). In warmth-exposed (31<degrees>C), feed-restricted pigs, the plasm a level of triiodothyronine was 30% lower than at 20 degreesC (P < 0.001), whereas VLDL-lipid concentration was more than fourfold higher, and plasma concentrations of NEFA and triglycerides were 2.6- and 3.6-fold higher, res pectively (P < 0.001). In conclusion, the chronic exposure of growing pigs to a high ambient temperature enhances lipid metabolism in both the liver ( VLDL production) and the adipose tissue (lipoprotein lipase activity). Cons equently, plasma triglyceride uptake and storage are facilitated in the adi pose tissue, which results in greater fatness.