INTERACTIVE EFFECTS OF THERMAL ENVIRONMENT AND DIETARY AMINO-ACID AND FAT LEVELS ON RATE AND EFFICIENCY OF GROWTH OF PIGS HOUSED IN A CONVENTIONAL NURSERY

In four trials, 480 weanling pigs were housed in a conventional nursery maintained at 20 or 30-degrees-C, which represented a cool and hot thermal environment, respectively. They were allowed ad libitum access to corn-soybean meal-dried whey diets containing .7, 1.0, or 1.3% lysine and 0 or 5% added fat (choice white grease). The pigs were weaned between 27 and 33 d of age (7.27 +/- .90 kg) and penned in groups of five for the duration of the 42-d trials. Pigs housed in the cool environment consumed more feed (P < .01), gained more weight (P < .01), and utilized feed more efficiently (P < .01) than those in the hot environment. As dietary lysine levels were increased in the 20 and 30-degrees-C environments, daily weight gains and gain:feed ratios increased linearly (P < .01) from d 0 to 21 and quadratically (P < .01) from d 21 to 42. However, the magnitudes of the increases were less in the cool environment, resulting in temperature x lysine interactions (P < .05). As the pig's feed intake, body weight, and heat production increased over time, the 20 and 30-degrees-C environments became progressively warmer relative to the animal's zone of thermoneutrality. The associated reductions over time in energy and lysine intakes relative to the pigs' maintenance needs resulted in an increase in the concentration of dietary lysine needed to maximize rate and efficiency of gain in the 30-degrees-C environment but not in the 20-degrees-C environment (temperature x lysine x period interaction, P < .10). The addition of fat to the low-lysine diet further decreased (P < .05) daily energy and lysine intakes, causing a reduction in growth rate of pigs in the 30-degrees-C environment but not in that of pigs in the 20-degrees-C environment, which resulted in a temperature x lysine x fat interaction (P < .05). Based on these results, the optimal dietary amino acid regimen for weanling pigs is dependent on the thermal environment in which the pigs are housed.