INFLUENCE OF DIETARY LYSINE LEVELS AND ARGININE-LYSINE RATIOS ON PERFORMANCE OF BROILERS EXPOSED TO HEAT OR COLD STRESS DURING THE PERIOD OF 3 TO 6 WEEKS OF AGE

Four trials of identical experimental design were conducted to determi ne the effects of temperature, dietary Lys level, and dietary Arg:Lys ratios on performance and carcass yield of male broilers. Birds of a c ommercial strain were grown from 21 to 42 d of age in wire-floored fin ishing batteries placed in environmental chambers. The chambers were p rogrammed to provide either a constant thermoneutral temperature (21.1 C), a constant cold temperature (15.5 C), or a cycling hot diurnal te mperature (25.5 to 33.3 C). Within each environment there was a factor ial arrangement of three Lys levels (1.0, 1.1, and 1.2%) with four Arg :Lys ratios (1.1:1, 1.2:1, 1.3:1, and 1.4:1). Environmental temperatur e significantly influenced virtually every characteristic examined. Ho t cyclic temperatures reduced weight gain, feed intake, and breast mea t yield, and increased feed conversion, dressing percentage, leg quart er yield, and abdominal fat content. The cold environment promoted inc reased feed intake and mortality. Ascites and cardiomyopathy were the leading causes of death under cold exposure and thermoneutral conditio ns, whereas complications arising from heat exposure were the main cau se of death under hot cyclic conditions. Levels of Lys affected leg qu arter yield and abdominal fat content over all environments but increa sed breast meat yield only under cold conditions. Increasing Arg:Lys r atios improved feed conversion and dressing percentage and reduced abd ominal fat content; it could not be determined whether these responses were consistent with Arg per se or were due to a nonspecific N respon se. As increasing Lys levels or Arg:Lys ratios did not improve weight gain, increase breast meat yield, or attenuate adverse effects due to heat or cold exposure, it is concluded that the levels of Lys and Arg suggested for 21 to 42 d by the NRC are adequate for birds of this age under the environmental conditions encountered.