Dietary Protein and Sulfur Amino Acid Levels for Laying Hens During Heat Stress

Two experiments were carried out with laying hens in order to evaluate the effects of environmental temperature on methionine requirements and total protein needs. In the first study, birds were housed at either 21.1 or 32.2°C. and fed diets containing 15.6% protein with methionine plus cystine levels of 0.5, 0.55, 0.59 or 20% protein with 0.59% sulfur amino acids. Birds housed at the lower environmental temperature consumed protein in amounts which varied from 12.5 to 14.0 gm./day when fed the 15.6% protein diet, while those on the 20% protein diet consumed 17.3 gm. protein/day. At the higher temperature feed consumption was reduced. Methionine supplementation significantly increased egg production and egg weight at both temperatures. No improvements in performance were obtained above 0.289% methionine or 0.549% methionine plus cystine at 21.1°C. At this level, the birds consumed an average of 211 mg. methionine or 494 mg. methionine plus cystine/day. The maximum egg production obtained at 32.2°C. was 51.8%; the birds in this treatment consumed an average of 63 gm. feed/day. No additional response was obtained at this higher protein level. Multiple regression analyses yielded prediction equations which estimated the sulfur amino acid requirements for 70% production at 497.7 and 514.1 mg./day for birds housed at 21.1 and 32.2°C., respectively. In a second experiment, protein intakes were equalized for birds housed at 21 and 35°C. over a range of 12.7 to 20.5 gm./day. Significant improvements in egg production were obtained with increased protein consumption at 21°C.; while no increase in production was obtained with increased protein intake at 35°C. Multiple regression analyses on these data suggested that energy intake was the limiting factor for egg production at 35°C.; however, the possibility exists of a number of other factors adversely affecting egg production at higher temperatures.