Sulfur amino acid utilization by growing broilers fed practical and semi-purified diets at two energy levels

A series of six experiments was conducted utilizing either corn-soybeal meal or semi-purified basal diets. All experiments utilized a total of 1807 Hubbard x White Mountain strain chicks with ages ranging from 1 to 49 days posthatching. The objective of these experiments was to determine total sulfur amino acid (methionine + cystine) requirements for growing broilers fed practical and semi-purified diets at two energy levels. Experiment 1 employed a corn-soybean basal diet at two energy levels to establish the sulfur amino acid requirement for maximal feed efficiency of chicks during the period 8 to 22 days posthatching. Five graded levels of DL-methionine (0 to .24% in the presence of .80% and .79% methionine + cystine, for low and high energy basal diets, respectively) were employed in a 2x5 factorial treatment arrangement. There was a marked growth response due to increased energy level. There was no significant gain response due to supplemental DL-methionine. Gain/feed ratio was maximized at .98% methionine + cystine for the low energy diet (2970 kcal ME/kg) and at .91% methionine + cystine for the high energy diet (3232 kcal ME/kg). Experiment 2 was conducted to determine the sulfur amino acid requirement for maximal feed efficiency of chicks during the period 21 to 34 days posthatching. DL-methionine additions were identical to those used in Experiment 1. As with the younger chicks there was a marked growth response to increased energy level and no significant gain response to supplemental DL-methionine. Gain/ feed ratio was maximized at .89% methionine + cystine for the low energy diet (3045 kcal ME/kg) and at .95% methionine + cystine for the high energy diet (3307 kcal ME/kg). Experiment 3 was conducted to confirm results of Experiment 1 and 2 that utilized battery-reared chicks. This trial was conducted in a grower house and in a manner more closely resembling those currently employed in the broiler industry. The basal diets were the same as employed for Experiment 2; however, methionine additions were decreased to .05, .10, .15, and .20%. There was a significant methionine effect for both the low and high energy diets. As DL-methionine was incrementally added from 0 to .20% (.91% methionine + cystine) there was a significant improvement in gain/feed ratio for birds on the high energy diet. However, unlike Experiments 1 and 2 there was no marked growth response due to increased energy levels. To further substantiate the results with practical corn soybean diets a semi-purified basal diet was employed for Experiments 4, 5, and 6. In Experiment 4, five graded levels of DL-methionine (0 to .60% in the presence of .59% methionine + cystine were employed in a 2 x 5 factorial treatment arrangement. As with previous experiments, there was a marked growth response in young broiler chicks due to increased energy levels. Gain/feed ratio was maximized at .89% methionine + cystine for the low energy diet (2750 kcal ME/kg) and at 1.04% methionine + cystine for the high energy diet (3200 kcal ME/kg). Based on gain data, the total sulfur amino acid requirement was estimated to be .78 + .227% for the low energy basal diet and .81 + .095% for the high energy diet. Both of these estimates are lower than the recommended .93% methionine + cystine requirement listed by the National Research Council (N.R.C.) for broiler chicks 0 to 3 weeks of age. Experiment 5 was conducted to determine if the same effects of energy level and methionine supplementation would occur in the older chicks (4 to 6 weeks of age). Similar diets and methionine additions were used for the older birds. A marked growth response occurred due to increased energy levels. There was also a significant gain response due to supplemental DL-methionine for both energy levels. Gain/feed ratio was significant over-all levels of supplemental DL-methionine for the high energy diet and was maximized at .90% methionine + cystine for the low energy diet. Based on gain data, the total sulfur amino acid requirement was estimated to be .96 ± .085% for the low energy diet and .75 ± .130% for the high energy diet. These estimates are both higher than the recommended .72% methionine + cystine requirement by the N.R.C. for broiler chicks 3 to 6 weeks of age. In Experiment 6 choline was incrementally added, from 600 to 1800 mg/kg diet, to a semi-purified basal diet containing .803% methionine + cystine, 22.1% crude protein and 3200 kcal ME/kg. Results indicated no significant differences for gain, feed comsumption, or gain/feed due to choline supplementation.