In a factorial arrangement of treatments Arbor Acres and Ross male broiler chicks were given four diets with 3,200 kcal ME/kg and four diets with 2,880 kcal ME/kg, two CP levels per energy level (23.1 and 33.6% in the high-energy diet and 21.0 and 29.7 in the low-energy diet) and two Lys levels per CP level per energy level (1.20 and 1.36% per CP level in the high-energy diets and 1.08 and 1.22% per CP level in the low-energy diets). The diets were given to 8 wk of age. Weight gain of Arbor Acres chicks was significantly higher (P less than .05) than that of Ross chicks at 6 and 7 wk of age, but feed to gain ratios were also significantly higher (P less than .05) at 6, 7, and 8 wk of age. Weight gain and feed to gain ratios were significantly better (P less than .05) on the high-energy diets than on the low-energy diets at 6, 7, and 8 wk of age. With equal Lys content, the normal-CP diets gave significantly higher gains (P less than .05) than the high-CP diets at 6, 7, and 8 wk of age. With equal CP content, the high-Lys diets gave significantly more gain (P less than .05) than the normal-Lys diets at 6, 7, and 8 wk of age. Oven-ready and breast meat yields of Ross chicks were significantly higher (P less than .001) compared with those of Arbor Acres chicks at 6, 7, and 8 wk of age and yields of edible organs, skin and fat, and remaining carcass were significantly lower (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

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1. An experiment with separately housed male and female broiler chicks was carried out during the period of 3 to 7 weeks of age to determine the limiting amino acids (AA) in a low protein maize-soyabean meal diet. Chicks were fed on diets containing 170, 180, 190 and 200 g crude protein (CP)/kg with or without combined additions of L-threonine (Thr), L-tryptophan (Trp) and L-arginine (Arg) to those in the 180, 190 or 200 g CP/kg diets and a 170 g CP/kg diet with or without combined additions of Thr, Trp, Arg, L-isoleucine (Ile), L-leucine (Leu) and L-valine (Val) to those in the 190 g CP/kg diet. The diets were iso-energetic and contained the same concentrations of lysine (Lys) and sulphur-containing amino acids. 2. Decreasing the dietary CP had a significantly negative effect on performance. 3. No significant effects on performance were found when diets with 180 and 190 g CP/kg were supplemented with Thr, Trp and Arg to those in the 200 g CP/kg diet. 4. There were no significant differences in performance between the groups fed on the diets with 170, 180 and 190 g CP/kg when the 170 and 180 g CP/kg diets were supplemented with Thr, Trp and Arg to those in the 190 g CP/kg diet.(ABSTRACT TRUNCATED AT 250 WORDS)

1. Two experiments were carried out to determine the response of broiler chicks to threonine-supplemented diets between 10 and 28 d and 7 and 21 d of age, respectively. 2. In the first experiment female broiler chicks were fed on 11 experimental diets. Two iso-energetic basal diets (diets 1 and 2) were prepared with 200 and 160 g CP/kg and 7.6 and 6.0 g threonine/kg respectively. Both diets contained 11.5 g lysine and 8.7 g sulphur-containing amino acids/kg. Diet 3 was composed of diet 2, supplemented with all essential and non-essential amino acids (EAA and NEAA, respectively) except threonine, to the concentrations of the amino acids in diet 1. The NEAA were added as a combination of glutamic acid and glycine. Diets 4 to 11 had the same compositions as diet 3, but contained increasing amounts of threonine. 3. For birds fed on diet 2, gain was significantly lower and food/gain ratio was significantly higher than for birds fed on diet 1. Supplementation with EAA, NEAA and threonine to the same concentrations in diet 1 resulted in a performance similar to that found on diet 1. 4. In experiment 2, male and female broiler chicks both received 10 experimental diets. Diet 1 contained 220 g CP/kg and 8.5 g threonine/kg, diet 2 contained 160 g CP/kg from natural raw materials and 6 g threonine/kg. Both diets contained 12.4 g lysine and 9.3 g sulphur-containing amino acids/kg. Basal diet 2 was supplemented with all EAA and NEAA to the concentrations of basal diet 1, except for threonine. Diets 3 to 10 had the same compositions as the supplemented diet 2, but contained increasing amounts of threonine. 5. For male and female chicks on diet 2, gain was significantly lower and food/gain ratio significantly higher than those on diet 1. Diet 10 (160 g CP/kg plus all EAA, including threonine, and NEAA supplemented to the concentrations of diet 1) resulted in the same performance as diet 1. 6. The results indicate that, when low protein maize-soyabean meal diets supplemented with EAA and NEAA with 13.31 MJ ME/kg were fed to male and female broiler chicks until 21 d of age, improvements in gain and food/gain ratio were obtained when the dietary threonine content was increased to 7.25 g/kg. When female chicks were fed threonine-supplemented diets to 28 d of age, improvement in gain and food/gain ratio was obtained when the threonine concentrations were increased to 6.32 g/kg diet.(ABSTRACT TRUNCATED AT 400 WORDS)

Diets containing 1.22 and 1.03% lysine (as obtained by reducing protein from 21.8 to 18.2%) were fed to male broiler chicks from 0 to 2 weeks of age. To each of these groups diets containing 1.22, 1.03, and .86% lysine (15.5% protein) were fed from 2 to 4 weeks of age. From 4 to 8 weeks of age chicks from each of the six prior treatments were fed diets containing 1.22, 1.03, .86, .74% lysine (13.7% protein), thus making possible the evaluation of potentially reduced requirements as well as compensatory growth.Averaged for all groups, the diet with 1.22% lysine supported superior growth through 8 weeks of age as compared to that with 1.03% lysine; however, feed conversion was superior with the lower lysine diet. For chicks fed the three diets from 2 to 8 weeks of age, the .86% lysine diet supported reduced weight gain. However, feed conversion was superior for that treatment from 4 to 8 weeks, although overall there were no differences in feed conversion. For chicks fed the four diets from 4 to 8 weeks of age, growth was reduced for chicks on the .74% lysine diet from 4 to 6 weeks and overall but not during the 6 to 8 weeks period. Feed conversion was reduced in reverse order with the reduction in lysine and protein content.The diets given from 0 to 4 weeks of age had only a slight effect on the carcass composition of 8-week-old male broilers. Irrespective of the diets given from 0 to 4 weeks of age, the diets given from 4 to 8 weeks of age had a pronounced effect on the carcass composition. Decreasing the dietary lysine content resulted in a significant decrease in carcass protein content and a significant increase in carcass fat content.