Effect of amino acid levels during broiler breeder pullet rearing on: 1. Growth and development

Adequate pullet nutrition is essential to obtain the BW and development suitable for reproduction. An experiment was conducted to determine the effects of four amino acid (AA) dietary levels fed to broiler breeder pullets during the rearing phase from 5 to 24wk on BW, abdominal fat deposition and development. A total of 1,360 Cobb-500 slow-feathering (SF) pullets were placed in 16 floor pens (85/pen). Up to 4wk all pullets were fed one starter diet in crumbles and after 29d of age fed with four mash grower diets containing 4 AA levels (0.40, 0.54, 0.60, and 0.66% of dLys with balanced protein) and 2,700 kcal/kg ME. From 16wk to 5% egg production, developer mash diets with 2,800 kcal/kg ME and 0.51, 0.57, 0.63, and 0.69% of dLys were offered. Feed amounts varied slightly (±3 g/d) among treatments in the developer phase to maintain BW close (±2%) to Cobb guideline. Individual BW was obtained at 4, 10, 15, 20 and 25wk of age. At these days 3 pullets per pen were selected, sacrificed and breast muscle with bones, liver, abdominal fat and intestines were collected and shanks measured. Fleshing scores were assessed at 11, 16, 21 and 25wk of age and shank length measured. Data was analyzed in a CRD with 4 AA treatments and 4 replicate pens each. One-way ANOVA and regression analyses were conducted. Results indicated no differences in BW (P > 0.05) at 4 wk. The two higher AA levels resulted in heavier (P < 0.01) pullets throughout the experimental phase being 2.4 and 3.6% above Cobb guideline at 20wk, while the other two levels were 0.6 and 0.4% below. At 16, 20 and 21wk of age pullets fed diets with the highest AA level resulted in greater (P < 0.05) relative breast muscle weight or fleshing score and shorter shanks as compared with pullets fed diets with the lowest AA levels. Pullets fed the lowest dietary AA level had the longest (P < 0.05) intestines at 10wk of age, the largest deposits of abdominal fat at 15 and 25wk, and the smallest liver at 20wk. Fleshing increased linearly (P < 0.01), while abdominal fat and shank length decreased (P < 0.05) as AA increased. In conclusion, AA dietary levels have important effects on pullet BW, fleshing, abdominal fat and organ development during rearing, but the best egg production was observed with the two highest AA levels.

Key Words: amino acids, pullet breeders, growth, development, breast muscle.