Date of Graduation

8-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Poultry Science (PhD)

Degree Level

Graduate

Department

Poultry Science

Advisor/Mentor

Waldroup, Park W.

Committee Member

Watkins, Susan E.

Second Committee Member

Rosenkrans, Charles F. Jr.

Third Committee Member

Huff, William E.

Keywords

Biological sciences; Broiler chickens; Lysine; Methionine

Abstract

Three experiments were conducted to evaluate the responses of broiler performance to Lysine (Lys) and Methionine (Met) during the starter, grower, and finisher feeding phases. All the experimental diets were formulated based on the Ideal Protein Concept.

Experiment 1 evaluated the responses to Lys and Met on live performance of young broiler chickens from 0 to 18 d of age. The mean amino acid ratios to Lys suggested by literature values were used in the formulation based on the Ideal Protein Concept. Six levels of Lys and eight levels of supplemental Met were used in the diets resulting in a total of 48 experimental treatments. There were significant effects of Lys levels and added Met levels on feed intake (FI), body weight (BW) and feed conversion ratio (FCR) (P¡Ü0.05). Significant interactions were also observed between Lys and added Met in response to these parameters (P¡Ü0.05). There were differences in the estimated ratios of Met or total sulfur amino acids (TSAA) to Lys required for optimizing FI, BW, and FCR for chicks fed different Lys levels. These results indicated that the optimal ratios of indispensable amino acids to Lys may depend on dietary Lys level in the diet.

Experiment 2 evaluated the response to Lys and Met in diets on live performance of young broiler chickens during the grower period of 14-35 d. Experimental diets were designed similarly as the experiment 1 with six levels of Lys and eight levels of supplemental Met. Two consecutive trials using the same experimental diets were conducted with identical design. There were significant effects of dietary Lys levels on FI, BW and FCR (P¡Ü0.05), with optimal Lys level for FI, BW and FCR of 1.20, 1.10 and 1.12, respectively. There were significant effects of added Met levels on BW and FCR (P¡Ü0.05). No significant interactions between Lys and Met were observed based on FI, BW and FCR. There were differences in the estimated ratios of Met or TSAA to Lys required for optimizing FI, BW, and FCR for broiler chickens fed different Lys levels. Results of this study suggest that the response to variation in Lys level is independent of Met level and optimal ratio of Met or TSAA to Lys varies with different dietary Lys level in the diets.

Experiment 3 was conducted to evaluate the response to Lys and Met in diets on live performance of broiler chickens during the finisher period of 35-49 d. Similar design as the previous two experiments was used with six levels of Lys and four levels of supplemental Met. There were significant effects of dietary Lys levels on body weight gain (BWG) and FCR, with optimal Lys level for BWG and FCR of 1.01 and 1.05, respectively. There was a significant effect of supplemental Met on FCR. No significant interactions were observed between Lys and supplemental Met for FI, BWG, and FCR. Increasing Lys level significantly improved dressing percentage and breast meat yield. There were differences in the estimated ratios of Met or TSAA to Lys required for optimizing FI, BWG, and FCR for broiler chickens fed different Lys levels. Results of this study suggest that the response to variation in Lys level is independent of Met level in broiler finisher diets and that the ideal amino acid profile may depend on the Lys level in the diets.

In conclusion, the ideal ratios of Met and TSAA to Lys based on the Ideal Protein Concept vary for broiler chickens fed different Lys level in the diets at each of the growing phases.

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