Semester of Graduation

Fall 2017


Master of Science (MS)


The School of Animal Sciences

Document Type



The objective of this research was to compare the growth performance of broilers from two commercial breeds with control, low protein and low protein supplemented with crystalline amino acids diets. This was a randomized block design, and identical experiments were conducted on successively in two years. In each experiment, day-old chicks, Ross 708 broilers and Cobb 405 broilers, were randomly assigned into three dietary treatments: 1) positive control, 2) low crude protein (LP), and 3) LP + crystalline amino acids (CAA). A three phase feeding program was used. Feed and water were provided ad-libitum. On d 12, 19, 26, 33, 40, 47, and 54, two birds per pen were randomly selected, weighed, and euthanized by carbon dioxide asphyxiation for further dissection. Three muscles (M. peronaeus longus, M. iliotibialis, and M. pectoralis thoracica), and three bones (tibia, femur, and radius), and organs were collected. Abdominal fat was only collected at the end of the experiment in the first year.

The results showed that dietary protein restriction by 6% units had a retarding influence on the growth and development of visceral organs, muscle tissues and bone mass. The supporting effect of CAA helped compensate the negative effect of low protein diet on the bodyweight, organs, muscles and bones growth, but only during the early growing stages. Cobb broilers had a significantly heavier bodyweight with both low protein and low protein with CAA diets. However, Ross broilers produced significant heavier pectoralis, and had more pectoralis yield than Cobb broilers by feeding the control and low protein with CAA diets. The relative growth of pectoralis in both breeds was significantly inhibited by feeding low protein diet, and the decrease of pectoralis proportion even showed a week earlier, compared to the absolute pectoralis growth. The CAA supplementation enabled both breeds to produce of close pectoralis proportion compared to those on control diet, and this supportive effect of CAA on Ross broiler lasted a week longer than on Cobb broilers.



Committee Chair

McMillin, Kenneth