Date of Graduation


Document Type


Degree Name

Doctor of Philosophy in Poultry Science (PhD)

Degree Level



Poultry Science


Park W. Waldroup

Committee Member

Charles Rosenkrans

Second Committee Member

Dustan Clark

Third Committee Member

William Huff


Biological sciences, Health and evironmental sciences, Amino acids, Broilers, Energy, Genetic selection, Nutrition, Poultry



Three studies were conducted to evaluate how the broiler has changed over the years due to intense genetic selection. Four different broiler genotypes, one unselected since the 1950's (HER) representing the old meat-type bird and three current strains (Ross 308, Ross 708, and a test product (TY)) were studied. Differences in growth, morphometry, and response in performance and processing yield to different nutrient levels were studied.

Experiment 1 evaluated growth and morphometric analysis. Birds of each strain were killed weekly from day 7 to day 56, necropsied and cut up parts and organs weighed. Measurement of small intestine segments was also done. Results show that current strains have significantly increased body weight (BW) and muscle accretion, especially breast meat. Jejunum and ileum segments are longer in the current genotypes but shorter when related to body weight. Heart and gizzard relative weight has reduced and tibia breaking strength has increased as a side effect of selection.

Experiment 2 evaluated performance and processing yield at four different energy levels. Results show that the HER bird is able to regulate feed intake (FI) in order to regulate energy intake. Increasing energy levels did not affect its performance. The Ross 308 bird is not able to modify FI in order to regulate energy intake. Also, Ross 308 responded to increasing levels of energy by increasing BW while Ross 708 and TY did not. Current genotypes increased caloric conversion ratio with higher levels of energy.

Experiment 3 evaluated performance and processing yield at six different amino acid (AA) levels (80, 85, 90, 95, 100, and 105% of the recommended levels). Results show that HER bird response to increasing levels of AA was moderate to absent while the response of the three current genotypes was similar increasing BW, FI, and breast meat yield, reducing feed conversion ratio.

In conclusion, results show that a substantial change has occurred in the broiler due to selection, modifying anatomy, and its responses to different nutrient levels. These changes need to be considered when formulating diets for the different broiler genotypes used in the US industry in order to get the best economic return.