Date of Graduation

12-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Animal Science (PhD)

Degree Level

Graduate

Department

Animal Science

Advisor/Mentor

Looper, Michael L.

Committee Member

Kellogg, D. Wayne

Second Committee Member

Gbur, Edward E. Jr.

Third Committee Member

Rosenkrans, Charles F. Jr.

Fourth Committee Member

Pohlman, Fred W.

Keywords

Animal performance; Breeding values; Genetic correlation; Heritability; IBK

Abstract

The economic impact of infectious bovine keratoconjunctivitis (IBK) has been documented in many parts of the world. Many researchers have observed that prevention of this disease is very difficult given current methodologies. This is primarily due to the multifactorial nature of this disease. The objective of this dissertation was to determine the impact of IBK on calf performance and estimate genetic parameters, heritability and estimated breeding values for IBK susceptibility. Data were analyzed using PROC GLIMMIX of SAS; while genetic parameters were estimated using a linear animal model for both single- and two-traits through MTDFREML. Additional evaluations calculated heritability using a linear animal model in DMU and using a binary animal model in ASREML. Significant differences were observed between producer locations (PL) and season of birth for the incidence of IBK. Spring born Angus and Angus-derived calves were determined to be 12.5 times more susceptible to IBK (P < 0.05) than were fall born calves. Heritability for IBK susceptibility was estimated to be rather low using a linear animal model 0.11 ± 0.053 and 0.12 ± 0.003, MTDFREML and DMU, respectively. The binary animal model estimation of heritability was moderate 0.33 ± 0.150. Estimates of genetic, environmental, and phenotypic variances for IBK susceptibility were 0.0077, 0.0600, and 0.0677, respectively. Genetic and environmental correlations between IBK and BWT and WWT were estimated to be 0.45 and -0.08: and 0.61 and -0.15, respectively. Model selection proved to have a substantial influence on heritability estimates while the breeding software program utilized did not. Regardless of program or model utilized, the estimation of the breeding values was minimally affected. These results indicate that genetic improvement through selection of animals which are less susceptible to IBK can be beneficial; however, the overall progress would be rather slow. There is evidence in the literature that coupling relationship information with genomic data can potentially increase estimates of genetic merit and reliability which could accelerate genetic improvement for this trait.

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