Date of Graduation

5-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Animal Science (PhD)

Degree Level

Graduate

Department

Animal Science

Advisor/Mentor

Fred W. Pohlman

Committee Member

Michael A. Brown

Second Committee Member

Zelpha B. Johnson

Third Committee Member

Nicholas B. Anthony

Fourth Committee Member

D. Wayne Kellogg

Keywords

Beefmaster cattle, birth weight, correlation, heritability, performance traits, underline score, weaning weight

Abstract

The objective of this study was to establish the relationship of underline scores (UDLS), production traits, and conformation scores in Beefmaster cattle born between 1976 through 2008. Records provided by Beefmaster Breeders United (BBU) were analyzed. Certified classifiers approved by the BBU recorded scores. Sizes and shapes of the underlines differentiated the scores (1-4). A score of one was used to designate the least amount of navel flap or sheath and a score of four represents the maximum amount of naval flap or sheath accepted for registration in the BBU. In this study the relationship of the traits was determined using the Pearson correlation analysis. The degree of relationship was then measured by regression procedure. No relationship (P>0.05) was detected between underline score and any carcass traits measured. Correlation of underline score with adjusted birth weight (n = 22,256, r = 0.128, P<.01), adjusted weaning weight (n = 40,305, r = 0.090, P<.01) and yearling weight (n = 16,884, r = 0.185, P<.01) were determined. For each increment increase in underline score, conformation score increased 0.051 score, adjusted birth weight increased 0.763kg, adjusted weaning weight increased 5.986kg, and yearling weight increased 16.488kg. In these data, the relationship of underline scores with maternal and growth traits suggest that underline score could be considered in performance programs. Because of these findings, a subsequent study was conducted to determine estimates of heritability for UDLS along with genetic, environmental, and phenotypic correlations of UDLS with conformation score (CONS), birth weight (BRWT), weaning weight (WNWT) and yearling weight (YRWT) in Beefmaster cattle. These data were analyzed using single- or 2-trait animal models with DFREML and DMU. The mixed model included fixed contemporary group effects constructed using herd, birth year, and sex information. Age of dam and animal age at inspection were included as covariates. Coefficients of heritability were 0.44 +/- 0.01, 0.43 +/- 0.01, 0.75 +/- 0.04, 0.60 +/- 0.02 and 0.85 +/- 0.06 for UDLS, CONS, BRWT, WNWT and YRWT respectively, from the single-trait analyses. From the 2-trait analyses, coefficients of heritability for UDLS with CONS, BRWT, WNWT, and YRWT were 0.43 +/- 0.01, 0.35 +/- 0.05, 0.39 +/- 0.03, and 0.40 +/- 0.06, respectively. Coefficient of rg for UDLS with CONS was -0.16 +/- 0.02, UDLS with BRWT was 0.02 +/- 0.07, ULDS with WNWT was 0.05 +/- 0.04, UDLS with YRWT was 0.13 +/- 0.08 from the 2-trait analyses. Mean EBV of UDLS was 0.00 +/- 0.40. These results suggest that artificial selection for UDLS would be effective in improving offspring of undesirable cattle and that sound selection should overcome any detriment to growth traits.

Keywords: Underline score, heritability, correlation, Beefmaster cattle, birth weight, weaning weight, yearling weight

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