Date of Award

8-2012

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

Dr. Neal Schrick

Committee Members

Dr. Fred Hopkins, Dr. Justin Rhinehart

Abstract

Profitability in the beef industry is a crucial aspect of management schemes. The overall aim of this study was to determine if carcass ultrasonography in replacement heifers could explain variation in traits such as reproduction, a major factor in beef cattle efficiency and profitability. During a 10-year period, data were obtained from 906 yearling heifers through the use of carcass ultrasonography. The measurements collected included adjusted values for ribeye area (REA), percent intramuscular fat (%IMF), rib fat (RF), and rump fat. A retrospective analysis was performed on data collected and variables were separated into the extreme high and low 25% and the median 50%. Analysis examined whether a relationship existed between reproductive traits (percentage calving at two years of age, age at first calving, first calving interval, lifetime calving interval) and carcass measurements determined by ultrasonography.

Age at first calving increased as ribeye area increased (Low REA 731.7±3.1 d; High REA 743.5±3.3 d; P=0.002). Rib fat was also related to age at first calving as heifers in the high grouping were approximately 9 days older at calving (Low RF, 734.5±3.1 d; High RF, 743.7±3.2 d; P=0.008). Expected progeny differences (EPD) for carcass traits such as REA also indicated differences between all three groups for age at first calving (Low REA EPD, 727.4±3.1 d; Med, 736.3±3.2 d; High, 746.2±3.2 d; P<0.0001). Observation of marbling EPD’s resulted in a difference of 10 days for age at first calving between the high and low groups (Low MARB EPD, 734.4±3.1 d; High, 744.0±3.2 d; P=0.002). Interval from first to second calving (Low RF, 374.3±3.2 d; High RF, 361.7±3.5 d; P=0.014) and average lifetime calving interval (Low RF, 369.9±1.8 d; High RF, 362.8±2.1d; P=0.048) were both correlated with adjusted rib fat. Evaluation of longevity (birth date to date of last calving) established that heifers with a higher carcass EPD for REA remained in the herd for an additional 7.2 months (Low REA EPD, 39.8±4.2 mo.; High REA EPD, 47.0±4.2 mo.; P=0.023). Ultrasonography-derived carcass measurements and calculated carcass EPDs may be used as potential tools to predict reproductive soundness of a replacement heifer before being retained in the herd.

Comments

William M. Mayfield

Pulaski, TN

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