Date of Graduation

5-2012

Document Type

Thesis

Degree Name

Master of Science in Animal Science (MS)

Degree Level

Graduate

Department

Animal Science

Advisor

Dr. Charles F. Rosenkrans, Jr

Committee Member

Dr. Michael L. Looper

Second Committee Member

Dr. Randy L. Raper

Third Committee Member

Dr. Rick W. Rorie

Keywords

Biological sciences; Bovine; Cattle breeds; Grazing; Molecular breeding values; Real-time ultrasound; Single nucleotide polymorphisms

Abstract

Forty-eight Gelbvieh x Angus steers (265 ¡À 40 kg) were utilized to determine the relationships among molecular breeding values (MBV), steer performance, and carcass traits. Body weight (BW), hip height (HH), hip width (HW), exit velocity (EV; rate at which steers exited the squeeze chute and traversed 1.8 m) and body ultrasound measurements of steers were recorded at d 0, 93 and 154 of grazing mixed stockpiled endophyte-infected and -free tall fescue. Tissue samples were collected for genomic profiling (Igenity, Merial Limited, Duluth, GA). Steers were transported to the Oklahoma State U fed for 159 d, harvested and carcass parameters recorded. At d 0 and 154 of grazing, BW was correlated (P < 0.05) with MBV for ADG (r = 0.31 and 0.32 for d 0 and 154, respectively). Hip width was correlated (P < 0.05) with MBV for ADG (r = 0.33 and 0.32 for d 0 and 154, respectively) at d 0 and 154. An inverse correlation between EV and MBV for LM area on d 0 (P < 0.01; r = -0.48) and d 154 (P < 0.03; r = -0.03) of grazing was observed; on d 93, EV and MBV for LM area tended to be inversely correlated. Ultrasound measurements for intramuscular fat on d 0 were correlated (P < 0.05) with MBV for docility (r = 0.40). Predictive potential of MBV from the stepwise procedure for steer performance and carcass composition was low (r2 ¡Ü 0.22). Molecular breeding values were correlated with several measurable traits that can be obtained on-farm. Incorporation of MBV may aid cattle producers in more accurate selection practices to increase profitability of beef production.

Environmental and managerial conditions are known to affect subsequent performance and carcass traits of beef cattle. The objective of the second study was to document the effect of stocking rate (SR), grazing method (GM) and breed of sire on carcass traits. Steers and heifers (n = 460) grazed ¡®Maton¡¯ rye (Secale cereale L.) and ¡®TAM90¡¯ annual ryegrass (Lolium multiflorum L.) pastures from January to mid-May during 5 yr. Cattle were allotted to stocking rates (SR) of high (9 animals/ha), medium (6 animals/ha), or low (4 animals/ha), GM of continuous (CONT) or rotational (RT), and fed in commercial feedyards. Calves were sired by bulls from the following breeds; Angus (n = 171), Bonsmara (n = 108), Brahman (n = 109), Braunvieh (n = 31), Hereford (n = 12), and Simmental (n = 29). Body condition score (BCS); ultrasound measurements of intramuscular fat (UIMF), longissimus dorsi muscle area , and rump fat at end of grazing; ADG during grazing (119 d ¡À 25) and feedyard (125 d ¡À 28) phases; hot carcass weight (HCW); carcass ribfat (CRF); carcass LM area (CLMA); and yield grade (YG) were determined. Effects of year, gender, SR, GM, breed of sire, and interactions were determined by ANOVA. Simmental offspring had greater (P < 0.01) amounts of UIMF than Bonsmara and Brahman (0.11 ¡À 0.03 and 0.13 ¡À 0.03, respectively). Stocking rate affected the HCW of cattle (P < 0.05) with high SR (314.1 ¡À 5.8 kg) cattle having lighter HCW than low SR (329.0 ¡À 4.9 kg). Stocking rates and breed of sire did affect carcass traits, and these variables can be managed to maximize carcass value.

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