Growth and Carcass Characteristics of Cull Cows after Different Times-on-Feed

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Abstract
Cull cows (N=48) of similar age from Angus and Hereford breed types were assigned to one of four feeding periods (0, 28, 56 or 84 d) and subdivided into two groups, one implanted with Synovex-H and a non-implanted control. Cows were fed a high energy diet and slaughtered at the end of each feeding period. Average daily gain and feed efficiency were evaluated on each animal during the trial. The following carcass traits were evaluated: USDA yield and quality grade characteristics, boning yield, muscle weights, bone weights, pH and Warner-Bratzler shear force of the longissimus muscle. The left side of each carcass was boned and proximate analysis was determined. No significant implant effects were encountered for any of the traits evaluated; therefore, data were pooled and evaluated by feeding period only. Carcass weight and boneless forequarter and hindquarter tissue weights increased significantly between each feeding period; percent kidney, pelvic and heart fat (KPH) and yield grade did not differ (P>.05) until d 56 and 84, respectively. Quality grade and marbling scores improved (P<.05) between 28 and 56 d of feeding. Biceps femoris weight changed during the 84-d experiment from 4.1 kg on d 0 to 5.3 kg on d 84 (P<.05). Proximate analysis of the boneless tissue indicated an increase (P<.05) in extractable fat of approximately 6% for each feeding period (6.3% fat on d 0 to 25.4% on d 84). Warner-Bratzler shear force values (1.27-cm cores) of the longissimus muscle decreased significantly (11.0 kg on d 28 to 6.4 kg on d 84). These data indicate that both fat and muscle content increased as days on feed increased for cull cows. Days of feeding cull cows would be dependent on the ultimate carcass characteristics desired; however, the rate and efficiency of gain must be considered to maximize profitability.