Vet Column 10-5-09 |

Vet Column 10-5-09

David L. Morris, DVM, Ph.D.
Fort Collins, Colo.

Identifying factors that affect feedlot performance and carcass value of beef cattle is important in managing feedlot cattle for optimal economic potential. Previous research has demonstrated that primary breed makeup, frame scores, and muscle scores of feeder cattle affect carcass composition and days on feed. Other issues such as heat stress, cold stress, disease, and social stress affect performance and carcass traits.

For several years, Iowa State University has sponsored the Tri-County Steer Carcass Futurity whereby data are collected measuring phenotypic traits and carcass characteristics of feedlot cattle. Investigators from Iowa State University, Kansas State University, and the Certified Angus Beef program recently evaluated data collected between 2002 and 2006 involving 15,631 steers and 5,897 heifers fed at 18 feedlots in southwest Iowa.

The objectives of this recently published study were to estimate the correlation between animal temperament, physical traits, animal breed makeup, feedlot performance, and carcass traits of individual feedlot animals. Disposition score was estimated with a 6-point scoring system (one being calm and six being extremely excitable) and was recorded at the initial on-test weighing, at reimplanting, and during final sorting before shipment to the abattoir.

Disposition of cattle in this study had a marked effect on carcass quality at harvest. Increasing disposition score was associated with lower initial body weight, less fat cover, smaller loin muscle area, lower yield grade, lower marbling score, and a lower percentage of cattle grading USDA Choice. This is similar to another published study indicating that more excitable calves in the feedlot was correlated with reduced feedlot average daily gain (ADG).

Increased disposition score was not related to the number of times cattle were treated for respiratory disease, subsequent mortality, or the presence of lung lesions post-mortem.

Cattle that had lung lesions post-mortem were lighter on arrival and had decreased ADG, hot carcass weight, loin muscle area, fat thickness, and calculated yield grade. These cattle are had a greater average number of respiratory treatments than cattle that had no lesions.

Cattle requiring treatment for respiratory disease were lighter on arrival at the feedlot, had reduced ADG, final body weight, fat thickness, marbling content, quality grade, and hot carcass weight.

Continental bred cattle such as Charolais, Simmental, Braunvieh, and Gelbvieh had greater initial body weight, final body weight, number of treatments, loin muscle area, and percent yield grade 1 and 2 carcasses, but had less marbling score, fat thickness, and measure of yield grade than Angus, Hereford, and Shorthorn bred cattle.

Another study reported that although small-framed steers had greater carcass fat content than large-framed steers, small framed steers also had a greater muscle-to-bone ratio. Large-framed steers carry an inordinate amount of non-muscle tissue relative to the actual amount of extra muscle that might exist along with the extra frame.

Conclusions made from this study indicate that animal disposition, health, breed type, and frame score have dramatic effects on live feedlot performance and carcass traits.

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