Early Life Measures of Size as Related to Weights and Productivity in Beef Cows and Carcass Traits in Steers
Cunningham, Samantha Fern
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The overall objective of this study was to investigate various measures of cattle size. Records from three separate studies (herds) at Texas A&M University were used to evaluate relationships of birth and weaning measures (n = 750) with size and productivity of females (n = 2,800 records from 450 animals) and carcass traits (n = 450) of steers. Cattle were F1 crosses sired by Angus, Brahman, Boran, Gir, Indu-Brazil, Nellore, and Tuli. Relationships between cow traits and carcass traits of steer mates were also investigated. Animals were classified into Small, Medium and Large frame size categories based on weaning age hip heights. Considerable differences in cow weight were observed within the same frame size category, and larger differences in weight within the same frame category was observed across study herds (which also differed in breed composition) than between different frame size categories within study herds in most cases; however, the large degree of confounding between frame size category and breed type prevented conclusive findings solely based on frame size category. Cow weight appeared to plateau at parity five, and in these data, this was considered to represent mature cow weight. Ranking of steer carcass weights based on frame score category followed expectations within study herds, but similar to cow weights these also varied considerably within the same frame category across study herds. Birth weight and cannon bone length accounted for 0 to 40% of the variation in parity-five weight of females and 1 to 52% of the variation in hot carcass weight of steer mates depending upon sire breed and study herd; use of weaning (weight, height, frame score) traits accounted for 2 to 46% of the variation in parity-five weight of females and 13 to 67% of the variation in hot carcass weight of steer mates, again depending upon sire breed. Different patterns were observed between females and males depending upon sire breed. Based on results seen here weaning age designation of cattle frame size may not be a precise classification of mature size, similar frame size designations can vary considerably in weight across different genetic types, and mature size classification of beef cows alone does not guarantee productivity measures, particularly when frame size is confounded with genetic background.