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Influence of Gender, Breed and Age on Maturity Characteristics of Sheep

University of Wyoming, Laramie 82071, U.S. Sheep Experiment Station, Dubois, ID 83423 and U.S. Department of Agriculture, Washington, DC 20250

Abstract

Fifty-one ewes, 50 wethers and 51 rams of Finn x whiteface or Suffolk x whiteface breeding were slaughtered at an average age of 271, 361, 459, 557 or 652 d to study changes in maturity characteristics with changes in age. When metacarpal epiphyseal cartilage (growth plates) ossifies with age, break joints on the distal end of the metacarpals fuse and the end of the bone then appears as a spool joint rather than as a break joint. This fusion occurs earlier chronologically in ewes than in rams or wethers. Most Finn x whiteface-cross ewes, which normally reach reproductive maturity earlier than Suffolk x whiteface-cross ewes, exhibited ossified metacarpal growth plates by 459 d of age; break joints of Suffolk x whiteface crosses were not fused until 557 d of age. Both breed groups of rams exhibited fused joints by 557 d of age, but only 3 of 10 wethers exhibited spool joints at 652 d of age. Microscopic examination showed that even in these three wethers the epiphyseal growth plate could still be detected. Yearling 2-yr-old classifications of sheep from teeth were not gender-dependent within the discrete age classes of this study. About half the sheep in each gender group were classified as yearlings at 459 d of age and about half in each group were classified as 2-yr-olds by 652 d of age. Stepwise multiple regression equations to estimate age of sheep in days were developed. Overall maturity, lean color and texture and rib bone maturity were the best carcass measures of maturity. Maturity scores for characteristics of the break joint did not enter any of the equations studied. When eye lens weight was included in equations with the best measures of carcass maturity, accuracy of estimates for age of sheep was improved.

¹ Dept. of Anim. Sci., Univ. of Wyoming.

² U.S. Sheep Exp. Sta.

³ Standardization and Review Branch, USDA, AMS.