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Effect of Region of the United States and Age of Dam on Birth Weight and 205-d Weight of Simmental Calves^1,2,

Montana State University, Bozeman 59717

Abstract

The objectives of this study were to estimate age-of-dam effects and evaluate two-way interactions between age of dam, region of United States, season of birth and preweaning management for birth weight and 205-d weight. Birth weight (BW) and 205-d weight (205W) records (46,129) from the American Simmental Association were analyzed using least-squares procedures. Independent variables were the random effect herd-year/region and the fixed effects of region of United States, age of dam (2 to 10 yr), percent Simmental of calf (50, 75 and 88%), sex of calf (bull, heifer and steer), preweaning management of the calf (creep or no creep), season of birth (Jan 1 to June 30 and July 1 to Dec 31) and all two-factor interactions among fixed effects that were significant in preliminary analyses. Regions were: Region 1 = Montana, North Dakota and South Dakota; Region 2 = Kansas and Nebraska; Region 3 = Texas and Oklahoma and Region 4 = Louisiana, Mississippi, Alabama, Georgia and Florida. Birth weight was affected (P<.05) by all main effects except preweaning management. Weaning weight was affected (P<.01) by all main effects except season of birth. Although region of United States x age of dam interaction was significant, BW and 2O5W means for age of dam were essentially parallel for Regions 1, 2 and 3, but did not tend to plateau for Region 4, as in the other regions, at mature ages of dams. Interaction of age of dam x season of birth indicated that differences between spring- and fall-born calves were greater in older cows than in younger cows. Sex of calf x age of dam interactions for 2O5W indicated that the differences between bulls and heifers became greater as age of dam increased; steers tended to be intermediate between bulls and heifers.

¹ The authors thank the Amer. Simmental Assoc. for supplying the data used in this study.

² Published with the approval of the Director of the Montana Agr. Exp. Sta. Journal Series No. J-1848.