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Relationships between Direct and Maternal Effects on Growth in Herefords: I. Environmental Factors during Preweaning Growth¹

Colorado State University, Fort Collins 80521

Abstract

Factors present during the preweaning growth period of the beef cow were studied to determine their relationship to the cow's subsequent productivity. The data included 2,286 calf weaning weight records collected at the Colorado Experiment Station, Hesperus, which were used to compute Most Probable Producing Ability values for 610 Hereford cows. Product moment correlations of the cow's weaning weight, weaning age and weaning score with MPPA values (0.14, 0.05, –.02,respectively) indicated a low relationship between these factors and cow productivity. Negative correlations of the cow's inbreeding level and her dam's inbreeding level with MPPA values ( –.17, –.23, respectively) indicated that increased inbreeding decreased cow productivity. Preliminary analyses indicated that effects from interactions among the independent variables upon MPPA values were small. Cow birth year, age of cow's dam, line of cow's sire, cow weaning weight and the cow's inbreeding level were factors which had significant effects upon the cow's subsequent MPPA values. The effects of line of sire of the cow's dam, weaning age, weaning score and the level of inbreeding of the cow's dam were not significant.The relationships of weaning weight means with least squares adjusted MPPA means among cow birth years and ages of the cow's dam were negative, indicating that higher preweaning nutritional levels were associated with lower MPPA values. The cyclic trends of weaning weight means and MPPA means over four generations for high, medium and low groups also indicated a detrimental effect upon cow productivity from rapid pre-weaning growth resulting from high nutritional levels.

The results of the study indicated that higher preweaning nutritional levels and high cow inbreeding levels have detrimental effects upon beef cow productivity. Results also indicated that weaning weight is a poor predictor of subsequent cow productivity.

¹ Approved for publication as Scientific Paper 1530 of the Colorado Experiment Station. This study was conducted in cooperation with Western Regional Research Project W-l, Improvement of Beef Cattle Through the Application of Breeding Methods.