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The Repeatability of the Yearly Production of Range Cows¹

New Mexico Agricultural Experiment Station²

Abstract

The repeatability of the yearly weaning weights and grades of calves from range cows was investigated by determining the correlations between various combinations of records and by analysis of variance of grades and of weights of calves from cows with five consecutive records.

The average correlation of the weight of all adjacent calves was .49. The correlation of the weight of first calf with that of the second was .66. When the first record was compared with the average of various members of subsequent records, the correlation coefficients varied from .51 to .53. When the average of the first two records was compared with various combinations of subsequent records, the coefficients varied from .54 to .59, being only slightly higher than when one record was included in the initial observation. Analysis of variance showed that after the influence of age of dam was removed, the permanent differences in cows amounted to 51 percent of the remaining variance.

The correlation of adjacent grades of calves was .2,4; that of the first grade and various combinations of subsequent records varied from .25 to .42. The inclusion of a second record in the initial observation almost doubled the magnitude of correlation with subsequent calf grades. Analysis of variance showed that after variance due to age of dam and different years was removed, differences in cows accounted for 33 per cent of the remaining variance.

These data indicate that considerable progress can be made in selecting breeding range cows on the basis of the first calf record, and that differences in the inherent producing abilities of cows frequently may need to be considered in making group comparisons.

¹ Published with the approval of the Director of the New Mexico Agricultural Experiment Station as paper No. 45 of the Journal series.

² Department of Animal Husbandry, State College, New Mexico.