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HERITABILITY OF THE LENGTH OF THE GESTATION PERIOD IN DAIRY CATTLE 1

HERITABILITY OF THE LENGTH OF THE GESTATION PERIOD IN DAIRY CATTLE 1,J. C. DEFRIES,R. W. TOUCHBERRY

HERITABILITY OF THE LENGTH OF THE GESTATION PERIOD IN DAIRY CATTLE 1   (Citations: 16)
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SUMMARY The data for this study consisted of 2,063 gestations representing the five major breeds of dairy cattle in the University of Illinois herd. These data were analyzed to determine the ~heritability and the variance of the length of the gestation period, so as to indicate the possibility of shortening the duration of pregnancy in dairy cattle. A comparison of the fiducial limits of the duration of pregnancy of each of the five breeds indicated breed differences in all possible comparisons, except between Jerseys and Holstein-Friesians. The effect of sex of fetus and the variance components for service sire and sire of the dam were estimated. The effects of the sex of the fetus of Ayrshires, Holstein-Friesians, and Jerseys were statistically significant and, in general, the male calves were carried about 1.5 days longer than the females. Heritability was estimated by multiplying the paternal half-sib correlation by four and by doubling the regression of offspring on dam. The paternal half-sib estimate of heritability refers to gestation as a characteristic of the fetus, whereas the regression estimate refers to gestation both as a characteristic of the fetus and of the dam. The pooled estimates for the five breeds by the two different methods were 0.420 and 0.474, respectively. A comparison between the two heritability estimates, as well as a com- parison of these estimates with repeatability estimates, demonstrated that the length of the gestation period was primarily a characteristic of the fetus. Regressions of birth weight on the length of the gestation period indicated that calves carried one day less than average are approximately 1 lb. lighter than average at birth. It was predicted that the mean length of the gestation period would be decreased by almost ten days in three generations, if 5% of the male and 50% of the female calves resulting from the shortest gestations were saved as breeding stock. Experimentation is necessary to determine if any deleterious effects would be asso- ciated with this change. Several investigators have reported estimates of the heritability of the length of the gestation period in cattle (4, 7, 8, 9). These estimates are quite variable and range from 0.00 to 0.64; however, the majority of the estimates fall within the range of from 0.30 to 0.50. Jafar et al. (4) and Wheat and Riggs (9) have indi- cated that it should be possible to change the length of the gestation period in cattle by selection because of the magnitude of the heritability of the characteristic. A shorter gestation period would be of economic importance in maintaining a short calving interval. It could be of some importance in shortening the genera- tion interval, thereby permitting a more rapid improvement of cattle through selection. The feasibility of changing the length of the gestation period is dic- tated by the ease and rapidity with which the length may be altered, as well as the frequency and magnitude of any deleterious effects which may accompany the change. The primary objectives of the present study were to determine the
Published in 1958.
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