Estimates of Genetic and Phenotypic Parameters of Calf Birth Weight and Calving Difficulty in Limousin Cattle

摘要

Genetic parameters for birth weight BW and calving difficulty CD were evaluated in a herd , located in Samalayuca, a representative rangeland system in the desertic region at north of M?xico. Progeny (n=18 and n=19) from 41 dams: heifers and mature cows of a total of 50 dams involving inheritance of Limousin L mated naturally to sires L were used. The objective was to estimate heritability values direct for BW and CD. Separate analyses for each trait used least squares mixed model, SAS (1989). The analytical model included: year of birth, age of dam, sex of the calf, with date of birth as a covariate to adjust a common age as fixed effects; sire and residual as random components. Mean BW was 39.97 kg. BW ranged from 36.00 to 37.94 kg in heifers 29 month-old at parturition. BW ranged from 38.5 to 43.70 kg in mature cows that produced calves at 57 month-old. CD was subjectively evaluated categorically using descriptive scores (i.e., 1=no difficulty, 2= little difficulty by hand, 3 = little difficulty with jack, 4= slight difficulty with a calf jack, 5= moderate difficulty with calf jack, 6= major difficulty with jack and 7= Caesarean birth presentation). Calving difficulty was greater (P<0.05) in heifers (29.8%) than mature cows (11.45%). The sex of the calf was the major source (P<0.05) of variation in levels of CD for both heifers and mature cows. The estimates of heritability values for BW and CD difficulty were (h2=.29?.07) and (h2=.05 ?.04), respectively.