Relationship between age of dam with calving ease and birth weight of Simmental calves

Records from 123,656 Simmental calves (75% and 88% Simmental) were used to study the effect of age of dam on calving ease and birth weight. Calving ease was scored from 1 to 4 (1 = unassisted, 2 to 4 = various levels of assistance). Scores were recorded so that the percentage of assisted births could be calculated. Mean percentage of assisted births and birth weights for each age of dam in months, sex and Simmental percentage subclass were subjected to statistical analysis. Although sex and Simmental percentage occasionally interacted with age of dam for percentage of assisted births, in general, as age of dam increased the percentage of assisted births decreased in dams normally classified as 2-yr-olds (21 mo to 33 mo of age), whereas birth weight remained fairly constant. These results suggest that including age of dam in months in the mixed-model equations for sire evaluation for calving ease could improve the accuracy of these procedures.