Factors Affecting Efficiency to Weaning in Angus, Charolais and Reciprocal Cross Cows

Abstract

Weaning data collected over a 3-year period from 73 individually fed 2-, 3- and 4-year-old Angus, Charolais and reciprocal cross cows and their calves were analyzed to examine factors affecting efficiency of nutrient utilization to weaning. Cows were fed in drylot to have monthly weight changes comparable to the average of contemporaries in a pasture management regimen. Progeny were produced by one Polled Hereford sire per year and were individually creep fed in addition to twice-daily nursing. Data analyzed included 157 reproductive records and 122 weaning records. Breed of dam had highly significant effects on cow TDN intake, cow and calf TDN intake, cow weight and cow condition but accounted for little variance in TDN requirement to produce a unit of weaning weight. Least-squares analyses indicated calf age and sex, cow milk production and year had highly significant effects on efficiency. Cow weight affected (P<.01) all TDN intake measures and progeny weaning weight but did not significantly (P<.25) affect efficiency. Regression analyses indicated cow weight, condition and milk production accounted for 24% of the variation in efficiency, while either weight or condition alone accounted for less than 1% and milk production alone accounted for 23 percent. Calf actual weaning weight, age and sex and cow weight, condition and milk production in combination accounted for 74% of the variance in efficiency. Weaning weight alone or in combination with calf age accounted for 62% and 68% of the variation, respectively, while cow weight or condition in combination with progeny weight and age accounted for 71% and 74%, respectively. Both Angus and crossbred cows were more fertile (P<.05) and weaned more calves (P<.05) than Charolais cows. Cow weight, condition and milk production had negligible effects on reproduction.