Factors Affecting Weaning Weight Production

Weaning weight records from a commercial cow herd were statistically analyzed to demonstrate suspected sources of variation in weaning weight. Data from first-calf heifers and mature cows (3 to 9 year olds) were analyzed separately. For every one day increase in calf age at weaning, weaning weight was increased by 1.65 and 1.76 Ib for first-calf heifers and mature cows, respectively. For every 1 percentage point increase in MPPA of the cow, weaning weight was increased by 4.5 Ib. A 10% advantage in weaning weights and weight per day of age (WDA) was observed in steers over heifers. A 3 and 6% advantage in WDA and weaning weight, respectively, was observed in bulls over steers. Weaning weight and WDA peaked among cows 4 to 6 years of age and then declined. Cows that were 3, 8 and 9 years of age produced calves with similar weaning weights. Calves nursing 3-, 7- and 8-year-old cows required more treatments for sickness than calves nursing 4- to 6-year-old cows. Production records provide valuable insight into causes of variation in cow productivity