Use of Linear and Non-linear Growth Curves to Describe Body Weight Changes of Young Angus Bulls and Heifers
The objectives of the current study were to describe bodyweight (BW) changes of purebred Angus bulls and heifer and to evaluate bias in the adjustment of weaning weight measures to a 205-d age.Linear and non-linear growth functions were used to evaluate changes in BW.Models used were a simple linear regression model fitting cubic polynomial of age at measurement (model I) and a Logistic model (model II) .Predicted mature weight for bulls was 763 kg (1,678.6 lbs.) as compared to 541.9 kg (1192.2 lbs.) for heifers.Bulls attained a maximum average daily weight gain (ADG) of 1.75 kg/d (3.85 lbs/d) at a mean age of 296 d.The maximum ADG attained by heifers was 1.24 lb/d (2.73 lb/d) at a mean age of 261 d.Beef Improvement Federation procedures underestimated 205 d BW of bull calves measured at relatively younger ages and overestimated those measured at later ages. However, the extent of this bias seems to vary depending on the rate of growth of individual calves.The current results suggest that producers should consider creating contemporary groups with a smaller spread in age.