Relationship between change in condition of beef cows during the pasture season and performance of their calves to weaning

One hundred and fifty-five Angus cows were measured ultrasonically for fat thickness using a Branson Model 12 Sonoray and visually scored for condition in April and October of 1966. Least-squares analyses of the data collected were conducted, using as a dependent variable in each analysis one of the three calf traits observed and recorded at weaning, viz., average daily gain, type score and condition score. The independent variables included in the model were age of dam, sex of calf, change in dam's fat thickness, squared change in dam's fat thickness, and age of calf. Change in fat thickness, as well as the squared change in dam's fat thickness, significantly affected weaning condition score but not weaning gain or weaning type score. The same analyses were conducted with change in dam's condition score substituted for change in fat thickness. Although cow condition score was highly correlated with each of the two ultrasonic estimates of fat thickness (r = 0.70 and 0.67 in spring and fall data, respectively), change in cow condition score did not affect weaning average daily gain, type or condition score of calf. A proposed explanation is that cow condition score may be influenced by cow size such that variation in condition score did not reflect differences in fatness as accurately as did the variation in ultrasonically measured fat thickness. The findings suggest that, under conditions similar to those in this study, change in fat thickness of the dam in conjunction with a measure of calf fatness might be useful in partitioning increases in calf weight into gain due to growth and gain due to fattening.