108 Influence of Cow Body Weight Changes on Calf Growth during the Summer Grazing Period
Abstract In spring calving beef herds, the summer grazing period allows the mature cow to recuperate prior to the next calving season. Cow body weight changes during the summer can vary from minimal to extreme, which may also alter calf growth rates. The objective of this study was to determine the influence of cow body weight changes on calf growth during the summer grazing season. Cows and calves were weighed at the beginning, mid-point and end of the summer grazing season with the end-point being weaning. Based on these weights, cows were categorized into one of four groups: low (LO), medium (MED), high (HI), and extreme (EXT). Groups were determined based on the percent body weight gained across the season with LO being less than 4.99%; 5–9.99% as MED; 10–14.99% as HI, and above 15% as EXT. Data were collected over a 3-yr period utilizing a total of 52 mature Angus cows and 102 Angus calves. Cows were rotationally grazed on mixed grass pastures containing tall fescue and supplemented with corn silage for part of the grazing season. Cows were managed in two groups, but all pastures were grazed by all cows during the season. Calves were provided ad libitum access to creep feed for the entire grazing season. All calves were treated similarly and bulls were left intact until weaning. Data were analyzed in the MIXED procedure of SAS with year and group effects with age of dam as a covariate. Calves had the lowest early ADG in LO cows compared to all other groups (P = 0.01). Overall calf ADG tended to be different between groups as LO cows had slower growing calves compared to EXT or HI dams (P = 0.09). Generally, cows that gained the least amount of weight over the grazing season had slower growing calves.