Effect of hair coat shedding on ADG in weaned Angus calves

Abstract Text: A retained winter hair coat into the summer months of a subtropical climate can be detrimental to cattle. Heat stress in cattle from decreased evaporative cooling due to a dense winter coat is a common occurrence in states that experience hot, humid summers. Hair coat shedding (HCS) has previously been studied in Angus dams and calf weaning weight was shown to be impacted by dam HCS (Gray et. al, 2011). A pilot study indicated that calves that shed their winter hair coat earlier in the summer were heavier and had greater ADG during late summer months (Richardson and Cassady, 2013). The objective of the current study was to further examine the relationship between HCS and post-weaning gain in calves. Data were available on Angus calves (n = 211) grazing pasture at the Upper Piedmont Research Station in Reidsville, NC over two consecutive years. Calves were scored for HCS three times during the summer by two trained technicians using a 1 to 5 scale, with 1 being a slick, summer coat and 5 being a full, winter coat. Body weight (BW) was recorded at time of HCS. For analysis, calves were classified into one of three groups based on HCS for date 3. These groups represented an early (n = 74), middle (n = 73) and late shed groups (n = 64). Data were analyzed using the Proc Mixed procedure of SAS. The model included fixed effects of sex, year, and shed group and random effect of sire. Traits analyzed were BW at date 3 and ADG from date 2 to date 3. Body weight was affected by sex, year, and shed group, with calves in the early shed group weighing 18.3 kg more than calves in the middle shed group and 28.5 kg more than calves in the late shed group (P < 0.05). ADG was affected by sex, year, and shed group, with calves in the early shed group gaining 0.23 kg per day more than calves in the middle and late shed groups (P < 0.05). It was concluded that significant differences in calf growth were associated with hair coat scores. At current market prices, the 18.3 kg difference in weight found between early shedding calves and the middle shed group is worth more than $100.00 per head.

Keywords: Beef cattle, Growth, Heat stress