139 Relationship of winter hair growth and performance in Angus dams

Abstract

Abstract The objectives of this study were to (1) evaluate the effect of rate of winter hair growth on Angus cow performance and (2) estimate the correlation between rate of winter growth and other physiological parameters. Data were collected on fall-calving Angus females (n = 127) approximately every 60 d from August to February from 2011 to 2019. Animals were observed by trained technicians for winter growth (WG) and length (WL) scores from 1 to 5. A 1 for winter growth indicated no winter growth and a 5 indicated a full winter coat. For winter length, a 1 indicated short hair and a 5 indicated long. At scoring, a 5.08 cm by 10.16 cm hair sample was clipped directly behind the left shoulder below the top line and weighed. A thermal image was taken to determine average surface temperature of both the shaved (SHAVE) and unshaved (UNSHAVED) areas. Month of first winter growth (MFWG) was determined when the female reached an average winter growth score of 2.5 or higher. Calf performance was considered a trait of the dam and included AdjBW and d205wt. Phenotypic correlations were estimated on SHAVE, UNSHAVED, WG, WL, MFWG, hair weight, and month of first shedding (MFS), which was assessed during the spring of each year. Data were analyzed using the MIXED procedure of SAS with AdjBW and d205wt as response variables. The model included fixed effects of calf sex and MFWG with sire as a random effect. SHAVE was weakly positively associated with WG, WL (P < 0.05). There was no association between MFWG and MFS. MFWG was significant for AdjBW and d205wt with females starting winter growth in October having lighter calves at birth and weaning compared to those in December. Results suggest an association between MFWG and performance traits in Angus dams.