Dickinson State University

Abstract Cattle hair shedding is vital for thermoregulation during high summer temperatures, reducing heat stress and enabling energy allocation to production characteristics. Research involving coat shedding in the Northern Great Plains climate is lacking. The objective of this study was to characterize and determine systematic effects influencing coat shedding in yearling, admixed beef heifers in the Northern Great Plains region. We hypothesized that apparent high temperatures would significantly affect shedding capability, with breed composition contributing to observed variability. Over a 4-year period, yearling-age heifers (12.73 +/- 0.51 mo) were transported from the Dickinson Research Extension Center near Manning, ND, to the Beef Cattle Research Complex in Fargo, ND, as part of a long-term study. The study population consisted of 289 heifers representing diverse breed compositions, including American Aberdeen, Angus, Red Angus, Gelbvieh, Limousin, Shorthorn, Simmental, and various first-cross hybrid groups. Photographs of the heifers taken in early June (date 1) and early July (date 2) as part of the annually conducted feed trial were used for scoring in this study. Hair shedding was assessed by 3 evaluators using a standardized 1 to 5 scoring system, where 5 represented a complete winter coat, with scores decreasing by 25% increments, and 1 indicating no winter coat remaining. The average score per date (n = 2) and average relative change value, calculated by subtracting the date 2 average score from the date 1 average score divided by the date 1 average score, was used to compare shedding capability among animals. Influential systematic effects investigated for average relative change of shedding included fixed covariates of average apparent high temperature 14 d or 30 d before date 1 and 14 d or 30 d before date 2 as well as fixed class effects of coat color (n = 2; red vs. black), pedigree-based breed group (n = 9), frame score group (n = 4), and heifer’s dam age category (n = 4). Heifer was included as a random effect in all models. A total of 60 models were explored using mixed model procedures and maximum likelihood estimation to assess model fit based on AIC and BIC values when including and excluding fixed effects. The model with the best fit included average apparent high temperature 30 d before date 1 (P = 0.0001), pedigree-based breed group (P = 0.3457), frame score group (P = 0.6285), and heifer’s dam age category (P = 0.1276). The slope estimate of the average apparent high temperature 30 d before indicates a 2.6% decrease in shedding score per degree increase in apparent high temperature. Day length and its potential interaction with apparent high temperature will be explored in subsequent analyses.