The influence of age and environmental conditions on supplement intake by beef cattle winter grazing northern mixed-grass rangelands

This study evaluated the influence of cow age and temperature adjusted for wind chill (T-windchill) on supplement intake behavior of beef cattle winter grazing northern mixed grass prairie rangelands. A commercial herd of 272 (year 1) and 302 (year 2) bred cows (Angus, Simmental x Angus) ranging in age from 1- to 12-yr-old grazed a 329-ha rangeland pasture (similar to 1.5 ha animal unit month(-1)) from November to January. Cows were grouped into seven age classes (1 yr old, 2 yr old, 3 yr old, 4 yr old, 5 yr old, 6 yr old, and >= 7 yr old) and were provided free-choice access to a 30% CP self-fed canola meal-based pelleted supplement with 25% salt to limit intake. The target daily intake was 0.91 kg cow(-1)d(-1). Supplement was provided in a SmartFeed Pro self-feeder system to measure individual animal supplement intake and behavior. An Onset HOBO U30-NRC Weather Station was placed near the supplement feeders to collect weather data for the entirety of the grazing period. Average daily supplement intake and the coefficient variation in supplement intake displayed a T-windchill x cow age x year interaction (P <= 0.02). There was a negative linear effect of age on supplement intake (kg cow(-1)d(-1)) for days with below average T-windchill conditions in both years (P < 0.01). There was also negative linear effect of age on supplement intake (g kg of BW(-1)d(-1) at average T-windchill in year 1 and below average T-windchill in year 2 (P < 0.01). Cow age had a quadratic effect on supplement intake for days with below average T-windchill in year 1 (P = 0.02); however, this was a curvilinear response where yearlings and 2-yr-olds consumed more supplement per kilogram of BW than other age cattle (P < 0.01). Cow age had positive linear effects on variation in supplement intake at below average T-windchill conditions in both years (P < 0.01). Daily visits to the supplement feeders displayed a T-windchill x cow age interaction (P < 0.01), where there was a linear decrease in visits with increasing age at below average T-windchill conditions (P < 0.01). In summary, both cow age and the winter environmental conditions interacted to influence animal supplement intake behavior and, as a result, nutrient delivery efficacy in winter grazing beef cattle.