Grazing behavior responses of rangeland beef cows to winter ambient temperatures and age

Abstract

A trial was conducted on Montana native rangeland to examine the effects of cow age and ambient air temperatures on mid-winter grazing activity of pregnant beef cows. Cows were fitted with vibracorders and pedometers for 50 continuous days in January and February to monitor daily grazing time ( DGT) and distance traveled. Three-year-old cows grazed 0.7 h day −1 longer ( P<0.005) and traveled 0.85 km day −1 further ( P<0.05) than 5-and 7-year-old cows. Total DGT averaged 8.8 h day −1 across ages and was insensitive ( P>0.05) to mean ambient temperature departures (either increases or decreases) from average temperatures of the previous 1–20 days. DGT did not remain below 8 h day −1 for more than one successive day. However, examination of grazing times within daily periods indicated significant linear respones to temperature changes. Morning (07.01–13.00 h) grazing times exhibited variable responses ( P<0.05) to temperature departures from averages across the previous 17, 19 and 20 days. Grazing times during afternoons (13.01–19.00 h) and evenings (19.01–07.00 h) declined ( P<0.05) when temperatures either increased or decreased from averages of the previous 6–10, and 1, 2 and 4 days, respectively. Only 17% of DGT occurred during the evening period. We concluded that in the foothill grasslands of the Northern Rockies, range beef cows maintained consistent total grazing time despite fluctuating mid-winter temperatures (8 to −26°C) and that cow age influenced grazing activity.