Grazing behavior of rangeland beef cows differing in milk production

Differences in grazing behavior among Hereford (HH), 50% Angus-50% Hereford (AH), 50% Simmental-50% Hereford (1S1H) and 75% Simmental-25% Hereford (3S1H) lactating cows grazing foothill range were measured using vibracorders and pedometers to estimate daily grazing hours and distance traveled, respectively. There were four 10-day grazing periods during July and August. Cow weight, calf weight and milk production estimates were taken prior to Periods 1 and 4. During Periods 1, 2 and 4, the 48 cows were located on a daily basis between 06.00 and 09.00 h, and each animal location was recorded on gridded aerial photo maps. Pasture use was defined as the amount of total area utilized for grazing for the four periods.The overall mean for daily grazing hours was 9.4 h day⁻¹ (633 observations) and no significant breed type differences were found. Daily grazing hours increased from 8.0 to 10.0 h day⁻¹ during the 40-day observation period. Milk production and calf age significantly influenced daily grazing hours and the partial regression coefficients were 0.05 h·day⁻¹·kg·day⁻¹ and −0.02 h·day⁻¹·day⁻¹, respectively. The overall mean distance traveled was 4.7 km day⁻¹ (82 observations) and followed the same trend as daily grazing hours. For each kilometer of travel, 2h were spent grazing during the four grazing periods. The 1S1H cows traveled less (P < 0.05) than HH, AH and 3S1H cows. Breed type means were 5.0, 4.8, 4.1 and 4.8 km day⁻¹ for HH, AH, 1S1H and 3S1H cows, respectively. The overall mean for pasture use was 103 ha per cow (47 observations) and breed type was not significant in explaining variation in pasture use. For each kilogram increase in calf weight (adjusted for cow condition), pasture use increased by 0.5 ha (P < 0.05). Thus, the grazing behavior of different breed types under rangeland conditions was similar.