Effects of Animal Behavior and Core-Body Temperature on Production Efficiency of Grass-Finished Beef Cattle.

Abstract

Forage nutrient quality and consumption have major impacts on ruminant production. Energy requirements of the grazing animal are influenced by several factors such as increased foraging activity, frame size, and physiological status, but is superseded by the requirement to maintain a homeothermic balance. Therefore, we hypothesized that changes in grazing behavior activities would affect core-body temperature (CBT) and animal performance measures. A two-year study utilizing two cohorts of 24 grass-finished cattle at the University of Hawai‘i, Mealani Agricultural Experiment Station. Animal behavior, CBT, weather variables, and forage quality were assessed during three, daily observation periods (AM, NOON, PM), for fall 2013, and summer and fall 2014 seasons. Over all seasons, active grazing (63.0%), standing (15.6%) and laying while chewing (10.4%) were the predominant behaviors observed. Grazing activity across daily periods was highest during the AM period, a time when mean CBT (38.3±0.01°C) was lowest. The CBT varied for all animals across seasons and periods and averaged 38.6 (±0.03) °C in 2013 and 38.4 (±0.04) °C in 2014. We did not find any significant relationship between CBT and grazing behavior. Forage quality varied seasonally, however crude protein (CP), and total digestible nutrients (TDN) were higher in summer 2014 compared to the fall seasons. Diurnal differences were observed in water-soluble carbohydrate (WSC) and non-fiber carbohydrates (NFC), which were higher in the PM across all seasons. Average Daily Gain (ADG) was not significantly different (P=0.78) between the years 2013 (0.87±0.04 kg/d) and 2014 (0.84±0.03 kg/d). Animals were slaughtered at approximately 21 (± 0.15) months of age and had an average live body weight of 527.1 (±8.98) kg in both years. In 2013, 75% of the animals graded Choice or higher compared with 90% in 2014.