Effects of metabolic modifiers and environment on cattle health and performance

Abstract

Holstein steers (n = 855; initial BW = 448 + 37 kg) were used in an experiment to determine the effects of dose (0, 300, or 400 mg hd-1d-1) and duration (28, 35 or 42 d) of ractopamine hydrochloride (RH) on growth, performance, and carcass characteristics. Duration did not affect performance or carcass characteristics (P > 0.12). Increasing RH dose tended to increased final BW (P = 0.07), increased ADG (P = 0.002), G:F (P = 0.002) but did not affect DMI (P = 0.84). Hot carcass weight and LM area increased with increasing RH dose (P < 0.001) and calculated yield grade and marbling score decreased with increasing RH dose (P < 0.03). Black-hided feedlot steers (n = 143; initial BW = 392 + 22 kg) and red-hided replacement heifers (n = 25; initial BW = 450 + 46 kg) were used in an experiment to determine the effect of environment on rumen temperature (RuTemp). Comprehensive climate index (CCI) and stress thresholds were used to assess the effects of multiple environmental variables into one index. Rumen temperatures were highest in PM and lowest in AM periods for steers (P < 0.001) and heifers (P < 0.001). For steers and heifers, RuTemp were impacted by CCI and environmental conditions. Feedlot steers in Exp. 1 (n = 54; BW = 391 + 13 kg) and Exp. 2 (n = 72; BW = 380 +18 kg) were used to predict daily water intake (DWI) based on changes in RuTemp. The following equation was used to predicted DWI: -59.04 + 1.41(water temperature) + 1.59(DMI) + 0.76(Average CCI) + 0.50(maximum CCI) + 0.23 (RuTemp deviation). As CCI stress threshold increased, DWI increased (P < 0.001) and DMI (P = 0.02) decreased. Continuous RuTemp monitoring can be utilized to predict DWI of feedlot steers.