Effects of growth-promoting agents and season on yearling feedlot heifer performance1

Abstract

Angus x crossbred heifers (270 per trial) were used in an experiment conducted over one 105-d summer and one 104-d winter feeding period. Treatments were identical for each trial and included: 1) control, 2) estrogenic implant (E), 3) trenbolone acetate implant (TBA), 4) E + TBA (ET), 5) melengestrol acetate (MGA) in the feed, and 6) ET + MGA (ETM). Each treatment was replicated in five pens, with nine heifers per pen in each season. Initial weights (mean = 384 kg, SE = 57) were the same for each season. There were no treatment x season interactions for final BW, ADG, G:F, water intake, or carcass characteristics. Heifers receiving a growth-promoting agent were 11.6 kg (SE = 4.08) heavier and gained 0.108 kg/d (SE = 0.04) more (P < 0.05) than control heifers. Heifers receiving ET gained 0.09 kg/d (SE = 0.032) more (P = 0.05) than heifers not receiving ET. Heifers receiving ET (with and without MGA) had greater G:F (P < 0.05) than control, E, and TBA heifers. Carcass weights of ET-treated heifers were greater (P < 0.05) than carcass weights for unimplanted heifers, those fed MGA only, and heifers receiving either E or TBA implants. Marbling scores were increased (P < 0.05) by feeding MGA to ET-treated heifers. Water intake was greater (P < 0.01) in the summer (31 L/d) than in the winter (18 L/ d), with no difference among implant treatments. Heifers fed in the winter had heavier carcasses, less 12th-rib fat, greater marbling scores, larger LM area, and a greater incidence of liver abscesses than heifers finished in the summer (P < 0.01). A treatment x season interaction (P = 0.07) was evident for DMI during the 35-d coldest and hottest portions of the year. Heifers fed MGA and implanted with ET tended (P = 0.07) to have greater DMI in the summer but lesser DMI in the winter. In general, differences among growth-promotant programs were relatively similar over the entire summer and in winter.

Effects of growth-promoting agents and season on blood metabolites and body temperature in heifers1,2

“…Performance data were analyzed within season with growth promotant treatment in- 77.8 ± 1.9 2.5 ± 0.5 31.5 ± 2.2 76.6 ± 2.4 83.6 ± 4.0 -Maximum 34.2 ± 0.9 95.8 ± 1.9 5.5 ± 1.7 45.8 ± 3.0 85.2 ± 1.9 100.2 ± 5.5 -Minimum 19.9 ± 2.5 48.9 ± 5.1 0.6 ± 0.2 17.8 ± 2.4 67.6 ± 4.4 63.9 ± 4.3 -Winter Mean −2.9 ± 3.5 67.6 ± 6.2 3.1 ± 1.0 −1.6 ± 3.5 -19.2 ± 4.6 20.3 ± 10.9 Maximum 5.2 ± 6.2 88.4 ± 6.3 7.3 ± 0.8 11.1 ± 8.2 -46.5 ± 11.4 47.1 ± 10.7 Minimum −9.6 ± 4.8 41.5 ± 8.3 0.6 ± 0.3 −11.2 ± 4.1 -−0.4 ± 4.7 −2.1 ± 6.6 1 Collected using a weather station located in the feeding facility; RH = relative humidity, WS = wind speed, BG = black globe temperature, THI = temperature-humidity index, BGTHI = THI using black globe temperature. THI = (0. cluded in the model according to the procedures outlined by Kreikemeier and Mader (2004). Tympanic temperature and ear surface temperature were analyzed according to procedures outlined by Davis et al (2003), and included season, growth promotant treatment, and the 2-way interaction in the model.…”

“…Facilities are located at 42°23′ N latitude and 96°57′ W longitude, with a mean elevation of 445 m above sea level. Details of the vaccination, parasite control, and diet regimens utilized for these experiments were reported by Kreikemeier and Mader (2004). Within a season, heifers had been stepped up to a 1.43 NEg (Mcal/kg; DM basis) high-energy finishing diet at the beginning of each study.…”

“…Diets were formulated to meet or exceed NRC (1996) nutrient requirements. Data reported herein were obtained from a subset of 540 heifers that were used in the experiment reported by Kreikemeier and Mader (2004). Experimental design, performance assessment procedures, and additional climate data were also reported by Kreikemeier and Mader (2004).…”

“…Data reported herein were obtained from a subset of 540 heifers that were used in the experiment reported by Kreikemeier and Mader (2004). Experimental design, performance assessment procedures, and additional climate data were also reported by Kreikemeier and Mader (2004). Respective indicators of heat and cold stress were based on the temperature-humidity index (THI; Thom, 1959;NOAA, 1976) and the windchill index (WCI; US National Weather Service, 2005).…”

Environmental factors affecting daily water intake on cattle finished in feedlots

“…1, the first 23 d of this study were not utilized because this was the period in which treatments were applied after cattle were fed and managed similarly. Experiments 3 and 4 utilized 540 heifers (270 animals·experiment −1 ) to compare the effect of different growth promotant strategies among winter and summer season (Kreikemeier and Mader, 2004). The experiments were conducted over 104-or 105-d feeding periods.…”