Comparative feeding value of distillers dried grains plus solubles as a partial replacement for steam-flaked corn in diets for calf-fed Holstein steers: characteristics of digestion, growth performance, and dietary energetics.

Two experiments were conducted to examine the effect of level of dried distillers grains plus solubles (DDGS) supplementation (0, 10, 20, and 30%; DM basis), replacing steam-flaked (SF) corn in finishing diets, on characteristics of digestion (Exp. 1) and growth performance (Exp. 2) in calf-fed Holstein steers. In Exp.1, 4 cannulated Holstein steers (349 ± 12 kg) were used to evaluate treatment effects on characteristics of digestion. Ruminal NDF digestion tended to increase (quadratic effect, P = 0.09) and ruminal OM digestion decreased (linear effect, P = 0.01) with DDGS substitution. There were no treatment effects on duodenal flow of microbial N (MN). Substitution with DDGS increased (linear effect, P < 0.01) N flow to the small intestine. The undegradable intake protein (UIP) value of DDGS was 35%. Postruminal digestion of OM (linear effect, P = 0.04) and fatty acids (linear effect, P = 0.03) and total tract digestion of OM and GE decreased (linear effect, P < 0.03) with increasing level of DDGS substitution. Substitution with DDGS did not affect (P = 0.80) ruminal pH but increased (linear effect, P = 0.01) acetate:propionate molar ratio. In Exp.2, 144 Holsteins steer (112 ± 6 kg) were used in a 305-d trial to evaluate treatment effects on growth performance and carcass characteristics. During the initial 126 d, DDGS substitution increased ADG (linear effect, P = 0.03), G:F (quadratic effect, P = 0.03), and dietary NE (quadratic effect, P = 0.02), maximal for both at 20% DDGS inclusion rate. Based on estimated indispensable AA supply to the small intestine as a percentage of requirements during the initial 126-d period, histidine was first limiting followed by methionine. During the final 179-d period and overall (305-d feeding period), treatment effects on ADG and G:F were small (P ≥ 0.22). Compared with the other treatments, HCW was greater (3.4; P = 0.03) at the 20% level of DDGS substitution. The NE value for DDGS in SF corn-based diets for the calf-fed Holstein are consistent with current tabular standards. Extra-caloric value of DDGS as a metabolizable AA source is apparent during the initial growing phase. The UIP value of DDGS used in this study (35%) was considerably less than current tabular estimates (52%; NRC, 2000).

Effects of preslaughter withdrawal period on response of feedlot heifers to zilpaterol hydrochloride supplementation: growth performance and carcass characteristics.

Sixty-four crossbred heifers (451 +/- 23 kg) were used in a 42-d feeding trial (4 pens per treatment in a randomized complete block design) to evaluate the influence of preslaughter zilpaterol hydrochloride withdrawal period on growth performance and carcass characteristics. Heifers were fed a diet based on steam-flaked corn (2.13 Mcal of NE(m)/kg). Treatments were 1) control, no zilpaterol supplementation; 2) zilpaterol supplementation for 30 d, drug withdrawn from the diet 3 d preslaughter (ZIL-3); 3) zilpaterol supplementation for 30 d, drug withdrawn 6 d preslaughter (ZIL-6), and 4) zilpaterol supplementation for 30 d, drug withdrawn 12 d preslaughter (ZIL-12). Zilpaterol was supplemented at the rate of 0.15 mg/kg of BW daily. Intake of DM averaged 9.2 +/- 0.26 kg/d and was not affected (P > or = 0.36) by treatment. Compared with control heifers, ZIL-3 increased (P < 0.01) carcass-adjusted ADG (59%), G:F (57%), apparent dietary NE(m) (31%), and decreased observed/expected DMI (25%). Treatment with ZIL-3 did not affect marbling score (P = 0.49) or backfat thickness (P = 0.17), but compared with the control group, increased HCW (3.6%, P = 0.03), carcass dressing percentage (3.2%, P = 0.02), LM area (6.3%, P = 0.05), and reduced trimmed fat (31%, P = 0.03). Prolonging the period of zilpaterol withdrawal preslaughter tended to decrease carcass-adjusted ADG (linear, P = 0.11), G:F (linear, P = 0.08), apparent dietary NE(m) (linear, P = 0.11), and carcass dressing percentage (linear, P = 0.11). We conclude that growth performance and carcass yield responses to zilpaterol supplementation are negatively affected by prolonging the period of zilpaterol withdrawal beyond 3 d (the required minimum withdrawal period according to label). Drug withdrawal period may be a relevant factor in explaining variation in performance response to zilpaterol supplementation in commercial feedlots.