Influence of Ionophore Supplementation on Growth Performance, Dietary Energetics and Carcass Characteristics in Finishing Cattle during Period of Heat Stress.

Forty-eight crossbred heifers (378.1±18 kg) were used in a 56-d feeding trial (four pens per treatment in a randomised complete block design) to evaluate the influence of ionophore supplementation on growth performance, dietary energetics and carcass characteristics in finishing cattle during a period of heat stress. Heifers were fed a diet based on steam-flaked corn (2.22 Mcal NEm/kg) with and without an ionophore. Treatments were: i) control, no ionophore; ii) 30 mg/kg monensin sodium (RUM30); iii) 20 mg/kg lasalocid sodium (BOV20), and iv) 30 mg/kg lasalocid sodium (BOV30). Both dry matter intake (DMI) and climatic variables were measured daily and the temperature humidity index (THI) was estimated. The maximum THI during the study averaged 93, while the minimum was 70 (THI average = 79.2±2.3). Compared to controls, monensin supplementation did not influence average daily gain, the estimated NE value of the diet, or observed-to-expected DMI, but tended (p = 0.07) to increase (4.8%) gain to feed. Compared to controls, the group fed BOV30 increased (p≤0.03) daily gain (11.8%), gain to feed (8.3%), net energy of the diet (5%), and observed-to-expected DMI (5.2%). Daily weight gain was greater (7.6%, p = 0.05) for heifers fed BOV30 than for heifers fed MON30. Otherwise, differences between the two treatments in DMI, gain to feed, and dietary NE were not statistically significant (p>0.11). Plotting weekly intakes versus THI, observed intake of controls was greater (p<0.05) at THI values ≤77 than ionophore groups. When THI values were greater than 79, DMI of control and MON30 were not different (p = 0.42), although less than that of groups fed lasalocid (p = 0.04). Variation in energy intake was lower (p>0.05) in the ionophores group (CV = 1.7%) than in the control group (CV = 4.5%). Inclusion of ionophores in the diet resulted in relatively minor changes in carcass characteristics. It is concluded that ionophore supplementation did not exacerbate the decline of DM intake in heat-stressed cattle fed a high-energy finishing diet; on the contrary, it stabilised feed intake and favoured feed efficiency. Ionophore supplementation reduced estimated maintenance coefficients around 10% in finishing cattle during a period of heat stress. This effect was greatest for heifers supplemented with 30 mg lasalocid/kg of diet.

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).

Influence of processing method on comparative digestion of white corn versus conventional steam-flaked yellow dent corn in finishing diets for feedlot cattle.

Four Holstein steers (137 ± 2 kg) with cannulas in the rumen and proximal duodenum were used in a 4 × 4 Latin square design to evaluate the influence of processing method on comparative digestion of white corn. Treatments consisted of a basal finishing diet containing 80% corn grain (DM basis) as 1) dry-rolled white corn (DRWC), 2) steam-flaked white corn (SFWC) with 0.36 kg/L flake density (SFWC36), 3) SFWC, 0.31 kg/L flake density (SFWC31), and 4) steam-flaked yellow corn (SFYC) with 0.31 kg/L flake density (SFYC31). Characteristics of ruminal, postruminal, and apparent total tract digestion of OM, starch, and N were similar (P ≥ 0.08) for SFYC31 and SFWC31 treatments. Decreasing flake density of white corn (from 0.36 to 0.31 kg/L) did not affect (P = 0.22) ruminal OM digestion, but increased (1.9%, P = 0.07) apparent total tract OM digestion. Compared with dry rolling, steam flaking white corn increased ruminal (9.4%, P = 0.05), postruminal (14.4%, P < 0.01), and apparent total tract OM digestion (8.2%, P < 0.01), reflecting corresponding increases in ruminal (13.3%, P < 0.01), postruminal (43%, P < 0.01), and apparent total tract (12.3%, P < 0.01) starch digestion. Apparent postruminal and apparent total-tract N digestion also were greater (6.5 and 5.6%, respectively, P = 0.04) for SFWC than for DRWC. The DE value of SFWC and SFYC diets was similar, averaging 3.39 Mcal/kg. The DE value of SFWC was greater (8.1%, P < 0.01) than that of DRWC. Ruminal pH (4 h postprandial) averaged 5.74 and was not affected (P ≥ 0.48) by dietary treatments. Compared with dry rolling, steam flaking markedly enhances the feeding value of white corn, with optimal flake density being less than 0.36 kg/L. Although white corn has greater vitreous endosperm content, characteristics of ruminal starch digestion and undegradable intake protein are similar to conventional yellow dent corn when processed to a similar flake density (0.31 kg/L). However, postruminal and apparent total tract starch digestion tends to be slightly less for flaked white corn than for yellow corn.