Ninety-six Hereford x Angus steers (mean initial BW = 295 kg) were used in two growth experiments conducted at moderate and high ambient temperatures (AT), 48 steers per AT. Within each AT, calves were assigned to six dietary treatments consisting of a basal diet (approximately 60% corn and 20% grass hay) supplemented with either 0, 2.5, or 5% fat and with either soybean meal (SBM) or Menhaden fish meal (FM) included at levels such that a ratio of 16.3 kcal of NEm per kilogram of CP was maintained. Blood and ruminal fluid were collected 40 d before slaughter. During the final 28 d of the moderate AT experiment, apparent digestibility of dietary components was measured in four individually fed steers from each dietary treatment. Steer ADG was not affected by fat, and DMI and efficiency of gain were not affected (P > .10) by treatment. Average daily gain was lower for steers fed FM than for those fed SBM at moderate AT but higher at high AT (CP source x AT interaction; P < .05). Ruminal ratio of acetate to propionate declined linearly with increasing fat at moderate AT but was not affected by fat at high AT (fat x AT interaction trend; P = .08). Plasma urea N concentration increased linearly (P < .05) with increasing fat and was higher (P < .05) in steers kept at high than in those kept at moderate AT. Although apparent digestibility was not altered in steers fed FM, DM and NDF (P < .05) and ADF (P = .07) digestibility decreased with increasing fat in steers fed SBM (CP source x fat interaction).(ABSTRACT TRUNCATED AT 250 WORDS)
Relationships among soil contamination of forages, elemental concentrations in forages samples, and grass tetany are not clear. Our objectives were to determine the extent and seasonal variation of soil contamination on annual ryegrass (Lolium multiflorum Lam.) samples, and to relate the contamination to various indicators of grass tetany. Seasonal variation of soil ingestion by grazing beef cattle was also investigated. Field experiments were conducted on a Tensas silty clay soil (fine, montmorillonitic, thermic Vertic Ochraqualf). Highly significant positive correlations were obtained among AI, Fe, and Ti concentrations within forage and rumen content samples. Concentrations of these elements occurred in the same ratios as in digested soil. Soil contamination during peak periods averaged approximately 70 g/kg in forage samples and 95 g/kg in rumen content samples. A washing procedure was ineffective in removing all of the soil contamination from forage samples. Forage samples taken in areas protected from grazing animals showed no apparent excessive uptake of AI by the plants at any time during the grazing season. The amount of soil contamination on forage plants and the amount of soil ingested by grazing animals increased with increased grazing pressure, decreased forage production, and saturated surface soils. A rapid decline in forage Mg and Ca concentrations may have been a major factor in the Occurrence of grass tetany, but was not associated with highest levels of soil contamination.
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