Effect of feed additives on in vitro and in vivo rumen characteristics and frothy bloat dynamics in steers grazing wheat pasture
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Research was conducted to determine the potential efficacy of feed additives (FA) to mitigate frothy bloat in yearling cattle grazing wheat pasture. Two experiments were conducted to: (1) quantify in vitro effect of FA on total rumen and methane gas production and foam potential and (2) quantify the influence of FA on rumen protein characteristics, bloat potential and weight gain of steers grazing wheat pasture. In Exp 1, duplicated analyses of in vitro gas production were measured as sequential plunger displacement (cc) at 0, 1, 2, 3, 4, 5, and 6 h incubation periods. In vitro rumen foam production and strength was measured at 0, 2, and 6 h incubation of minced wheat forage. In Exp 2, eight ruminally cannulated steers (386 35.8 kg/steer) were randomly allocated to one of four FA treatments that included control, monensin, poloxalene, and condensed tannins (CT). Treatments were administered daily through rumen cannulla as pre-mixes with a mixed ration (300 mg/steer/day; as-fed basis). Steers grazed on wheat during a 2-week adaptation period prior to data collection from 05 March to 12 April, 2004. Rumen contents were collected 2 h post-FA infusion (1030 to 1130 h) on day -5, 0, 5, 15, and 22. Cattle were weighed at 28-days intervals. Bloat was visually scored weekly. In Exp 1, in vitro ruminal gas and methane gas production per gram of forage were similar between control and poloxalene, but were lower for monensin (P<0.01) and CT (P<0.05) treatments. The lowest (P<0.01) in vitro foam strength occurred with the addition of poloxalene and the highest occurred in control and monensin treatments. CT was intermediate in rumen foam strength. Mean bloat score was lower in poloxalene and CT than that in monensin and control treatments. Among six-rumen protein components assayed, steers receiving CT after 10, 15, and 22 day had greater protein concentrations in whole rumen content, particulate matter, cheese-cloth filtrate, and protozoa and plant particle fractions than steers fed other treatments. Bacterial and cell-free supernatant protein fractions were comparable among treatments. Ruminal dry matter (DM) content, cell-free supernatant, protozoal and bacterial fractions were similar between the bloated and non-bloated steers. In bloated animals, ruminal pH was lower, and whole rumen content and cheese-cloth filtrate protein fractions tended to be greater (P=0.08) than in non-bloated animals. Animal average daily gain (ADG) was not affected by FA during experimental period. The results of this trial suggest that wheat pasture bloat was associated with dietary protein and low ruminal pH. Feeding FA can be used to decrease either ruminal gas or foam production or both, and it may protect against the incidence of frothy bloat. 2005 Elsevier B.V. All rights reserved.
