Montana ranchers should watch carefully for bloat problems in their cattle this fall, particularly those grazing alfalfa or alfalfa-mix pastures. So warn Dennis Cash and Rachel Endecott, Montana State University (MSU) Extension forage and beef specialists, respectively.
Substantial rain across the state has helped produce a supply of alfalfa and alfalfa-grasses. The high-quality feed is used for preconditioning calves, putting body condition on bred cows and flushing ewes.
But the potential for pasture bloat is real, the specialists say, and warn ranchers to be cautious when grazing alfalfa-dominated hayfields.
Livestock grazing lush pastures of alfalfa, clovers and small grains can rapidly digest forage containing highly soluble proteins. The end result: A stable foam is produced that prevents rumen gases from being expelled by belching, called frothy bloat.
Individual animals or a herd can experience severe bloat symptoms, including rapid death. Bloat hazards generally increase with lush, vegetative alfalfa growth during spring or fall frosts, rain, and with high soil fertility, but can also occur in summer. Animals grazed season-long can adjust and become bloat-tolerant. Alfalfa-based pastures are very productive for grazing yearlings, for example. However, rapid changes in diet quality, such as moving cows from dry grass to lush alfalfa, are risky.
Bloat can also be caused by a cow’s pre-existing health conditions and its mineral status. Good descriptions of bloat and its prevention are in the Cattle Producer’s Library.
A particularly risky time for grazing alfalfa is immediately following frost. From 1998 through 2000, MSU conducted grazing experiments with cattle and sheep on pure alfalfa stands. Data was taken from 10 grazing trials in late spring through late summer. Bloat was evaluated by incidence (percent of animals with symptoms) and a subjective severity score (1 = no symptoms; 6 = dead) of bloat, assigned multiple times during the day.
Due to paddock sizes and animal numbers (24-40 ewes), sheep-grazing data were the most useful. All three years, grazing incidence was most severe in late spring and late summer, but occasional bloat “storms” occurred in mid-summer.
In 1999, MSU monitored bloat over several days in which the weather forecast predicted first frost. On Sept. 3, 8, 9 and 10, overnight minimum temperatures were, respectively, 34, 36, 33 and 26 degrees F.
On Sept. 10, one of the worst bloat days during the study, more than 80% of the ewes bloated (average severity score = 3.6). Immediately following a hard freeze (defined as adequately cold to rupture cell walls), concentrations of soluble proteins and sugars are very high in alfalfa forage and increase its risk for bloat. In general, forage becomes safer to graze after stems have collapsed and dried for several days after freezing, Cash and Endecott say.
To prevent bloat, ranchers who need to renovate pastures can choose legumes such as sainfoin, cicer milkvetch and birdsfoot trefoil, which don’t cause bloat. A number of products are promoted as “bloat preventatives,” including specific alfalfa varieties, ionophores and mineral mixes.
However, the most studied and effective treatment is Poloxalene (Bloatguard) combined with good animal health practices such as mineral supplementation and vaccinations. The alfalfa should be flowering when using the product, the experts advise.
Feed livestock dry roughage before turning them out onto alfalfa pasture. The pasture should be dry, and grazing should be continuous rather than frequent corralling or movement. Rotate paddocks in the afternoon and monitor animals multiple times each day initially and daily thereafter. Monitor Poloxalene’s intake, as it varies among animals and days.
Clinical Signs of Frothy Bloat
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