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Supplementation to Save Forage During Drought

08 January 2013

Forage shortages have lead to advice about early culling, early weaning and utilising failed crops and summer annuals. Ken Olson, Beef Specialist at South Dakota State University examines another forage emergency option.

Those of you that are regular readers of the popular ag press have received a barrage of advice on ways to meet forage needs of grazing cattle during drought. There has been a lot of good advice about saving forage by doing things like early weaning or early culling. Lots more good advice has been provided about using failed crops, planting summer annuals for emergency feed, and using crop residues to extend the forage supply. In this column, I am going to provide another option to conserve limited forage.

Typically, nutritionists talk about supplementing with protein when forage quality is low to stimulate digestion and intake of the forage. We also usually warn against supplementing with cereal grains or feed grains because high levels of starch in the supplement create an opposite effect and cause a decrease in forage digestion and intake. However, in times that we need to conserve forage and would actually like to decrease forage intake, we can use this negative effect to our advantage. Basically, we are substituting the grain for limited forage.

The concern with this idea, however, is that we cause depression of both forage digestibility and intake. It would be best to depress intake without harming digestion so we still meet the cows’ requirements. To counteract this issue, we need to consider part two of the supplement. Rumensin® is a feed additive that is very effective at altering feed digestion and intake in ruminants. It has the ability to improve digestion and reduce intake in forage-based diets, leading to the exact effect that we are pursuing.

All of this was untested theory a few years ago, so I had a former grad student conduct a study during the drought in 2003 to evaluate how effective this supplementation strategy would be. The study was conducted in Utah, but I am very comfortable that the response will be the same in the Northern Plains.

Cattle were divided into three treatment groups: 1) an unsupplemented control, 2) a group that received 2 lb. of cracked corn per day, and 3) a group that received Rumensin® added to 2 lb. of cracked corn. Sampling periods were in June and September to collect samples to assess forage digestibility and intake. The drought was moderately severe during the sampling in early summer, but some late summer rains partially alleviated the drought and stimulated some new grass growth.

During June, the results were exactly what we predicted: Corn by itself reduced fiber digestion in the forage by 6 percentage points (58 to 52% for control and corn groups, respectively), but adding the Rumensin® eliminated the reduction in digestibility. In turn, corn reduced forage intake as a percentage of body weight by 0.8% (3.2 to 2.4 % of body weight for control and corn, respectively). This translates into forage intake for a 1300 lb. cow being reduced from 41.6 lb. per day for the control group to 31.2 lb. per day for the corn-supplemented group. That’s a 10 lb. per day or 25% savings! Forage intake for the Rumensin®-supplemented group was further reduced to 2.0 % of body weight, which would be 26 lb. per day for the 1300 lb. cow. The total savings due to the combination of corn and Rumensin® was a 37.5% reduction in forage intake.

We should have stopped and left well enough alone with good results, because the results in September were not as encouraging. In September, results indicated corn grain and Rumensin® both actually increased forage fiber digestion (38, 47, and 55% digestibility for control, corn, and Rumensin® groups, respectively). Further, forage intake was not influenced by either supplement, but was much lower in September (1.26% of body weight for all groups, or about 16 lb. for a 1300 lb. cow). I don’t know if the late summer rain played a role or if some other influence on forage quality in September eliminated the ability for digestibility and intake to respond to the supplements.

Regardless, I am comfortable recommending that supplementing cows with a grain-based supplement that includes Rumensin® would definitely be effective during a droughty summer to conserve dwindling range forage. The desired influence continuing into the fall and winter is not as certain. However, where most producers did not receive late summer rains to stimulate new growth in late summer as occurred in the year of our study, the Rumensin® and corn may still be effective.

A concern will be the cost of the supplement. Corn prices are up, so it would be wise to have a conversation with your feed dealer soon to see if they could provide this mix at a reasonable cost.

Further Reading

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January 2013

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