Regular readers of Tri-State Livestock News and other popular ag press are receiving a barrage of advice on ways to meet forage needs of grazing cattle during drought.
There has been plenty of good advice about saving forage by early weaning and culling; using failed crops; planting summer annuals for emergency feed; and using crop residues to extend the forage supply. In this column, I will 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 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, during times when forage needs to be conserved and intake decreased, we can use this negative effect to our advantage. Basically, we substitute 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 to still meet the cow’s 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 an untested theory a few years ago. I had a former grad student conduct a study during the 2003 drought 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.
The study involved three groups of cows: an unsupplemented control; a group that received 2 pounds of cracked corn per day; and a group that received Rumensin added to 2 pounds of cracked corn. We had sampling periods in June and September to assess forage digestibility and intake. The drought was moderately severe during early summer, but late summer rains partially alleviated the severity of the drought by September.
During June, the results were exactly what we predicted: Corn by itself reduced fiber digestion in the forage by 8 percentage points (58 to 52 percent 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 percent (3.2 to 2.4 percent of body weight for control and corn, respectively).
This translates into forage intake for a 1,300-pound cow being reduced from 41.6 pounds per day for the control group to 31.2 pounds per day for the corn-supplemented group. That’s a 10-pound per day savings! Forage intake for the Rumensin-supplemented group was further reduced to 2.0 percent of body weight, which would be 26 pounds per day for the 1,300-pound cow. The total savings due to the combination of corn and Rumensin was a 37.5 percent 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 percent 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 percent of body weight, or about 16 pounds for a 1,300-pound cow).
I don’t know if the late summer rain played a role, or if decreasing forage quality as the forage started to go dormant in September eliminated the ability for digestibility and intake to respond to the supplements. Regardless, I am comfortable recommending producers supplement cows with a grain-based supplement that includes Rumensin as a way to conserve dwindling range forage. It should be done now because it probably won’t be as effective in the fall or later.
A concern will be the cost of the supplement. Corn prices are going 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. This may be another reason to do it now rather than later because expectations are that corn and other grain prices will continue to rise as drought conditions limit the expected yields of this year’s corn crop.