Feeding some tallow is a good way to pack extra energy into a dairy diet, but too much tallow can disrupt rumen function and depress milk fat production, particularly when diets are high in corn silage. Some studies have shown that adding alfalfa hay to corn silage diets can revive some of that fat production. However, alfalfa silage may not have the same curative powers as alfalfa hay, University of Wisconsin-Madison research has shown.
Florida researchers found that feeding tallow at 2.5 percent of ration dry matter depressed milk fat production in diets using corn silage as the sole forage source. When they substituted alfalfa hay for some of the corn silage, fat test returned to normal, according to Ric Grummer, a dairy nutritionist at UW-Madison”s College of Agricultural and Life Sciences.
Working with UW-Madison extension dairy nutritionist Randy Shaver and graduate student Silvia Onetti, Grummer looked at the effects of tallow on milk production in cows fed diets containing corn silage or corn silage plus alfalfa silage.
“We don”t usually see milk fat depression when feeding modest amounts of tallow, but in Wisconsin we don”t typically feed diets with corn silage as the sole forage source. However, the use of corn silage is increasing,” Grummer notes. “In our first trial we re-examined the Florida study and attempted to duplicate the milk fat depression with a corn-silage diet. We also looked at choice white grease. There is very little research on it, but a lot of it is sold in Wisconsin,” he says. This grease is more unsaturated than tallow. As rule, more unsaturated fats are more likely to cause milk fat depression.
In trial 1, the researchers fed 2 percent tallow or grease (the high end of what is typically fed) and 4 percent tallow or grease (extremely high level). Both fats, and both fat-feeding levels, depressed milk fat production to a similar extent. In trial 2, Grummer fed 2 percent tallow in corn silage-based diets, and replaced either 25 percent or 50 percent of the corn silage with alfalfa silage, which is a typical Midwestern forage. In the Florida studies, replacing some corn silage with dry hay lessened the milk fat depression problem.
He was surprised to see that neither alfalfa silage level corrected the milk fat depression. “We were looking for a fat-by-forage interaction, where fat would have a greater detrimental effect with more corn silage, but a less detrimental effect with more alfalfa silage. We didn”t see this,” Grummer says. “All the forage combinations showed milk fat depression when we fed added tallow.”
There are several possible explanations for this, he says. Maybe the Florida diets, which contained hay instead of alfalfa silage, made the difference. Or maybe it was something else – for example, the Florida diets contained a different concentrate mix.
In an upcoming trial, Grummer plans to look at how alfalfa silage compares with dry hay in alleviating milk fat depression in Midwest diets. “At this point, we can”t say that the negative effects of tallow are unique to just high corn silage diets – they may apply to all silage diets, so to alleviate milk fat depression, we may have to feed dry hay.”
In the second trial, cows were fed about one pound of tallow per day. “We”ve run previous trials where that level hasn”t caused a problem, but this trial has made us much more conservative in our recommendations for tallow feeding,” Grummer says. “I”d recommend no more than a half-pound of tallow per cow per day. If you want to feed more than that, you”ll need to closely monitor cow performance. Depressed fat test is a pretty good indicator of potential problems with rumen fermentation.”
There is probably not much difference between tallow and choice white grease as far as dairy diets go. Their fatty acid profiles are different, but not that different, Grummer says, so producers getting good results with tallow should be able to substitute similar levels of grease with no problems. Prices of the two fats are similar now in the Chicago commodities market, but delivered prices may differ depending on distance from the source.
In these trials, mid-lactation Holstein cows from the UW-Madison herd were fed twice daily with a total mixed ration containing 18 percent crude protein and 32 percent neutral detergent fiber. Control cows that got no supplemental fat averaged 3.1 percent to 3.3 percent milk fat; cows eating supplemental fat averaged 2.8 percent to 3 percent milk fat.
This research was supported by the Fats and Proteins Research Foundation and the College of Agricultural and Life Sciences.