As researchers continue to find ways the bull is to blame for reproduction shortfalls in a beef herd, it was inevitable questions about feed would circle back around.
This is not the first time what a bull eats has been analyzed in connection with development and fertility. Cottonseed, for example, has long been a concern due to the gossypol it contains. Lawton Stewart, Extension animal scientist at the University of Georgia, says he gets phone calls and emails every year asking if bulls are going to be sterile because there was whole cottonseed in the ration.
"My answer is always, absolutely not if you stay within the recommended feeding levels," he reports.
Lawton says the recommendations are pretty simple. Don't feed whole cottonseed to calves under 400 pounds. Limit whole cottonseed to 20% of total daily intake, or no more than 6 pounds per day.
From cottonseed, now to concerns over distillers grain. University of Illinois (UofI) researchers have just completed a study looking at the effects this common feed ingredient may have on bull development and fertility.
Daniel Shike, with the department of animal sciences at UofI, says they were getting questions after a recent study showed some negative fertility effects in rams. But there was no data to indicate what sort of impact, if any, might be expected in beef bulls.
"Even though there have been hundreds of experiments done on distillers grains with growing and finishing cattle, there's very limited bull development research from a breeding standpoint," says Shike.
The UofI study looked at two groups of 8-month-old SimAngus bulls. One group was given a 40% distillers grain diet, the other a standard corn-based diet. This lasted 140 days. At the end of that time both groups were switched to a common low-energy diet for 70 days.
Shike notes they "chose the 40% inclusion rate, which is kind of on the high end, thinking there's really no reason to have distillers inclusion greater than that in most practical situations. Then we collected data on just about everything under the sun."
Researchers looked at things like growth performance, body condition, hoof development and reproductive metrics. At the end of the treatment, one reproductive metric differed between the two groups of bulls. Those in the group eating distillers grain had a higher percentage of sperm with "proximal droplets". These are fluid-filled sacs near the head of the sperm. When retained, these proximal droplets are considered a major defect that can affect reproductive capacity. However, it's important to note, after 70 days on the low-energy diet the problem resolved.
Shike said overall this is good news, but added a disclaimer noting the source of distillers used in the study was relatively low in Sulphur (0.23%).
"If your distillers had elevated Sulphur content, I would recommend a lower inclusion than 40%," he said. "Sources vary, and that's a potential problem. The bottom line is assuming Sulphur content is not at a toxic level, we can utilize distillers in bull development rations with very similar results as if they were developed on a corn-based diet."
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