by Courtney Llewellyn

Looking for ways to be both more efficient and environmentally friendly, farmers have increasingly been feeding their cattle spent distillers grains as an inexpensive alternative to corn and soybean meal. A team from the University of Illinois decided to see what kind of impact this feed ingredient had on bull development and fertility.

Daniel Shike, associate professor in the Department of Animal Sciences at the university, said, “We get questions occasionally about the effects of distillers grains on bulls, and a recent study showed some negative effects in rams. 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.”

Shike and his team of researchers studied eight-month-old Simmental x Angus bulls who were fed either a 40% distillers grain diet or a corn-based diet for 20 weeks. They were then switched to a low-energy diet for the next 10 weeks. The researchers measured growth performance, body condition, hoof development and a wide variety of reproductive metrics. They wanted a detailed look at overall bull development.

What did they discover? At the end of the 20 weeks, the bull that had been fed the distillers grains had a higher percentage of sperm with proximal droplets – tiny, fluid-filled sacs near the head of the sperm. The droplets usually shake down the tail with movement, but when they’re closer to the head, it’s considered a major defect that could affect reproductive capacity.

“The droplets are probably the most common defect seen by veterinarians when performing breeding soundness exams in the spring,” said Roy Lewis, DVM, with Merck Animal Health. “We see more droplets on average in young immature bulls just reaching sexual maturity. They are less sexually active and droplets are a frequent occurrence, especially when the bulls are not housed close to cycling females.”

Fortunately, after being fed the low-energy diet for 10 weeks, the issue seemed to resolve itself with the bulls in the study.

Shike said one of the main reasons the bulls had fewer droplets after the low-energy diet is also because they were older. “Age is a significant contributing factor to proximal droplets,” he stated.

It was also noted that the bulls that consumed distillers grains had greater body weight and fat at a couple of points during the experiment, but by the end of the study there was only a slight difference in body fat between the two groups.

“The distillers grain is a little higher in fat and energy, so they’re really being developed on a higher plane of nutrition to get ready for sale time. When people go to bull sales, they like to see well-developed heavyweight bulls. But then we’ve got to cool them back down again, back into their working condition. So that’s why we evaluated them at the end of that low-energy common diet period as well,” Shike explained.

Since the two groups of bulls were basically indistinguishable at the end of the experiment, feeders can feel safe continuing to use distillers grains – with a caveat. Shike noted the source of distillers grains used in the study was relatively low in sulfur (containing 0.23% sulfur, below the 0.3% threshold for potential toxicity).

“If your distillers had elevated sulfur content, I would recommend a lower inclusion than 40%,” he said. “Sources vary, and that’s a potential problem. It’s getting better, though. They’re getting more predictable and they’re getting lower across the board. The bottom line is, assuming sulfur content is not at a toxic level, we can utilize distillers grains in bull development rations, with very similar results as if they were developed on a corn-based diet.”