THE LATEST scientists to sing the praises of soy aren't human nutritionists but dairy scientists. Their current research shows that feeding whole but cracked raw soybeans to cows reduces the amount of body heat they generate, while improving their reproductive efficiency.
“Until now, we've been mostly focused on helping a cow lose body heat through the use of fans, sprinklers and misters,” explains University of Missouri animal scientist Jim Spain. “But another approach is to reduce the amount of heat her body generates in the first place. Adjusting her diet may be the best way to do that.”
Working with fellow animal scientists Matt Lucy and Don Spiers, Spain is looking at the role of fatty acids found in soybeans in optimizing cow performance. These specific essential fatty acids are influential in the reproduction of high-producing dairy cows, he says. “Fat has a lower heat increment, meaning when a cow eats it, she'll generate less heat that her body needs to lose.”
The researchers believe that higher levels of polyunsaturated fatty acids boost hormone synthesis, specifically progesterone, which is necessary for development of the reproductive system. “In high-producing, nutritionally stressed animals, we think these relationships are important, and especially pertinent in the case of heat-stressed cows,” Spain says.
Finding the soybean link
A few years back, Spain stumbled onto a doctoral thesis written in the 1960s that stated dairy cow sweat is high in concentrations of the essential fatty acid found in soybeans. Spain says it was the missing piece to this small but complicated dairy nutrition puzzle. “The cow is losing the fatty acid through her skin secretions as well as her milk. What we're finding is that we can add it through her diet,” he says.
His current research is focused on finding whether a cow's fatty acid balance changes when she is heat stressed. “We're also trying to measure how much effect feeding her soybeans has on her fatty acid balance,” he says.
The other part of their research challenge, he says, is finding out if heat stress can be reduced by feeding cows a diet that generates less body heat. After measuring these factors, the researchers plan to induce reproductive synchronization in each group of cows and to compare the responses. “We can measure parameters that we know are associated with cow fertility, such as the size of the ovarian follicles and the amount of steroid hormones,” he explains.
Bean form is key
Spain and his colleagues started their experiments by looking at which form of soybeans is best in dairy diets and have settled on including between 4 and 6 lbs. of the raw soybeans, straight out of the bin, in each cow's ration. Spain says he thinks roasted beans could be used, as well. “We've found that the beans need to be cracked, though, to help the cow break down the seed coating,” he says. “Otherwise, they go right through the animal whole.
“Ground or extruded soybeans don't have the same effect as whole,” he adds, “since the rumen breaks down the fatty acids too thoroughly.
“Before producers could successfully implement this concept into their herd diets, they would need to have all their other herd nutrition in line,” he says. “This is a way to fine-tune already good herd management.”
Over the years, as the industry has selected cows for milk production, “we've made them much more sensitive to heat stress,” Spain says. “One of the negative impacts of heat stress is decreased fertility. It's hard to overstate the economic importance of reproductive efficiency on a high-production dairy farm.
“We can't eliminate heat stress, but we can minimize the effects of it and improve the cow's recovery from it,” he notes. “This is simply another tool that could help dairy farmers improve overall herd health and performance.”