By Jim Massey
Freelance writer
Cole Diepersloot didn’t know what to expect when he made the decision to follow his mentor from the University of Florida to UW-Madison in May of 2020.
He was already in the midst of a master’s degree program in Florida under the supervision of Luiz Ferraretto, at the time an assistant professor of livestock nutrition at the University of Florida. So, when Ferraretto told him he had accepted a position in Wisconsin as an assistant professor and extension specialist in ruminant nutrition in the Department of Animal and Dairy Sciences, Diepersloot had a decision to make – continue his graduate studies in Florida, or travel 1,200 miles to the north and continue those studies in Wisconsin.
He chose Wisconsin.
“I had never seen snow before, so I wasn’t really sure what to expect with the weather,” Diepersloot says. “But it’s been a good experience. It has definitely been nice to get out of my comfort zone.”
Diepersloot completed his master’s degree in dairy science and began a Ph.D. program under Ferraretto’s tutelage. He plans to graduate in May with a doctorate degree in dairy science, after spending nearly eight years under Ferraretto’s supervision.
Ferraretto says it was gratifying for him when Diepersloot and other graduate students working with him in Florida opted to follow him from Florida to Wisconsin.
“I can’t complain (about having the students move with him to Wisconsin),” Ferraretto says. “It says something about the program we have here in Madison. I guess we’re doing something right.”
Diepersloot spent a good share of his four-year Ph.D. program helping update the 18-year-old MILK index that farmers use to rank corn hybrids for energy content and yield. It’s also known as the “milk per ton” model. The MILK index is used to help select corn hybrids for dairy operations.
The MILK index was last updated in 2006 based on energy equations from the National Research Council. An updated version of those energy equations, by the National Academies of Sciences, Engineering and Medicine, was released in 2021, but the MILK index was not updated at that time. Officials in the UW-Madison Department of Animal and Dairy Sciences decided it was time to factor in updated information and make the MILK index a more usable tool for dairy farmers and dove into the project in 2023.
Ferraretto says UW officials decided the basis of the updated MILK index would be the new nutrient guidelines developed by NASEM in 2021, which cover energy, protein, amino acids, carbohydrates, fats, minerals, and vitamins. The guidelines, as part of the MILK index, are used to develop diets for calves, heifers, dry cows and lactating cows.
“The theme of the project was developing an index that will help farmers make better management decisions on corn silage production,” Diepersloot says. “We made it a little more biologically representative and also updated digestibility predictions so it would be more representative of what digestibility would be in an actual cow.”
The composition of the predicted milk yield was also changed so it would be more representative of a modern cow.
“Since MILK2006 was released in 2006, many advancements have been made in dairy nutrition,” Ferraretto says.
While Diepersloot worked with Ferraretto on the project, they also called on the expertise of Randy Shaver, an ADS department emeritus professor in nutrition.
“We went to Dr. Shaver and said, ‘Here’s what we’re planning on doing, what do you think?’” Diepersloot says. “He was able to give us feedback about different things we might do to make sure the index was easy enough to use.”
The updated index was released in 2024, and the spreadsheet is now being used by dairy farmers across the U.S. and even in foreign countries. Ferraretto and other ADS officials are in the process of working on a research paper to compare the new index to previous models.
Ferraretto says the MILK index couldn’t have been updated without Diepersloot’s months of data collection and research.
“I decided to have a more hands-off approach for this project, so I gave him a little bit of freedom to dig into different models,” Ferraretto says. “He basically had to build the new model from scratch. I also gave him the freedom to discuss this project with our collaborators to get their ideas and suggestions, so it was a good exercise for him.”
Ferraretto describes Diepersloot as “very dedicated” to his work on the MILK index but the other components of his Ph.D. as well.
“His work habits are superb,” Ferraretto says. “He never complains, and when you tell him to do something, you know it’s going to get done. Besides that, he has a very good (grade point average), which is not always the case for students who work too much. Plus, he’s a fun kid.”
Another component of Diepersloot’s Ph.D. project was focusing on the effect of feed additives and live-cell yeast supplementation on lactation performance, feeding behavior and nutrient digestibility by dairy cows. While considerable research has been done on feed additives, Diepersloot says not as much research has been done on the interaction between those additives. He conducted feeding trials on cows to test different additives side by side.
Diepersloot was primarily exposed to dairy farming while growing up and working on the large dairy farm that his father manages in north Florida, ironically near a city called Madison.
“They milk almost 4,000 cows, so it’s a lot different than the average farm in Wisconsin, that’s for sure,” he says. He started working on the farm when he was 16 during weekends and school breaks.
Diepersloot will have nearly eight years under Ferraretto’s tutelage by the time he leaves the university.
“I think he’s a great adviser, he’s always available for questions,” Diepersloot says. “He also does applied research, which I think is valuable. I’ve really enjoyed doing the type of research that we do.”
Diepersloot has secured a position as a dairy and forage consultant with the Vita Plus Corp. after he graduates in May. His new job will take him to Michigan.
“With his mindset, he has learned the required skills for his new job and tasks,” Ferraretto says. “Everything we’ve offered him in terms of opportunities, he took and did a very good job with them.”