Tim Lundeen, the staff editor of Feedstuffs, an online animal agriculture industry source of news, information and analysis based in Bloomington, Minnesota, recently detailed the work of a research team that included Kristin Hales, the Thornton Distinguished Chair in Animal Science at Texas Tech University. Here's part of the report.

Jersey cows are known to produce milk with higher component values than Holsteins, leading to specialized nutrient requirements for the smaller-sized Jersey dairy cow. Now, in the Journal of Dairy Science, a research team has determined the effects of isoenergetic high-starch or high-fat diets on energy and nitrogen partitioning, as well as energy utilization of Jersey cows.

Kristin Hales, a nationally-recognized expert in ruminant nutrition and beef cattle energetics who also serves as an associate professor in Texas Tech's Department of Animal and Food Sciences, along with Logan Morris, Tami Brown-Brandl and Paul Kononoff at the University of Nebraska-Lincoln, and Kevin Harvatine at Pennsylvania State University, found a high-starch diet had a greater metabolizable energy and NEl content, increased nitrogen partitioning toward milk secretion and away from urinary excretion, and may have increased energy partitioning toward tissue energy deposited as fat.

In other words, the composition of energy supply, starch vs. fat in this case, may alter milk protein synthesis and should be incorporated into future nutritional models focused on lactating dairy cows. Hales role in the project included providing input on the dietary treatments, assisting in data interpretation and analysis, and assisting in publication of results. She also serves as a member of Morris' Ph.D. committee and mentors him on cattle energetics.

In developing the study, the research team enrolled 12 multiparous Jersey cows in the study in a crossover design with 28-day periods to compare two treatment diets. Treatments were high starch or high fat. Diets were formulated to have net energy for lactation (NEl) content of 1.55 Mcal/kg of dry matter, according to the National Research Council dairy model.

Nutrient composition was varied primarily by replacing corn grain in the high-starch diet with a rumen-inert fat source and cottonseed hulls in the high-fat diet, the researchers noted. Gross energy content was lower for the high-starch diet, whereas digestible energy, metabolizable energy and NEl content were all greater than for the high-fat diet.

Tissue energy deposited as body fat tended to be greater for the high-starch diet, the researchers reported. For nitrogen partitioning, the high-starch diet increased milk nitrogen secretion and decreased urinary nitrogen excretion. In addition, the high-starch diet increased apparent total-tract digestibility of dry matter, organic matter, energy and 18-carbon fatty acids, compared with the high-fat diet. However, the team reported that apparent total-tract digestibility of starch decreased for the high-starch diet from 97.0 percent to 94.5 percent.

Hales, a Texas panhandle native, indicated that her research efforts are broadly focused on beef cattle nutrition and management, specifically focusing on rumen microbiome, antimicrobial resistance, beef cattle energetics, and improving feed efficiency of beef cattle. For eight years, prior to joining the Tech faculty last year, she served as a research animal scientist with the USDA Agricultural Research Service's U.S. Meat Animal Research Center in Clay Center, Nebraska. Hales received her bachelor's and her master's degrees in animal science from Oklahoma State University-Stillwater. Her doctorate in animal science is from Texas Tech.

CONTACT: Kristin Hales, the Thornton Distinguished Chair in Animal Science, Department of Animal and Food Sciences, Texas Tech University at (806) 834-5354 or Kristin.Hales@ttu.edu

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