Impacts of Skeletal Muscle Depletion and Accretion Across Lactation with guests Dr. Jackie Boerman, Purdue University; Dr. Bill Weiss, Emeritus The Ohio State University; Dr. Jim Aldrich, CSA Animal Nutrition

This episode was recorded in Fort Wayne, Indiana, during the 2025 Tri-State Dairy Conference.

Dr. Boerman notes we know cows experience a negative metabolizable protein balance in early lactation, which means they’re mobilizing skeletal muscle to make up for that. Dr. Boerman and her group have been interested in strategies to measure how much muscle they’re mobilizing, when they’re losing it and when they gain it back.  (3:51)

Cows are ultrasounded during the dry period to determine longissimus dorsi muscle reserves, then divided into low vs high muscle groups. Weekly ultrasounds follow them through lactation.  Animals with high muscle reserves during the dry period mobilized muscle before calving, which resulted in increased calf birth weights. Animals with less muscle during the dry period can gain muscle during that time and have more muscle reserves at calving than they had in the middle of the dry period. Dr. Boerman discusses possible nutrition interventions to manage muscle depletion and accretion, as well as timing of muscle loss and gain.  (5:14)

The panel discusses how cows were assigned to high- and low-muscle groups and how representative those groups might be to the general population of dairy cows. Dr. Boerman mentions they’ve recently started evaluating primiparous cows as well to see if they perform differently than multiparous cows. (10:33)

Dr. Boerman notes that cows are mobilizing between 30 and 35% of their longissimus dorsi depth during lactation and muscle biopsies have shown a reduction in muscle fiber size. They also measure 3-methyl histidine and creatinine as biomarkers of muscle loss and gain. The panel discusses increased calf birth weights and impacts on colostrum for high-muscle groups. Body condition score is not a good predictor of muscle depth. (16:52)

The group discusses how parity might impact protein loss and gain, the influence of genetics on these muscle measurements, how health events might affect muscle mobilization and what kind of hormonal regulation might be occurring to control muscle losses and gains. (23:41)

Dr. Weiss shares about a project from his group where muscle and fat losses were measured by dilution. They fed 20% protein diets using soy alone or with supplementation of rumen-protected amino acids. He emphasized the differences between heifers and cows, similar to what Dr. Boerman’s group has observed as well. (29:54)

Dr. Boerman shares some ideas of what kind of experiments she’d like to conduct next to continue this line of research. (33:42)

Panelists share their take-home thoughts. (35:29)

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