Dr. Jackie Boerman presents an in‑depth look at her research on skeletal muscle dynamics in dairy cows. Rather than focusing solely on fat mobilization, the presentation highlights skeletal muscle as an essential and highly responsive source of amino acids during the challenging transition from late gestation into lactation. This perspective offers new insight. It shows how cows meet the metabolic demands of fetal growth and early milk production.
Dr. Boerman begins by explaining how muscle mobilization is measured in research settings. She discusses the use of ultrasound technology to track changes in the longissimus dorsi, or loin muscle, over time. Moreover, she mentions blood metabolite analysis. Key indicators include 3‑methylhistidine, which is released during muscle protein breakdown, and creatinine, a marker of total muscle mass. Additionally, evaluating the relationship between these two biomarkers provides a precise method for assessing muscle degradation. It shows muscle degradation relative to a cow’s overall muscle reserves.
Research findings show that muscle protein mobilization starts several weeks before calving and typically ends three to four weeks into lactation. This pattern is distinct from fat mobilization, which peaks closer to calving and continues for a longer period. Importantly, a cow’s response depends on her initial muscle reserves. Cows entering the dry period with little muscle tend to gain muscle prior to calving. In contrast, cows with greater muscle depth begin mobilizing protein earlier to support fetal development. They also do it to prepare for milk production.
The webinar also highlights strong connections between muscle reserves and animal performance. Multiple studies demonstrate that multiparous cows with higher muscle mass consistently deliver heavier calves, averaging seven to eight pounds more at birth. These cows also tend to produce more energy‑corrected milk and higher levels of milk fat and protein. The improved performance is linked to increased amino acid availability. Moreover, this increased availability supports both fetal growth and mammary gland development.
Dr. Boerman emphasizes that primiparous cows, or heifers, differ metabolically from mature cows. Heifers generally have greater muscle depth but delay mobilization until just before calving. This is likely due to the competing demands of their own growth and higher baseline insulin concentrations. These demands can restrict tissue mobilization. Therefore, these differences highlight the importance of parity‑specific management and nutritional approaches. This is necessary to optimize outcomes.
Long‑term research tracking cows across an entire lactation provides additional insight into muscle dynamics. Muscle depth is highest at calving, declines to its lowest point around 60 days in milk, and remains suppressed through mid‑lactation. Muscle accretion only begins again in late lactation and continues into the dry period. Notably, cows do not fully regain their original muscle depth before the next lactation begins. This finding suggests that inadequate recovery could lead to cumulative muscle depletion over multiple lactations. It can occur if not carefully managed.
In closing, Dr. Boerman emphasizes that skeletal muscle is a highly dynamic tissue, with cows losing an average of 30 to 35 percent of muscle depth during early lactation. The dry period is a critical window for rebuilding muscle reserves, particularly for cows starting with lower muscle mass. Higher muscle reserves in mature cows are consistently associated with improved production, healthier calves, and greater overall resilience. Furthermore, future research will expand these studies into large commercial herds. Researchers will better understand how muscle dynamics influence reproduction, health outcomes, and genetic selection.
