Extent and timing of skeletal muscle changing throughout a dairy cow lactation

Why this research is being done

As an adaptation to the start of lactation, dairy cows mobilize tissue reserves, primarily muscle and fat. It is not well documented when in lactation, cows start to gain these reserves back to prepare for the next lactation. Skeletal muscle makes up the largest internal organ in dairy cattle and plays a critical role in maintaining metabolic homeostasis. The amount of skeletal muscle can be assessed by ultrasound imaging of specific locations on the dairy cow and quantification of metabolites related to muscle turnover or muscle mass.

Results

Dairy cows with greater muscle reserves prepartum, mobilized a greater amount of their muscle depth by 60 days in milk and subsequently produced greater milk yields in early and mid-lactation. Cows then lost muscle depth until 60 DIM and did not appreciably gain muscle until 270 DIM. Cows on average mobilized 30-35% of their muscle reserves between parturition and 60 DIM. At 300 DIM, cows were not back to their muscle depth that they had at parturition. Interestingly, even when cows were post-peak and gaining body weight and adipose tissue (after 90 DIM) they did not appreciably gain muscle until much later in lactation. These findings indicate that as cows approach the dry period, they may have less muscle than they did at their last parturition.

Conclusions

Considerable variation exists between cows regarding skeletal muscle depletion. The extent of skeletal muscle depletion in early lactation is dependent on the amount of muscle present, as cows with greater reserves deplete more of their skeletal muscle reserves. From recent work done in our laboratory, muscle depletion occurs in early lactation with appreciable accretion not occurring until late lactation. Further work is needed to understand how nutrition can impact skeletal muscle depletion and accretion across stages of lactation.

Contact information

Dr. Jackie Boerman jboerma@purdue.edu | 765-496-6290 | Boerman Lab