INVITED REVIEW: Quantifying protein mobilization in dairy cows during the transition period

Abstract

Purpose: Published literature reporting protein mobilization measurements and potential methods to quantify protein mobilization were reviewed to provide information about the timing and extent of tissue mobilization for dairy cattle. Sources: The main sources for information and data included in the review were peer-reviewed literature. Synthesis: During late gestation, the dairy cow undergoes a homeorhetic change for protein metabolism by mobilizing muscle to meet AA and potentially glucose requirements of the fetus and uterus in addition to provide AA for body maintenance and colostrogenesis. The onset of lactation represents a large increase in the demand for AA to support milk production before sufficient dietary protein intake is able to meet those requirements. To meet AA demands in late gestation and early lactation, high-producing dairy cows mobilize muscle. Some studies suggest the extent of muscle mobilization of a cow exceeds 13% of body protein in well-fed transition dairy cattle and 25% in N-limiting diets; however, there appears to be large variation in the extent of protein that is mobilized. Conclusions and Applications: There are several non-terminal approaches (e.g., ultrasound imaging and measuring metabolites from muscle degradation) to provide information about the extent of mobilization that allow us to evaluate how much protein is being mobilized and when mobilization occurs in a lactating dairy cow. Each of these techniques comes with their own tradeoffs but can ultimately provide information regarding protein mobilization. Further research will need to evaluate how these techniques can be combined to allow for both ease of use and accurate representation of the quantity of muscle present and therefore estimate the extent of mobilization over time.