The relationship between plasma 3-methylhistidine concentration and forage intake in early lactating dairy cows

Plasma 3-MH and amino acids were measured in high yielding dairy cows between one week prepartum and four weeks postpartum to evaluate the relationship between these parameters and forage intake. Cows received low forage or high forage content after calving with the same crude protein (CP), 17% (11% rumen-degradable protein; 6% rumen-undegradable protein) in the diets. Nine cows received a control (CON) diet (35% forage; 12% forage neutral detergent fiber (NDF)) and five cows received a low-forage (LF) diet (25% forage; 7% forage NDF). Plasma 3-methylhistidine concentration at four weeks after parturition was significantly higher in LF than CON cows (9.1 vs. 5.1 μM). Plasma urea concentrations were significantly higher in LF cows than in CON cows, ranging from 3.71 to 7.33 mM and 2.78 to 4.98 mM, respectively. Plasma methionine remained at a significantly lower level in LF, ranging from 17.5 to 24.1 μM, compared with CON cows ranging from 26.6 to 39.5 μM during the entire experimental period. Other amino acids were not affected by the LF diet but they decreased significantly towards parturition and returned to precalving levels by 4 weeks postcalving, except for leucine, glutamic acid, histidine and aspartic acid. Milk performance was not significantly different between the groups. The results indicate that a LF diet affects later plasma 3-MH increase, indicating the extension of body protein mobilization, which is commonly observed in early lactating dairy cows.