Interaction of Sorting Behavior with the Health and Production of Early Lactation Dairy Cows

Through a study where 41 multiparous Holstein cows were fed 1 of 2 diets varying in wheat straw particle size immediately after calving, this thesis sought to identify the effect of straw particle size on the feed sorting behavior, health, and production of early lactation dairy cows. It was hypothesized that a reduction in the wheat straw particle size would minimize sorting behavior, which would maintain intake and rumination while stabilizing reticulorumen pH. Cows fed the shorter wheat straw particle size sorted the ration to increase intake of physically-effective fiber, which may have contributed to a more stable reticulorumen pH and a tendency for greater milk production. Whereas cows fed the longer straw particle size sorted against the most physically-effective components of the diet and suffered from greater variability in time spent below a reticulorumen pH of 5.8 as well as time spent ruminating. In a secondary analysis, cows were further categorized by risk for SARA as either high risk or low risk. Cows fed longer straw sorted against long particle regardless of risk category, while cows fed shorter straw did not sort these particles. High risk cows fed the shorter straw diet sorted to increase intake of physically-effective fiber, possibly in an attempt to ameliorate the effects of low reticulorumen pH. This study suggests that reducing wheat straw particle size in the diets of early lactation dairy cows may stabilize reticulorumen pH and increase milk production by minimizing sorting behavior, which maintains intake and rumination. NSERC, Omafra-University of Guelph Research Partnership, Eastgen, Canadian Dairy Commission MSc Scholarship