Online

Campbell, Mackenzie Andrew

Animal, Nutrition and Food Sciences Program

2017

Ph.D.

Stocking density serves as a sub-clinical stressor impacting natural behavior and affective state of dairy cows. However, cows rarely experience stocking density as an isolated stressor. Understanding the effects of stocking density with additional management stressors such as low-fiber diets or feed restriction is the next step in alleviating stress and improving the well-being of lactating dairy cows housed in freestall barns. The overall goal of this dissertation was to evaluate the interaction of stocking density and the feeding environment on short-term production, behavioral, ruminal fermentation, and stress responses of lactating dairy cattle. The first two studies (Chapter 2 and 3) served as preliminary research for the main studies of this dissertation. The first study objective was to evaluate the effectiveness of using chopped wheat straw to reduce sub-acute ruminal acidosis (SARA) in order to formulate diets for the first main study. Treatments were low straw (0 kg dry matter (DM)/d; LS) and high straw (1.36 kg DM/d; HS). High straw appeared to effectively reduce SARA by lowering time below pH 5.8 with minimal impact on feed intake and rumination. The second study objective was to evaluate the effect of type of blood collection tube on haptoglobin concentration across two commercially-available haptoglobin assays and evaluate assay agreement in order to determine haptoglobin concentrations for the main studies. Lithium heparinized, sodium heparinized, and K2-EDTA plasma resulted in increased haptoglobin concentrations compared to serum using the Tri-Delta colorimetric assay, but no differences were observed using the Life Diagnostics ELISA assay. However, there was a lack of agreement between assays and further identification of a gold-standard assay is needed before analyzing haptoglobin for the main studies. The third study (Chapter 4) investigated the interaction of stocking density (100% and 142% of freestalls and headlocks) and source of forage fiber (no added straw and added straw at 3.5% ration DM). Treatments did not impact feed intake, but straw diets tended to reduce milk production. Increasing stocking density reduced lying time but increased efficiency of stall use. Though feeding and rumination times were unaffected, overstocking shifted the location of rumination away from the freestall. Increased stocking density tended to increase stress responses. Both greater stocking density and no straw diets increased SARA, and the combination of these stressors tended to exacerbate this pH response. Adding straw to the diet reduced the negative impacts of overstocking on ruminal pH. The fourth study (Chapter 5) evaluated the interaction of stocking density (100% and 142%) and feed access (5-h reduced feed access and no reduced feed access). Treatments had minimal impact on short-term feed intake and production. Overstocking affected behavior similar to responses observed in Chapter 4. Reducing feed access decreased feeding time, though cows altered feeding and rumination responses to maintain daily rumination. Both treatments shifted priorities for feeding and lying behavior, though increased stocking density had the larger impact. Though reduced feed access did not impact ruminal pH, an exacerbated response was observed when combined with increased stocking density. The combination of stocking density and feeding environment stressors exacerbate negative effects on biological function and should be avoided.