Why are some cows skinny? An evaluation of stress and immune factors

Authors: Lindholm-Perry, Amanda; Kuehn, Larry; Redifer, Colby; Chitko-Mckown, Carol; MCCARTHY, KACIE - University Of Nebraska; Crouse, Matthew; Keel-Mercer, Brittney

Submitted to: Beef Magazine
Publication Type: Trade Journal
Publication Acceptance Date: 1/22/2025
Publication Date: 2/12/2025
Citation: Lindholm-Perry, A.K., Kuehn, L.A., Redifer, C.A., Chitko-McKown, C.G., McCarthy, K.L., Crouse, M.S., Keel-Mercer, B.N. 2025. Why are some cows skinny? An evaluation of stress and immune factors. Beef Magazine. January/February:11-14.

Interpretive Summary:

Technical Abstract: Mature cow body condition is a critical component of production because of its close relationships with feed consumed, forage availability, nutrient requirements and productivity. While there have been research studies to evaluate the effects of dietary restriction or low-quality forage on cows at different productions stages, there is limited research studying the potential underlying causes of mature cows that naturally have low body condition scores. We hypothesized that low body condition may be caused by higher levels of stress or subclinical illness that may have effects on animal well-being and overall health. At pregnancy diagnosis, blood and hair samples were collected from cows with low body condition scores (BCS = 4 on a 1-9 scale), and a matched control cow with a moderate BCS of 5 or 6 under the same management conditions and genetic influence. The blood samples were used to assess hematology parameters that included both white blood cell and red blood cell data, which is a measurement of immune and health status. Blood was also used to evaluate the concentrations of cytokines which are protein messengers that help to signal immune cells to fight bacterial or viral infections, and they also help to control inflammation. The hair samples were used to evaluate long-term cortisol concentrations, which serves as an indicator of chronic stress. Hemoglobin, hematocrit, and red blood cell count were associated with BCS, all were lower among low BCS cows. Neutrophils and monocytes were associated with BCS and were greater among low BCS cows. Lymphocyte count was also associated and was lower in the low BCS cows. The ratio of white blood cells is important and a higher ratio of neutrophils and monocytes with lower concentrations of lymphocytes is indicative of a stress leukogram. A stress leukogram is a change in neutrophil cell counts in response to the release of cortisol triggered by pain, stress, or excitement. In this study, higher cortisol concentrations were identified in the low BCS cows. Along with elevated neutrophils and monocytes, and lower lymphocytes, the high cortisol suggests that low BCS cows may be more chronically stressed than those with a BCS of 5 to 6. While skinny cows may not directly cause management issues or financial loss, it stands to reason that cows with less chronic stress are more likely to be productive over their lifetime.