Evaluation of injectable vitamin C as a management strategy to mitigate the negative effects of transit stress in beef steers

Abstract

Beef calves are exposed to a multitude of stressors within the first year of life, and the two most common stressors upon a calf are weaning and transportation. Weaning commonly occurs when calves are 6 to 8 months of age and results in stress from the separation from their dam, exposure to an unfamiliar environment, introduction to novel feedstuffs, and the administration of vaccinations. Weaning results in physiological and psychological stress upon the calf, leading to a suppressed immune system, poor response to vaccinations, and decreased performance. Following weaning, calves are likely to be transported to an auction market or feedyard due to the segmented nature of the United States’ beef industry. During transport, calves remain standing for long-periods of time without feed and water, resulting in physiological stress and physical exertion upon the calf. Transportation has been shown to decrease antioxidant capacity, elicit an inflammation response, and hinder production efficiency. Weaning and transit are inevitable, and the investigation into strategies to mitigate the negative physiological effects upon calves is imperative. Previous research has evidenced that exogenous administration of vitamin C, an antioxidant, prior to the stress event of transit can improve post-transit performance. There is currently no established requirement for vitamin C by cattle (NASEM, 2016) because of their capacity to produce vitamin C via glucose in the liver. However, during times of stress, synthesis of vitamin C may be downregulated, resulting in decreased antioxidant capacity. Therefore, the administration of injectable vitamin C at weaning has not been evaluated and additional research is needed to determine the mechanisms by which injectable vitamin C affects growth. The research trials described in this thesis were designed to 1) determine the effect of injectable vitamin C given at the time of weaning and again prior to transit on growth performance of early-weaned beef steers and 2) examine the effects of injectable vitamin C before transport, as well as duration of transit (8-h vs. 18-h) on feedlot performance, inflammation, and muscle fatigue of beef steers. Through our first research aim, early-weaned steer calves (92 ± 5 kg; 65 ± 11 days of age) receiving injectable vitamin C had increased plasma ascorbate concentrations, but exhibited no improvement in growth or antibody titer response to booster vaccinations. Interestingly, the calves had remarkably low initial plasma ascorbate concentrations. These drastic differences in circulating vitamin C concentrations due to age warrant further investigation before supplementation strategies can be developed. In our second study, cattle receiving injectable vitamin C had a 38% increase in plasma ascorbate concentration post-transit, and vitamin C mitigated the decrease in antioxidant capacity for calves transported for 18-h. While injectable vitamin C appears to improve antioxidant capacity of the calf, it did not improve overall post-transit performance. Although steers transported for a longer duration exhibited increased markers of muscle fatigue and inflammation, performance was not overly different between transit durations during the post-transit period. Collectively, these data support the existing body of literature indicating longer transit durations increase markers of inflammation, muscle fatigue, and decrease antioxidant capacity. Furthermore, these data reveal plasma ascorbate concentrations differ with age and 5 grams of injectable vitamin C does not appear to improve performance during periods of physiological stress. Future research should seek to determine reference ranges for plasma ascorbate and antioxidant capacity of beef cattle to better refine supplementation strategies to nutritionally prepare calves prior to a stress event. In addition, further understanding of vitamin C synthesis and metabolism for different ages and production stages of modern beef cattle is needed to optimize dosage and timing of supplementation to improve cattle performance during periods of common production stressors.