Effect of injectable trace mineral supplementation on oxidative stress, immune parameters, and reproductive performance in dairy cows undergoing the transition period in heat stress conditions

Abstract

Dairy cows that undergo the transition period in elevated ambient temperatures experiences higher degrees of feed intake depression, decreased milk production and fertility and increased degree of oxidative stress and immunosuppression.In the proposed study, we aim to evaluate if ITMS would improve the oxidative and immune status, and reproductive outcomes of dairy cows undergoing the transition period in heat stress conditions. Findings from this study will provide crucial information to dairy producers regarding alternative strategies to mitigate heat stress burden in hot climate areas. The study will be conducted during summer months (June to August) on a commercial dairy farm located in Eastern New Mexico or West Texas. Cows are housed in dry-lot corrals with shaded areas and are fed a diet formulated to meet or exceed the NRC nutrient requirements for lactating Holstein cows weighing 650 kg and producing 45 kg of 3.5% FCM. Based on previously reported data, we expect that ITMS will increase pregnancy per AI (P/AI) at first service in 9 percentage units (e.g. 30% to 39%). Considering a significance level of ±=0.05 and a power of 80%, a total of 437 cows should be enrolled in each treatment group. Considering attrition recurring to variety of experimental issues, a convenient samples size of 500 cows/treatment will be used. Hence, a total of 1000 multiparous cows will be randomly allocated into 1 of 2 treatments groups: ITMS or control. Cows that were randomly assigned to the ITMS group will receive 3 injections of trace minerals containing Zn, Cu, Se, and Mn (Multimin North America, Inc., Fort Collins, Co) at 230±3 and 260±3 d of gestation, and at 35±3 days postpartum (approximately 4 weeks prior to first AI); following the manufacturer's dosage recommendations for cattle over 2 years of age. For a subset of 100 cows, blood samples will be collected to measure circulating biomarkers of oxidative stress (superoxide dismutase; glutathione peroxidase; and Thiobarbituric Acid Reactive Substances), immune parameters (cell blood count and neutrophil phagocytosis and oxidative burst activity), and haptoglobin (Hp) levels. During the study period, weekly samples of the fresh and pre-fresh diets will be collected for wet chemistry analysis. The samples will be pooled (for both pre-fresh and lactation diets) and submitted to a commercial laboratory for chemical components. Data regarding reproductive outcomes will be extracted and from the farm's database software (DairyComp305, Tulare, CA).