Abstract
The objective was to reduce oxidative stress (OS) and improve grazing distribution with an injectable trace mineral (ITM; 1mL/90kg MultiMin90). Mature cows (2021: n=35; 2022: n=34) were classified by residual feed intake (RFI) as inefficient (INE) or efficient (EFF) across two ITM subgroups (Treated, T and Control, C). Blood (venipuncture) was utilized to assess superoxide dismutase (SOD; u/ml), glutathione peroxidase (GPx; nmol/min/ml), and heat shock protein 70 (HSP70; ng/ml) at d 0 and ~120. At d 26 in both years, cows were collared with global positioning system (GPS) and accelerometer sensors, which were removed (d 52) and reinstalled (d 78), with ITM administered at d 0 and d 52. Behavior was analyzed within sample period by mixed model procedures with RFI, ITM, Date, RFI × ITM, RFI × Date and ITM × Date as fixed effects, with cow within RFI × ITM as the repeated random effect. HSP70 and antioxidants were analyzed similarly, with period within Year as the repeated measure. Serum SOD and GPx were greater (P < 0.05) in August than April of 2021. In May of 2021, T cows tended to travel more than C cows (P = 0.09); with INE T traveling more (P = 0.04), as well as spending more time on steeper slopes (P = 0.07) and south facing slopes (P = 0.09) than INE C. Additionally, INE T cows tended to graze longer than EFF C cows in early July 2021 (P=0.08). In 2022, HSP70 was greater in April than in August (P = 0.05) and was also greater in T cows in April than in August (P = 0.01). T cows had greater SOD (P = 0.01) than C cows. INE T cows tended to have greater GPx than INE C (P = 0.07) cows. In May of 2022, T cows rested less and grazed more (P < 0.05), while spending more time on north facing slopes (P = 0.04). EFF T cows traveled more than EFF C (P = 0.05), INE C (P = 0.04) and INE T (P = 0.03) cows, as well as tending to use steeper slopes than EFF C (P = 0.07). In July 2022, T cows spent more time grazing from 0400 to 0600 (P = 0.01), 0800 to 1000 (P = 0.04) and 1200 to 1400 (P = 0.01) than did C cows. EFF T utilized greater maximum slopes than EFF C cows (P = 0.01) and spent more time on slopes >15% (P = 0.01). Overall, implementing ITM mitigated indicators of OS and improved cow foraging on western rangeland in two consecutive summers.