Analysis of Serial Vaginal Temperature Measurements in Crossbred Beef Cattle Grazing Novel or Toxic Fescue

Fescue toxicosis causes hyperthermia, reduced hair shedding, decreased weight gain and reproductive success in cattle. The objective of this study was to determine if grazing toxic vs. novel (non-toxic) fescue changed the heating and cooling cycles during hot weather. An equal number (N=50) animals were grazed on novel or toxic fescue for 6 mo (March-August) as part of a larger trial examining chronic effects of toxic fescue. Half of the animals on toxic and half on novel were given access to a pond. All animals had shade access. Pastures were monitored monthly for toxic levels of ergot valine mycotoxins (> 300ppb). In early August, intravaginal devices containing an iButton thermosensor were placed in each cow to measure vaginal temperatures every 5 min for 1 wk (max THI > 100/day). Data from only 5 d were analyzed to exclude the impact of animal handling stress on body temperature. One pasture was excluded due to toxic fescue contamination. In addition, intravaginal devices from 3 animals were lost on pasture during the trial. A total of 71 cows were analyzed from 1 of 3 remaining pasture treatments, including: toxic no pond (TF-NP: n=26, toxic with pond (TF-P: n=23), and novel with pond (NF-P: n=22). Temperatures were averaged by hour each day for each animal. Vaginal temperature was analyzed using a repeated measures model with Proc Mixed of SAS, including: pasture treatment, breed (Charolais, Hereford), hide color (black, red, white, smoke), parity (2,3, 4), day, hour of the day, treatment-by-hour, treatment-by-sire, and treatment-by-sire-by-hour interactions. Hours within a day were fit as repeated. All variables in the model were significant (P<0.002). Animals on NF-P were 0.15°C warmer than animals on TF-P (P<0.0001), and 0.06°C cooler than animals on TF-NP (P<0.0001). Animals grazing TF-P were 0.18°C cooler than those with no pond access (P<0.0001). Hours of the day showed significant difference in hour of day-by-treatment interaction (P<0.0001). Additionally, NF-P appear cooler than TF-P from 7-11 AM, while TF-P showed decreasing temperatures during some of the hottest times of the day (3-10PM). A significant breed-by-treatment interaction was identified, indicating Charolais cattle on TF-P were significantly hotter than Herefords on the same pasture after 3PM (P<0.0001). This study indicates that toxic fescue increases body temperature even during cool morning hours, though ponds may reduce body temperature. Additional studies are needed to determine impact on hair shedding, weight gain and grazing time.