Abstract
Body temperature and movement patterns of Angus Hereford crossbred (AH) vs. Raramuri Criollo (RC) nursing cows were monitored in summer 2016 and 2017. AH and RC cows grazed separately in two adjacent Chihuahuan Desert pastures (1190ha, 1165ha) in a crossover design for 4 weeks each year. Body temperature (BodyT) was monitored at 10 min intervals by placing blank CIDRs containing a temperature logger in 10 cows per breed. Seven to 9 AH and RC cows were also fitted with GPS collars that recorded position and ambient temperature (CollarT) at 10 min intervals. A landscape thermal map (LandT) was developed for habitat analysis. Data were analyzed within four daytime segments: dawn (sunrise to 9AM); pre-noon (9AM to noon); post-noon (noon to 3PM); and dusk (3PM to sunset). ANOVA was used to determine whether BodyT, animal movement, CollarT, and mean LandT position within each day segment were different for AH vs. RC cows. Breed nested within Year*Pasture was treated as the experimental unit. BodyT increased as a day progressed and was higher (P < 0.05) in AH vs. RC during post-noon (38.83 vs. 38.42oC) and dusk (39.22 vs. 38.70oC). Compared to AH counterparts, RC cows traveled farther (4.7 vs. 2.7 km*daytime h-1, P < 0.05), at higher velocities (5.9 vs. 3.5 m*min-1, P < 0.05) and spent more time grazing (5.6 vs. 4.3 daytime h; P < 0.05) and traveling (0.7 vs. 0.3 daytime h; P < 0.05) during all four daytime segments. Largest breed differences were observed during the hottest segments of the day (post-noon and dusk). Increasing CollarT throughout a day was associated with selection of cooler landscape locations (LandT) in both breeds. Apparent lower body heat load in RC cows may reduce constraints on their movement patterns compared to AH cows grazing Chihuahuan Desert rangeland in summer.
PSVII-3 Body temperature and movement patterns of Raramuri Criollo versus Angus-crossbred cows grazing Chihuahuan Desert rangeland in summer