We studied foraging patterns of Raramuri Criollo (heritage breed, “RC”) and Angus x Hereford (commercial beef breed, “AH”) cows in relation to ambient heat and body temperature during summer (2016 and 2017) and winter (2017 and 2018) in the Chihuahuan Desert. Cows of each breed grazed separately in two adjacent pastures (~1100 ha) in a crossover design for four weeks in each season/year. Animals were fitted with temperature loggers attached to blank CIDRs (Controlled Internal Drug Release device) devoid of hormones that recorded body temperature (BodyT), and GPS collars that recorded position and ambient temperature (CollarT). All sensor data were logged at 10 min intervals. A landscape thermal map (LandT) was developed from Landsat satellite imagery for habitat analysis using GPS locations chosen by individual collared cows, and air temperature (AirT) was recorded by a nearby weather station. Data were analyzed within four daytime segments: dawn (sunrise – 9AM); pre-noon (9AM – noon); post-noon (noon – 3PM); and dusk (3PM – sunset). ANOVA was used to determine whether BodyT, CollarT, LandT selection, or animal movement variables within each of the four daily segments differed (P < 0.05) for RC vs. AH cows. BodyT and CollarT increased as day progressed in both seasons. During summer, RC had lower BodyT and higher CollarT than AH (P < 0.05) during the hottest hours of the day. Increasing AirT throughout the day was associated with selection of cooler LandT in RC but not AH during summer. In winter, both breeds selected warmer landscape locations as the day progressed. Compared to AH, RC cows traveled farther, at higher velocities, and spent more time grazing and traveling and less time resting, with largest breed differences observed during the hottest hours of summer days. These results suggest that Raramuri Criollo cows exhibited higher thermotolerance than did AH. Elevated ambient summer temperatures in the Chihuahuan Desert appear to impose fewer constraints on heritage RC movement patterns compared to mainstream commercial AH cows.

我们研究了 Raramuri Criollo（传统品种，“RC”）和 Angus x Hereford（商业牛肉品种，“AH”）奶牛在夏季（2016 年和 2017 年）和冬季（2017 年和 2018 年）与环境热量和体温的关系）在奇瓦瓦沙漠。每个品种的奶牛在两个相邻的牧场（约 1100 公顷）中以交叉设计分别在每个季节/年放牧 4 周。动物配备温度记录仪，该记录仪连接到空白 CIDR（受控内部药物释放装置），没有记录体温 (BodyT) 的激素，以及记录位置和环境温度 (CollarT) 的 GPS 项圈。所有传感器数据以 10 分钟的间隔记录。景观热图 (LandT) 是根据 Landsat 卫星图像开发的，用于栖息地分析，使用由个别圈养奶牛选择的 GPS 位置，附近的气象站记录了气温 (AirT)。在四个白天时段内分析数据：黎明（日出 - 上午 9 点）；中午前（上午 9 点 - 中午）；午后（中午 – 下午 3 点）；和黄昏（下午 3 点 - 日落）。方差分析用于确定 RC 与 AH 奶牛的 BodyT、CollarT、LandT 选择或四个每日时段中的每一个中的动物运动变量是否不同（P < 0.05）。BodyT 和 CollarT 在两个季节都随着时间的推移而增加。在夏季，在一天中最热的时间，RC 的 BodyT 和 CollarT 都比 AH 低（P < 0.05）。全天增加 AirT 与在 RC 中选择较冷的 LandT 有关，但在夏季与 AH 无关。在冬天，随着时间的推移，这两个品种都选择了温暖的景观位置。与 AH 相比，RC 奶牛以更高的速度走得更远，并且花更多的时间放牧和旅行而休息的时间更少，在夏季最热的时间观察到最大的品种差异。这些结果表明 Raramuri Criollo 奶牛表现出比 AH 更高的耐热性。与主流商业 AH 奶牛相比，奇瓦瓦沙漠夏季环境温度升高似乎对传统 RC 运动模式施加的限制较少。