107. Cumulative Feed Intake Resilience of Hays Converter, Angus, Charolais, and A Composite Breed Heifers Exposed to Canadian Winter Under Intensive Conditions.

Abstract In Western Canada, cattle may experience brief heat stress events during summer, whereas cold stress can persist for prolonged periods in winter. Animals with greater tolerance to these environmental extremes may exhibit improved performance, health, profitability, and longevity within the herd. However, resilience is inherently complex and difficult to quantify. The objective of this study was to evaluate cumulative feed intake (CFI) resilience in response to cold stress during winter across four breeds: Hays Converter (HC), Angus (AN), Charolais (CH), and Kinsella Composite (KC). A total of 102 beef heifers were intensively fed, and their feed intake and feeding behavior were monitored continuously through the Vytelle GrowSafe feed bunks from January to March 2026. The CFI was modeled using median cubic basis splines with three knots, and perturbations defined as deviations greater than 3% from the predicted CFI curve, greater than 2 standard deviations from the mean, and lasting longer than two days. Once identified, perturbation-derived resilience parameters were derived to quantify the magnitude of the deviation (amplitude), the velocity with which CFI changes (average velocity; AV), the variation in the deviation variance (DV) from the predicted CFI, the time spent in perturbation, the speed of recovery (recovery duration), and the overall recovery pattern following the disturbance (observed CFI/modeled CFI). To associate with environmental parameters, weather variables were monitored hourly and averaged daily for average temperature, temperature range, wind chill, wind speed, solar radiation, and relative humidity. Data were analyzed using linear mixed models with animal as random effect and as linear models when singularity was detected. The timing of perturbation onset was significantly influenced by all environmental variables (P < 0.05). Colder temperatures, greater wind chill, and precipitation were associated with an earlier onset, whereas warmer temperatures, larger diurnal temperature ranges, higher wind speeds, greater solar radiation, and increased relative humidity were associated with a delayed onset. Perturbation onset tended to differ by breed (P = 0.093), with KC heifers exhibiting a later (2 d) onset compared to AN, while no other breed differences were detected. When examining the resilience parameters in response to the perturbations, a significant breed effect was detected in AV (P = 0.011), where KC heifers had a 1.2 kg greater AV than all other breeds. Additionally, a breed tendency was observed for DV (P = 0.095), where KC heifers had 8-20 kg2 greater DV compared to all other breeds. In conclusion, cold stress is a key driver of perturbations in cumulative feed intake, with environmental conditions strongly influencing their onset. Breed differences in resilience were evident, with KC heifers exhibiting greater variability and larger deviations, indicating reduced resilience compared to purebred cattle.