Simple SummaryOptimizing feed efficiency (FE) is crucial for dairy farming as it enables better use of energy and reduces costs. Factors such as milk yield, diet composition, and genetic value can affect feed efficiency in dairy herds. Crossbred Holstein × Simmental cows have been shown to have better milk quality, fertility, and longevity, but no studies have compared their feed efficiency to purebred Holstein cows. With our study, we aimed to evaluate the FE and physiological parameters of Holstein and crossbred Holstein × Simmental cows to generate information that can help farmers make better decisions about the use of crossbreeding programs in their herds, especially regarding FE, which is a factor with higher economic impact. The results showed that crossbred cows had similar FE and milk production as purebred Holsteins, making them a viable alternative for high-production systems. Additionally, crossbred cows were found to be better at dissipating body heat in a heat-stress situation compared to purebred Holsteins.AbstractThis study aimed to compare the feed efficiency (FE) and physiological parameters of Holstein and crossbred Holstein × Simmental cows in a confinement system during winter and summer. The study was conducted in a dairy farm in southern Brazil by including a total of 48 multiparous cows. The cows were studied for 21 days in two periods, summer and winter, and their daily dry matter intake (DMI), milk yield (MY), rectal temperature (RT), respiratory rate (RR), body weight, and body condition score were recorded. An analysis of variance was conducted using the SAS statistical package. The results showed that crossbred Holstein × Simmental cows have a similar FE as Holstein cows in a high-production system (1.83 × 1.81 kg DMI/kg MY, respectively), and they can achieve the same production levels as purebred Holstein cows (43.8 vs. 44.5 milk/cow/day). Our findings indicated a difference for the period as both genetic groups achieved higher FE in winter than in summer (1.98 vs. 1.67 DMI/kg MY, respectively). In addition, we found evidence that crossbred cows are better at dissipating body heat during heat-stress situations, as they have higher RR in summer compared to purebred cows, while Holstein cows have higher RT in summer afternoons than crossbred cows. Therefore, using crossbred Holstein × Simmental cows is an alternative for high-production systems.