Simple SummaryWinter cold stress is a major environmental factor affecting cattle industry production in northern China. Determining the effects of prolonged cold stress on the relevant biological mechanisms in cattle can help develop effective mitigation measures. Therefore, this study evaluated the effects of long-term cold stress on growth performance, physiological mechanisms, blood biochemical, and stress hormones of Simmental crossbred bulls. Results indicated that the physiological behavior, digestive function, and contents of enzymes and hormones in the body changed in Simmental cattle during winter, which enhanced the body’s heat production to maintain the body temperature constant and ultimately led to impaired growth and development.AbstractThis study aimed to evaluate the effects of a long-term cold environment on growth performance, physiological behavior, biochemical blood indexes, and hormone levels in Simmental cattle. Thirty Simmental crossbred bulls (weight = 350 ± 17 kg, 13–14 months old) were selected for two trials at autumn suitable temperatures (A-ST) and winter cold temperatures (W-CT) (15 cattle per season). The results showed that compared with the A-ST group, dry matter intake (p< 0.05) and feed:gain (p< 0.01) of the W-CT group increased, while body weight (p< 0.01) and average daily gain (p< 0.01) significantly decreased. Long-term cold stress also increased lying time (p< 0.01), feeding time (p< 0.05), and pulse rate (p< 0.01) in the W-CT group, while the rumen volatile fatty acids content (p< 0.01) and apparent digestibility of nutrients (p< 0.05) were significantly decreased. In terms of blood indicators, long-term cold stress increased the concentrations of glucose, glucose metabolic enzymes, glucocorticoids, triiodothyronine, and tetraiodothyronine in the plasma of the W-CT group (p< 0.05), but the levels of triglycerides, β-hydroxybutyrate, propionate, insulin, and growth hormone were decreased (p< 0.01). In summary, long-term cold stress may inhibit the digestive function of Simmental cattle and enhance the body’s energy metabolism and stress hormone imbalance, ultimately damaging the normal growth and development of the body.