Dairy cows are suffering from heat stress (HS) worldwide, and this has become a continual challenge in dairy production systems. The objective of this study was to investigate the effects of the shade of poplar trees on alleviating HS via measuring milk production, nutrient digestibility, immunity, and antioxidant capability in the serum of dairy cows in open cowsheds. A total of 540 lactating Holstein cows were assigned to 2 groups (3 cowsheds per group, 90 cows per cowshed), including the treatment group with poplar trees on the west side of sheds and the control group without trees. This study was carried out in the early-hot season, hot season, and late-hot season. The results showed the following: (1) During the hot season, shaded cows exhibited lower respiration rate (p < 0.05) and higher dry matter intake (p < 0.05) and daily milk yield (p < 0.05), compared with the control. Also, apparent digestibility of crude protein, acid detergent fiber, and neutral detergent fiber demonstrated an increase (p < 0.05) in shaded cows during the hot season. (2) Total antioxidant capacity and superoxide dismutase activity in the serum of shaded cows increased (p < 0.05) during the hot season and late-hot season, compared with the control. (3) Serum interleukin-4, immunoglobulin G, and immunoglobulin M concentrations of shaded cows were greater (p < 0.05) than the control during the hot season. Additionally, serum concentrations of HSP60, HSP70, and HSP90 in shaded cows showed a decrease (p < 0.05) during the hot season. In conclusion, shade from poplar trees can mitigate the adverse impact of high-temperature environments on cows in open cowsheds.

Balancing muscle growth and antioxidant/anti-inflammatory homeostasis is a core requirement for modern beef production. This study investigated whether cysteamine hydrochloride (CSH) co-supplementation with guanidinoacetic acid (GAA) enhances growth and antioxidant status through fecal microbiome and serum metabolome modulation in Simmental beef cattle. A 60-day trial randomly assigned 45 10-month-old cattle to control (CON), GAA-supplemented, and GAA + CSH-supplemented groups (n = 15 per group). Growth performance was recorded throughout the trial. Fecal samples were collected for 16S rRNA sequencing, and serum samples for non-targeted metabolomics. Both GAA and GAA + CSH (GCSH) improved growth performance versus CON (p < 0.05), with no differences between supplemented groups. However, GCSH uniquely elevated antioxidant enzymes and reduced malondialdehyde (p < 0.05). GCSH treatment was associated with higher abundance of Adlercreutzia, Anaerofustis, and Monoglobus, alongside elevated indole-3-propionic acid and salicylsulfuric acid. In contrast, GAA reduced phenylacetyl-L-glutamine and indole-3-acetic acid. iCAMP analysis revealed that GCSH relieved homogenizing selection while enhancing heterogeneous selection, promoting beneficial taxa colonization. GAA primarily enhances nitrogen utilization, while CSH enriches beneficial microbiota and antioxidant metabolites. These findings suggest that GAA and CSH co-supplementation improves growth and antioxidant homeostasis through complementary mechanisms.