High Dietary Cation and Anion Difference and High-Dose Ascorbic Acid Modify Acid–Base and Antioxidant Balance in Dairy Goats Fed under Tropical Conditions

SIMPLE SUMMARY: The high environmental temperature of the tropical area compromises milk production in dairy animals, and an increase in the energy required for heat dissipation produces both acid and reactive oxygen species. This response causes an acid–base imbalance and oxidative stress which indirectly affect milk synthesis. We previously showed that a high dietary cation and anion difference (DCAD) supplement increased heat dissipation. Moreover, a high-dose vitamin C (vit C) supplement has been used in dairy ruminants to decrease oxidative stress. The present experiment aimed to investigate the relationship between acid–base balance, oxidative stress, and mammary gland function under high environmental temperature conditions. The results showed that high DCAD and vit C could change acid–base balance and oxidative status. In addition, milk compositions were changed when the oxidative stress was compromised. We conclude that the high environmental temperature compromises milk synthesis in part by changing acid–base balance and oxidative stress. ABSTRACT: High ambient temperature (HTa) causes acid–base imbalance and systemic oxidative stress, and this may indirectly affect the mammary gland. Furthermore, HTa induces intracellular oxidative stress, which has been proposed to affect cell metabolism directly. We previously showed in dairy goats that the negative effect of HTa was compromised by enhancing heat dissipation during a high dietary cation and anion difference (DCAD) regimen. Moreover, high-dose vitamin C or ascorbic acid (AA) supplements have been used to manage oxidative stress in ruminants. The present study hypothesized that high DCAD and AA supplements that could alleviate the HTa effect would influence the milk synthesis pathway and mammary gland function. The results showed that goats fed with high DCAD had higher blood pH than control goats in the 4th week. The high dose of AA supplement decreases urine pH in the 8th week. The percent reduction of urine pH from the AA supplement was significant in the DCAD group. The high-dose AA supplement decreased plasma glutathione peroxidase activity and malonaldehyde. This effect was enhanced by a high DCAD supplement. In addition, supplementation with AA increased milk protein and citrate and decreased milk FFA. These alterations indicate the intracellular biochemical pathway of energy metabolism and milk synthesis. It can be concluded that a high DCAD regimen and AA supplement in dairy goats fed under HTa could influence the milk synthesis pathway. The evidence suggests that HTa decreases mammary gland function by modification of acid–base homeostasis and oxidative stress.