Salt tolerance threshold and physiological responses in Bach Thao goats drinking diluted seawater under tropical conditions

Background and Aim: Climate change challenges with incremental sea level cause saltwater intrusion, which has affected the quality of freshwater and groundwater in coastal provinces, particularly the Mekong River Delta provinces of Vietnam. Interestingly, Bach Thao goats are predominant in this area and well adapted to saline water under tropical conditions. Therefore, this study investigated the salt tolerance threshold of Bach Thao goats drinking diluted seawater (DSW). Materials and Methods: The experiment was performed using seven Bach Thao male goats (20.60 +/- 1.12 kg) and divided into two phases. In Phase 1 (control, C), all goats were provided fresh water (FW) for 7 days from two identical buckets, and daily water intake (WI) was recorded from both buckets. In Phase 2 (preference test, PT), each goat was provided FW from the first bucket and DSW from the second bucket or vice versa. The concentration of DSW for the preference test was 0.5%-2.0%. Results: Body weight and dry matter intake showed no differences according to DSW consumption; however, WI was significantly lower during Phase 2 (p < 0.05), which was due to the lower WI with 1.5% and 2% of DSW (p < 0.05). Goats showed a similar preference for fluid intake between FW and DSW at 0.0%-1.0% levels and began avoiding DSW at 1.5% and rejected at 2.0% of DSW. Goats consuming 1.5% of DSW showed increased respiration rate from 13:00 to 19:00 h and rectal temperature at 13:00 h (p < 0.05). Conclusion: Goats can tolerate up to 1.0% of DSW. Shifting to FW activated aversive drinking to 1.5% and 2.0% of DSW. This behavioral response was prominent at 0.5% DSW. Moreover, goats that drank 1.5% of DSW had decreased thermoregulation.