Effects of Different Rain Tree Pod Pellet Proportions on a Fixed Amount of Leucaena in Supplements and Ammonium Hydroxide-Treated Rice Straw as a Basal Diet in Male Thai Swamp Buffaloes

The study aimed to measure total tract digestibility, nitrogen (N) balance, urinary purine derivative excretion, and levels of mimosine (MMS) and dihydroxy pyridine (DHP) in urine and plasma. Also assessed testosterone levels and blood metabolites in the plasma of Thai male swamp buffaloes fed different levels of rain tree pod pellets (RTPP), alongside a fixed amount of chopped fresh Leucaena leaves (CFLL) in supplements and ammonium hydroxide-treated rice straw (AHRS) as a basal diet. The results showed that total dry matter (DM) and organic matter (OM) intakes were highest when animals were supplemented with 3.2 kg RTPP, compared to 0.6, 1.2, and 2.2 kg RTPP. Total neutral detergent fiber (NDF) and acid detergent fiber (ADF) intakes decreased linearly with increasing RTPP proportions in the diet. Animals fed 0.6 kg RTPP had higher total intakes of NDF and ADF compared to those fed 1.2, 2.2, and 3.2 kg RTPP. The total tract digestibility of NDF and ADF in buffaloes fed 0.6–1.2 kg RTPP was significantly higher than in those fed 2.2–3.2 kg RTPP per day. Dietary fiber digestion was affected in buffaloes fed 2.2–3.2 kg RTPP per day. Buffaloes fed 1.2, 2.2, and 3.2 kg RTPP had better nitrogen balance than those fed 0.6 kg RTPP. The efficiency of ruminal microbial protein synthesis and nitrogen balance were positively related to nitrogen consumption. However, nitrogen losses in urine and feces were greater in the 1.2, 2.2, and 3.2 kg RTPP groups than in the 0.6 kg RTPP group. Approximately 90.2–91.3% (average 90.7 ± 0.069%) of MMS intake may be detoxified through various processes, which can be explained as follows: (1) chelation, (2) excretion, and (3) conjugation. Testosterone concentrations observed were lower (range: 0.163–0.220 ng/mL, mean = 0.190 ± 0.002 ng/mL) than those reported in other studies. Elevated circulating blood glucose, non-esterified fatty acids (NEFA), and β-hydroxybutyrate (β-HBA) levels were associated with increased RTPP levels in the diet, as well as increased nitrogen balance and microbial protein synthesis in the rumen. In conclusion the right proportion of Leucaena and RTPP provides maximum benefits, such as improved feed intake, digestion, nitrogen balance, microbial production in the rumen, sexual performance, and the absence of negative energy balance indicators. However, Leucaena consumption should be limited to avoid side effects, including the risk of goiter.