The effect of different zinc sources on in vitro ruminal microbial populations, hydrolytic enzymes and fermentation products in sheep

This research was conducted to compare the effect of different zinc sources on in vitro microbial populations, hydrolytic enzymes and ruminal fermentation products in sheep. Five diets without zinc supplement (control) or containing ZnSO4, ZnO, nano-ZnO and Zn-methionine were assessed. The 24 and 72-h gas tests were conducted in a completely randomized design where the microbial populations, hydrolytic enzymes, methane, antioxidant activity, organic matter digestibility (OMD), metabolizable energy (ME), truly degraded substrate (TDS), microbial biomass, partitioning factor (PF) and volatile fatty acids (VFA) were determined. Total proteolytic bacteria count and protease activity decreased due to the usage of organic, inorganic and nano-particle sources of zinc (P<0.05). The use of methionine, oxide and sulfate sources of zinc increased alpha-amylase activity (P<0.05). Total protozoa number in the 24-h incubation tended to decrease owing to dietary zinc supplements. Total cellulolytic bacteria, carboxymethyl-cellulase, microcrystalline-cellulase, filter paper-degrading activity, antioxidant capacity, microbial biomass and PF were the same among treatments. Zinc methionine, oxide and sulfate supplements increased OMD, ME, TDS and total VFA, whereas decreased ammonia and acetate:propionate ratio (P<0.05). Also, 24-h methane production decreased with the use of zinc supplements (P<0.05). Overall, the dietary addition of sulfate, oxide and methionine- sources of zinc is recommended with the aim of improving alpha-amylase activity and digestibility and reducing proteolytic activity, ammonia accumulation and methane, but feeding nano-ZnO is not recommended. More research is needed on the effect of zinc sources on rumen microorganisms and enzymes in different dietary conditions.