Effects of exogenous fibrolytic enzyme supplementation to diets with different NFC/NDF ratios on the growth performance, nutrient digestibility and ruminal fermentation in Chinese domesticated black goats

This study was conducted to evaluate the effects of exogenous fibrolytic enzymes (EFE) supplementation into diets with different non-fiber carbohydrates (NFC)/neutral detergent fiber (NDF) ratios on growth performance, nutrient digestibility, ruminal fermentation, and microbiome in Chinese domesticated Lezhi black goats. Treatments were 2 × 2 factorial arrangement of diets using low vs. high NFC/NDF ratios (1.06 or 1.66) and with or without EFE supplementation (0 or 0.4 g cellulase and xylanase/kg dry matter of diet). Sixty four Lezhi black goats (11 ± 0.8 kg of live weight) were randomly assigned to the four treatments. High NFC/NDF ratio and EFE supplementation achieved greater average daily gain and improve feed conversion ratio (P < .05). The same treatments also significantly increased digestibility of organic matter (OM), acid detergent fiber (ADF) and NDF. In addition, the high NFC/NDF ratio diet, but not the EFE supplement, improved digestibility of crude protein (CP) and reduced ruminal pH (P < .001). Both high NFC/NDF ratio and EFE supplement decreased ruminal NH3-N concentrations significantly (P < .001), and increased the production of rumen total volatile fatty acids (VFA, P < .001), especially the molar proportion of propionate (P < .05). They reduced the molar proportion of acetate and thus the ratio of acetate to propionate (A: P) (P < .05). Both the high NFC/NDF ratio and the EFE supplement elevated the levels of microbial crude proteins (P < .01). Importantly, the combination of high NFC/NDF ratio and the EFE supplement diet raised the content of the microbial crude proteins to the highest levels among the 4 different treatment groups (P = .012). However, the high NFC/NDF ratio and the EFE supplementation had different impacts on fiber degrading activities. The high NFC/NDF ratio diet decreased, while EFE supplementation increased, the activities of cellulase and xylanase (P < .05). Among the three cellulytic bacteria detected (Ruminococcus albus, Ruminococcus flavefaciens, Fibrobacter succinogenes), only the abundance of Fibrobacter succinogenes was significantly decreased with the high NFC/NDF ratio (P = .004). These results illustrate that the diet with a high NFC/NDF ratio and EFE supplementation can improve ADG, feed conversion ratio and nutrient utilization in Lezhi black goats. These improvements are likely attributed to the elevated production of microbial crude proteins and a shift in the molar proportions of VFA in the rumen, rather than increase of cellulolytic bacteria in the rumen microbiota.