These results observed that feeding probiotics combined with enzymes enhanced the growth performance and slaughter performance of fattening goats. Besides, COM had more advanced effects than PRO. In addition, the immunity was enhanced and the rumen bacterial structure was changed in the PRO group and COM group, which might be the reasons to improve the performance of fattening goats.
A number of studies have shown the profound effects on pigs supplemented with B. subtilis and B. licheniformis [20–24]. Nevertheless, there were little researches into which the influence of B. subtilis and B. licheniformis were conducted on goats. Moreover, various researches have studied the effects of compound enzymes on weaned pigs [25, 26]. In addition, combined feed probiotics and enzymes had predominant effects on growth performance and rumen bacteria of sheep . Based on these reports, we investigated the functions of B. subtilis, B. licheniformis and multiple enzymes on fattening goats, individually and in combination. Importantly, the effects of combined feed were better than single feed which was explored in this study.
The results observed that ADG significantly increased of fattening goats in the PRO group. A previous study reported that the basal diet administration of B. subtilis and B. licheniformis significantly improved the growth performance of piglets . The growth performance of finisher pigs was noteworthily improved supplemented with B. subtilis and B. licheniformis . Adding B. subtilis, B. licheniformis, B. coagulans and C. butyricum ameliorated the weaning pig performance . Some findings above indicated that feeding B. subtilis and B. licheniformis played a central role in improving the growth performance of pigs. In our study, supplementing B. subtilis and B. licheniformis also accelerated the improvement of goat performance. Furthermore, COM group raised the final weight, ADG and ADFI in goats in comparison with CON group. There was a report that supplementing cellulose increased the growth performance of Hu sheep . Previous research found that treatment of compound probiotics and cellulase enabled the increase of the total weight gain and ADG in sheep . It may be explained that supplementation with enzymes could promote the absorption of nutrients, enhance the feed efficiency, keep the healthy condition [29–31]. Additionally, more combinations of probiotics and enzymes should be investigated to put to good use in the feed industry.
Slaughter performance reflects the applicability in animals, which decides the economic profit in the practical application . Adding cellulase and xylanase to steers failed to improve the carcass and slaughter percentage, which were similar to our research results . Pigs fed probiotics included Bacillus subtilis and Clostridium butyricum had no effect on loin eye area . A previous study reported that supplementation with cellulose did not significantly change the dressing percentage and loin eye area of Hu sheep . Consistently, PRO and COM feed unaffected the loin eye area of fattening goats. Compared with the CON group, the GR value dramatically in PRO group and COM group, while there was no significant difference between PRO group and COM group, which indicated that probiotics administration helped to deposit the muscle fat, besides, combined feed cannot enhance the deposition effect. The results showed that probiotics alone or combined with enzymes could improve the slaughter performance of fattening goats.
We elucidated that PRO and COM feed enriched the contents of IL-10 and TNF-α compared with CON feed. IL-10 and TNF-α play vital roles in inflammation . TNF-α affects the carbohydrate and immune response of animals, which is a kind of proinflammatory cytokines [36, 37], and the content of TNF-α would enrich if the tissues were inflammatory . IL-10 performs an important effect on inflammatory reaction as an anti-inflammatory factor, importantly, inducing the function of immunity [39, 40]. Supplementing probiotics could influence the immune function, inducing the improvement of immune cytokines contents [41–43]. Studies reported that administration of B. subtilis lead to the benefit of the host immune system [44, 45]. CD4+ cells are part of the T lymphocytes, whose subpopulations are Th cells that include Th1 and Th2 cells . Th2 secretes different cytokines, such as IL-2, IL-4, IL-6 and IL-10, which play a major role in immune regulation and inflammatory responses [46, 47]. Importantly, Th2 accelerates the multiplication and differentiation of B lymphocytes, resulting in the production of antibody and intense responses of immune systems . Apparently, B. subtilis secretes the anti-inflammatory cytokines IL-10 to regulate the immune response . Consequently, supplementation with B. subtilis, B. licheniformis and in combination with compound enzymes had an intense importance for enhancing the immunity of fattening goats.
Rumen pH, NH3-N and VFA contents are vital parameters in ruminants which illustrate the function and steady state of the rumen , and VFA are principal products of rumen fermentation, which relate the balance of energy in ruminants . Probiotics could improve the function of rumen via maintaining the pH and enriching the VFA concentrations . A previous study found that Lactobacillus plantarum and Bacillus subtilis feed unaffected the pH, NH3-N and VFA concentrations, which is consistent with our results . Administration of B. licheniformis enriched the total VFA contents and reduced the NH3-N content . There were no remarkable changes in the rumen fermentation parameters of cows fed with B. subtilis . Nevertheless, the influence of rumen fermentation of fattening goats fed with probiotics or combined with enzymes still remains unclear. In our study, we found that adding probiotics (B. subtilis and B. licheniformis) or blended enzymes insignificantly influenced the rumen pH, NH3-N and VFA concentrations of fattening goats in basal diet. Moreover, PRO and COM had potential tendencies to increase the isobutyrate contents. Isobutyrate predominantly produced from the oxidative-deamination and decarboxylation of ruminal isoleucine, which illustrated that PRO feed and COM feed had the potential to enhance the metabolism of isoleucine .
The microbiota has profound effects on the health and performance of animals. Hence, it is necessary to regulate diversity based on the composition and structure of bacteria in the host . Interestingly, the alpha diversity of rumen microorganisms (Chao 1 index, Goods_coverage index, Observed_species index, Shannon index and Simpson index) showed no significant differences (P > 0.05). Administration of probiotics combined with enzymes had no impact on the bacterial diversity of goat rumen. At the phylum level of rumen microorganisms, COM group remarkably upregulated the relative abundance of Proteobacteria in contrast with CON group and PRO group (P < 0.05). Besides, the relative abundance of Actinobacteria in both PRO and COM significantly decreased compared with that in CON (P < 0.05). The combined feed showed notable upregulation of Ruminococcaceae, Lachnospiraceae and Succinaceae in ruminal microorganisms (P < 0.05). Prevobacteriaceae, Clostridium and Succinaceae are strict anaerobes, and Ruminococcus can produce a large amount of VFA in the hindgut of cows [54–55], which may lead to the enrichment of isobutyrate in goat rumen. A previous study found that supplementation with compound enzymes (xylanase, α-amylase, β-glucanase and protease) to pigs resulted in the increase of the abundance of Firmicutes in treatment group, which is in coherence with our findings . The colonization of anaerobic microbes contributes to the creation of an anaerobic environment in rumen, which is conducive to the maintenance of rumen health and effective digestion in rumen, therefore, promoting the health of fattening goats. Butyrivibrio was one of the distinct bacteria in the COM group (P < 0.05), which was in agreement with that previously reported . Prevotella is a kind of potential pathogenic bacterium . The relative abundance of Prevotella_1 significantly reduced in COM in comparison with that in PRO, indicating that combined feed of probiotics and enzymes could decrease the number of pathogenic bacteria to keep the health of fattening goats. Clostridiales beneficially maintained the balance of animal intestines and optimized the structure of intestinal microenvironments, thus inhibiting the reproduction of harmful bacteria in the intestine . The relative abundance of Clostridiales_unclassified dramatically enriched in COM compared with that in PRO, which plays a central role in keeping the balance of goat rumen.
This study first revealed the metabolic functions added to probiotics or blended enzymes of fattening goats. COM group significantly upregulated nitrogen metabolism, DNA synthesis, glyoxylate cycle, nucleotide synthesis and TCA cycle. COM greatly regulated the rumen microbes possibly be a reason to the differences of functional metabolism .
The correlation analysis confirmed there were relevance among goat performance, serum biochemical, immune and antioxidant indexes, rumen fermentation parameters and rumen microorganisms, which indicated that feeding probiotics or combined with enzymes regulated the rumen microbiota to ameliorate the performance and immunity of fattening goats. Particularly, Saccharofermentans and Olsenella positively related to VFA and improved the performance and serum indexes of goats. Consequently, these results above emphasized that PRO feed and COM feed had beneficial effects on the rumen microflora to facilitate the performance of goats. The performance and healthy state of lactating sows were promoted supplementation with B. subtilis and B. licheniformis , which was aligned to our research results. Accordingly, it elucidated an original method to enhance the performance and immunity of fattening goats by attenuation of the relative abundance of Saccharofermentans and Olsenella in rumen.