| Carbohydrates are important components of ruminant diet and are the major source of energy. Neutral detergent fiber( NDF) is the main indicator of the fiber, non-fiber carbohydrates(NFC)was defined as rapid degradation carbohydrates in rumen. NFC/NDF ratio could not only expound the composition of carbohydrates in diet accurately, but also is an important index of the subacute ruminal acidosis(SARA), proper NFC/NDF ratio is ensurence for maintaining normal fermentation function and keeping health of the rumen. In recent years, the application of exogenous fibrolytic enzymes(EFE)in ruminant diet has become focus of extensive researches, however, the results have not been consistent, this possibly due to the application effects of EFE are influenced by lots of factors, and limited research has explored the efficiency of adding EFE in diets with different NFC/NDF ratios in small ruminants. For that reason, the current study that took the domesticated black goat as the research object was designed to evaluate the interaction between EFE and substrate with different NFC/NDF ratios by in vitro fermentation, and select the optimal supplementing level of EFE; then animal trials were carried out to explore the mechanism of EFE in goat diets on the basis of in vitro fermentation results. Hope to provide a theoretical basis for EFE application in the goat diet. Trial 1:Research on the optimal supplementing level of exogenous fibrolytic enzymes into diets with different NFC/NDF ratiosThe objective of this study was to investigate effects of different levels of EFE supplement in substrates with different NFC/NDF ratios on in vitro gas production, ruminal fermentation and fiber degradation, and select the optimal supplementing level of EFE. The experiment used a 3×6 factorial design with three level of NFC/NDF ratios(sub1=0.66, sub2=1.16, sub3=1.66)and six dosages of EFE(0, 0.2, 0.4, 0.8, 1.6 and 3.2 mg/g DM). The results showed that:(1)High NFC/NDF ratio resulted in greater gas production(GP), asymptotic gas production(b), dry matter disappearance(DMD), neutral detergent fibre degradability(NDFD), acid detergent fibre degradability(ADFD)and CP degradability(ND)(P<0.001), DMD, ND and fiber degradation were significantly effected by EFE addtion(P?0.001), significantly interaction between EFE and NFC/NDF ratio were observed on discrete lag time(L), DMD, NDFD and ADFD(P?0.001).(2)With the increasing EFE dosage, GP, NDFD and ADFD increased(P<0.05, quadratic effect)in sub 1, especially highest in 0.8 mg/g EFE. Greater GP, b, DMD, NDFD and ADFD were detected in sub 2 and sub 3 when 0.4 mg/g EFE were added.(3)NFC/NDF ratio and EFE addition significantly influenced ruminal fermentation characteristics and microbial protein(MCP)synthesis(P<0.05)but ruminal p H did not affected by EFE supplementation(P=0.105), and significant NFC/NDF ratio×EFE interactions were observed on ammonia-N and A:P.(4)Molar proportion of acetate and concentration of ammonia-N decreased(P<0.001, quadratic effect)with the addition of EFE in sub 1, but MCP, molar proportion of propionate and total volatile fatty acids(TVFA)were higher than other treatments when sub 1 treated with 0.8 mg/g EFE. TVFA and MCP were greater and ammonia-N was less respectively when adding 0.4 mg/g EFE into sub 2 and sub 3. Trial 2:Effect of diets with different NFC/NDF ratio and exogenous fibrolytic enzymes on growth performance, ruminal fermentation characteristics and cellulolytic bacteria of goatThe objective this study was to investigated the effects of supplementing EFE into goat diets with different NFC/NDF ratio on growth performance, nutrient digestibility, ruminal fermentation and microbial populations. Treatments were 2×2 factorial arrangement of diets using low vs. high NFC/NDF ratios(1.16 or 1.66)and with vs. without(0 or 0.4 g/kg)supplementation of EFE. Treatments consisted of: CON A(1.16+0),EXP A(1.16+0.4),CON B(1.66+0)and EXP B(1.66+0.4). Sixty four Lezhi black goats(11 ± 0.8 kg of live weight)were randomly assigned to four treatments, each treatment had 4 replicates, with 4 goats in each replicate. The results showed that:(1)high NFC/NDF ratio(1.66)and enzymes supplementation resulted in greater average daily gain(ADG)and lower feed conversion efficiency(P<0.05), treatment EXP B had greatest ADG and lowest F:G, but no difference on ADG and dry matter intake(DMI)between EXP A and CON B.(2)High NFC/NDF ratio(1.66)diets and supplementing EFE can significantly increased the digestibility of organic matter(OM), crude protein(CP), ADF and NDF(P<0.05), except for EFE on CP, EXP B had the greatest nutrient digestibility.(3)High NFC/NDF ratio and the supplementation of EFE dramatically increased the production of TVFA, MCP and the molar proportion of propionate(P<0.01), ruminal p H was decreased in high NFC/NDF ratio diets(P<0.001)but did not affected by EFE supplementation. Ammonia-N and molar proportion of acetate were less in EFE added diets, EXP B had the greatest TVFA, MCP and the molar proportion of propionate.(4)The activities of cellulase and xylanase increased with EFE addition(P<0.05), but decreased with increasing NFC/NDF ratio(P<0.05). Among the three cellulolytic bacteria detected, only the abundance of F. succinogenes was significantly decreased with the increasing NFC/NDF ratio(P=0.004), R. flavefaciens tended to decrease in high NFC/NDF ratio diets(P=0.066), but the relative quantifications of three cellulolytic bacteria did not effected by EFE supplementation.Comprehensively, the optimal supplementing level of EFE was 0.8 mg/g in sub 1, and 0.4 mg/g in sub 2 and sub 3 in vitro fermentation. The high NFC/NDF ratio diet and supplementing diets with 0.4 mg/g EFE can improve growth performance and ruminal fermentation of goat, the activities of cellulase and xylanase increased with EFE addition but no difference on rumen liquid cellulolytic bacteria, thus it is inferred that EFE could improve the digestibility of fiber in diets by making for the deficiency of endogenous enzyme in growing goats. |
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