Effect of yeast culture or cellulolytic enzymes in licking blocks on rumen fermentation and fi bre degradation in vitro

An in vitro gas production experiment was conducted to determine the effect of yeast culture (YC) and cellulolytic enzyme (CE) included in urea-molasses-mineral (UMM) licking blocks on ruminal fermentation characteristics and fi bre degradation of wheat straw. Five treatment blocks were: 1. control (CON, no UMM block added), 2. typical block (B), 3. yeast culture block (YCB), 4. cellulolytic enzyme block (CEB) and 5. yeast culture plus cellulolytic enzyme block (YCCEB). The results showed that gas production and both dry matter and cell wall degradabilities were signifi cantly enhanced by supplemental UMM licking blocks (P<0.01), of which the greatest gas production and the fi bre degradabilities were found with the treatment YCB, followed by YCCEB, CEB, and B. It is concluded that yeast culture, cellulolytic enzymes or their combination included in licking blocks has a potential to boost rumen fermentation and fi bre degradation.


INTRODUCTION
Low quality crop residues, like wheat straw, are the primary energy source for ruminants during a considerable time of the year.Due to low contents of crude proteins (<70 g/kg DM) and high contents of cell walls, however, these residues are unpalatable and less degradable in the rumen.To optimize microbial fermentation of these residues, it is necessary to synchronize carbohydrate and protein supply and to supplement certain biologically active substances to the diet.It has well established that supplementing nitrogen, readily fermentable energy, minerals and monensin together in licking blocks improved rumen fermentation and nutrient utilization (Debasis and Singh, 2002).However, the data is limited about the effect of including cellulolytic enzymes (CE) or yeast culture (YC) in the licking blocks on rumen fermentation characteristics and fi bre degradation.
Using an in vitro gas production technique, the present study was conducted to investigate the effect of including YC or CE in the licking blocks on rumen fermentation characteristics and fi bre degradation.

MATERIAL AND METHODS
The urea-molasses-mineral (UMM) block was manufactured by using a special press (Model YTD32-315, Xuzhou Special Machine Tool Manufacture).The ingredients of UMM blocks were (on DM basis), %: fi ne salt 38, urea 12, sugar cane molasses 6, trace mineral premix 6, zeolite 4, bentonite 12, MgO 4, calcium carbonate 5, sodium sulphate 3, dicalcium phosphate 5, paraffi n oil 2, and additives 3.All ingredients were mixed in a stainless mixer and then pressed at the pressure of 25 MPa/cm 2 for 0.8 min.The size of each block was 22×7 cm with a weight of approximately 5 kg.All blocks after forming were covered with polyethylene fi lm to prevent contamination.
Four different blocks were made with addition of different additives in this study: typical block (B, only bentonite as an additive), yeast culture block (YCB), cellulolytic enzyme block (CEB) and yeast culture plus cellulolytic enzyme block (YCCEB).The products of yeast culture and cellulolytic enzyme are obtained from some commercial companies.Yeast culture (Saccharomyces cerevisiae, Type Diamond V XP) is obtained from Diamond V Mills, Inc., Cedar Rapids, IA.The enzyme product, containing activities of cellulase, hemicellulase, xylanase, and amylase, is locally derived from Bacillus licheniformis, compliant with the specifi cation for food-grade enzymes and generally recognized as safe in China.The inclusion percentages of additives in the blocks were 3% for yeast culture, cellulolytic enzyme preparation, and both combinations (1.5% yeast culture plus 1.5% cellulolytic enzymes).The typical block only contained 3% bentonite in replacement of the biological active substances.
Dynamic gas production parameters were calculated by non-linear Model in SAS (1999).The model was GP = B × (1-exp (-c × (t -lag))).GP is gas production (ml) of 0.2 g DM wheat straw sample (DM basis) at time t; B is potentially maximum gas production (ml) of 0.2 g DM sample; c is rate of gas production (h -1 ); Lag is delaying time of gas production (h); t is time of incubation in vitro (h).All data was analysed using a completely randomized design nonlinear of procedures of SAS Institute Inc. (SAS, 1999).Signifi cance level was set as P<0.05 unless indicated otherwise.Data presented in the tables are in the form of mean values with the standard error of the difference.

RESULT AND DISCUSSIONS
As shown in Figure 1, in vitro gas production of wheat straw was signifi cantly (P<0.01)infl uenced by supplemental UMM licking blocks.The fermentation pattern of gas production within 72 h incubation was similar among the fi ve treatments.The greatest gas production was found in YCB, followed by CEB, YCCEB, CEB and B, with the lowest gas production in CON.The reason for higher gas production due to supplemental UMM licking blocks over control can be attributed to the supply of carbohydrates, nitrogen and minerals that are favourable to rumen fi bre fermentation.Moreover, yeast culture, cellulolytic enzymes or their combinations further increased ruminal gas production, suggesting stimulation of rumen fi bre degradation by these biological substances, especially the yeast culture product.This result is well consisted with other observations (Moloney and Drennan, 1994;Callaway and Martin, 1997).
Fitting the mathematical model of GP = B × (1 -exp-c*(t-lag)) to these gas production data showed a satisfactory fi t to the gas production data (R 2 = 0.97~ 0.99; Table 1).The greatest potential gas production was found in the treatment YCB, followed by YCCEB, CEB, B and CON.Compared with the treatment of CON and B, the treatment of YCB, YCCEB or CEB had faster (P<0.01)gas production rates.In contrast to the rate of gas production, the fermentation lag time showed a decreased order of: YCCEB<CEB<YCB<B<CON (P<0.01).The result of wheat straw degradation after 48 h fermentation is illustrated in Figure 2. The 48-h degradation rates of wheat straw were increased with supplement of UMM blocks.UMM block supplement showed higher (P<0.01)degradabilities of DM (IVDMD) and NDF (IVNDFD) than CON.Compared with CON, the supplement of B, YCB, CEB and YCCEB resulted in increased IVDMDs by 24.56, 35.73, 26.82 and 29.32%, respectively.However, there were no signifi cant differences of IVDMD among the treatments of B, CEB and YCCEB (P>0.05).Similar to the results of IVDMD, the 48-h IVNDFD values of B, YCB, CEB and YCCEB were increased by 15.81, 27.25, 20.79 and 24.67% over CON, respectively.Furthermore, compared with treatment B, the treatment of YCB, CEB Figure 2. Effect of supplement of UMM blocks on 48-h IVDMD and IVNDF of wheat straw and YCCB had higher (P<0.05)IVNDFD.This result further demonstrated that improvement of degradation by supplemental UMM licking blocks, especially those containing yeast culture, cellulolytic enzymes or their combinations.Yoon and Stem (1996) also observed that yeast culture may provide soluble growth factors (i.e.maltate, organic acid, B vitamins, and amino acid), that are required by ruminal bacteria for growth.
The data of fermentation parameters after 48 h fermentation are presented in Table 2. Supplement of UMM licking blocks decreased (P<0.01)ruminal pH, but there was no difference in rumen pH values among UMM block treatments (P>0.05).Ruminal concentration of NH 3 -N was signifi cantly affected by supplemented UMM blocks (P<0.01).Compared with treatment B, supplement of yeast culture, cellulolytic enzyme, or their combination in the UMM blocks signifi cantly (P<0.05)increased ruminal NH 3 -N concentrations.
The total VFA concentration and the individual VFA molar proportions were prominently affected by supplemented UMM blocks (P<0.01).Among the supplemental blocks, the greatest VFA concentration was found in YCB, followed by YCCEB, CEB, and B at last.As to individual VFA molar proportions, compared with CON, supplement of UMM blocks signifi cantly decreased the proportion of acetate (P<0.01),but signifi cantly (P<0.05)increased the percentages of propionate and butyrate.Compared with treatment B, YCB, CEB and YCCEB also increased (P<0.01) the percentage of propionate.Compared with CON, treatments of B, YCB, CEB and YCCEB also signifi cantly decreased the percentages of isobutyrate, isovalerate and valerate (P<0.05).

CONCLUSIONS
Yeast culture, cellulolytic enzymes or their combinations included in ureamolasses-mineral licking blocks enhanced gas production, rumen ammonia and VFA concentrations and fi bre degradation, when wheat straw was used as a sole fi brous source.These results indicate that yeast culture, cellulolytic enzymes or their combination included in the licking blocks has a potential to boost rumen fermentation and fi bre degradation.

Figure 1 .
Figure 1.The dynamic gas production of wheat straw (0.2 g DM) with different UMM blocks within 72 h of incubation.Data points represent the mean of gas production adjusted to 0.2 g dry substrate

Table 1 .
The amount and dynamic gas production of wheat straw with different UMM blocks (0.2 g DM) fermented within 72 h incubation in vitro

Table 2 .
Effect of supplemental UMM blocks on ruminal fermentation parameters of wheat straw