Abstract:

Five animals from a cross between male small tail Han sheep and female native ibex （second generation）， about 10 months of age and （45±5） kg weight， fitted with permanent rumen fistula were used in this research. Treatments comprised four additives： Carrier （Car）， carrier+essential oil （CarEO）， carrier+cobalt （CarCo） and carrier+essential oil+cobalt （CarEOC） inserted into the rumen different sheep via the fistulae， with a fifth sheep having no additives as control （CK）. A Latin square design was used for 5 rounds of tests and the nylon bag method was used to determine the nutrient degradation dynamics of maize straw silage at 0， 6， 12， 24 and 48 h， and to explore the effects of the different additives on the rumen fermentation characteristics of the sheep. It was found that the dry matter degradation rate （DMD）， crude protein degradation rate （CPD）， neutral detergent fiber degradation rate （NDFD） and acid detergent fiber degradation rate （ADFD） of silage maize stalks in each treatment group increased with increasing rumen degradation time and reached their maxima at 48 h. After adding CarEOC， NDFD and ADFD of silage maize stalks added at 48 h were numerically higher than CK， but the difference was not significant （P>0.05）. Compared with CK， the DMD of silage maize stalk was increased after addition of CarEO， CarCo and CarEOC， with the DMD and CPD increased by 3.33% and 3.89%， respectively， at 48 hours after addition of CarEOC. After 24 and 48 h degradation， CPD differed significantly （P<0.05） between CarEOC and CK. None of the additive treatments significantly affected the pH of sheep rumen fluid （P>0.05）， but after addition of CarEOC， the rumen fluid pH and NH₃-N showed a trend of initial decrease followed by an increase. However， there was no obvious change in NH₃-N after adding CarEO. Under the CarEO and CarEOC treatments， the total volatile fatty acid， acetic acid， propionic acid， and butyric acid levels in the rumen fluid showed a tendency of initial increase， then decrease， and finally increase， especially for the CarEOC treatment. These results were interpreted as indicating that the addition of CarEO and CarEOC were beneficial to rumen microbial activity. After adding Car in this experiment， none of the rumen degradation indexes differed significantly from those of CK at any of the sampling times （P>0.05）. Based on grey correlation multivariate analysis， the correlation value of the degradation quality and fermentation characteristics of silage maize stalks in the rumen was CarEOC>CarCo>CarEO>Car>CK， indicating that CarEOC promoted the degradation of fiber compounds in the rumen of sheep， and could therefore be used as a green feed additive to promote more efficient use of roughage resources as feedstuffs for sheep in commercial meat production systems.

Key words: feed additive, silage maize stalk, rumen degradation dynamics, rumen fermentation characteristics