Effects Of Different Levels Of Cottonseed In Diets On Rumen Fermentation And Digestibility Of Nutrients For Beef Cattle

Three 7-year old Simmcntal crossbred beef cattle(600±100kg body weight) fitted with ruminal cannulas were used in a 3 X 3 Latin square design to investigate the effects of different levels of cottonseed in diets on rumen fermentation and digestibility of nutrients for beef cattle,and to make reference to optimum level of cottonseed in beef cattle diets.The experimental diets consisted of forage and concentrate were fed 8.7kg per day.Forage consisted of dried straw and whole cottonseed and concentrate consisted of corn grain and cottonseed meal, were all fixed quantity.Three experimental diets contained [1]contral(CT):basal diet; [2]middle cottonseed(MC):13% cottonseed and [3]high cottonseed(HC):25% cottonseed.The experiment included 3 feeding periods of 16 days each,and each period comprised a 10-day adaptation and 6-day collection.In the period of data collection,parameters about ruminal fermentation(pH, NH3-N, VFA), degradability of straw and cottonseed, and digestibity of dietary nutrients (DM,OM, CP, EE, ADF) were determined.The results showed that:1) Effect of different levels of cottonseed on ruminal fluid pH:During a feeding period,the mean pH of three treatments CT,MC,HC were 6.69, 6.58, 6.60,respectively.The mean pH of treatments MC,HC in a feeding period,decreased a little(-0.11,-0.09),compared with treatment CT.There were no differences among treatments in pH of the same time(P>0.05).But the changing trend after feeding 2h was different,treatment CT,MC declined(-0.10,-0.32),while treatment HC rose(+0.07).2) Effect of different levels of cottonseed on ruminal NH3-N concentration: During a feeding period,the mean NHs-N of three treatments CT,MC,HC were 6.72mmol/1,7.01 mmol/1,6.65 mmol/1 ,respectively,and that of MC was the highest.Compared with treatment CT,the mean NHs-N of treatment MC increased by 0.29 mmol/l,while treatment HC decreased by 0.07 mmol/1. There were no differences among treatments inNH3-N of the same time(P>0.05).3) Effect of different levels of cottonseed on ruminal VFA concentration:During a experimental period, the mean total VFA of three treatments CT,MC,HC were 97.59 mmol/1, 104.82 mmol/1,101.00 mmol/l,and compared with CT the others increased by 7.4%,3.5%, respectively.The mean acetate concentration and propionate concentration of treatment MC,HC were higher than that of treatment CT too,while butyrate concentrate and the ratio of acetate to propionate concentrate were lower than it.There were significant differences among the mean values of A/P in three diets(P< 0.05),and the mean values were 4.49,4.35,4.05,respectively.4) Effect of different levels of cottonseed on degradability of nutrients in rice straw and cottonseed:With ruminal fermentation continuing the degradability of nutrients in rice straw rose gradually. During a experimental period, with cottonseed level rising ,EDP of DM, OM, NDF, ADF of rice straw in three treatments droped significantly (P<0.05).During a experimental period, No differences were observed in the degradability of DM and EE(except 24h) of whole cottonseed at the same time among treatments(P > 0.05).5) Effect of different levels of cottonseed on digestibility of nutrients in diets: Except the differences in the digestibilities of EE and ADF among CT,MC and HC,no differences(P > 0.05)were observed in other nutrients during a whole feeding period.Compared with treatment CT, DM digestibility in treament MC,HC decreased by 0.06%,3.88%,respectively;OM digestibility of treament MC increased by 0.69%,and that of treatment HC decreased by 3.53%. There is a upward tendency in CP digestibility with the level of cottonseed increasing.Compared with treatment CT treatment MC,HC increased CP digestibility by 4.52%,6.06%,respectively. Differences in EE digestibility were not significant between treatment CT,MC and treatment HC,but it was significant (P <0.05)between treatment CT and MC. Compared with treatment CT treatment MC,HC increased ADF digestibility by 14.24%, 10.05%, respectively.