| The shortage of high quality forage is an important reason to limit the development of animal husbandry in China.In recent years,the continuous increase of corn planting area has restricted the development of traditional dominant industry and forage.The dry climate and fragile ecology in Northwest of China are not suitable for developing water-consuming forage resources.Compared with corn,sweet sorghum is a kind of high energy crop,which not only produces grain,but also produces energy and resistant to drought,flood,salt and alkali.It is a typical water-saving crop and can be popularized as a new forage.At present,in many applications of sweet sorghum,wrapping silage has been used to feed dairy cows and beef cattle,but rarely reported in the sheep breeding industry.In this study,the rumen fermentation characteristics of sweet sorghum silage,corn silage and alfalfa meals in sheep were preliminarily evaluated by in vitro;Secondly,the mixed diet composed of wrapped silage(sweet sorghum silage or corn silage),alfalfa,and concentrate supplements was fed to sheep,and animal feeding trials was conducted to explore the effects of different silage type diets on nutrient utilization and meat quality of sheep under this rearing mode,as to provide theoretical basis and guidance for scientific fattening sheep with new forage resources.The main findings are as follows:(1)The rumen fermentation characteristics of different roughage in sheep were compared in vitro,the results showed that: The p H of corn silage at 12 h and 24 h were lower than alfalfa and sweet sorghum silage(P<0.01).The p H of three roughages cultured to 48 h were relatively stable,with no significantly difference(P>0.05);The NH3-N content of corn silage and alfalfa were significantly higher than sweet sorghum silage(P<0.05);There was no significant difference in volatile fatty acids(VFA)between different roughages(P>0.05).The highest gas production(GP)of sweet sorghum silage was 136.05 m L,compared with corn silage,alfalfa increased 20.25% and 45.75%,respectively.The gas production parameter of corn silage was significantly higher than sweet sorghum silage(P<0.05);The gas production parameters b,a+b of sweet sorghum silage were the highest,which was significantly higher than alfalfa(P<0.05);There was no significant difference in gas production rate c among three types of forage(P<0.05).After fermentation for 24 h,the dry matter digestibility(DMD)and organic matter digestibility(OMD)of corn silage were higher than sweet sorghum silage and alfalfa(P<0.05);At 12 h and 48 h,there were no significant difference among the three roughages(P>0.05).(2)Effects of silage-type diets on nutrient utilization of mutton sheep: The content of NH3-N in corn silage group was significantly lower than sweet sorghum silage group(P<0.01),and the content of NH3-N in HY group was the lowest,and in DG group was the highest.Acid detergent fiber(ADF)and neutral detergent fiber(NDF)apparent digestibility of sweet sorghum silage group were not different from that in corn silage group(P>0.05),and nitrogen loss was also significantly less than the later(P<0.01).However,the corn silage group was significantly higher than the sweet sorghum silage group in nutrient intake,dry matter(DM)and organic matter(OM)digestibility,nitrogen retention,rumen microbial protein yield and so on.The HY group had a stronger advantage in nitrogen retention.The expressions of small peptide transporter(Pep T1)and amino acid transporters(Y+LAT1,Y+LAT2)in the gastrointestinal tract of HG and DG groups were different(P<0.05),except the expression of Pep T2 m RNA in kidney and liver were not significantly different(P>0.05).The expression of Pep T1 m RNA of rumen and Y+LAT1 m RNA of reticulum in DG group were significantly higher than HG group(P<0.05),the expression of HG group in duodenum was significantly higher than DG group(P>0.01);The expression of Y+LAT2 in HG group was significantly higher than DG group(P<0.05).(3)Effects of silage type diet on fattening performance and meat quality: average daily food intake(ADFI)and average daily gain(ADG)of corn silage group were significantly higher than sweet sorghum silage group(P<0.01),and the food intake/gain(F/G)was significantly lower than the latter(P<0.05).There were significant differences in slaughter weight and carcass weight between breed and diet(P<0.01),Dorper sheep was significantly higher than Small-tailed Han sheep(P<0.01),corn silage was significantly higher than sweet sorghum silage(P<0.01),but there was no significant effect on slaughter rate and back fat thickness(P>0.05);The eye muscle area in sweet sorghum silage group was significantly lower than corn silage group.In corn silage group,the meat color,p H1,p H24,p H72,water loss rate were significantly higher than sweet sorghum silage group.The interactions between breed and diet had extremely significant differences in longissimus muscle color’s b* and p H24,and there was a significant difference in p H1(P<0.05).HY group had the highest color’s b* of longissimus muscle,and the lowest p H24;The p H1 of HG group was significantly higher than the other groups(P<0.05).The content of crude fat in DG group was significantly higher than other three groups(P<0.05),the contents of crude protein,ash and amino acids were not significantly different among all groups(P>0.05),but fatty acid content had significant difference(P<0.05);C15:0,C16:0,anteiso-C17:0,C18:1n9t,C18:2n6c,C18:3n-6,C18:3n-3 and saturated fatty acids(SFA)and polyunsaturated fatty acids(PUFA)were significantly affected by diet(P<0.05),C16:0 in corn silage group was significantly higher than sweet sorghum silage group(P<0.05),C18:3n-6 and SFA were significantly affected by breed(P<0.05),the Small-tailed Han sheep was significantly higher than the Dorper sheep;Others in sweet sorghum silage group were higher than corn silage group(P<0.05);There were significant interaction between C18:1n9t,C18:2n6c,C18:3n-6,SFA,monounsaturated fatty acids(MUFA)and PUFA content(P<0.05),the content of C18:1n9t in HG group was highest,the content of C18:2n6c and PUFA in DG group were significantly higher than the other groups(P<0.05),the content of C18:3n-6 in DY group was lowest,the content of SFA in HY group was highest,and MUFA content in DY and HG group were extremely significantly higher than in HY and DG group(P<0.01).In summary,for ruminant,sweet sorghum silage,corn silage and alfalfa have feeding value,but the nutritive value of sweet sorghum silage and alfalfa are lower than corn silage.Under the conditions of this experiment,the sweet sorghum silage diet affect the weight gain and nutrient utilization of mutton sheep,especially the nitrogen utilization is lower than corn silage diet,and we feed sweet sorghum silage to different sheep has different expression patterns of gastrointestinal nutrient transporters.The fattening effect of sweet sorghum silage diet on mutton is not as good as corn silage,but sweet sorghum silage diet can improve water retention of muscle and increased PUFA content which is beneficial to human health. |
