高山美利奴育成公羊在返青期与盛草期牧场的营养监测

本研究以祁连山放牧地的高山美利奴育成公羊为研究对象,于返青期和盛草期,采用粪袋全收粪和酸不溶灰分(AIA)结合法测定其采食量,并探究其放牧地牧草营养物质的供给规律和其营养的盈缺。结果显示,盛草期放牧草地植物群落优势度指数、地上生物量、多样性指数、物种丰富度指数、均匀度指数均显著高于返青期(P<0.05)。在牧草养分化学指标上,粗蛋白和粗灰分含量在盛草期显著高于返青期(P<0.05),盛草期牧草粗饲料分级指数(GI)也显著高于返青期(P<0.05)。返青期和盛草期高山美利奴育成公羊干物质、粗蛋白采食量差异不显著(P>0.05),代谢能采食量在盛草期显著高于返青期(P<0.05)。牧草有机物和干物质消化率返青期和盛草期差异不显著(P>0.05),牧草粗蛋白、中性洗涤纤维和酸性洗涤纤维消化率在返青期显著高于盛草期(P<0.05)。盛草期高山美利奴育成公羊瘤胃氨态氮(NH3-N)含量、丁酸、支链脂肪酸比例显著高于返青期(P<0.05),高山美利奴育成公羊瘤胃内总挥发性脂肪酸含量返青期显著高于盛草期(P<0.05)。参照中国美利奴育成公羊(体重70 kg,日增重100 g)营养需要推荐量,高山美利奴育成公羊每只日代谢能和粗蛋白采食量在返青期分别比推荐量低9.32 MJ和45.23 g·d^?1;而在盛草期二者则分别低7.32 MJ和32.64 g·d^?1。综上所述,盛草期牧草GI值、牧草生产力显著高于返青期;体重为70 kg的高山美利奴育成公羊在返青期和盛草期牧场,日增重达到100 g时,代谢能和粗蛋白摄入量均不足,需补饲一定量的能量和蛋白饲料。

Effects of different graded index alfalfa hay and wheat straw on yak rumen fermentation characteristics in vitro

The purpose of this study was to optimize the forage nutritional combination of yak diet with the grading index (GI). Five combinations of alfalfa hay and wheat straw with different GI (7.03, 6.21, 5.38, 4.55, and 3.72) were selected to study yak rumen fermentation in vitro. The fermentation time was 48 h and 3 replicates were performed for each sample. At 3 ~ 48 h of fermentation, the gas production (GP) of the GI = 6.21 combination was significantly higher than that using the other GI values (P < 0.05). At 3 h and 48 h of fermentation, the dry matter degradation in vitro (IVDMD) showed a decreasing trend with a decrease in GI. At 3, 12, and 48 h of fermentation, the difference between the neutral detergent fiber in vitro (IVNDFD) of GI = 7.03 and GI = 6.21 is not significant, but they were higher than other GI combinations (P < 0.05). At 3 ~ 48 h of fermentation, the concentration of ammonia nitrogen (NH3-N) showed an initial increasing trend followed by a decrease as the GI decreased. At 48 h of fermentation, the microbial protein (MCP) showed a trend of an initial increase followed by a decrease as the GI decreased. At 48 h of fermentation, the concentrations of acetic acid, propionic acid, and total volatile fatty acids (TVFAs) showed an initial trend of increase followed by a decrease as the GI decreased. At 3 ~ 24 h of fermentation, the concentration of CH4 and DE showed an initial trend of increase followed by a decrease as the GI decreased. The GIs of 7.03, 6.21, 5.38 showed a positive combination effect from 3 ~ 48 h of fermentation, whereas GI = 4.55 and 3.72 showed a positive combination effect beyond 48 h of fermentation. The results of multiple factor associative effects index (MFAEI) were first increased and then showed a decreasing trend as the GI decreased. The GI = 6.21 combination of MFAEI was higher than other GI combinations. Overall, in vitro fermentation of yak rumen with GI = 6.21 alfalfa hay and wheat straw combination were found to be optimal.