Effect Of Different Fast/Slow Fermenting Carbohydrate Ratios In Rations On Milk Yield And Milk Composition Of Donkeys

The digestion of carbohydrates in equids differs from that in ruminants,where carbohydrates are divided into non-structural carbohydrates(NSC)and neutral detergent fibers(NDF);in equids,where carbohydration is roughly divided into hydrolyzable carbohydrates(CHO-H),rapidly fermentable carbohydrates(CHO-FR),and slowly fermentable carbohydrates(CHO-FS)CHO-FR is actually equal to NSC minus CHO-H,which can be distinguished as CHO-H is hydrolyzed by enzymes in the front part of the digestive tract,while CHO-FR is absorbed and utilized by microorganisms in the back part of the digestive tract,mainly in the cecum by faster fermentation,and CHO-FS is equivalent to NDF,which means that CHO-FS is fermented and utilized by microorganisms in the digestive tract at a slower rate.Nutrient composition in rations is an important factor affecting lactation performance and milk composition of lactating donkeys,but there are few studies on the effects of feeding different levels of carbohydrates on milk composition and milk fatty acids of lactating donkeys.In this thesis,the nutritional value of common feeds was evaluated according to the digestive characteristics of equine animals,and the changes in milk yield,milk composition,milk fatty acid composition,digestibility,body weight and feed intake were analyzed by feeding different carbohydrate ratios to provide data support for the reasonable configuration of ration composition during lactation of donkeys.This thesis includes the following three experiments.Experiment 1: Assessment of the nutritional value of common feedstuffsIn this experiment,we determined the CP、EE、Ash、NDF and NDIP components of commonly used feeds,and calculated and evaluated the CHO-H,CHO-FR and CHO-FS contents according to the digestive characteristics of equine animals,aiming to provide data reference for the configuration of different CHO-FR/CHO-FS ratio rations.The results showed that: the hydrolyzable carbohydrate content of the measured roughage was much smaller than the fermentable carbohydrate content;whole corn silage had higher CHO-H and CHO-FR content,presumably with faster digestion rate in the digestive tract;cottonseed hulls had low CHO-FR and CHO-H content,and high CHO-FS content would be poorly digested,which was consistent with the general belief that cottonseed hulls are slower to digest.The higher CHO-H content of energy feeds,as CHO-H includes hexoses,disaccharides,oligosaccharides and most starch,indicates that energy feeds are better digested.This study provides a better understanding of the nutrient composition and carbohydrate composition of commonly used feeds.Experiment 2: Effect of different fast/slow fermenting carbohydrate ratios in rations on milk yield and nutrient digestibility in donkeysIn this experiment,40 female donkeys of similar age(5±2 years),weight(200±50 kg),litter size(≥2),and lactation days(30±5 days)were divided into 5 groups of 8 donkeys each and fed diets with CHO-FR/CHO-FS ratios of 0.85,0.95,1.16,1.43,and 1.94,respectively,and the diets of the 5 groups had the The protein and energy levels were the same in all five groups.Milk yield and milk composition were measured weekly for 15 d during the pre-feeding period and 8 weeks during the regular feeding period,and feces were collected for 5 consecutive days at the end of the experiment using the partial collection method.The effect of different fast/slow fermented carbohydrate ratios on milk yield and nutrient digestibility of donkeys was investigated to improve the digestibility of nutrients for lactating donkeys and to improve the data support for greater use of the rations.The results showed that there was no significant difference in DMI among the five experimental groups(P > 0.05),and the DMI among the groups was: Ⅰ > V > Ⅲ > Ⅳ >Ⅱ.The highest weight increase in lactating female donkeys was in group I,which was significantly higher than group IV(P < 0.05),and although numerically higher than the other three groups but not significantly different from the other three groups(P > 0.05),but the weight increased in all five treatment groups.The daily milk yield of each test group ranged from 4.10 to 4.48 kg,and the performance between the groups was: Ⅳ > V > II > I > III,with no significant difference between the groups(P > 0.05).Effect on nutrient digestion: The digestibility of EE and NDF in the ration was the highest in the first group of lactating donkeys and was significantly higher than that in the fourth and fifth groups(P<0.05),the digestibility of CP in the ration was the highest in the second group of lactating donkeys and was significantly higher than that in the fourth and fifth groups(P<0.05),and there was no significant difference in the digestibility of ADF in the ration among the experimental groups of lactating donkeys(P > 0.05),with the following variations: Ⅰ > Ⅱ > Ⅲ > The digestibility of NDIP in the ration of female donkeys was the highest in the first group,which was significantly higher than that in the fifth group(P < 0.05).In conclusion,the best digestibility of EE,NDF,ADF and NDIP in the ration and the most weight gain were observed in the female donkeys when the ratio of CHO-FR/CHO-FS in the ration was 0.85.Experiment 3: Effect of different fast/slow fermenting carbohydrate ratios in the diet on milk composition and milk fatty acidsExperiment 3 investigated the effect of feeding diets with different fast/slow fermentable carbohydrate ratios on milk composition and milk fatty acids in lactating donkeys.The test animals and feeding trials were performed as above,and milk samples were collected at the end of the formal period for fatty acid determination.The results showed that: Effect on donkey milk composition,the milk fat rate of the first group was higher than the other four groups(P < 0.05),the milk fat rate of the fourth group was the lowest,the milk protein rate and non-fat solids of the third group were significantly higher than those of the fourth and fifth groups(P < 0.05),and the lactose rate and milk ash fraction of the third group were significantly higher than those of the first,fourth and fifth groups(P < 0.05).Effects on milk fatty acids: C6:0 and C18:3n3 in the first group were the highest and significantly higher than those in the fifth group(P < 0.05),C18:2n6 content in the first group was the highest and significantly higher than those in the third and fifth groups(P < 0.05),C17:0 content in the fifth group was the highest and significantly higher than those in the third group(P < 0.05),and C20:1 and C18:2n6t content were the highest and significantly In terms of FA classification,increasing CHO-FR/CHO-FS from 0.85 to 1.94 significantly increased MUFA content(P < 0.05)、significantly reduced PUFA,n-3 PUFA,n-6 PUFA and PUFA/SFA content(P < 0.05).while the remaining indicators did not differ significantly among the groups.According to the FA classification in the table rations,as the CHO-FR/CHO-FS ratio increased,the MUFA and n-3 PUFA contents in the rations decreased,and the PUFA,n-3PUFA,n-6 PUFA,and PUFA/SFA contents in the milk also decreased.In conclusion,with the increase of CHO-FR/CHO-FS ratio in the ration,some milk FA components will be subsequently reduced,which will have a significant effect on milk composition content and a tendency to reduce milk fat percentage.ConclusionUnder isoenergetic and isoprotein conditions,an increase in CHO-FR/CHO-FS from 0.85 to 1.94 reduced the digestibility of EE,NDF,ADF,and NDIP in the ration of female donkeys,and also reduced some FA contents in milk,including C18:3n3,C18:2n6c,PUFA,n-3 PUFA,n-6 PUFA,PUFA/SFA content,which affected the milk quality,with the highest daily milk yield at CHO-FR/CHO-FS of 1.43.The highest values of milk protein rate,non-fat solids,lactose rate,and lactic ash content were reached at CHO-FR/CHO-FS of 1.16.