Effects Of Maize Processing Methods On The Growth Performance And Rumen Fermentation Parameters Of Castrated Male Goats

Starch is an important source of energy for ruminants and is often used to meet the growth or production needs of high-yielding animals by increasing the starch content of the diet.The rumen is the main digestive organ for ruminants to utilize starch,and the level of starch digestion and utilization has an important impact on the growth and development of the organism.However,excessive starch degradation in the rumen causes metabolic diseases such as rumen acidosis,which affects animal health.As a major source of starch,maize is processed in a way that significantly changes the site and extent of starch digestion in the digestive tract,which in turn changes the rumen degraded starch（RDS）content of the diet.Therefore,in this experiment,maize was processed whole,crushed and pulverized under identical diet composition to observe the effects on growth performance,slaughter performance,rumen fermentation,blood biochemistry and muscle antioxidant indexes of depressed male goats,and to determine the rumen degradation parameters of maize using in vitro fermentation methods to study the effects of maize processing methods on the performance of depressed male goats and the preliminary mechanisms for efficient maize utilization and development of RDS diets for goats.To provide basic information for efficient utilization of maize and formulation of RDS content in goat diets.Exp.1:Effects of maize processing on growth and slaughter performance of castration male goats.Eighteen castration male goats in good health and of similar body weight（50.84±5.58 kg）were randomly and equally divided into three groups and fed diets containing whole corn,rolled corn,and ground corn,respectively,with identical formulations in the three groups.To prevent picky eating,the daily leftover amount was controlled to be about 5%of the feeding amount,and water was given freely.Body weight and feed intake were measured during the50-day trial period,and slaughter samples were taken 3 h after the morning feeding on the 50^thday.The results showed that corn processing method did not affect feed intake,final weight,feed-to-weight ratio,slaughter performance,and tissue and organ weight and proportion（P>0.05）;feeding diets containing whole corn tended to increase mean daily weight gain（P=0.070）and tended to decrease kidney proportion（P=0.068）.Exp.2:Effects of maize processing on rumen fermentation,blood biochemistry and muscle antioxidant capacity in castration male goatsOn the 28^th day of the experiment,rumen fluid was collected orally from the test goats before morning feeding and 2 and 6 h after morning feeding,and the rumen fluid samples were filtered and separated and stored in a refrigerator at-80°C for measurement.Blood was collected from the jugular vein 3 h after morning feeding on the 50^th day to determine the biochemical indexes.The results showed that the 6-h rumen fluid NH₃-N concentrations were significantly higher in the whole corn group than in the other two groups（P<0.05）,while there were no significant differences in rumen fluid p H and bacterial protein concentrations between the three groups（P>0.05）.Compared with the crushed corn group,the whole kernel corn group significantly increased serum TP,ALB,GLO concentrations and A/G（P<0.05）,tended to increase muscle protein deposition（0.05≤P<0.10）,and had no significant effect on protein deposition and nitrogen metabolism in other tissues and organs（P>0.05）.Compared to the other two groups,the whole maize group significantly increased muscle glutathione transaminase activity as well as creatinine concentration,muscle T-AOC activity and GSH-Px concentration（P<0.05）and tended to increase liver glutathione transaminase activity and muscle T-SOD concentration（0.05≤P<0.10）.Exp.3:Effects of corn crushing particle size on rumen fermentation parametersRuminal fluid was collected from 2 goats fitted with permanent rumen fistula after morning feeding,filtered through 4 layers of gauze,mixed in equal volume with filtered rumen fluid and mixed with artificial saliva in a 1:2 ratio to form an artificial rumen culture.The fermentation parameters of the feeds were determined by gas production method,and the fermentation substrates were three groups of diets containing crushed corn（after 1 mm sieve）,coarse meal corn（after 2 mm sieve）and broken corn（after 4 mm sieve）,and the formulations of the three groups of diets were identical.The results showed that compared with the other two groups,the dry matter degradation rate,total gas production,methane production and carbon dioxide production were significantly increased in the crushed group（P<0.05）,the p H and NH₃-N content of the fermentation broth were significantly reduced at 6 and 12 h（P<0.05）,and the production of bacterial protein was increased,but not significantly（P>0.05）.at 6 h,the propionic acid content was significantly higher in the crushed group than in the other two groups（P<0.05）,and at 24 h,total VFA,acetic acid,propionic acid,butyric acid,valeric acid and isovaleric acid contents were significantly higher in the crushed group than in the broken group（P<0.05）,while acetic acid and butyric acid contents were significantly higher in the coarse powder group than in the broken group（P<0.05）.The crushed group had a significantly higher ethylene to propionate ratio at 6-12 h than the other two groups（P<0.05）,while at 24 h the crushed group was significantly lower than the crushed group（P<0.05）.In conclusion,feeding diets containing whole grain corn tended to increase daily weight gain,muscle protein deposition and muscle antioxidant capacity in castrated male goats with the same diet formulation.