Effects Of Different Forage Supplementary Patterns On The Growth And Gastrointestinal Development Of Holstein Calves

This study was conducted to investigate the effects of different forage sources supplemented at different days on the growth and gastrointestinal development of Holstein bull calves. The feeding trial recorded and analyzed the feed intake, average daily gain, incidence of diarrhea, body measurement indexes and blood biochemical indexes of calves; The slaughter trial determined the rumen fermentation parameters, enzyme activity of small intestine and the liveweight percentage of different organ of calves.The first part was to determine the effect of different forage sources supplemented at different days on the growthof Holstein bull calves. Forty Holstein bull calves with similar body weights and birthdate were selected and randomly assigned to5treatments with8replicates each:control (CON) calves were fed starter feed without any forage provision, and the4other treatments consisted of the same starter feed plus two forage sources started at two different days after birth:chopped alfalfa hay started at15th day (AW), chopped oat hay started at15th day (OW), chopped alfalfa hay started at3rd day (AD),chopped oat hay started at3rd day (OD).All calves were weaned at56d old, and the study finished when calves were70d old. In the pre-weaning period, the starter feed intake was not significantly affected by different forage sources supplemented at different days. The starter feed intake and the total dry matter intake (TDMI) were increased in the first week of post-weaning by supplementing forage at the15th day and the provision of oat hay. The average daily gain of calves supplemented forage at the15th day was tended to be higher than the calves provided forage at the3rd day in the pre-weaning period (P=0.079) and the second week of post-weaning (P=0.072). In the first week of post-weaning, the average daily gain of calves supplemented forage at the15th day was significantly higher than the CON calves (P=0.032) and the calves provided forage at the2rd day (P=0.045). The body length index of calves supplemented alfalfa tended to be higher than the CON calves (P=0.014) inpre-weaning period and the first week of post-weaning. In the pre-weaning period, the body trunk index of CON calves was tended to be lower than the calves supplemented oat hay (P=0.051) and alfalfa hay (P=0.081).Cannon circumference index of calves was not affected significantly by the supplementation of different forage sources at different days.No significantly differencewas detected in the serum metabolite of calves in different treatments in the pre-weaning period.In the first week of post-weaning, the globulin (GLB) concentration in the serum of calves provided forage from3d old was significantly higher than the calve supplemented forage at the15th day (P=0.026). The contents of lactic dehydrogenase (LDH), alkaline phosphatase (AKP), glutamic oxalacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT) in the serum of calves was improved by the supplementation of oat hay and the forage provision from15d old. The number of diarrhea and the diarrhea frequency of CON calves were higher than the calves provided forage, but the difference was not significant.The second part was to assess the effects of different forage sources supplemented at different days on thegastrointestinal development of Holstein bull calves. Twenty Holstein bull calves with similar body weights and birthdate were selected and randomly allotted to5treatments with4replicates each. Feeding patterns and weaning date were the same with Experiment1, and all calves were slaughtered at56d old. The pH value and the concentration of ammonia nitrogen, acetic acid, propionic acid, butyric acid and total volatile fatty acids in the rumen were not affected significantly by the supplementation of different forage sources at different days. The content ofamylase in the duodenum was significantly enhanced by the provision of forage, while the lactase and protease concentration in the small intestine had no significant difference among the treatments. The ratios of the liverweight, ruminoreticular weight and small intestine weight to body weight of CON calves were higher than the calves supplemented forage. In conclusion, supplementing calves with oat hay from the15d old had certain advantages to improve average daily gain and alleviateweanling stress.Therefore, it is better that the mainstream calf feeding pattern existed in domestic large farms, which is ’milk+starter feed’, would be changed to ’milk+starter feed+oat hay (from the15th day)’ pre-weaning and ’starter feed+oat hay’ after transferring to the yard.