Study On The Rule Of Degradation Of Vitamin A In Rumen And Evaluation Of Effects Of Ruminal Protected Vitamin A On Dairy Cows

The present study was divided into 9 trials to discuss the rule of degradation of vitamin A in rumen and evaluate the effects of ruminal protected vitamin A on dairy cows. All of the results obtained were very important to enrich the theoretics of ruminant vitamin A nutrition, and to provide foundation to prepare and use ruminal protected vitamin A. and to propose reasonable adding levels of vitamin A in order to improve body vitamin A status and enhance the performance and immune function of dairy cows.Trial 1 and 2 were conducted to study the influences of different sources and levels of vitamin A and different concentrate to forage ratio diets on the ruminal vitamin A degradability and the rumen fermentation during in vitro ruminal fermentation. The experiment was a 2×2×3 factorial arrangement, and the first factor was concentrate to forage ratio of incubating substrate(2:8 and 5:5), and the second factor was the source of vitamin A (domestic and imported). The third factor was vitamin A level added to incubating system (5.8, 11.7, 23.3 IU per milliliter medium).In order to discuss the degradation mechanism of VA in rumen, trial 3 was conducted to study the effect of ruminal microbe on degradation of vitamin A during in vitro ruminal fermentation and trial 4 was conducted to test the effect of different types of microflora in rumen on the degradation of vitamin A during in vitro ruminal fermentation. Microcapsules of ruminal protected vitamin A were prepared in trial 5 by using spray-dried technology and its degradability during in vitro ruminal fermentation was determined.Trial 6 was a 2×2 factorial arrangement. 20 dairy cows which were similar in weight and milk performance were randomly divided into 4 groups, with 5 each group. Different groups were fed the different diets in vitamin A treatments (ruminal protected vitamin A, untreated vitamin A) and levels (110IU/kgBW, 165IU/kgBW) . Pre-trial period was 15 d and the experimental period was 60 d. The rumen fluid was collected from the cows in different groups in the last two days of the experimental periods to evaluate the effect of the different treatments and levels of vitamin A on ruminal vitamin A content and rumen fermentation in dairy cows.Trial 6 was a 2×2 factorial arrangement. 20 dairy cows which were similar in weight and milk performance were randomly divided into 4 groups, with 6 each group. Different groups were fed the different diets in vitamin A treatments (ruminal protected vitamin A, untreated vitamin A) and levels (110IU/kgBW, 165IU/kgBW). Pre-trial period was 15 d and the experimental period was 60 d. The purpose of these experiments was to discuss the influences of different treatments and levels of vitamin A in dairy cows diet on milk yield, immune function, anti-oxidation function and vitamin A nutritional status.Under the present experimental conditions, the results showed as follows:1) The degradability of both the vitamin A sources was all higher for high or low concentrates dies during in vitro ruminal fermentation, and it was about 60% at 8h and was more than 70% at 24h.2) The vitamin A degradability during in vitro ruminal fermentation for the high concentrates diet was significantly higher than for the low concentrates diet. With the increasing level of vitamin A in incubating system from 5.8 to 23.3 IU/mL, the disappearance of vitamin A had a certain attendency to be increased..3) The degradation of vitamin A in rumen was mainly related to ruminal bacteria. Both amylolytic bacteria and cellulose-digesting bacteria could result in the degradation of vitamin A, but amylolytic bacteria had a dominant effect for vitamin A degradation. The results also showed that rumen environment had a little effect on the degradation of vitamin A.4) Microcapsule of ruminal protected vitamin A was more stable in rumen than untreated vitamin A. During in vitro fermentation the degradation rate of vitamin A was 30.38% fro ruminal protected vitamin A at 24h, but it was more than 70% for untreated vitamin A.5) Supplementation of ruminal protected vitamin A(110IU/kgBW and 165IU/kgBW)in diet significantly reduced the vitamin A content and increased acetic acid and TVFA concentrations in rumen, but had little effect on the other fermentation parameters. The supplementation of high dose of untreated vitamin A (165IU/kgBW) had little effect on rumen fermentation.6) Supplementation of microcapsules of ruminal protected vitamin A(110IU/kgBW and 165IU/kgBW, respectively)in diet resulted in an significant improvement in milk yield , immune function ,anti-oxidation function and vitamin A nutritional status of dairy cows and vitamin A content of milk. The 165 IU/kgBW ruminal protected vitamin A group had the best effect on above indexes, but 110IU/kgBW untreated vitamin A group had the worst effect.7) Either supplementation of ruminal protected vitamin A microcapsules or increasing untreated vitamin A level in diet could promote the performance and immune fuction and anti-oxidation function of dairy cows, but the effect was better for microcapsules of ruminal protected vitamin A.