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Changes of protozoal diversity in response to forage and protein of diets in the rumen of dairy cows
The present study was conducted to investigate the changes of quantity and diversity of rumen protozoa in dairy cows fed with different forage and protein diets. Forty-eight healthy Chinese Holstein dairy cows were utilized in randomized block design, and the sixteen cows in every group had similar body conditions. The treatments were as follows: MF (forage sources: alfalfa hay and corn silage; protein sources: soybean meal and miscellaneous meals), CSA (forage sources: corn stover; protein sources: soybean meal and miscellaneous meals), CSB (forage sources: corn stover; protein sources: miscellaneous meals). Rumen fluid was collected via a stomach tube before and after morning feeding on 31, 61, and 91 d of experiment. Microbial DNA in rumen fluid sampled on 91 d was extracted by a CTAB plus bead beating method. The 18S rRNA gene sequences were trimmed and imported to MOTHUR for OTU analysis at 98% identity level. Results showed that the number of protozoa was not different among three groups based on microscopic counting and qPCR. Totally, 726 clones were obtained from three groups. There were 61 OTUs in three groups, 20 OTUs in CSA, 20 OTUs in CSB and 22 OTUs in MF. The three groups shared 10 OTUs, while CSA, CSB and MF had 6, 5 and 7 unique OTUs respectively. Compared with CSA (54.0), MF (46.2) and CSB (30.1) had lower species richness of protozoa based on ACE index. Compared with CSA (0.25), MF (0.11) and CSB (0.23) had higher diversity of protozoa based on Simpson index. Taxonomy analysis showed that Dasytricha (54.8%), Entodinium (16.4%), Eudiplodinium (14.2%), Diplodinium (7.7%) and Isotricha (3.3%) were the predominant genera in the rumen fluid. In different forage groups, Diplodinium dentatum, Epidinium caudatum, Eudiplodinium maggii were only found in CSA, while Isotricha intestinalis, Ophryoscolex purkynjei were only found in MF. But in different protein groups, there was no apparently changed protozoal species. In conclusion, different sources of forage and protein in diets had no significant effect on the number of rum. However, feeding corn stover can result in higher protozoal abundance, and feeding soybean meal can lead to lower protozoal diversity.
Keywords: protozoa; diversity; forages.