Received: 5 March 2017
Accepted: 18 January 2018
First Online: 12 February 2018
: The study was approved by the farm owner and all experimental animals were conducted according to the International Guiding Principles for Biomedical Research. The protocol was approved by the Committee on the Ethics of Animal Experiments of the Jilin University.
: Not applicable.
: The authors declare that they have no competing interests.
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