$sqlstr = "select *,IF(shengxiao='猪啊',1, IF(shengxiao='狗啊',2,3)) as s from table order by s";

create temporary table T
  select '猪啊' as f
  union select '牛啊'
  union select '狗啊';


select *, if(locate('猪', f), '猪',if(locate('牛',f),'牛', if(locate('狗',f),'狗',''))) as x 
 from T order by find_in_set(x, '猪,狗,牛')

f    x 
猪啊 猪 
狗啊 狗 
牛啊 牛