sheep是单复数同形的名词，所以即使是复数，也用sheep。英语中有些名词单复数同形，无论句意是单数还是复数，都用同一个单词。sheep就是其一，所以在这里要用sheep不用sheeps。

sheep：n.羊;绵羊，复数： sheep

例句：

The first task was to fence the wood to exclude sheep

第一项任务就是把树林围起来不让羊进去。

I'd kinda like to have a sheep farm in New Mexico

我有点儿想在新墨西哥州开一个牧羊场。

Sheep's milk is produced in much the same way as goat's milk。

绵羊奶和山羊奶的生产过程差不多。

Dogs were allowed to roam free and 48 sheep were killed。

没有对狗加以约束而让它们四处乱跑，结果有48只羊被咬死