Fiqh-us-Sunnah Volume 3, Zakaat and Fasting, Fiqh 3.041A.

Section : Zakah on Sheep (Including Goats).

Sheep are subject to zakah when their number reaches forty. When the herd counts forty freely grazing heads at the end of the year, its zakah is one sheep. This is applicable until the number reaches 120, at which point, up until 200, the zakah is two sheep. From 201 to 300, their zakah is three sheep. When the number is above 300, one additional sheep is added for each increment of one hundred. Young sheep (jazh’) are levied in the case of sheep and young goats (thany) in the case of goats. It is permissible, say scholars without exception, to levy rams as a form of zakah if all of the nisab of sheep are male. If the sheep are ewes, or a grouping of males and females, the Hanafiyyah holds it is optional to levy a zakah rams, whereas others specify ewes.