ˁēz clearly denotes a single she-goat in the singular (cf. the symmetrical opposition ˁizzīm ~ tǝyāšīm vs. rǝḥēlīm ~ ˀēlīm in Gn 32.14), but may have a collective meaning without gender distinction in the plural.
PS
*ˁVnz- - goat
(SED II No. 35, Fron. VI 29, HSED No. 240)