An interesting Indo-European word for ‘goats’ with a limited distribution is *dig-: Old English ticcen ‘kid’, German Ziege, Albanese dhi, Greek díza ‘she-goat’.
The tendency to be applied to the adult female, as is the case with *H2ówis ‘sheep’ > English ewe, would indicate that this word has some antiquity but it is lacking in several peripheral branches: Celtic, Italic, Tocharian and Anatolian, which is a problem. In addition its structure *dig- is abnormal, as PIE roots normally do not have two voiced phonemes. The attempt to transform *dig- into a regular *dik- in Mallory-Adams (2006: 141) cannot be accepted. This latter form with a voiceless velar stop does not account for Greek and Germanic.
This abnormal root *dig- is of Caucasic origin: Proto-Tsezian *tˀiqˀw ‘one-year-old kid’: Ginukh tˀeqˀʷi, Khvarshi tˀiqˀʷa, Inkhokvari tˀɨqˀo, Bezhta tˀöqˀä, Gunzib tˀoq-či. Besides Proto-Tsezian has *tˀika, *tˀiga ‘he-goat’: Tsezi tˀeka, Ginukh tˀeka, Khvarshi tˀeka, Inkhokvari tˀɨka, Bezhta tˀiga, Gunzib tˀiga.
Incidentally it can be noted that the Caucasic borrowing *tˀiqˀw > pseudo-PIE root *dig- supports the glottalic theory of PIE, as the ejectives of Caucasic have been adapted as voiced phonemes.