'Muc throm' (pregnant  pig) is the only example in the Survey of a noun appearing with an adjective.  'Muc' has similar properties to be seen in the 'Aspiration' page (i.e. with similarities to 'cat' and 'cù', while a feature of 'trom' is seen in the 'Lengthening and 'Diphthongisation' page (i.e. with 'chùm').

 

Nouns in Gaelic are either masculine or feminine. With a feminine noun (in this case, 'muc'), the following adjective (in this case, 'trom') is lenited, causing the pronunciation to change from 'traum' to 'hraum'.  Lenition, in written Scottish Gaelic, is indicated by inserting the letter 'h' after the affected consonant.

 

It can be seen on the map that there is a distinct preference to lenite 'muc' in the western half of the Gaelic Highlands, i.e. to treat this noun as being feminine, while in the eastern half, 'muc' is treated as being masculine. There is also a wide overlap zone where both uses are apparent.

 

Dwelly's authoritative dictionary, first published  1901-1911 i.e. well before the time of the Survey, gives 'muc' as being feminine, with the meaning of 'sow' or 'pig'.  There are, however, other words in Gaelic for 'sow' or 'pig' - Dwelly gives 'giusaidh' also, which he notes is masculine in east Perthshire. Perhaps a similar usage also applies to 'muc' - especially if the word is taken to mean 'pig', with the gender unspecified, though this is hardly the case if the pig is pregnant!