"madra" is of the fourth declension
confirmed by the dictionary, which also shows its male...
rules for fourth declension are here
so, "madra" nom. sing. has modified to "madra" gen. sing.
No other rules apply because no articles nor possessives are present
One of the options in the selection list was "
*madraí*" (ie "bia madraí"). Duolingo rejected this. NEID, however, gives "bia madraí" as the translation of "dog food"
Some other examples found:
bia madraíagus beatha éan
bia madraíar na seilfeanna
From a story in Feasta
cuóta taraife bliantúil Comhphobail le haghaidh
bia madraínó bia cat
From the Corpas Comhthreomhar on Gaois.ie
[Note how the similar, emphasised, examples also use the genitive plural of the qualifying noun "cat" and "éan"]
Obekim didn't get a "type what you hear" exercise, he got a "Select All Correct" exercise - I'm not sure if Duolingo still presents that type of exercise any more.
As Obekim wrote his post over two years ago, it's possible that there wasn't even any audio for this exercise at that time.
unlenited after masculine nouns in the nominative singular
e.g. fear céile = husband
lenited after masculine nouns in the weak plural (on slender consonants)
e.g. na fir chéile = the husbands
lenited after masculine nouns, that are in the genitive themselves (on slender consonants)
e.g. an fhir chéile = of the husband, teach pobail bhaile = the church of a town
lenited after feminine nouns in the nominative singular
e.g. bean chéile = wife
It says "pending approval". So tearma.ie is considering someone's submission. They haven't decided yet.
Foclóir is the most up-to-date source for vocab.
"Bia madraí" is the logical construction because it is food suitable for dogs not just one dog. "Bia madra" is a calque, i.e., a direct translation from English.
At the very least, Duolingo should make "bia madraí" an acceptable alternative answer.
PS: I've lodged a complaint with tearma.ie about the error.
It says "pending approval", but it doesn't say bia madraí.
bia madra doesn't mean food for "just one dog", it means food that is suitable for a dog - any dog. As one of the functions of the tuiseal ginideach is to allow you to use a noun as an attribute of another noun, a case can be made for bia madra, and teanglann.ie follows this logic for bia cait - "cat food", bia linbh - "baby food", bia planda - "plant food" and briosca madra - "dog biscuit", all using the genitive singular.
But bia éan - "bird food", bia coiníní - "rabbit food" and bia peataí - "pet food" use the genitive plural (and tearma.ie agrees on bia peataí).
Given the inconsistency on this point in teanglann.ie, Duolingo should probably accept both forms.
"Duolingo should probably accept both forms." That would be greatly appreciated, thank you.
I have also proposed "bia madraí" to tearma.ie and have received a message informing me that they would be considering it at their next meeting on 1 July. I'll let you know if I hear anything further from them.