More than you think! A first word is something that your child says intentionally, the same way every time and consistently - to get or communicate what they want.
E.g. A 7 month old babbling "dada" whilst with parents and playing with toys is likely NOT a true word. But a 10 month old who says "dada" whilst looking at Daddy and says it consistently every time Daddy walks in the room is most likely saying a real word.
With talking, the word your child says has to sound similar to the real word but it doesn't have to be perfect. It takes YEARS to perfect all the sounds in speech so we can't expect too much! If your baby says "ta" in the same way every time they see a cat, it's likely they're saying their first word they just can't say all the sounds correctly yet!
YES animal noises count! If your baby says "moo" every time they see a cow, that's them knowing what a cow is and communicating with you that they know by naming it in the only way they know how - the way you've modelled!!! That's a word!
SIGN. If your baby signs then they've communicated their first words. Most babies can sign MONTHS BEFORE they can verbally communicate as it takes way more practice to coordinate the muscles of the mouth than it does to move their hands. This means babies who are taught to sign are developing expressive language earlier than those who aren't taught sign. This has a ton of benefits including well being and ongoing learning/intelligence, So SIGN TO YOUR BABIES!
Some children never get the mouth control to talk verbally or take a little longer to get there and need an alternative way to communicate, but that doesn't mean they won't have first words! They might share using a picture system on paper or on a device like an ipad. As long as they point to/indicate on the same thing CONSISTENTLY in the presence of the object, those are first words too!!
My son's first words were signs 'milk' and 'again'. His first verbal words were "cheese", "banana", "eat" and a handful of other foods! He's very food driven!
What were your baby's first words?