Commentary
The pronoun in: بُطُونِہٖ (butunihi: their bellies) reverts back to: (al-an am: cattle). Since the word al-an’ am is plural in the feminine gender, it required that the word used for it should have been: بُطُونِھَا (butuniha), as it appears in Surah Al-Mu'minun: نُّسْقِيكُم مِّمَّا فِي بُطُونِهَا (We provide you, out of what there is in their bellies - 23:21).
Al-Qurtubi explains this by saying that consideration has been made of the meaning of the plural in Surah Al-Mu'minun where the pronoun has been used in the feminine gender. And, in Surah Al-Nahl, the pronoun has been used in the masculine gender in consideration of the plural word as such. Examples of this usage abound in Arabic where a singular pronoun is made to revert to a plural word.
As for bringing out pure milk from between feces and blood, Sayyidna ` Abdullah ibn ` Abbss ؓ said: When the fodder eaten by an animal settles in its stomach, the stomach heats it up as a result of which the waste by-product from the fodder settles down leaving milk above with blood being on top of it. Then, nature has entrusted the next job with the liver. It separates the three and directs them to where they be-long. Blood goes to veins. Milk goes to the udder of the animal. Now, left in the stomach is waste which is excreted as feces or dung.
Rulings
1. From this verse we learn that eating good food is not against Zuhd (the way of life marked by not inclining towards worldly enjoyments for the sake of maintaining an ideal state of spiritual purity) specially when it has been acquired with Halal (lawful) means and provided that no extravagance has been made in it. This is as stated by Hadrat Hasan al-Basri (رح) . (Al-Qurtubi)
2. The Holy Prophet ﷺ has said: When you eat something, say: اللھم بارک لٰنا فیہ وَ اَطعِمنَا خَیراً مِّنہُ Y Allah, bless it for us and have us eat better than it.
And he said: When you drink milk, say اللھم بارک لٰنا فیہ وَ زِدنَا مِنہُ Allah, bless it for us and give us more of it.
In the second prayer, he did not ask for something 'better than it' (as in the first prayer) for, in human cuisine, there is no nutrient better than milk. Therefore, nature has made milk the very first food given to every man and animal through breast-feeding by mothers. (Al-Qurtubi)