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Can I say,

He is feeding at the coop.

He is feeding chickens at the chicken coop.

He is feeding chickens with grains at the coop.
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He is feeding his chickens at the coop.

He is feeding the chickens at the chicken coop.

He is feeding his chickens with grain at the coop.
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Can I say,

He is feeding his chickens grain at the coop.

P/s: Grain is a plural or singular uncountable?
'Grain' is a non-count noun when it refers to a kind of cereal. As a tiny unit (a grain of salt) it is countable.
Thanks, if i say,

She is feeding milk to her baby.

She is feeding her baby with milk / with a bottle of milk.
Students: We have free audio pronunciation exercises.
She is feeding her baby. -- Any more than this is not normal.