нигоҳ доштан: to keep, to look after
Milk and dairy products are kept in the fridge.
Дар нигоҳ доштани саломатӣ дуруст хӯрок хӯрдан муҳим аст.
Eating right is important for looking after your health.
гов (мурғ) нигоҳ доштан: to keep/raise cows (chickens)
нигоҳдор: keeper, protector, guard
In Tajik it is less common to use the passive voice and more common to use the third person plural, as in the first sentence. You could also translate it “They keep milk and dairy products in the fridge”.