What Entails Significant Moral Status?

I think it was very clear that Harlan Miller thought that significant moral status for, say, cows, entailed that humans are not justified in taking their life, even for purposes of efficient and respectful consumption.  With that being said, cows demonstrate much more intelligence and capacity to suffer than say, shellfish?  Would significant moral status entail the same method of treatment for nonhuman animals that are mainstream in many human diets, such as clams, oysters, muscles, scallops, ect.?