By analyzing the chemical composition of a cows rumen, researchers can determine the effects of different feeds and processes on bovine digestion. Many of the earliest documented reports of cannulated cows were made by researchers working to understand how feed is processed through cows. For instance, a 1939 study discovered via cannulated cows that the pH of rumen varies throughout the day, becoming most alkaline just prior to feeding. A 1956 study used cannulated cows to determine that a hay-only diet does not change the proportion of fatty acids in a cows rumen, but every other type of feed measured does.