AbstractWe calculated seasonal accumulation of dry matter and crude protein in sainfoin and alfalfa and feed quality at three stages of maturity when species were grown on irrigated and dryland. Maximum accumulation of dry matter and crude protein occurred between 2 and 45% bloom for alfalfa and at 100% bloom for sainfoin on irrigated land. Dry matter and crude protein yield trends for both crops were similar on irrigated land and dryland. The maximum dry matter and crude protein contents for both sainfoin and alfalfa occurred at about the same calendar date on dryland but at different dates under irrigation. Decreases in the percentage of crude protein were similar in both species with time. At all sampling dates crude protein percentage of alfalfa was greater than for sainfoin.At similar stages of maturity alfalfa was consistently higher than sainfoin in crude protein, ash, calcium, and crude fiber; and with few exceptions it was lower in nitrogen‐free extract, total digestible nutrients, and P. At the point of maximum yield for each species (10% bloom for alfalfa, 100% bloom for sainfoin) crude fiber and total digestible nutrient content was similar, but alfalfa contained 6% more protein and 9 to 10% less nitrogen‐free extract than sainfoin. We concluded that sainfoin hay would supply adequate protein to meet the needs of beef animals, and that it would supply total available energy equal or superior to that of alfalfa.