PROTEIN QUALITY EVALUATIONS OF SELECTED CULTIVARS OF WHEAT, MEASURED BY CHEMICAL SCORES AND MOUSE BIOASSAYS
Wheat cultivars, Glenlea, Inia-66, Neepawa, Pitic-62 and Twin, and Bonanza barley, were fed to mice in digestibility and protein quality evaluation trials. In the digestibility trial each diet contained 94.7% test grain, plus mineral and vitamin supplements and 0.55% chromic oxide fecal marker. Digestibility of energy ranged from 79.3% (Twin) to 83.4% (Neepawa). Digestibility of protein ranged from 71.0% (Twin) to 84.4% (Neepawa). Crude protein (CP) (N × 6.25) ranged from 11.8% (Twin) to 15.8% (Neepawa) and affected the protein apparent digestibility coefficients. In the 14-day growth trials the grains were compared in four ways: (a) as 94.7% of the diet, (b) in diets containing 9% CP, (c) in diets containing 9% CP plus amino acids to meet the requirements for growth of the mouse and (d) in diets containing 7% CP. Casein control diets were used. In (a) mice fed Twin wheat and Bonanza barley gained less than all others. In (b) all wheats resulted in slower growth than barley or casein but Twin had better protein than Inia-66 and Pitic-62, reflecting lysine contents. In (c) all wheats supplemented with amino acids equalled casein in terms of growth. In (d) the responses to 7% CP diets were inferior but parallel to those from 9% CP diets. In the protein quality evaluations barley ranked highest in relative growth index, protein efficiency ratio and net protein ratio. Twin wheat ranked second and Pitic-62 ranked last. Lysine was the first-limiting amino acid in all wheats, having from about 59 to 64% of the level required by 20- to 35-kg pigs. Isoleucine was second-limiting except for Glenlea with threonine. Key words: Wheat, cultivars, protein quality, mouse assays, digestibility