The diet is now adequate in digestible energy but is 4.4 percent deficient in protein.
4. Substitute soybean meal for barley to provide for the protein deficiency. Determine the difference in crude protein content of the two feeds: 51.5 percent (soybean meal) - 13.0 percent (barley) = 38.5 percent protein. Divide the amount of protein that is deficient (4.4 percent) by the amount provided when soybean meal is substituted for a unit of barley: 4.4 percent divided by 38.5 percent = 0.114, or 11.4 percent of the entire ration will be soybean meal. The diet becomes (Table C):
The diet is now adequate in both digestible energy and protein.
The Pearson square method may also be used for determining the amount of soybean meal to add to the barley. The hay contains 9.2 percent protein (see Table A) but constitutes only 63.0 percent of the ration (see Table C). Thus, the hay provides 5.8 percent (9.2 percent × 0.63) protein to the total ration. The dietary requirement of 15.0 percent protein (see Table C) - 5.8 percent protein from hay = 9.2 percent protein that must be provided in the 37.0 percent barley-soybean meal part of the ration. Thus, 9.2 percent ÷ 37.0 percent of the ration = 24.9 percent protein required in the barley-soybean meal mixture. The next step is to determine the parts of barley and soybean meal needed in the ration to provide the 24.9 percent protein requirement.
The parts of barley needed in the barley-soybean mixture can be calculated by subtracting diagonally the percent protein required (24.9) from the percent protein in the soybean meal (51.5), which equals 26.6 parts barley. The same method gives 11.9 parts soybean meal required. Then, 26.6 parts barley ÷ 38.5 total parts equals 69.1 percent barley required in the mixture; 11.9 parts soybean meal ÷ 38.5 total parts equals 30.9 percent soybean meal:
If there is 30.9 percent soybean meal in the 37 percent portion of the ration that is provided by the barley-soybean meal mix, then in the entire hay-barley-soybean meal diet there is 0.37 × 30.9 = 0.114 = 11.4 percent soybean meal.
5. Write down the calcium and phosphorus requirements and compare these with the amounts provided by the hay-barley-soybean meal diet (Table D).
The diet is adequate in phosphorus but is 0.17 percent deficient in calcium. Limestone is a rich (34 percent) and inexpensive source of calcium (Table 14). Dividing the 0.17 percent deficiency by the 34 percent calcium in limestone gives 0.5 parts limestone that should be added to the diet.
The final diet now becomes as shown in Table E (parts, DM basis). When fed at the levels recommended in Table 1, it will satisfy the daily requirements for this category of sheep.