Page 36

6—
Formulating Diets for Sheep

Sheep should be fed an economical, nutritionally adequate diet. This is accomplished by combining the information given in Tables 1 and 2 on the nutritional requirements of sheep with the information in Tables 13 and 14 on the nutrients provided by various feedstuffs. The weight category is based on normal weight. If a ewe normally weights 60 kg and gains 10 kg during early gestation, the weight category to use for late gestation in determining nutritional requirements is 60 kg, not 70 kg.

Rations can be formulated on the basis of (1) providing a complete diet containing the recommended composition shown in Table 2, which, when fed at recommended levels, will provide the daily requirements recommended in Table 1 or (2) providing the specific amount of nutrients per sheep daily as presented in Table 1.

Sheep rations usually are formulated by first selecting a major feed energy source, such as hay or silage. Next, determine what nutrients the source provides and compare these values with the requirements in Table 1 or 2. Finally, determine the composition and amount of supplement that must be fed with the hay or silage to compensate for nutrient shortages.

In the following examples rations will be formulated for a 60-kg ewe suckling twin lambs during the first 8 weeks lactation. Oat hay, barley, and soybean meal are the available feeds.

Complete diet formulation

Write down the recommended nutrient composition of the diet (from Table 2) and the nutrient content of the feeds (from Table A). In this example, feeds used were analyzed by a commercial laboratory; if analyzed values are not available, use average values from Table 13.

TABLE A  Recommended Nutrient Concentration in Diets for 60-kg Ewes, First 6 to 8 Weeks Lactation Suckling Twins, and Nutrient Content of Feeds, Both on DM Basis

Item

DE (Mcal/kg)

Crude protein (%)

Ca (%)

P (%)

Carotene (mg/kg)

Vitamin A (IU/kg)

Diet
concentration

2.9

15.0

0.39

0.29

2,500

Oat hay

2.38

9.2

0.26

0.24

101.0

 

Barley

3.79

13.0

0.09

0.47

 

Soybean meal

3.53

51.5

0.36

0.75

 

Procedure

1. Compare the composition of oat hay with the ewe's requirements. The oat hay is inadequate in all nutrients except carotene (5 mg of carotene would supply the vitamin A requirement; see the section on Vitamin A on pp. 22).

2. Determine the substitution value of barley for oat hay: 3.79 Mcal DE (barley) - 2.38 Mcal DE (hay) = 1.41 Mcal DE/kg. The DE deficiency in an oat hay diet is 2.90 Mcal (required) - 2.38 Mcal (hay) = 0.52 Mcal DE. Determine the percent barley to substitute for part of the hay to provide the 0.52 Mcal DE/kg deficiency (0.52 Mcal ÷ 1.41 Mcal = 0.37). The diet at this stage becomes 37 percent barley and 63 percent oat hay.

3. Compare this combination of oat hay and barley with the dietary requirements for DM, DE, and protein (Table B).



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Page 36 6— Formulating Diets for Sheep Sheep should be fed an economical, nutritionally adequate diet. This is accomplished by combining the information given in Tables 1 and 2 on the nutritional requirements of sheep with the information in Tables 13 and 14 on the nutrients provided by various feedstuffs. The weight category is based on normal weight. If a ewe normally weights 60 kg and gains 10 kg during early gestation, the weight category to use for late gestation in determining nutritional requirements is 60 kg, not 70 kg. Rations can be formulated on the basis of (1) providing a complete diet containing the recommended composition shown in Table 2, which, when fed at recommended levels, will provide the daily requirements recommended in Table 1 or (2) providing the specific amount of nutrients per sheep daily as presented in Table 1. Sheep rations usually are formulated by first selecting a major feed energy source, such as hay or silage. Next, determine what nutrients the source provides and compare these values with the requirements in Table 1 or 2. Finally, determine the composition and amount of supplement that must be fed with the hay or silage to compensate for nutrient shortages. In the following examples rations will be formulated for a 60-kg ewe suckling twin lambs during the first 8 weeks lactation. Oat hay, barley, and soybean meal are the available feeds. Complete diet formulation Write down the recommended nutrient composition of the diet (from Table 2) and the nutrient content of the feeds (from Table A). In this example, feeds used were analyzed by a commercial laboratory; if analyzed values are not available, use average values from Table 13. TABLE A  Recommended Nutrient Concentration in Diets for 60-kg Ewes, First 6 to 8 Weeks Lactation Suckling Twins, and Nutrient Content of Feeds, Both on DM Basis Item DE (Mcal/kg) Crude protein (%) Ca (%) P (%) Carotene (mg/kg) Vitamin A (IU/kg) Diet concentration 2.9 15.0 0.39 0.29 – 2,500 Oat hay 2.38 9.2 0.26 0.24 101.0   Barley 3.79 13.0 0.09 0.47 –   Soybean meal 3.53 51.5 0.36 0.75 –   Procedure 1. Compare the composition of oat hay with the ewe's requirements. The oat hay is inadequate in all nutrients except carotene (5 mg of carotene would supply the vitamin A requirement; see the section on Vitamin A on pp. 22). 2. Determine the substitution value of barley for oat hay: 3.79 Mcal DE (barley) - 2.38 Mcal DE (hay) = 1.41 Mcal DE/kg. The DE deficiency in an oat hay diet is 2.90 Mcal (required) - 2.38 Mcal (hay) = 0.52 Mcal DE. Determine the percent barley to substitute for part of the hay to provide the 0.52 Mcal DE/kg deficiency (0.52 Mcal ÷ 1.41 Mcal = 0.37). The diet at this stage becomes 37 percent barley and 63 percent oat hay. 3. Compare this combination of oat hay and barley with the dietary requirements for DM, DE, and protein (Table B).

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Page 37 TABLE B Comparison of Dietary Requirements with Amount of Nutrients Provided in Hay-Barley Diet Item DM (% of diet) DE (Mcal) Protein (%) Dietary requirement 100.0 2.9 15.0 Oat hay 63.0 1.5a 5.8a Barley 37.0 1.4 4.8 Total 100.0 2.9 10.6 Difference – – -4.4 aValues obtained by multiplying energy or protein content in feeds by percent of feeds in diet. 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): TABLE C  Comparison of Dietary Requirements with Energy and Protein Provided by the Oat Hay-Barley-Soybean Meal Diet Item DM (%) DE (Mcal) Protein (%) Requirement 100.0 2.9 15.0 Oat hay 63.0 1.5 5.8 Barley 25.6 1.0 3.3 Soybean meal 11.4 0.4 5.9 Total 100.0 2.9 15.0 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:   Parts Percent Barley 26.6 69.1 Soybean meal 11.9 30.9 Total 38.5 100.0 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). TABLE D  Comparison of Dietary Requirements with Calcium and Phosphorus Provided by the Oat Hay-Barley-Soybean Meal Diet Item DM (%) Calcium (%) Phosphorus (%) Requirement 100.0 0.39 0.29 Oat hay 63.0 0.16 0.15 Barley 25.6 0.02 0.12 Soybean meal 11.4 0.04 0.08 Total 100.0 0.22 0.35 Difference – -0.17 +0.06 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.

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Page 38 TABLE E  Complete Diet for 60-kg Ewes, First 6 to 8 Weeks Lactation Suckling Twins Ingredient DM (%) Parts in Diet DMa Air Dry or As-Fed Basis Partsb Percentc Oat hay 88.2 63.0 71.4 62.9 Barley 89.0 25.6 28.8 25.4 Soybean meal 89.0 11.4 12.8 11.3 Limestone 100.0 0.5 0.5 0.4 Total     113.5 100.0 aAs determined in above steps. bCalculated as 63.0/0.882 = 71.4. cCalculated as 71.4/1.135 = 62.9. Up to this point, all calculations have been made on a DM basis; however, few feeds are 100 percent dry matter. To convert the portions of feeds on a DM basis to an as-fed basis (Table E), divide the contribution of the feed in question by the percent of dry matter it contains (oat hay: 63 parts of the diet DM ÷ 88.2 percent dry matter = 71.4 parts, air dry). To convert the various component parts of the diet back to percentage values, divide the number of parts for each of the ration components by the total number of parts (oat hay: 71.4 parts air dry ÷ 113.5 total parts = 62.9 percent on an as-fed basis). Dry matter intake is converted to an as-fed basis by dividing the daily feed intake given in Table 1 (2.6 kg) by 0.89 (approximate DM in the total ration) = 2.92 kg (6.4 lb) of the complete diet per day. If the feeds were hand fed separately to the ewes, 62.9 percent or 1.84 kg (0.629 × 2.92) of the as-fed diet would be oat hay and 1.08 kg (2.92 - 1.84 kg) of the diet would consist of barley, soybean meal, and limestone. The total air dry part of the barley-soybean meal-lime-stone portion of the diet is 42.1. Each feed part is divided by this value and multiplied by 100 to obtain the percent it contributes. The composition of this mixture becomes 68.4 percent barley, 30.4 percent soybean meal, and 1.2 percent limestone on an air dry basis. Formulation to provide specific amounts of nutrients (same category of ewe and same feeds) 1. Write down the ewe's daily requirement (from Table 1) and the nutrient composition of the three feed ingredients (Table F). (Dry matter per se is not a nutrient, but it is an important indication of the amount of feed the ewe can and should consume.) 2. Determine the amount of energy that the designated DM intake of the major feed ingredient (oat hay) provides (2.6 kg DM × 2.38 Mcal DE/kg of hay = 6.19 Mcal DE). The ewe requires 7.4 Mcal DE and the oat hay provides 6.19 Mcal; thus, the diet is deficient by 1.21 Mcal De. TABLE F  Daily Nutrient Requirements and Feed Composition for 60-kg Ewes, First 6 to 8 Weeks Lactation Suckling Twins Item DM (kg) DE (Mcal) Crude protein (kg) Ca (g) P (g) Carotene (mg/kg feed) Vitamin A (IU) Daily Requirements   2.6 7.4 0.405 10.7 7.7   6,000 Feed composition, dry matter basis Oat hay 88.2% 2.38 9.2% 0.26% 0.24% 101.0   Barley 89.0% 3.79 13.0% 0.09% 0.47% –   Soybean meal 89.0% 3.53 51.5% 0.36% 0.75% –   3. Assume that 2.6 kg of dry matter is the maximum amount a 60-kg ewe can consume in a day. The shortage of digestible energy in the oat hay is provided by substituting barley for oat hay: 3.79 Mcal DE/kg (barley) — 2.38 Mcal DE/kg (hay) = 1.41 Mcal DE. Divide the 1.21 Mcal DE in which the hay is deficient (step 2) by the 1.41 Mcal of additional DE that one unit of barley provides to determine the amount of barley required in addition to hay (1.21 ÷ 1.41 = 0.86 kg of barley). Thus, the 2.6-kg ration of dry matter should comprise 0.86 kg of barley DM + 1.74 kg (i.e., 2.6 - 0.86 kg) of hay. 4. Determine whether the hay-barley ration provides sufficient protein (1.74 kg of hay DM × 9.2 percent protein [from Table A] = 0.160 kg of protein from hay; 0.86 kg barley DM × 13.0 percent = 0.112 kg protein from barley; total protein from the hay — barley ration is 0.272 kg). Thus, 0.405 kg required — 0.272 kg provided by the hay-barley ration gives a 0.133-kg protein deficiency in the hay-barley ration. 5. To determine the amount of soybean meal to substitute for barley to provide the required amount of protein, calculate the difference in the protein content of soybean meal and that of barley from Table F (0.515 - 0.13 = 0.385 percent). To compensate for the 0.133 kg protein lacking in the hay-barley ration, divide 0.133 by 0.385 = 0.345 kg DM from soybean meal. The ewe's ration becomes 1.74 kg DM from hay, 0.51 kg DM from barley, and 0.35 kg DM from soybean meal. The amount of soybean meal needed to substitute for part of the barley may also be determined by the Pearson square method. 6. The calcium provided by the hay (1.74 kg × 0.26 percent = 4.5 g), barley (0.51 kg × 0.09 percent = 0.5 g), and soybean meal (0.35 kg × 0.36 percent = 1.3 g) adds up to 6.3 g, leaving a deficiency of 4.4 g (10.7 - 6.3). To determine the amount of limestone to add to compensate for the calcium deficiency, divide 4.4 by 0.34 (calcium content of limestone) = 13 g or 0.013 kg. A similar comparison for phosphorus shows the diet to be adequate in this mineral. Therefore, the daily diet per ewe on a DM basis becomes 1.74 kg oat hay, 0.51 kg barley, 0.35 kg soybean meal, and 0.01 kg limestone.

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Page 39 To convert to an as-fed basis, divide each amount of dry matter by the percent dry matter in that feed. On an as-fed basis the daily diet per ewe is 1.97 kg oat hay, 0.57 kg barley, 0.39 kg soybean meal, and 0.01 kg limestone. These are only two methods of formulating diets. Other methods include the use of simultaneous equations to algebraically arrive at a solution and the use of computers to solve more complex sets of equations. The procedures discussed in this section do not include all nutrients or effects of feed palatability, economics, and other factors that nutritionists and feed producers should consider.