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Sheep Nutrition & Balancing Rations

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Sheep Nutrition & Balancing Rations
Sheep are ruminants, which means they have a four-chambered stomach, consisting of the rumen, the reticulum, the omasum, and the abomasum. They also chew cud and have no teeth on their frontal upper jaw. As ruminants, they are efficient converters of vegetation to meat, milk, and wool, becoming the base to a profitable farming operation.

Feeding sheep to meet their nutritional needs will help keep them healthy and perform to their maximum genetic potential, including maximizing their growth rate, feed efficiency, prolificacy, and fertility.

All sheep should have access to fresh clean water, sheep-specific loose minerals (sheep will chew on mineral blocks which will cause wear on their teeth and may even break their teeth), and hay or pasture. Follow the directions on the feed tag when feeding minerals or any bagged feed or supplement. When you first put minerals out, the sheep will eat a lot of it, but consumption will level off as they begin to meet their needs.

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Sheep have a few basic requirements:

ENERGY
Energy is also referred to as calories. Energy deficiencies cause slow growth rates, loss of weight, reduced fertility, lowered milk production, and reduced quality and quantity of wool. In animal nutrition, energy (calories) are measured in Total Digestible Nutrients (TDN) or Digestible Energy (DE). TDN is measured as a percent of the Dry Matter (DM) in the feed. Conversely, DE is measured as the difference between the gross energy in the feed and the gross energy left in the manure in terms of megacalories (equivalent to 1,000,000 calories) per pound (Mcal/lb).

To calculate the % TDN of a feed (often it is not listed on tag labels), subtract the % crude protein from 80. So for example, Southern States' 16% textured sheep feed is 9% fiber.

% TDN = 80 - 9
% TDN = 71

To convert DE to % TDN, divide the Mcal/lb by 2. If DE is listed as Mcal/kg, divide it by 4.4. Many sheep producers convert DE to TDN because TDN is easier to work with and a lot of ration calculators developed by universities use TDN.

PROTEIN
Protein is a measurement of nitrogen in the feed. It is important to sheep because it promotes growth, wool production, and milk production. Protein is often measured as Crude Protein (CP) in terms of grams or pounds.

The best protein supplements are animal byproduct meals, however, most are illegal to use in ruminants. The next best option is oil seed meals, such as soybeans, cottonseed, sunflowers, linseed, and peanuts. Lastly, legume hays, are adequate protein supplements, though some pregnant ewes may require more protein than provided in the hay.

DRY MATTER
Dry Matter (DM) is measured in pounds and is the weight of the feed with moisture (water) taken out. The weight of the feed with moisture (water) in it is called "As-Fed." As-fed is the actual amount of feed you are putting out to your sheep for them to consume. Sheep require anywhere from 1.5 - 6% of their body weight in dry matter daily, depending on age and stage of production. To determine how much feed you need on an as-fed basis to meet the requirement for dry matter, divide the percent of dry matter by the dry matter requirement to get the amount to feed in pounds. For example, you have a 154 lb ewe in maintenance with a 2.6 lb DM requirement. You plan on feeding a grass mix hay with 89% dry matter.

As-Fed = 2.6 lbs DM / 89% DM
As-Fed = 2.92 lbs

In short, you would need to feed this ewe 2.92 lbs of your grass mix hay to meet her dry matter requirement.

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MINERALS

Around 15 minerals have been deemed essential for sheep; seven are major and eight are trace. The major mineral elements include sodium, chlorine, calcium, phosphorus, magnesium, potassium, and sulfur. The trace mineral elements include iodine, iron, molybdenum, copper, cobalt, manganese, zinc, and selenium.

About the Calcium: Phosphorus ratio: Sheep require a 2:1 Ca: P ratio in their ration. However, the ratio is more important in most cases than the total amount of calcium or the total amount of phosphorus in the ratio. That said, sheep can tolerate a ratio of up to 7:1 as long as the amount of phosphorus is adequate. When diets contain too much calcium (above the 7:1 ratio usually), there may be a deficiency of other minerals, such as phosphorus, magnesium, iron, iodine, zinc, and manganese. When the ratio becomes lopsided (too much phosphorus and not enough calcium), metabolic issues such as tetany and urinary calculi tend to appear quickly; slower issues such as skeletal signs of Calcium deficiency will begin to appear.

Minerals are often measured in grams, which need to be converted to pounds for most ration balancing. One gram is equivalent to 0.0022 lbs.

Mineral Deficiencies
Salt (NaCl): Decreased feed and water intake (Sodium Requirement: 0.09 - 0.18%)
Calcium (Ca): Urinary calculi, grass tetany, poor bone development (Requirement: 0.20 - 0.82%)
Phosphorus (P): Poor bone development/rickets, poor growth, lack of appetite, unthrifty appearance, listlessness (Requirement: 0.16 - 0.38%)
Magnesium (Mg): Grass tetany, excess salivation, frothing at mouth (Requirement: 0.12 - 0.18%)
Potassium (K): Lack of appetite, poor growth, listlessness, stiffness (Requirement: 0.50 - 0.80%)
Sulfur (S): Lack of appetite, poor growth, poor growth of wool, shedding wool (Requirement: 0.14 - 0.26%)

Iodine (I): Goiter, lambs born with no wool (Requirement: 0.10 - 0.80 ppm; Toxic Level: 50 ppm)
Iron (Fe): Poor growth, increased respiration rate, anemia, lethargy/depression (Requirement: 30 - 50 ppm; Toxic Level: 500 ppm)
Molybdenum (Mo): (Requirement: 0.50 ppm; Toxic Level: 10 ppm)
Copper (Cu): Steely/stringy wool (adults), swayback (lambs) (Requirement: 7 - 11 ppm; Toxic Level: 25 ppm)
Cobalt (Co): Lack of appetite, weight loss, few heat cycles (Requirement: 0.10 - 0.20 ppm; Toxic Level: 10 ppm)
Manganese (Mn): Stunted growth, abnormal skeleton development, incoordination of lambs (Requirement: 20 - 40 ppm; Toxic Level: 1000 ppm)
Zinc (Zn): Lack of appetite, stunted growth, parakeratosis, reduced reproduction (Requirement: 20 - 33 ppm; Toxic Level: 750 ppm)
Selenium (Se): White muscle disease, unthriftiness, abortion/miscarriage (Requirement: 0.10 - 0.20 ppm; Toxic Level: 2 ppm)

BALANCING RATIONS
Sheep should always have their rations balanced (except for when they are on pasture or on range, where it is difficult to get nutrient composition and consumption levels for the grass) to make sure they are meeting their nutritional requirements to prevent deficiencies and toxicities and to save the producer money (why pay for extra nutrients your animals don't need?).

Rations should be balanced on a dry matter basis first and then be converted to an as-fed basis plus any waste (such as 10% for hay).

To balance a ration, you should balance it for energy first, then protein, and then minerals. Use your roughage (such as hay, silage, or haylage, etc) as a starting point, and then add grain or feed to the roughage to balance it.

Knowing the nutritional requirements of sheep and the nutritional composition of feedstuffs is the key to balancing rations.
  • For an excel spreadsheet of nutritional requirements of sheep, click here.
  • For an excel spreadsheet of nutritional composition of feedstuffs, click here.

Example
You have a 132 lb ewe in late gestation expecting twins. She requires 4 lbs of DM, 2.6 lbs of TDN, 0.45 lbs of CP, 6.9 g of Ca, and 5.2 g of P.

You plan on feeding orchardgrass hay, which consists of 88% DM, 59% TDN, 10% CP, 0.32% Ca, and 0.30% P.

So first, calculate the amount of TDN in the 4 lb DM requirement of the ewe for the orchardgrass hay.

4 lbs of DM x 59% TDN = 2.36 lbs TDN in orchardgrass hay

Your ewe requires 2.6 lbs of TDN.
2.36 lbs TDN provided in hay - 2.6 lbs TDN requirement = -0.24 lb TDN deficiency

Because of the deficiency, you will need to add an extra source of energy to her ration. To do this, you could use hay at 59% TDN, or you can add a more nutrient dense feed, such as corn, which is 88% TDN. Because corn is higher in TDN, it is also a cheaper source of energy than hay, so it may be an economical energy supplement to your ration.

But before we get to that, let's see how much protein the hay provides the ewe.

4 lbs DM x 0.1% CP = 0.04 lb CP

Your ewe requires 0.45 lbs of CP.
0.4 lb CP provided in hay - 0.45 lb CP requirement = -0.05 CP deficiency

You may need a protein supplement if the energy supplement does not provide enough protein (in late gestation, that is usually not the case).

To calculate the additional energy requirement, you can use a Pearson's square. In the upper lefthand corner, write the % TDN in the hay. In the lower lefthand corner, write the % TDN in the corn. In the center, write the % TDN requirement for your ewe (lb TDN requirement / lb DM requirement). Subtract the % TDN in the hay by the requirement in the center box and the % TDN in the corn by the requirement in the center box to get the ratio of hay and corn needed to meet the ewe's need for energy.

For energy:
Hay: 59...................Hay: 23
.................65..................
Corn: 88...................Corn: 6
...........................Total: 29

Essentially what the Pearson's Square tells you is how many parts of hay to feed to how many parts of corn. So, for the hay, you need 23 out of 29 parts, which is equal to 79.3%. And corn is 6 out of 29, which is equal to 20.7%.

So then you take the ewe's DM requirement again and multiply it by the percentages calculated in the Pearson's Square.

So 4 lbs DM x 79.3% = 3.172 DM lbs of hay
And 4 lbs DM x 20.7% = 0.828 DM lbs of corn

Now, we have to go back and calculate the CP in the new ration. Again, the hay is 10% protein, and corn is 9% protein.

3.172 DM lbs of hay x 10% CP = 0.3172 lb CP
0.828 DM lbs of corn x 9% CP = 0.07452 lb CP

0.3172 lb CP + 0.07452 lb CP = 0.39172 lb CP in the ration

0.39172 lb CP - 0.45 lb CP (requirement) = -0.05828 lb CP deficiency

Now because of the CP deficiency, we have to add a protein supplement to the ration.

First, we have to figure out the % CP in the current hay/corn ration. So take 0.39172 lb CP in the ration and divide it by 4 lb DM requirement and the % CP is around 9.8%.

Now, we set up another Pearson's Square -- this time, for CP. The requirement for CP for this ewe is 11.25% (0.45 lb CP / 4 lb DM requirements). You decide to use soybean meal, as it is cost effective for adding protein to a ration.

For protein:
Hay/corn: 9.8..................Hay/corn: 36.75
.........................11.25..........................
Soybean meal: 48..............Soybean meal: 1.45
...................................Total: 38.2

So now, your new ration will consist of 96.2% of your hay/corn ration and 3.8% of soybean meal.

4 lb DM requirement x 96.2% = 3.848 DM lbs hay/corn
4 lb DM requirement x 3.8% = 0.152 DM lbs SBM

We're not quite done yet!

Our hay and corn ration consisted of 79.3% hay and 20.7% corn.

So now, we take the 3.848 DM lbs and multiply it by 79.3% (hay) and 20.7% (corn) and get 3.05 DM lbs and 0.8 DM lbs, respectively.

Now we have to convert our DM lbs to as-fed.

3.05 DM lbs / 88% DM = 3.47 lbs orchardgrass hay
0.8 DM lbs / 88% DM = 0.91 lbs corn
0.152 DM lbs / 91% DM = 0.14 lbs SBM

So, to feed a 132 lb ewe in late gestation who is expecting twins, you can feed her 3.47 lbs of orchardgrass hay, 0.91 lbs of corn, and 0.14 lbs SBM to meet her energy, protein, and DM requirements. You can go further and do more Pearson's Squares for Ca and P.

To make your work speedier, many university extension programs have developed spreadsheets to automatically calculate your rations for you.

Note: In this example, I used sheep nutritional requirements from the 1985 published edition of Nutrient Requirements of Sheep. It has been revised in 2007 to account for internal capacity of the ewe for the amount of feed she has to eat to meet her needs. So the amounts of the feeds calculated in this example are likely higher than what they should be.

SOURCES
  • "Balancing Rations" by Susan Schoenian, Sheep 201
  • "Balancing Rations for Sheep & Goats" by David Fernandez, Extension Livestock Specialist at University of Arkansas at Pine Bluff Cooperative Extension Program
  • Nutrient Requirements of Sheep, 6th Revised Edition, 1985
  • Sheep Pocket Guide by Roger G. Haugen, Extension Sheep Specialist at North Dakota State University Extension Service
  • SID: Sheep Production Handbook, American Sheep Industry Association, Inc.
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  1. Nutrient requirements, nutritent composition of feedstuff, Ca: P ratio info added

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Well written and easy to understand for the reader. Great information!
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