Introduction
Feed costs account for approximately 80% of the expenses for an average Ontario farm. Therefore, it is imperative that producers evaluate and manage their feed resources to maximize farm profit and flock productivity. To this end, producers should work with extension personnel and nutritionists to build a solid nutritional program that includes feed analysis and ration formulation to meet the needs of the flock.
Feed Analysis
It is difficult to assess feed quality without performing a detailed chemical analysis to determine the quantity of nutrients present. A basic feed analysis will provide the producer with information on the dry matter (DM), fibre (neutral detergent fibre and acid detergent fibre), total digestible nutrients (TDN), protein, vitamin and mineral content of the feed. Knowing the level of nutrients that are available in a given feed allows for the formulation of rations that meet the nutritional requirements of animals in a given stage of production.
Water
It should be noted, however, that while formulating diets to meet the production needs of the flock is important in order to maximize productivity; all the planning and formulating can go to waste if water is not adequately supplied. It is essential that a fresh source of water be available to the flock at all times. This is particularly important for lactating ewes that require a large amount of water to produce adequate amounts of milk - and young lambs. It is recommended that one square foot of water surface be provided for every 40 ewes.
Dry Matter (DM)
Dry matter analysis actually measures the amount of moisture in the feed and is widely variable depending on the feed source. Hay and grain usually contain roughly 10% moisture, silage can contain anywhere from 50-75% and pasture plants are often 80-85% moisture. DM content is an important measurement, as it affects animal intake. For example, a ewe is that is capable of consuming 2 kg (4.4 lb) of leafy grass hay (10% moisture; 90% DM) can also consume 9 kg (19.8 lb) of leafy grass pasture (80% moisture; 20% DM). In both cases 1.8 kg (4 lb) of DM will be consumed. Therefore, expressing feed analysis, animal intake and nutrient requirement on a DM basis eliminates moisture as a variable in the comparison of different feeds and in the calculation of balanced rations.
Fibre
The fibre content of feed is expressed as Neutral Detergent Fibre (NDF) and Acid Detergent Fibre (ADF). NDF is a chemical estimate of the plant cell wall. The plant cell wall is composed largely of difficult to digest cellulose, whereas the inside of the cell contains much more soluble carbohydrates (e.g. starch). Although the animal can make use of both cellulose and soluble carbohydrates, cellulose is a more complex carbohydrate and takes longer to break down. Various types of plants will vary in proportion of cell wall versus cell contents, and generally as a plant matures the percentage of wall content will increase. A high NDF indicates that the feed has a large percentage of cell wall material. As NDF increases the animal’s intake will decrease. This is because the more fibrous the feed, the bulkier it is and the sooner the rumen will reach capacity. Very fibrous feed will also take longer to break down and be passed from the rumen.
Therefore, feed intake will be restricted by the size of the rumen. If only very fibrous feeds (high NDF) are fed, the animal may not be able to eat enough to maintain production. ADF is a measure of the digestibility of the feed (i.e. how much of the feed can actually be used by the animal). ADF values are used to calculate other measures of energy content such as total digestible nutrients.
Total Digestible Nutrients (TDN)
TDN is a measure of the energy content of the feed and is reported as a percentage. How much energy an animal requires in their diet will depend on their age, sex and stage of production. The energy content can also be expressed as digestible energy (DE), which is measured in megacalories per kg (Mcal/kg). Energy is the nutrient that is most often below the level required for production (limiting nutrient) and energy usually accounts for the largest portion of feed costs. Most energy in sheep diets comes from the cellulose and hemicellulose in forage and the starches in grain. Fats and oil are very high in energy, but are not often used in sheep diets.
Protein
It is the quantity and not necessarily the quality of protein that is important in sheep rations. Proteins vary in how easily they can be broken down in the rumen, from being completely insoluble to 100% soluble. Most types of proteins fed to sheep are relatively soluble, meaning that the rumen bacteria can digest them.
During bacterial digestion the nitrogen in the protein is released and used to maintain growth and reproduction of the microbe population. Microbes are constantly being passed out of the rumen into the abomasum and intestine, where they are broken down by the sheep’s digestive enzymes. Once they are digested they are absorbed and utilized by the animal as a protein source.
Therefore, the quality of protein fed to sheep can vary, but the quality of the microbial cell protein is consistent. Hence, relatively low quality (low cost) proteins can at times be used to supplement sheep rations. This includes non-protein nitrogen (NPN) sources, such as urea, which provide nitrogen to the rumen microbes, without having to be first broken down from a more complex true protein. In order for rumen microbes to utilize NPN, however, sufficient soluble carbohydrates (e.g. starch) must included in the diet. If there isn’t enough energy or if the NPN is fed in excess of the microbes ability to use it, the animal may suffer from toxicity. NPN use as a protein source should be restricted to maintenance diets, as it will generally not meet the protein requirements for late gestation, lactation, or lamb growth.
Protein that is not soluble in the rumen passes intact to the lower digestive tract, where it will be digested and absorbed. This type of protein is called ‘bypass protein’ as it bypasses the rumen bacteria. Bypass protein is efficiently utilized and is a means of providing protein directly to the animal, rather than indirectly through the microbes. Bypass proteins tend to be higher quality and generally more expensive.
Feeding a very high percentage of bypass protein and little soluble protein, however, is not advisable as it would result in poor microbe performance.
Minerals
Calcium (Ca), phosphorus (P), potassium (K), magnesium (Mg), salt (NaCl), cobalt (Co), iodine (I), copper (Cu), and selenium (Se) are the minerals most commonly analysed and are reported as percentages or parts per hundred (Ca, P, K, Mg, NaCl), parts per million (Co) or parts per billion (Se).
Calcium and phosphorous are expressed on feed tags as a ratio (Ca:P). Sheep can handle a Ca:P ratio anywhere from 1:1 to 7:1 as long as the minimum requirements of available calcium and phosphorous are being met. It is important that the Ca level is at least as high as the P in the diet. This is necessary as P interferes with the absorption of Ca, creating a deficiency in the animal even if the actual level in the diet is adequate. This is particularly important in growing animals and lactating ewes. Most grass and legume hays contain an adequate level of Ca while grains tend to have relatively high P levels. Ca and P are required for the maintenance of bone structure and proper muscle and nerve function. Signs of deficiency include abnormal bone development (rickets), knock knees, slow growth, “runtiness”, listlessness, depraved appetite (chewing on rocks, wood and bone) and “downer ewes”. Ewes in late pregnancy should not be fed very high levels of dietary Ca (e.g. only alfalfa hay), as this may interfere with the release of body reserves of Ca required at the onset of lactation causing hypocalcaemia.
Magnesium is closely associated with the metabolism of Ca and P and is required for proper nervous system function. Normally feeds contain adequate levels of magnesium, however, deficiency can cause grass tetany.
Cobalt is an essential trace mineral that is needed in order for vitamin B2 to be manufactured by the rumen microbes. A deficiency in cobalt may cause sheep to become thin, unthrifty and anaemic. Co is often included in salt (blue salt block)
Iodine, another trace mineral, is required by the thyroid gland for regulation of food utilization. Deficiency in iodine can cause goiter, which is commonly seen in newborn lambs born to iodine deficient ewes. Goiter can be recognized in young lambs by abnormal swelling under the throat due to an enlarged thyroid gland, abnormal wool coat at birth, still births and neonatal mortality (also frequently added to salt blocks).
Copper is widely distributed in natural feedstuffs and deficiency is rare as the recommended daily intake is low (8-15 mg/kg DM). However, copper poisoning and toxicity are common. For this reason it is not advisable to feed mineral supplements for other livestock to sheep, as the tolerance for copper is generally higher in other species. Under normal conditions, the copper supplied in feed is adequate for sheep, however, high levels of molybdenum, iron and zinc can interfere with copper uptake.
Selenium is important because of its role, along with vitamin E, in the prevention of nutritional muscular dystrophy (white muscle disease). The minimum requirement of selenium for sheep is 100 parts per billion, and when fed to ewes at this level it will prevent white muscle disease in young lambs.
Vitamins
Vitamins can be broken down into two main groups: fat-soluble and water-soluble. Fat -soluble vitamins include vitamins A, D, E, and K, which can be stored in the liver and body fat during periods of abundant supply and rationed out from these organs when supplies become scant. Water-soluble vitamins, which cannot be stored for future use, include B-complex vitamins and vitamin C. B-complex vitamins are manufactured by rumen bacteria in adequate amounts on a daily basis, provided the animals are supplied with enough energy, protein and minerals to enable the bacteria to do so. Vitamin C is manufactured in the animals’ tissue.
Vitamin A is not synthesized by ruminants and, therefore, needs to be supplemented in the diet. It is essential for sight and the maintenance of tissues (the lining of the digestive tract and the reproductive tract), lungs, eyes and skin. Vitamin A is provided through green forages. However, it is lost as stored hay ages. Therefore, vitamin A supplementation may be needed if you are feeding hay older than 4-5 months.
Ration Formulation
The goal of ration formulation is to prepare a feeding program which meets the animal’s nutrient requirements, is properly balanced, palatable, promotes or discourages intake (depending on the purpose of the ration), is suitable for a given management situation and is reasonably priced. To this end, there are a number of questions that need to be asked:
What type, age, weight of sheep is being fed?
- What is desired production level and rate of gain?
- What feeds are available for use for the formulation?
- Are these feeds home-grown or are they purchased?
The Ontario Ministry of Agriculture and Food offers a Sheep Ration Formulation Service, as do most feed companies.
Feedstuffs
Sheep can utilize a wide variety of feedstuffs. Feeds are classified into groups based on their nutrient content and physical form. Most common feeds can be placed in one of the following groups:
Roughages (forages): (Note: Most mature sheep will require ~4-5lbs of hay/day through the winter)
Grass forages (hay or pasture)
- high in fibre (cellulose) and usually low to intermediate in energy
- protein content varies, depending on the plant species and stage of maturity, typical range in crude protein could be as varied as 5 to 12% (i.e. grass are highest in protein and lowest in fibre early in the growth period, as the stem matures and after ‘setting seed’ the protein level will drop significantly)
- examples are timothy, crested wheat, fescues, etc.
Legume forages (hay or pasture)
- fibre dependent on stage of growth and leave content (e.g. mature alfalfa has a high stem to leaf ratio)
- protein content is higher than grass forages, generally above 16-20% (legumes are able to fix nitrogen in the soil)
- because of particular proteins in legumes, caution should be taken when first feeding legume forages (i.e switching from grass hay, or turning onto pasture in the spring) to prevent frothy bloat.
- Examples are alfalfa, clovers, etc.
Silage
- silage is produced when green forage is preserved using fermentation (acidification in the absence of oxygen)
- the major advantage of silage is that the crop can be harvested when it is ready in almost all weather conditions (hay must be dried to ~90% dry matter before baling to prevent spoilage, whereas silage is stored with a dry matter content of 40-60%).
- when exposed to oxygen, silage may spoil. Improperly stored silage may cause problems such as listeriosis in sheep including corn, barley etc ensiling is not restricted to grasses and legumes; silage can be made from a wide range of crops
- compared to hay, harvesting, storing, and feeding silage can require a greater capital investment in equipment and facilities.
Green Feed
- forage is not dried thoroughly before baling
- may be used as a means of making use of a poor harvest or if conditions are poor during haying
- mildew and moulds can be a problem
Concentrates (grains and commercially mixed rations)
- high in energy and relatively low in fibre
- fibre level depends on processing of the grain; grains that are pelleted or crushed will have a much lower fibre content than whole grains with the hull included (some studies indicate that lamb performance is better and there are fewer digestive upsets with whole grains)
- most have a moderate protein content (~12% crude protein)
- examples are corn, barley, oats, commercial mixes
Protein Supplements
- high in protein, usually high in energy
- variable fibre content
- examples are oilseeds (soybeans, canola meal)
Mineral Supplements
- may be included in a commercially mixed ration or supplied by free choice access to mineral blocks or loose mineral
- do NOT purchase cattle mineral supplements, as the copper is often too high for sheep. A list of the energy and protein content of some common feeds is contained in Table 1. Remember that although these figures will give you a good idea of nutrients in different feeds, you must have you feed analysis for accurate values.
Feeder Space and Design
In confinement production systems, adequate feeder space is a must in order to ensure that all animals have an equal opportunity to consume their daily ration. Feeder space requirements vary according to sheep size, fleece length and type of feed. The amount of space required is lower when feed is available free-choice than when sheep are hand fed. When hand feeding is practiced, feeder length should allow all the sheep in a group to feed at one time. When free-choice feeding occurs, sheep have access to the feed at all times.
It is recommended that that 400 mm (16”) of feeder space be provided for ewes and rams if all animals are hand fed. When free choice feed is offered, 150 mm (6”) per animal is required for ewes and rams. Feeder lambs that are hand fed require 300 mm (12”) per animal; whereas, when fed free-choice the animals require only 100 mm (4”) per animal. The type of operation and feeding space required will influence feeder design. Other considerations include:
- obtaining feed is natural and comfortable for all sheep
- feed does not become contaminated by animals defecating or jumping into feeders
- openings are sized to allow easy access to feed but prevent sheep being injured or trapped
- the sheep cannot be injured by sharp corners, nails etc.
Body Condition Scoring
Body condition scoring is an aspect of flock nutrition that is often overlooked. It is important to condition score the flock in order to determine how it is responding to the current feeding regime. If body condition scoring is not done, it is difficult to determine if the current feeding program is meeting the production needs of the flock.
Body condition scoring is easy to use and implement. The system is based on a scale of 0 to 5, where 0 depicts the thinnest animals and 5 the fattest. The score is based on the amount of fat present at key points on the animal – specifically around the vertebrae and the loin region. Visual assessment for condition can be obscured by differences in individual conformation and wool.
Therefore, to accurately determine an animal’s body condition it is often necessary to actually feel for fat cover by hand. A description of each condition score is listed in the Code of Practice at the back of this binder. If you are undecided between two values, it is recommended that you assign a half score. For example, if undecided about whether an animal is a 3 or a 4, you should assign a condition score of 3.5. Body condition scoring is a subjective means of categorizing animals - in that people may have differing opinions for what type of fat cover will constitute a particular score. For instance one person may consistently rank a particular fat cover as a ‘4’, while another may rank it as a ‘3.5’. As long as you are relatively constant in your assessment of your sheep, this variation between people is not overly important. It is advisable, however, to have the same person scoring the same group of animals each time they are assessed. See the Recommended Code of Practice at the back of this binder for details on how to condition score sheep
Author: Reprinted in part from ‘Nutrition Guide for BC Sheep Producers’ written by Dr. Steve Mason and published by the Province of British Columbia. (Modified by OSMA, 2010)
