Sheep nutrition over summer and autumn

Dry pastures and stubbles lack energy and protein and hence supplementary feeding often becomes a large component of sheep diets later in summer and autumn. In addition, some vitamins and minerals may be lacking during the dry period. In this article, we cover some of the key nutritional supplements that may be required and animal health issues to keep an eye out for over summer and autumn.

Energy and protein

Meeting the energy and protein requirements of sheep is the highest priority of managing sheep nutrition. Remember that energy requirements will vary depending on how far sheep need to walk to access feed and water. Containment feeding may reduce the energy requirements of sheep because they spend less time walking in search of feed and water.

On poor to average quality pastures or hay, sheep may reach their maximum dry matter intake before their metabolisable energy requirements are met, meaning that the animal will lose weight. Grain remaining in stubble paddocks can provide a valuable source of nutrition. However, the non-grain components of stubble (stem and leaf/chaff) are typically below maintenance energy requirements for sheep. 

Dry pastures and stubbles are typically low in protein and hence supplementary feeding with a high-protein supplement is important for the growth of weaners. Supplementing rams and ewes with protein in the lead-up to joining can also help to optimise scanning results. Protein supplementation can help with the utilisation of dry pastures and stubbles, provided that the amount of feed-on-offer from the dry pasture is at least 1500 kg DM/ha (i.e. non-limiting) and digestibility is at least 50%. Energy becomes limiting for the maintenance of all classes of sheep when pasture digestibility is less than 50% and therefore feeding protein will not improve the utilisation of the dry feed. 

You can find the energy and protein requirements of sheep here to assist you with feed budgeting. Feed budget tables are available for dry/drought conditions here and for the break of season here. Regularly monitoring the weight of weaners and the weight or condition score of adult sheep is important to determine if the rate of supplementary feeding is meeting your production targets. Testing your supplementary feeds will help to more accurately calculate feed budgets and determine the cheapest source of feed per megajoule of energy and/or per kilogram of protein.

Supplementary feeding also reduces grazing pressure on pastures with limited groundcover to manage erosion and reduces the grazing pressure on establishing pastures to ensure that pasture growth rates are optimised in winter.

Vitamin and mineral supplementation

The requirement for mineral supplementation of sheep depends on several factors including your annual/winter rainfall, soil type, pasture type, whether sheep are grazing green or dry feed and the type of supplementary feed they are being fed. The following information serves as a guide for some of the vitamin and mineral deficiencies that can occur during summer and autumn. 

Vitamin E

Vitamin E and selenium work together to prevent and repair cell damage in the body. They play important roles in immune function, growth, wool production and reproduction. Vitamin E is found in green feed and hence vitamin E deficiency is a risk in late summer/autumn, after 2 to 3 months of grazing dry feed and grain. Growing lambs and weaners are most at risk, particularly those that have been born late because they will have limited body reserves from grazing green feed for less than 3 months. Selenium deficiencies are normally seen in winter/spring when green feed is rapidly growing. Symptoms of deficiencies of vitamin E and/or selenium include poor growth, stiff gait, arched back, apparent lameness, reluctance to move and sudden deaths. Vitamin E and/or selenium deficiency of sheep in Western Australia most commonly manifests as white muscle disease. Early diagnosis and treatment are needed to reduce production losses and deaths. 

Consider supplementing weaners with vitamin E in the coming weeks, particularly with the short spring in many regions. Vitamin E is available for drenching, injection or application to feed. Vitamin E drenches are an accurate method of supplementation and typically last for about 6 weeks. Multiple treatments may be required until green feed becomes available, depending on the level of deficiency. Vitamin E powder can be applied to grain and fed to sheep, which is an option where mobs are too weak to bring into the yards. Bear in mind that vitamin E degrades quickly when exposed to sunlight. Access to perennial pastures and shrubs will also supply vitamin E.

Find more information on the DPIRD webpage here.

Calcium and sodium

Cereal grains and cereal hay are high in phosphorus and low in calcium and sodium. An imbalance in the ratio of calcium to phosphorus in sheep diets can cause poor growth and disease including water belly (a.k.a. urinary calculi), hypocalcaemia and rickets or osteoporosis. Addressing the imbalance of calcium to phosphorus is important to ensure that weaners have enough calcium for bone development and that calcium reserves in the bones of ewes are not depleted before pregnancy. Sheep can be supplemented by mixing 0.5% salt and 2% limestone into the supplementary feed ration. Alternatively, they can be provided limestone and salt ad lib as a loose lick. The salt serves two purposes - it provides supplementary sodium and it increases the intake of the limestone.

Thiamine (vitamin B1) deficiency

Sheep obtain vitamin B1 through the production of the vitamin by rumen bacteria when sheep are eating a well-balanced roughage diet. Stubble tends to be low in thiamine and stubble diets also encourage the growth of bacteria in the rumen that produce an enzyme that breaks down and inactivates thiamine. Thiamine deficiency can also occur with prolonged feeding of grain, possibly due to inadequate roughage, or high sulphur intake. Thiamine is essential for brain functioning and hence sheep with thiamine deficiency become dopey, will stargaze and may look blind. Treatment is provided through drenching or injection with thiamine. Sheep treated in the early stages of disease will generally recover whilst those treated later may still recover but may have permanent nervous system issues including blindness. Disease outbreaks are sporadic and may only affect a few animals in the mob, but deaths of up to 10% have been reported.

Cobalt and vitamin B12 

Sheep require cobalt in their diet for the rumen microbes to synthesise vitamin B12, which is important for energy metabolism and the production of red blood cells. Cobalt is obtained by sheep through consuming soil and pastures/fodder crops. Hence, grazing paddocks with soils that are deficient in cobalt, mainly sandy and well-drained soils, can result in animal deficiencies. Signs of cobalt deficiency include reduced appetite, poor growth, ill-thrift, weepy eyes, anaemia and scaly ears due to photosensitisation. Cobalt deficiency is more often seen in young lambs and weaners because of their high energy demand for growth. High winter rainfall leaches cobalt from soils and results in rapid plant growth which dilutes the cobalt concentration in the plant. If lambs have been born onto pastures that are known or expected to be low in cobalt, an injectable treatment of vitamin B12 should be provided at 6-8 weeks of age (i.e. lamb marking). Cobalt deficiency can be prevented long-term by giving weaners or adult sheep an intraruminal cobalt pellet, a.k.a. bullet. Cobalt is also available as a drench or lick and it is often included in multi-mineral drenches. Cobalt sulphate is the form present in drenches and only lasts for about 2 weeks, therefore regular drenching is needed.

Other things to watch

Acidosis (a.k.a. grain poisoning): feeding sheep a high-starch diet without an adaptation period can cause rapid fermentation of the grain and overproduction of lactic acid by bacteria in the rumen, resulting in acidosis, slowing of the gut, dehydration and often death. Sheep may have a depressed appearance or be lying down, dehydrated, scouring, bloated on the left side of the abdomen or stagger. Diets high in cereal grains, particularly wheat and barley, present a risk of acidosis. Sheep should gradually be introduced to cereal grains and pellets over 10 to 20 days, depending on the feed and scenario, to allow the rumen to adapt. Find more information about how to gradually introduce grain and pellets in this DPIRD article. 

Lupinosis: lupinosis is a liver disease that results from sheep eating lupin stalks colonised by the fungus Diaporthe toxica. It is most often seen in summer and autumn. Acute disease is seen as reduced appetite, severe depression, jaundice (yellow mucous membranes), lethargy and deaths, and is most common on sandplain or WA blue lupins after summer rains. Chronic disease is expressed as loss of condition, weak animals that don’t keep up with the mob or are isolated, stiff-legged gait and hunched back, and wandering in a disorientated manner, often becoming stuck in fences or pressing their head against objects. Chronic disease is most often seen with narrow-leafed lupin stubbles or when feeding lupin seed. Treatment requires sheep to be immediately removed from the lupins and placed in a paddock with access to shade, water and good-quality hay. Lupinosis can be prevented through good management and monitoring when grazing lupin stems, and checking lupin seed for fungal infection before feeding. Find more information on the DPIRD webpage here.

Nitrate and nitrite poisoning: nitrate is normally broken down by rumen microbes into nitrite and then ammonia. Sheep can tolerate fairly high levels of nitrate in their diet provided that the intake is spread over the day and they also have access to good quality pasture or grain (i.e. readily available carbohydrates) that are needed for the activity of the rumen microbes. Relevant to summer/autumn, some stubbles, silage and hay can have high levels of nitrate, which can cause nitrate and nitrite poisoning in sheep. Several crop, pasture and weed species are associated with nitrate and nitrate poisoning, including capeweed, pigweed and variegated thistle. Other risk factors include water contaminated with nitrogen, application of nitrogen-rich fertilisers to crops and pastures, and incorporation of legumes into pastures, which can cause pastures to have high levels of nitrate. Nitrate irritates the rumen and intestine leading to scouring. Nitrite poisoning is worse and can be caused by the accumulation of nitrite in the rumen leading to high levels entering the bloodstream which subsequently prevents oxygen from being transported throughout the body. Animals are often found dead or if still alive they may have blue- or chocolate-coloured mucous membranes, difficulty breathing with gasping and rapid breaths, or be observed staggering, collapsing or convulsing before ultimately dying. Nitrate and nitrite poisoning can be prevented through grazing management, testing feed for nitrate and controlling capeweed and other risky plant species. You should seek immediate veterinary advice if you suspect nitrate or nitrite poisoning. More information is available from Agriculture Victoria and the NSW Department of Primary Industries.

Pulpy kidney: pulpy kidney is a clostridial disease that occurs when sheep are suddenly introduced to a diet high in starch and low in fibre. This causes a bacteria, Clostridium perfringens type D, that is normally found in the intestines without causing problems, to rapidly multiply and produce a toxin that poisons the animal. Lambs are often found dead or die quickly with convulsions. Adult sheep may scour or stagger and are often found dead. Pulpy kidney can be prevented through vaccination. Sheep with pulpy kidney should immediately be vaccinated, or given a booster dose if previously vaccinated, and then placed onto hay or poorer quality feed for at least two weeks whilst immunity develops. Shifting sheep onto poorer quality feed will normally stop a disease outbreak alone, however, the disease could reappear later without vaccination.

Other information sources used in this article: 

• Supplementary feeding - DPIRD
• Sheep nutritional requirements when grazing stubble - Agriculture Victoria
• AWI Extension NSW Webinar - Summer Sheep Nutrition
• Why, when & how to supplement for success - AWI Extension NSW
• Selenium and vitamin B12/cobalt - Agriculture Victoria
• Cobalt deficiency - DPIRD
• Acidosis - DPIRD
• Pulpy kidney - DPIRD

Amy Lockwood, AWI Extension WA