Cassava
Cassava (tapioca, manioc; Manihot esculentis crantz) is a perennial woody shrub that is grown almost entirely in the tropics. It is one of the world’s most productive crops, with possible yields of 20 to 30 tonnes of starchy tubers per hectare (Oke, 1990). Cassava is an approved ingredient in organic pig diets, although in many countries it will represent an imported product not produced regionally.
NUTRITIONAL FEATURES Oke (1990) reviewed the nutritional features of cassava. Fresh cassava contains about 65% moisture. The DM portion is high in starch and low in protein (20–30 g/kg, of which only about 50% is in the form of true protein). Cassava can be fed fresh, cooked, ensiled, or as dried chips or (usually) as dried meal. The meal is quite powdery and tends to produce a powdery, dusty diet when included at high levels. Cassava meal is an excellent energy source because of its highly digestible carbohydrates (700–800 g/kg), mainly in the form of starch. However its main drawback is the negligible content of protein and micronutrients.
ANTI-NUTRITIONAL FACTORS Fresh cassava contains cyanogenic glucosides (mainly linamarin), which on ingestion are hydrolysed to hydrocyanic acid and reduce pig growth. Boiling, roasting, soaking, ensiling or sun-drying can be used to reduce the levels of these compounds (Oke, 1990). Sulphur is required by the body to detoxify cyanide; therefore the diet needs to be
adequate in methionine and cystine. The normal range of cyanide in fresh cassava is about 15–500 mg/kg fresh weight. It is recommended that pig diets should contain no more than 100 mg HCN equivalent/kg.
PIG DIETS Research has shown that properly processed cassava can replace maize in pig diets (Oke, 1990). Because of its powdery nature, low levels of protein and economics, the usual recommended maximum inclusion level is 400 g/kg diet. Dustiness of cassava-based diets can be reduced by adding molasses, suitable oils and by pelleting. Another possible limiting factor is the ash content. Mülleret al. (1974) suggested that, with ash content less than 22 g/kg and CF content of 28 g/kg, the maximal inclusion of cassava can be 600 g/kg for grower diets and 750 g/kg for finisher diets. With ash and CF contents greater than 50 g/kg the corresponding maximal inclusion rates can be 200 and 400 g/kg, respectively. Limited studies suggest that cassava can be incorporated successfully in gestation and lactation diets for sows (Oke, 1990).
Potatoes (Solanum tuberosum)
On a worldwide basis this crop is superior to any of the major cereal crops in its yield of DM and protein per hectare. However the potato is especially susceptible to disease and insect problems and may have received chemical treatment. Therefore any potatoes should meet organic guidelines, including being from non-GM varieties.
This tuber crop originated in the Andes but is now cultivated all over the world except in the humid tropics. It is grown in some countries as a feed crop. In others it is available for animal feeding as cull potatoes or as potatoes surplus to the human market. In addition to raw potatoes, the processing of potatoes as human food products has become increasingly common. Potatoes are also used in the industrial production of starch and alcohol. By-products of these industries are potentially useful feedstuffs.
The nutritive value of these by-products depends on the industry from which they were derived. Potato protein concentrate provides a high-quality protein source, whereas potato pulp, the total residue from the starch extraction industry, or steamed peelings from the human food processing industry provide lower-quality products for swine feeding because of their higher CF and lower starch content.
NUTRITIONAL FEATURES As with most root crops, the major drawback is the relatively low DM content and consequent low nutrient density.
Potatoes are variable in composition, depending on variety, soil type, growing and storage conditions and processing treatment. About 70% of the DM is starch, the CP content is similar to that of maize and the fibre and mineral contents are low (with the exception of potassium). Potatoes are very low in magnesium. Since magnesium is not usually added to pig diets, special attention should be paid to this mineral to ensure it is not deficient
in pig diets containing potatoes. Of the total nitrogen in the potato tuber, 30–50% is in the form of soluble protein, 10% is insoluble protein (located mainly in the skin) and the remainder is NPN (Edwards and Livingstone, 1990). Thus potatoes are essentially a source of energy.
The DM concentration of raw potatoes varies from 180 to 250 g/kg.
Consequently, when fed raw, the low DM content results in a very low concentration of nutrients per unit of weight. Expressed on a DM basis per kg, whole potatoes contain about 60–120 g CP, 2–6 g fat, 20–50 g CF and 40–70 g ash. Potato protein has a high biological value, among the highest of the plant proteins, and similar to that of soybeans. The AA profile, g/100 g CP, is typically lysine 5.3, cystine + methionine 2.7, threonine 3.2 and tryptophan 1.1. In potato protein concentrate, these values are higher (6.8, 3.6, 5.5 and 1.2 g/100 g CP, respectively) and compare very favourably with the composition of the ideal protein for pig growth (Edwards and Livingstone, 1990). The first-limiting AA in potato is generally methionine or isoleucine, and the high lysine content makes potato protein a good complement to cereal protein. Whittemore (1977) and Edwards and Livingstone (1990) published extensive reviews of the value of potatoes as a feedstuff for pigs, calves and fowl. They concluded that potatoes are potentially important as stock feed but that their use in pig feeding has given mixed results.
Raw potatoes are unpalatable to pigs (Braude and Mitchell, 1951) and are not well digested. It is now known that factors associated with the low digestibility include the structure of the starch granule, which in raw potatoes is resistant to attack by amylase in the digestive tract of the pig.
Much of the starch therefore passes undigested into the caecum and large intestine where it is degraded by bacterial action (Whittemore, 1977;
Livingstone, 1985), usually resulting in digestive upsets. Therefore raw potatoes should be boiled or steamed before being fed. Cooking disrupts the granular structure of the starch, allowing it to be broken down by digestive enzyme and digested. Livingstoneet al. (1979) reported that for best results potatoes should be boiled for 30–40 min, steamed at 100°C for 20–30 min or simmered for 1 h, to ensure thorough cooking through to the centre, and then rapidly cooled. Prolonged heating, or slow cooling after heating, results in damage to the protein and a reduction in its digestibility.
A typical analysis of cooked potatoes is 222 g DM/kg, 23 g CP/kg, 7 g CF/kg, 4 g ether extract/kg and 1 g ash/kg, with a DE value of 3.83–4.02 kcal/g DM (Whittemore, 1975; Pond and Maner, 1984). Whittemore (1977) and Edwards and Livingstone (1990) concluded that cooked potato is approximately equal to maize in DE and digestible protein contents and is palatable to pigs of all ages.
ANTI-NUTRITIONAL FACTORS The protein fraction in raw potato is poorly digested, due to the presence of a powerful protease inhibitor (Whittemore et al., 1975). This inhibitor is destroyed by cooking, being absent in cooked potato (Livingstone et al., 1979). The inhibitor has been shown to cause a reduction in nitrogen digestibility not only in the potato itself but also in
other feedstuffs in the diet (Edwards and Livingstone, 1990). Potatoes may contain the glycoside solanin, particularly if the potatoes are green and sprouted, and may result in poisoning. Consequently, such potatoes should be avoided for feeding. The water used for cooking should he discarded and not fed to pigs because it may contain the water-soluble solanin.
Ensiling was found to be ineffective in removing the factors associated with the low palatability and low digestibility in raw potatoes (Edwards and Livingstone, 1990).
PIG DIETS Growth performance has been shown to be similar when cooked potato replaced ground maize in grower-finisher diets and that problems with reduced nutrient intake were only likely to occur in young animals unable to consume the necessary daily bulk (Whittemore, 1977;
Edwards and Livingstone, 1990). Growth response was also similar in young pigs given diets containing either cooked potato flakes or maize meal at 780 g/kg. In general, about 4 kg of cooked potato could replace 1 kg of barley as a source of energy and protein in the diet. Pond and Maner (1984) recommended that growing and finishing pigs could be fed up to 6 kg of cooked potatoes per day, representing about 50% of the dietary DM. They reported good results when cooked potatoes were fed to appetite along with a concentrate (1.0–1.15 kg/day) that supplied the remaining energy and nutrient needs. One benefit of potato feeding was a firm backfat. Another finding was that pellet quality of the diets was improved, the diets containing potato flakes or flour being firmer than those containing cereals.
To avoid overfatness Edwards and Livingstone (1990) recommended that dry sows be restricted daily to 4–6 kg of cooked potato fed in conjunction with 1 kg of a supplementary concentrate, suggesting a similar daily amount (5–7 kg depending on live weight and litter size) in conjunction with a higher level of supplement for lactating sows.
Potato by-products
Several dehydrated processed potato products may be available for feeding to pigs. These include potato meal, potato flakes, potato slices and potato pulp. These products are very variable in their nutritive value depending on the processing method. This is particularly true of potato pulp, whose protein and fibre content depends on the proportion of potato solubles added back into the material. Therefore, it is necessary to have such materials analysed chemically before using them for feeding to pigs or to purchase them on the basis of a guaranteed analysis.
Dehydrated cooked potato flakes or flour are very palatable and can be used as a cereal replacement (Whittemore, 1977; Edwards and Livingstone, 1990). Good performance was reported when potato flakes replaced up to 50–60% of the cereals in the diets of starting, growing and finishing pigs.
However, because of the high energy costs involved in their production, they are generally limited to diets for young pigs or lactating sows.
Dehydrated potato waste
This product (dehydrated potato waste meal as defined by AAFCO, 2005) consists of the dehydrated ground by-product of whole potatoes (culls), potato peelings, pulp, potato chips and off-colour French fries obtained from the manufacture of processed potato products for human consumption. It may contain calcium carbonate up to 30 g/kg added as an aid in processing. It is generally marketed with guarantees for minimum CP, minimum crude fat, maximum CF, maximum ash and maximum moisture.
If heated sufficiently during processing, this product can be used successfully in pig diets.
Potato pulp
This by-product comprises the residue remaining after starch removal. The composition of the dehydrated product can be quite variable (Edwards and Livingstone, 1990) depending on the content of potato solubles. The product has characteristics similar to those of raw potato and should not be used in diets for young pigs (Edwards and Livingstone, 1990). Dietary inclusion rates of up to 15% could be used with growing-finishing pigs with little detriment to performance, provided protein supplementation was adequate, but was found to result in a reduction of killing-out percentage (Edwards and Livingstone, 1990). Higher levels were found to result in a marked deterioration in growth rate and feed conversion efficiency.
Steamed peelings
This product, sometimes called ‘liquid potato feed’, contains only partially cooked starch and has low and variable DM content (Edwardset al., 1986;
Nicholsonet al., 1988). For this reason, it is best treated in the same way as raw potato and restricted to use in diets fed to dry sows and finishing swine. Dry sows can be given 6–8 kg with 1.0–1.5 kg of a concentrate supplement daily. Steamed peelings can be included in finishing swine diets at up to 25 g/kg DM (Edwards and Livingstone, 1990), but a 5–10%
reduction in performance in comparison with cereal diets should be expected. Higher inclusion levels result in decreased feed intake and poor performance. Because of the high potassium level in the product, swine should have a plentiful supply of water available. The product is best fed as soon as possible after production since it undergoes fermentation during storage with consequent loss of nutrient value. Separation of the solids, which float towards the top of the container, and moulding of the crust can also occur over time (Edwards and Livingstone, 1990). Steamed peelings which have been produced under heat and pressure contain partly denatured starch and a low concentration of protease inhibitor.
Waste potato chips
Waste or scrap potato chips, French fries or crisps, which have been cooked in oil for human consumption, are very palatable and high in energy (> 5000 kcal DE/kg) due to the fat taken up in deep frying. On a per kg basis they consist of about 500 g starch, 350 g fat, 50 g CP and 30 g minerals, mainly potassium and sodium salts. Generally they have a high salt content and a plentiful supply of fresh water should be made available if they are used in pig diets. They can be included in diets for sows and growing swine at up to 250 g/kg and in diets for younger pigs at up to 150 g/kg.
Potato protein concentrate
Potato protein concentrate is a high-quality product, widely used in the human food industry because of its high digestibility and high biological value of the protein. It is a high-quality protein source that is suitable for use in all pig diets. However, its high cost makes it most appropriate for use in diets for young pigs. Potato protein concentrate can replace milk and fish protein in diets for young pigs at inclusion levels of up to 150 g/kg with no detrimental effects on growth or feed conversion ratio (Seve, 1977).
Sundrum et al. (2000) examined the effects of on-farm organic diets containing potato protein (no details on its manufacture or chemical analysis) on growth performance and carcass quality. Four dietary protein treatments were compared: a conventional diet supplemented with pure AA; faba beans supplemented with potato protein to the same AA level as the control diet; peas and lupins; or faba beans and lupins – the latter two without further supplementation, leading to a lower level of limiting AA.
Supplementation of organic diets with potato protein resulted in the same performance as supplementing the conventional diet with pure AA, although CP levels differed markedly. The data from this experiment showed that the omission of AA supplementation resulted in a reduction in pig performance but in an increase in intramuscular fat content.
Swedes (Brassica napus)
There is current interest in root crops such as swedes for organic pig feeding, as a roughage source and as a crop to allow the animals to express natural foraging behaviour.
Livingstoneet al. (1977) reported details of the chemical composition of swedes as a feedstuff for growing pigs and their potential as a dietary replacement for barley. Macerated swedes of the variety Balmoral were studied and were found to contain 100 g DM/kg and per kg (DM basis) 16.7 MJ DE, 128 g CP, 50 g true protein, 4 g total lysine, 26 g methionine+cystine, 408 g total sugars, 206 g ADF and 109 g ash. The composition suggested that swedes might be a replacement for barley. Pigs were grown from a live weight of 57 kg to market weight on diets containing 890 g barley plus 90 g
soybean meal per kg, or on diets in which swede DM replaced 20 or 40% of barley DM. Live-weight gain per day on the three diets was 785, 735 and 732 g, respectively, and feed conversion ratios were 3.24, 3.41 and 3.45. Carcass weight gain per day was 638, 591 and 517 g, respectively, a significant reduction at each level of swede inclusion. The authors suggested that for equivalent carcass growth about 1.5 units of swede DM could replace 1 unit of barley DM, although the basis for that conclusion is not clear. This study showed that pigs given the diets containing swedes were able to consume daily amounts of DM equivalent to that of pigs receiving the control diet, but that continuous access to the feed trough was necessary. This finding indicates that sufficient feed trough space must be provided to allow all animals in the group to feed at all times when bulky feeds are used.
In subsequent work these authors tried to explain the reason for the low replacement value of swedes in relation to barley (Livingstone and Jones, 1977). Rations based on 2 kg barley plus either 0.2 or 0.4 kg soybean meal were used as controls and similar rations had swedes replacing 40% of the DM of barley. Replacement of barley with swedes reduced carcass weight gain from 620 to 510 g/day and increasing the content of soybean meal increased it from 540 to 590 g/day. The authors concluded that the low replacement value of swedes was not due to its protein component but to other factors.
Sows appear to like swedes and when they have access to this crop spend less time rooting in paddocks (Edgeet al., 2005). This study suggested that the daily concentrate ration could be reduced by 0.5 kg in sows provided with access to swedes.
Forages and Roughages
Cabbage (Brassica oleracea,Capitatagroup)
Cabbages have a high yield of nutrients per hectare and are of potential interest for organic feeding as a source of roughage. However, little research appears to have been conducted on this crop as a feed ingredient for pigs.
Livingstoneet al. (1980) used comminuted cabbage (variety Drumhead) in diets for growing-finishing pigs as a partial replacement for barley and soybean meal. The cabbage contained 100 g DM/kg and contained per kg (DM basis) 18 MJ GE, 230 g CP, 79 g true protein, 7.6 g total lysine, 4.7 g methionine + cystine, 142 g ADF and 132 g ash. Replacing a mixture of 805 g barley and 180 g soybean meal with 150 or 300 g cabbage (DM basis) reduced the rate of carcass weight gain by 12.2 and 18.5%, respectively.
Grass meal
NUTRITIONAL FEATURES There is a lack of recent documented information on the nutritive value of grass meal for pigs. However, this product is an
established feed ingredient in Europe, based on research carried out over 50 years ago. For instance, Karunskii (1988) described a traditional Moldavian diet for growing pigs as containing maize meal, pea meal, barley meal, meat-and-bone meal, grass meal, wheat bran, protein and vitamin–mineral supplement. Artificially dried young grass at levels up to 200 g/kg has been used with growing-finishing pigs, in diets containing grains and other feeds of equivalent energy value plus 2 litres of skimmed milk per head per day (Frens, 1943). Woodman and Evans (1948) recommended that grass meal should form not more than 33% of the diet up to 150 lb (68 kg) live weight and that above 150 lb live weight it was advantageous to reduce it to 25%.
Grass meal does not appear to be utilized by growing pigs as well as lucerne meal. Meal prepared from lucerne cut at the budding stage and awn-less bromegrass cut at ear formation were compared by Popelov (1981). The lucerne meal contained 148 g digestible protein/kg and the grass meal 80 g/kg. Large White pigs were fed from a body weight of 31 kg for 120 days on a control diet of 950 g mixed feed/kg and 50 g lucerne meal/kg, on 850 g mixed feed/kg and 150 g lucerne meal/kg, or on 850 g mixed feed/kg and 150 g bromegrass meal/kg. Average daily gain was 575, 548 and 489 g, respectively, and the pigs required 4.57, 4.82 and 5.40 feed units/kg gain. A study by Andersson and Lindberg (1997a,b) found that the grass meal was not as well digested as lucerne (Table 4.3), although containing less CF and more sugars than lucerne. Their results indicated that much of the breakdown in the gut was in the form of fermentation in the large intestine, and suggested that grass meal would be more suitable for sows than growing-finishing pigs.
Another factor influencing the utilization of grass meal is the stage of maturity at harvesting. Vestergaardet al. (1995) reported the composition of Table 4.3. Digestibility of lucerne and grass meals in growing pigs (from
Andersson and Lindberg, 1997a,b).
Lucerne (Medicago sativa)
Ryegrass (Loliumspp.) Composition (g/kg dry matter)
Crude fibre 341 236
Sugars 6 29
Crude protein 174 152
Ileal digestibility
Organic matter 0.12 −0.02
Crude protein 0.52 0.09
Energy 0.10 −0.20
Total tract digestibility 0.40
Organic matter 0.49 0.22
Crude protein 0.35 0.08
Energy 0.35 0.04