Cow’s milk is an excellent source of nutrients and, when surplus to requirements for the human market, can be used with all classes of pig.
Generally it is milk by-products that are used in pig feeding, in either liquid or dried (dehydrated) form, and mainly in diets for young pigs because of cost and availability. Adequate heat treatment (pasteurization) should have been applied to all milk products to ensure that any pathogenic organisms have been destroyed. Generally, the AA availability of milk products is considered high, but their quality can be impaired by overheating.
By-products in liquid form
Skimmed (separated) milk
This product consists of milk from which most of the fat has been removed but which contains all of the protein. The protein has a high biological value and is very digestible. Skimmed milk is a good source of B vitamins, but the fat-soluble vitamins (A and D) have been removed with the fat. Growth rates in growing pigs were increased when skimmed milk was included in the diet (Dunshea et al., 1999). Scouring can be a problem with skimmed milk feeding if precautions are not taken to feed at regular intervals.
Skimmed milk should either be fresh or always at the same degree of sourness. Attention should be paid to the cleanliness of the equipment used for feeding. Normal bacterial acidification can be used as an effective and convenient method of stabilization.
Recommendations for the feeding of liquid skimmed milk to growing-finishing pigs are given in Table 4.5. The feed composition for this particular use can contain 50 g premix/kg. The premix should contain calcium, phosphorus, iron, zinc, iodine, selenium, sodium chloride (salt) and vitamins A, D and E.
Dunshea et al. (1999) reported that the feeding of skimmed milk to early-weaned pigs before and after weaning improved their growth performance. In this study, litters suckled the sow only or received supplemental liquid skimmed milk (200 g/l) ad libitum from day 10 until day 20. On day 20 the four heaviest pigs of each sex were allocated to two pairs and were weaned. Each pair was offered either pelleted feed or pelleted plus liquid feed. For the first two days post-weaning, each pair of liquid-supplemented pigs received liquid skimmed milk (250 g/l). On day 23, pelleted feed was added to the milk. The ratio of liquid to pelleted feed was adjusted daily so that on day 28 pigs were provided with pelleted feed only until 41 days of age. Supplemental skimmed milk increased growth (223 versus 291 g/day) between days 10 and 20 of age, so that by weaning the pigs fed the supplemented diets were 10% heavier (6.13 versus 6.74 kg).
The growth lag usually experienced after weaning was reduced in this study, pigs weaned onto skimmed milk and pellets eating more (257 versus 30 g DM/day) and growing faster (+213 versus –151 g/day) over the first two days post-weaning than pigs weaned onto pellets only. Piglets provided with Table 4.5. Feeding recommendations for the feeding of liquid skimmed milk to growing-finishing pigs.
Weight of pig (kg)
Ratio feed : skimmed milk
Feed per pig per day (kg)
Skimmed milk (l or kg)
20–40 1:4 0.6–1.1 2.3–2.7
40–60 1:3 1.2–1.6 3.2–3.6
60–100 1:2 2.3–2.5 3.6–4.1
skimmed milk after weaning continued to grow faster to at least 41 days of age (14.1 versus 12.8 kg).
Buttermilk
This is the liquid product remaining after whole milk is churned and the butter removed. It usually contains more fat than skimmed milk. Buttermilk is more acidic than skimmed milk and can have more of a laxative action in pigs. It is an excellent source of supplemental protein for young pigs, daily gain being improved when buttermilk replaced soybean meal (Christison and de Solano, 1982).
Whey
Whey is the liquid by-product remaining after cheese production. Whey contains about 90% of the lactose, 20% of the protein, 40% of the calcium and 43% of the phosphorus originally present in milk. However, its DM content is low, around 70 g/kg. Most of the fat and protein are removed during processing, leaving the whey high in lactose and minerals. The high lactose content does not normally cause problems in young pigs which have been adapted to a milk-based diet, but may cause problems in older pigs and sows due to an inadequate production of intestinal lactase. As a result, whey should be fed in restricted quantities to finishing pigs and sows.
In addition to providing nutrients, whey can also be used as a source of water. Whey should be warmed or allowed to reach room temperature before being offered to pigs. Cold whey may reduce intake. Also, pigs should be introduced gradually to the product, to prevent digestive disturbances and diarrhoea. Usually two types of whey are available commercially, fresh and acidified. Fresh (sweet) whey is used in pig diets in the fresh state, without storage during which it is allowed to ferment and become acidic. However, fresh whey deteriorates rapidly and needs to be used within a short time of production. Acid whey is allowed to ferment and become acidic naturally. It is more stable than fresh whey as a result of the acidity. However, acid whey is less palatable than fresh whey.
Sometimes acids, such as formic acid and hydrochloric acid, are used to stabilize whey. If used, they should be acceptable for organic pig production.
Whey is a very dilute feed, consisting of 930 g water and 70 g DM per kg, and contains less than 10 g CP/kg on a wet basis (130 g CP/kg on a DM basis). The protein is of excellent quality because of the AA balance. It should be introduced into the diet gradually. Thead libitumfeeding of liquid whey to young pigs has been shown not to cause any problems (Brocksopp, 1979). A common feeding system used on conventional farms is to utilize grain such as barley supplemented with minerals and vitamins and wheyad libitumas the complete diet. The DM in liquid whey can be used to supply up to 30% of the total diet, about 7–14 l per pig daily depending on body weight. A feeding system that gave satisfactory results with
growing-finishing pigs was described by Cortez et al. (cited in Pond and Maner, 1984). During the growing phase (to 50 kg) the pigs consumed on a daily basis an average of 11 l of liquid whey onad libitumfeeding plus an average of 1.25 kg of a dietary mixture containing 160 g CP/kg. During the finishing phase (to 95 kg) the intakes were, respectively, 16 l and 2.25 kg of a dietary mixture with 130 g CP/kg.
An interesting finding was that whey feeding was found to reduce ascarid egg count in the faeces of pigs (Alfredsen, 1980), suggesting that this product could be used as a natural de-wormer.
Lactase appears to be produced in the gut in sufficient quantity in older pigs fed whole milk or skimmed milk, but the higher concentration of lactose in liquid whey may cause problems in older pigs such as sows (Pond and Maner, 1984), resulting in digestive problems due to excessive fermentation of undigested lactose in the large intestine. Should this occur the amount fed should be restricted.
Dried milk products
Dried milk products include dried whole milk, dried skimmed milk and dried whey. The products derived from whole milk and skimmed milk are very palatable and highly digestible protein supplements with an excellent balance of AA. They are good sources of vitamins and minerals (Seerley, 1991), except fat-soluble vitamins, iron and copper. Although generally too expensive for use as a feed ingredient, some dried skimmed milk has been used in pig starter diets when available economically. Research emphasis in this area has been to replace dried skimmed milk with alternative protein supplements in weanling pig diets rather than evaluating the value of the dried milk per se. Dried whole milk and skimmed milk can be fed successfully to all classes of pig; thus, the use of these products in pig diets should be determined mostly on economics (Seerley, 1991).
Whey, dried
Dried whey contains about 650 g of lactose per kg, which has been shown to be the best sugar for baby pigs (Cunha, 1977). It contains about 130–170 g of high-quality protein per kg (Seerley, 1991). Dried whey is an excellent source of B vitamins, most of which remain in the whey during cheese production, but it may be low in vitamins A and D, which are retained in the cheese (Seerley, 1991). Season, type of cheese produced and geographic location can have an effect on the mineral content (Leibbrandt and Benevenga, 1991). The efficacy of high-quality dried whey in enhancing growth performance of weanling pigs has been well established over the years (e.g. Graham et al., 1981; Cera et al., 1988). The composition and quality of dried whey is, however, more variable than that of other milk products (Tomkins, 1989); therefore it is important to use a high-quality product. Mahan (1984) found that low-quality dried whey added to a
maize/soybean meal diet did not result in improved growth rate, whereas dried whey of high quality improved growth rate by approximately 15%.
Studies have been carried out to determine whether factors other than lactose content and high nutrient digestibility might be responsible for the beneficial effects of dried whey on weanling pig performance. By including either lactalbumin or lactose in the diet, Tokachet al. (1989) concluded that both the protein and carbohydrate fractions of dried whey are important.
Lepine et al. (1991) and Mahan et al. (1993), however, reported that the protein fraction was not a limiting factor in weanling pig diets. After evaluating the efficacy of lactalbumin and lactose components of dried whey, Mahan (1992) concluded that the lactose component of dried whey was primarily responsible for the beneficial effects of dried whey. It has been shown that edible-grade de-proteinized whey and crystalline lactose can replace the lactose provided by high-quality dried whey without affecting pig performance (Nessmith et al., 1997). In other research Mavromichalis et al. (2001) reported that replacing lactose with sucrose or molasses did not affect weight gain, feed intake, or efficiency of feed utilization or nutrient digestibility. Apparent digestibilities of DM and nitrogen were greater in pigs fed complex diets vs. simple diets, but they were not affected by sugar additions. The distinction between simple and complex diets was based on the type of ingredients used. The complex diets were supplemented with whey protein concentrate, animal plasma protein and wheat gluten, whereas simple diets were supplemented with fishmeal only.
Dried whey can be fed to all classes of pig, but it is primarily used for weanling pigs. As reviewed by Pond and Maner (1984) and Seerley (1991), an inclusion rate of 100–300 g/kg is commonly used, although 300–450 g/kg can be included without any adverse effects. The optimum inclusion rate of dried whey in pig diets should be determined mainly by cost. Pond and Maner (1984) suggested a gradual reduction in the level of dried whey in the diet as pigs reach market weight.