Gary L. Cromwell
　　　　　　　　　　　　Department of Animal and Food Sciences
　　　　　　　　　　　　　　　　University of Kentucky
　　　　　　　　　　　　　　　Lexington, Kentucky 40546

　　　　　　　　　　　　　　　　　　　　　Introduction

　　Dried milk powder and dried products originating from milk have been used in pig starter diets for many years. These products have been shown to enhance feed intake, growth rate, and health of newly weaned pigs, especially those weaned at young ages. Furthermore, the beneficial effects of dried milk and dried milk products continue to benefit weanling pigs for several weeks following weaning.

　　Milk contains many important components that have superior nutritional value to animals. One of these important components in milk is the carbohydrate fraction, which is predominately the disaccharide sugar, lactose. In addition, the individual protein fractions of milk and the excellent profile of amino acids in these proteins contribute to the excellent nutritional properties of milk. The lipids (mainly butterfat) in milk serve as a concentrated source of energy. In addition, calcium and phosphorus are found in relatively high concentrations in milk and they, along with other minerals and vitamins, contribute to its nutritional value.

　　Dried skim milk, dried buttermilk, and casein are examples of fractions derived from liquid milk that can be used in animal feeds. An important product derived from cheese production is liquid whey. Dried whole whey powder is an excellent component for inclusion in pig diets. Liquid whey can be subjected to a crystallization process that yields lactose and delactosed whey, or it can be subjected to an ultrafiltration process which results in two end products – whey permeate and whey protein concentrate. These various components and fractions of the milk and cheese industries will be addressed, but this paper will give the most attention to dried whole whey and lactose.

　　　　　　　　　　　　　　　Dried Products from Liquid Milk

　　Dried skim milk at one time was commonly used in diets of pigs weaned at an early age. Fifty to seventy-five years ago, pigs were routinely weaned at 6 to 8 weeks of age. However, swine producers began to adopt more intensive production practices in the 1960’s, and this trend necessitated earlier weaning of pigs. Weaning pigs at 3 to 4 weeks, or earlier, became more common. Inclusion of dried milk powder in diets for the first week or two after early weaning was a common practice. Although dried milk was expensive, it was an excellent source of highly digestible nutrients (Table 1) and was a necessary component of the diet in order to keep early weaned pigs alive, healthy, and growing.

　　Today, with improved environments and ingredients such as dried whey, lactose, dried animal plasma, dried blood cells, and high quality fish meal that were not readily available during those early years, the more expensive dried milk products are less commonly used in today’s pig diets. In addition, the exceptionally high cost of dried skim milk relative to the cost of dried whey prevents the use of dried skim milk in pig starter diets. The same can be said for dried buttermilk and casein.

　　　　　　　　　Dried Milk-Based Products from Cheese Production

Dried Whey
　　Large amounts of milk are used in the production of cheese. One of the major products resulting from cheese production is liquid whey. Years ago, liquid whey was considered a waste product and was disposed by dumping it into waterways, spreading it on crop land, or transported it to land fills. In some areas of the world, liquid whey was, and still is, fed directly to pigs both as a source of nutrients and as a means of disposal, but this practice is not common in the USA.

　　If whey is carefully dried, it makes an excellent ingredient for animal feeds. In fact, dried whey is the largest milk-based feed ingredient used in the feed and pet food industries in the USA. Approximately one-half of the dried whey produced in the USA is used in pig starter feeds (Halpin et al., 2000). Almost all pig starter diets contain this important ingredient and/or one of its major components, lactose.

　　Dried whey typically contains about 68% lactose and 12% protein (Table 1, NRC, 1998). The major proteins in whey are β-lactoglobulin (56-60%), α-lactalbumin (18-24%), bovine serum albumin (6-12%), and immunoglobulin (6-12%) (Harper, 2000). These specific proteins not only served as a source of amino acids, but they also serve as a defense against microbial infections and as a source of growth factors and modulators (Harper, 2000). Other proteins in whey that are found in lower concentrations and that are thought to have important biological properties include lactoferrin, lactoperoxidase, lysozyme, casein glycomacropeptide, phosphopeptides, and fat globule membrane proteins (Harper, 2000).

　　Dried whey is classified as edible grade or feed grade depending on its bacterial count. Most of the dried whey used in pig feeds originates from cheddar cheese plants and it is called “sweet whey”. Dried whey originating from cottage cheese plants is called “acid whey” and it is less commonly used in pig feeds. Whey can be dried by either a spraying process or by rolling thin layers of whey on heated drums followed by scraping the dry material from the drums. The spray-drying process involves atomizing liquid whey into superheated air for a short period of time, and results in a powdery and hygroscopic product. This type of drying results in both α- and β-lactose. Roller dried whey uses a lower heat for a longer time; it results in a granular, non-hygroscopic product in which all of the lactose is in the β form. From a taste standpoint, β-lactose is sweeter than α-lactose.

1NRC (1998). NRC does not list levels of magnesium, sulfur, trace minerals, or vitamins for

dried whey permeate.

The quality of dried whey from a nutritional standpoint can vary depending on source of whey, drying conditions, and age (Mahan, 1984). Two of the best indications of the quality is color and ash content. A light, creamy color is desirable. Whey that is overheated during drying may have a brown color or dark flakes. A dark yellow color is an indication that the whey has been stored for a long period of time. These off-colors are indications that the Milliard reaction may have occurred, meaning that the ε-amino group of lysine becomes bound to carbohydrate, rendering it unavailable to the animal. A high ash content is also undersirable because it indicates that the whey became acidic during storage and large amounts of sodium hydroxide (a strong base) were added before drying to raise the pH. This type of whey has excess salt and can cause diarrhea in pigs.

Other Whey Products

　　Dried delactosed whey has had a portion of the lactose removed during crystallization. It still contains significant amounts of lactose (~54%) and has slightly more protein (~18%) than normal dried whey (Table 1).

　　 Ultrafiltration of liquid whey separates most of the protein fractions from the other fractions and results in two products – whey permeate and whey protein concentrate. Dried whey permeate has less than 4% protein but it is quite high (~80%) in lactose (Table 1). A commercial brand of dried whey permeate (Dairylac?80, International Ingredient Corp., St. Louis, MO) is widely used in the USA swine industry in pig feeds as a source of lactose. It has nutritional properties that are similar to dried whey (Cromwell et al., 1994). Whey protein concentrate is considerably higher in protein than permeate, and is used primarily in the human food industry.

Lactose

　　As stated previously, the predominant carbohydrate in whey is lactose. This disaccharide sugar consists of two monosaccharide sugar units, galactose and glucose, joined in a β1,4-linkage. The bond between the two sugar units must be cleaved so that the glucose and galactose units can be absorbed (galactose is converted to glucose in the liver following absorption), metabolized, and utilized by animals. Young mammals, including pigs, have an abundant supply of lactase in the small intestine, so they are able to efficiently digest lactose and utilize the two polysaccharide sugars for energy.

　　On the other hand, the enzymes needed to degrade other disaccharides, sucrose (glucose-fructose, α1,2-linkage), maltose (glucose-glucose, α1,4-linkage), and isomaltose (glucose-glucose, α1,6-linkage) and more complex carbohydrates such as starch are very low and almost non-existant at birth. These digestive enzymes are still relatively low at 2-3 weeks of age, so the starch from cereal grains (mainly long chains of glucose) is not as well utilized as after pigs reach 4-6 weeks of age or older. Thus, a readily digestible carbohydrate must be present in the diet for pigs weaned at an early age in order for the pig to receive adequate energy. Lactose fits this role ideally.

　　　　　　　　　　　　Nutritional Value of Dried Whey and Lactose

　　One of the first studies to assess the possible benefits of dried whey in diets for swine was conducted in 1949 by Krider et al. at the University of Illinois. These researchers found that as little as 2 to 4% dried whey resulted in a 30% improvement in growth rate of young pigs. However, they also reported that higher levels of dried whey produced diarrhea in their pigs.

　　Except for a few studies (Becker et al., 1957; Danielson et al., 1960), relatively little research was conducted with dried whey until several decades later. In the early 1970’s we conducted studies at the University of Kentucky to evaluate dried whey in diets for pigs weaned at 3 weeks of age. In one study, we evaluated three levels of dried whey (5, 10, and 15%) added to corn-soybean meal-based diets for early weaned pigs and found that growth rate and feed intake increased linearly as level of dried whey was increased in the diet (Baird et al., 1974; Table 2). In those studies, we also found that the addition of lactose at the same level as provided by dried whey produced a similar growth rate and feed intake response as achieved by feeding the dried whey.

　　The two performance traits in pigs that are affected most by whey or lactose additions are feed intake and growth rate. The improved growth response may be due to the effect of these ingredients in stimulating feed intake. In addition, lactose has been shown to maintain an enhanced intestinal environment (Wolter et al., 2003).

　　Questions often arise as to how much lactose should be included in various phases during the nursery period. A recent study (Mahan et al., 2004) investigated this and found that pigs responded to high levels of lactose in the diet during the initial 14 days post weaning (Table 4), and during days 7 to 21 postweaning (Table 5). From their studies, these researchers recommended that 25-30% lactose be included during the first week postweaning (to 7 kg body weight), and 20% lactose for the subsequent 2 weeks (to 12.5 kg body weight).

　　While it is clear from many studies that most of the response to lactose occurs during the first 2 to 3 weeks following weaning (i.e., starter phases 1 and 2), there has been some question as to whether the response to lactose continues during the mid to late nursery period (phase 3). To more clearly answer this question, a large study involving 1,320 pigs was conducted (Cromwell et al., 2005). The study was conducted at the University of Kentucky, the University of Missouri, and The Ohio State University.

　　Crossbred pigs were weaned at 15 to 20 days (6.2 kg initial weight) and allotted to five dietary treatments. The pigs were penned in groups of five pigs per pen at the Kentucky and Ohio stations and in groups of 23 pigs per pen at the Missouri station. There were eight replications per treatment at each station for a total of 24 replications per treatment in the study. Commercial style, temperature-controlled, slotted-floor nursery buildings were used, and pens were equipped with nursery-type self feeders and nipple waterers. Diets and water were made available on an ad libitum basis. Pigs were weighed and feed intake was determined at weekly intervals.

　　The study consisted of four phases. Phases 1 and 2 were each 1 week in length, phase 3 was 2 weeks, and phase 4 varied from 1 to 2 weeks in length. Average pig weights at the end of the four phases were 7.5, 10.3, 17.9, and 25.3 kg, respectively. All pigs received the same diet during the first two phases of the study (Table 6). The two diets were calculated to contain 20.0 and 15.0% lactose, respectively, and 1.60% lysine (total).

　　During phase 3, five dietary levels of lactose (0, 2.5, 5.0, 7.5, and 10.0%) were fed (Table 6). These diets were formulated to contain 1.56% lysine (total) and 1.42% true ileal digestible lysine. In the phase 3 diets, Dairylac?80 was the source of lactose and was substituted for an equal amount of corn. Levels of dicalcium phosphate, ground limestone, and salt were adjusted to maintain constant dietary levels of calcium, phosphorus, and sodium. Also, levels of supplemental lysine, threonine, and methionine were adjusted to maintain similar levels of total lysine, threonine, and methionine + cystine in the five diets. During phase 4, a common diet (mainly corn and soybean meal with amino acids, but with no lactose) containing 1.44% lysine (total) was fed to all pigs. The diets were formulated to meet or exceed NRC (1998) standards for amino acids, minerals, and vitamins. Carbadox was included in all diets at 55 mg/kg. In addition, zinc oxide and copper sulfate were included in phase 1 and 2 diets at pharmacologic levels (2,150 mg zinc and 125 mg copper/kg) in phase 1 and 2 diets, and copper was included at 250 mg/kg in the phase 3 and 4 diets.

　　Dairylac?80, a product of International Ingredient Corp. (St. Louis, MO) was used as the source of lactose in the experimental diets (phase 3). This product is a granular, nonhygroscopic product produced from sweet dried whey solubles. A single source of Dairylac?80 was used in the experiment. It analyzed 96% DM, 79.3% lactose, 4.6% CP, 0.46% fat, 0.12% crude fiber, and 9.84% ash. Although not analyzed for amino acids or minerals, Dairylac?80 typically contains 0.15% lysine, 0.52% Ca, 0.63% P, and 3.0% NaCl (product sheet, International Ingredient Corp., St. Louis, MO).

　　The results of the study for the three stations are presented in Table 7. In all instances, daily gain and daily feed intake differed (P < 0.01) among the three stations, and in most cases, so did feed:gain. However, there was no evidence of a station x treatment interaction for gain, feed intake, or feed:gain during any of the test periods.

　　As expected, pig performance was not affected (P = 0.10) during the initial 2-week experimental period (phase 1 and phase 2) during which time all pigs received a common diet. During the 2-week period of phase 3 when the five levels of lactose were fed, both daily gain and daily feed intake increased linearly (P < 0.01) with increasing levels of lactose, but feed:gain was not affected (P = 0.10). Although the quadratic component was not significant, growth rate and feed consumption appeared to reach a plateau at the 7.5% level of lactose inclusion during phase 3 and during phases 1, 2, and 3 combined.

　　During phase 4, when all pigs received a common diet, pigs that had previously consumed the phase 3 diet containing 10% lactose gained slower than pigs in the other treatment groups (linear, P < 0.04). Feed intake and feed:gain during phase 4 varied slightly, but the differences among treatments were not significant (P = 0.10). Over the entire 5 to 6-week study, growth rate and feed intake were numerically greatest in pigs that had been fed the 7.5% level of lactose during phase 3.

　　To determine whether the response to lactose during phase 3 was maintained after pigs were fed a common diet without lactose, the improvement in growth rate of pigs fed the lactose diets compared with the control diet was evaluated. The 7.5% level of lactose resulted in 350 g of additional weight gain per pig during phase 3 ([557 g/day – 532 g/day] x 14 days) and this was associated with 420 g of additional feed consumed per pig during this period ([753 g/day – 723 g/day] x 14 days). A determination of the additional weight gain from the time that the additional lactose was fed until the end of the study indicated that most of the additional weight gain (294 g per pig) was maintained throughout the study. The additional weight gain was associated with an additional 409 g of feed consumed per pig through the end of the study. Nearly all of the additional feed consumed by this particular treatment was during phase 3 of the study.

　　The results of this large collaborative study clearly indicated that early weaned pigs continue to respond to the feeding of lactose the third and fourth week following weaning, and that this response is maintained after the lactose source is removed from the diet. Furthermore, the data suggest that 7.5% lactose is the most effective level during the mid- to late nursery phase.

　　　　　　　　　　　　　　　　　　　　　　　　Summary

　　Numerous research studies conducted during the past 30 years clearly demonstrate that the inclusion of dried milk products, specifically those originating from cheese production such as dried whey, dried whey permeate or crystalline lactose in starter diets for pigs stimulate feed intake and growth rate during the postweaning period. These products are widely used in the swine industry and their cost makes them economically feasible to use in diets for early-weaned pigs.

　　　　　　　　　　　　　　　　　　　　　　References

Baird, J., G.L. Cromwell, and V.W. Hays. 1974. Effects of lactose and whey on performance and diet digestibility by weanling pigs. J. Anim. Sci. 39:179 (abstr.).

Becker, D.E., S.W. Terrill, A.H. Jensen, and L.J. Hanson. 1957. High levels of dried whey powder in the diet of swine. J. Anim. Sci. 16:404.

Cromwell, G.L., Hollis, G.R., and R.A. Easter. 1994. Assessment of DAIRYLAC 80TM, spray- and roller-dried whey, and lactose in starter diets for weanling pigs. J. Anim. Sci. 72 (Suppl. 1):263 (abstr.).

Cromwell, G.L., G.L. Allee, and D.C. Mahan. 2006. Assessment of lactose levels in Phase 3 nursery diets for young pigs. Abstract No. 289 of the Midwestern Section, American Society of Animal Science, Des Moines, IA, March 20-22, 2006.

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