| 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.
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Other studies at Ohio State University, Kansas State
University, and the University of Missouri have also demonstrated
the effectiveness of relatively high levels of dried whey
in diets for early weaned pigs. A study by Mahan (1992)
showed that pigs responded to levels of dried whey up
to 35% of the diet (Table 3). Similar results have been
shown in other studies (Graham et al., 1981; Tokach et
al., 1989; Nessmith et al., 1997). While some of the benefits
of whey have been attributed to the protein fractions
(Tokach et al., 1989), most of the research shows that
the benefits of whey are largely attributable to its lactose
fraction (Baird et al., 1974; Mahan, 1992). 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).
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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.
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