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OCR for page 244
Dairy Cattle Nutrition
and the Environment
The dairy industry is developing intensive management
systems in which cows are fed and housed in large groups.
Consolidation of large numbers of dairy cattle into small
land areas to improve the efficiency of milk production
may contribute to environmental problems unless animals
are fed and managed properly. However, any size dairy
herd that does not have proper nutrition, feeding, manage-
ment, and waste-disposal programs has the potential to
pollute the environment. If cows are fed excessive amounts
of dietary nutrients that are not used efficiently for milk
production, large amounts of the nutrients will be excreted
in feces andurine, resulting in pollution ofthe environment
and increased cost of milk production (Chandler, 1996~.
Developments in dairy cattle nutrition will be important
in determining the ability of the dairy industry to produce a
nutritious, wholesome product at an economic cost without
polluting the environment (Clark and Overton, 1995~.
Dairy cattle should continue to be fed and managed to
increase the production and the efficiency of production
of milk and milk components because this will require
fewer cows to produce the same quantity of milk and milk
components; this will increase the efficiency of nutrient
use and decrease the excretion of waste products. Although
high-producing dairy cows are the ruminants most efficient
at converting nutrients in feed to food for human consump-
tion, not all nutrients consumed by dairy cows are secreted
in milk. Dairy cattle must be fed to meet their requirements
with minimal excesses of nutrients in the diet if the eff~-
ciency of nutrient use and milk production by dairy cows
are to be maximized and nutrient losses to the environment
reduced. The most successful feeding regimens will be the
ones that supply nutrients in amounts required to optimize
synthesis of milk and milk components, maximize ruminal
fermentation and growth of ruminal microbes, and mini-
mize nutrient losses to the environment. Development and
adoption of improved dairy cattle feeding systems driven
by the concept of nutrient management to meet nutrient
requirements and to prevent environmental pollution will
result in increased efficiency of nutrient use.
The U. S. Environmental Protection Agency has issued
its definition of the term "concentrated animal feeding
operation" for purposes of permit requirements and speci-
fying limits on pollutant discharges from feedlots (Meyer
and Mullinax, 1999; Meyer, 2000~. The U.S. Environmen-
tal Protection Agency and the U. S. Department of Agricul-
ture have drafted national guidelines that suggest compre-
hensive nutrient management plans for concentrated ani-
mal feeding operations. Users should become informed to
be sure they are in compliance with all federal and state
regulations. These activities have taken place because of
the quantity and odor of the solid, liquid, and gaseous
waste products produced when waste from large numbers
of animals concentrated in a small area is not well managed
(Lanyon, 1994; Miner, 1997; Van Horn et al., 1994~. Large
amounts of waste can create disposal problems and odors
and result in more strict actions for waste disposal unless
the cows are fed to meet but not exceed the required
amount of nutrients and waste is properly managed to
prevent environmental pollution. Components of voluntary
guidelines and future plans, if implemented by the govern-
ment, are concerned with feed management to reduce
excreted nutrients, manure handling and storage, the appli-
cation of manure and other wastes to crops and land, and
recordkeeping.
From an environmental standpoint, nitrogen and phos-
phorus are the nutrients of primary concern, and ammonia,
carbon dioxide, hydrogen sulfide, and methane are the
gases of primary concern (Tamminga, 1992; Chase, 1994;
Van Horn et al., 1994; Chandler, 1996; Johnson et al.,
1996; Koelsch and Lesoing, 1999; Kuipers et al., 1999;
Nelson, 19991. The loss of other mineral nutrients in animal
waste might become important in the future. Successfully
defining nutrient requirements of dairy cattle will minimize
nutrient losses in feces, urine, and gases. Reducing nutrient
244
OCR for page 245
Dairy Cattle Nutrition and the Environment 245
losses in waste from cattle and developing good waste Some 40-50 percent of the total nitrogen excreted in
management practices will decrease the concerns about manure is from urea and ammonia nitrogen excreted in
the effects of waste disposal on the environment. urine (Van Horn et al., 19941. Urea is rapidly converted
to ammonia in the presence of urease. In an acidic environ-
ment ammonia (NH3) reacts with H+ to form the nongas-
eous ammonium ion (NH4+~; this reaction prevents the
loss of NH3 to the atmosphere. However, most dairy cow
manure provides little acid for converting NH3 to NH4+,
and it releases large amounts of NH3 into the atmosphere.
In fact, 50-75 percent of the nitrogen can be lost from
manure mostly as NH3 before vitrification to nitrate (NO3-)
(Van Horn et al., 19941. Excessive concentrations of NH3
in closed buildings can lower animal performance and pose
a potential health hazard for cows and people. In addition,
NH3 emitted into the air can cause acid rain. If excessive
nitrogen is applied to land in manure, NO3- can contami-
nate surface water and leach into the groundwater.
Many aspects of dairy cattle nutrition will probably con-
tribute to improving the efficiency of nitrogen use in the
future, including optimizing the intake of nitrogen, ruminal
fermentation, the synthesis of microbial protein, and the
passage of ruminally protected amino acids to the small
intestine; absorption and postabsorption metabolism of
nitrogen; and the further development of integrated com-
puter models, feeding systems, and waste-management sys-
tems based on new scientific information generated from
research to determine nutrient requirements, increase eff~-
ciency of nutrient use, and decrease excretion of nutrients
into the environment (Clark and Overton, 19951.
It will be difficult to determine an exact amount of crude
protein to include in the diet that will provide optimal
performance in all situations. The amount of crude protein
needed in the diet will be influenced by milk yield, milk
protein percentage, growth rate, body size, amount and
type of energy in the diet, and amino acid composition
and degradability of dietary protein. Feeding diets that do
not meet requirements of ruminal microbes and dairy cows
decrease nutrient digestibility and production of milk and
milk components. An adequate supply of nitrogen is essen-
tial for maximizing carbohydrate digestibility in the rumen
(Oldham, 19841. Carbohydrate makes up the largest per-
centage of diets fed to dairy cattle, and anything that
increases carbohydrate digestibility increases energy avail-
ability to cows, decreases the volume of manure produced,
and reduces concerns about waste disposal. In contrast,
feeding a diet that contains too much crude protein is
wasteful, detrimental to the environment, inefficient for
dairy cattle because energy must be used to synthesize
urea that is excreted in urine, and costly to dairy farmers
because the protein is not used for productive functions
by dairy cows.
Feeding high-quality forages that are produced on the
farm will improve nutrient management and increase dry
matter (DM) intake. Maximizing DM intake will allow
NITROGEN
Nitrogen is of primary environmental concern because
of losses of ammonia in the air and because of nitrate
contamination of surface water and groundwater (Tam-
minga, 1992; Van Horn et al., 19941. Large amounts of
nitrogen are brought onto dairy farms in purchased feeds.
Much of this nitrogen remains on the farm rather than
being incorporated into milk, animal tissue, and crops that
are sold from the farm (Korevaar, 1992; Aarts et al., 1992;
Klausner, 19931. Klausner (1993) indicated that purchased
feeds supplied 62-87 percent ofthe total nitrogen on farms
and that the percentage of total nitrogen taken to farms
in feeds increased as herd size increased because a larger
percentage of the feeds was purchased rather than grown
on the farms. The percentage of the total nitrogen inputs
that remained on the farm ranged between 64 and 76
percent but was not related to herd size (Klausner, 19931.
The fraction of total nitrogen that remained on Dutch
farms was 85 percent (Korevaar, 19921. To prevent envi-
ronmental pollution and ensure efficient nutrient use, a
nutrient management plan should be developed for the
farm that will determine the movement and quantity of
nutrients entering, leaving, and remaining on the farm; a
nutrient application schedule that ensures that the rate
and timing of manure and fertilizer applications are in
concert with crop requirements while minimizing loss; and
a crop selection and rotational sequence that provides qual-
ity feed, improves nutrient recycling, and reduces runoff
and erosion (Klausner, 19931.
Dairy cows on average secrete in milk 25-35 percent of
the nitrogen that they consume (Chase, 1994; Chandler,
1996), and almost all the remaining nitrogen is excreted
in feces and urine. Van Horn et al. (1994) indicated that
total excretion of nitrogen in waste products can be deter-
mined by subtracting the amount secreted in milk from
the amount consumed. Feeding nitrogen in excess of
requirements, feeding excessive amounts of ruminally
degradable protein, or feeding diets not properly balanced
for ruminally degradable and undegradable protein, amino
acids, or energy may increase nitrogen excretion in feces
or urine (Pell, 1992; St-Pierre and Thraen, 19991. As milk
production increases, nitrogen excretion in feces and urine
per unit of milk produced decreases (Chandler, 1996; St-
Pierre and Thraen, 19991.
Ammonia and organic nitrogen are the major forms of
nitrogen in manure (Van Horn et al., 19941. This nitrogen
is from undigested feed, microbial protein, endogenous
nitrogen, and urea and ammonia nitrogen excreted in urine.
~ . . .. _ ~ _
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246 Nutrient Requirements of Dairy Cattle
dairy producers to feed diets that contain a lower percent-
age of crude protein and that will improve the efficiency
of nitrogen use by dairy cows and decrease the amount of
protein supplement that must be purchased (Chase, 19941.
A 5 percent increase in DM intake decreases the percent-
age of crude protein required in diets by about 1 percentage
point (Chase, 19941. Feeding total mixed rations formu-
lated from feeds analyzed to supply the exact amount of
nutrients required by dairy cows on the basis of milk pro-
duction, milk composition, body size, and pregnancy status
will be essential for maximizing efficiency of nitrogen use
and minimizing environmental pollution.
Optimizing ruminal fermentation, microbial protein syn-
thesis, and passage of selected nutrients to the small intes-
tine of dairy cattle offers potential for improving nutrient
management (Clark and Davis, 19831. During ruminal fer-
mentation, dietary protein is degraded to a mixture of
peptides, amino acids, and ammonia, and this supplies
precursors for synthesis of microbial protein. Excess
ammonia is absorbed through the ruminal wall and trans-
ported to the liver to be detoxified by synthesizing urea.
Any urea that is not recycled to the gastrointestinal tract
is excreted in urine; this represents a nitrogen loss from
cows to the environment. Both nitrogen and carbohydrates
are required for microbial growth; synchronization of car-
bohydrate and protein degradation should increase incor-
poration of nitrogen into microbial protein (Hoover and
Stokes, 1991; Clark et al., 19921. Digestibility of dry matter,
efficiency of microbial protein synthesis, and synthesis of
microbial protein in the rumen were maximized when diets
contained 10-13 percent of the dietary DM as ruminally
degradable protein and 56 percent of the total carbohy-
drate as nonstructural carbohydrate (Hoover and Stokes,
19911; however, further refinement of these estimates is
needed. Increasing feed intake and the amount of organic
matter digested in the rumen will supply additional energy
to fuel microbial growth if both protein and carbohydrates
are in adequate supply and their degradation is synchro-
nized (Clark et al., 19921. Faster growth of microorganisms
coupled with faster passage of microorganisms to the small
intestine resulting from increased feed intake should
decrease recycling of energy and nitrogen in the rumen
because of decreased cell lysis; this will decrease mainte-
nance requirements and trap more nutrients for growth of
the microorganisms (Clark et al., 1992; Russell et al., 19921.
Microbial protein supplies a large quantity of the total
amino acids passing to the small intestine; therefore, differ-
ences in passage of individual amino acids to the small
intestine when different diets are fed often are small (Clark
et al., 19921. From a nutrient-management perspective,
it is essential that use of amino acids be optimized for
production of milk and milk protein if dairy cows are to
use crude protein from the diet most efficiently. Schwab
(1994) reported that methionine and lysine were limiting
for production of milk and milk protein when they made
up less than 5 and 15 percent respectively of the total
essential amino acids passing to the small intestine. Feeding
protein supplements of low ruminal degradability to cows
has not consistently increased the passage of methionine
and lysine to the small intestine, probably because synthesis
of microbial protein often is decreased (Clark et al., 19921.
Even though passage of methionine and lysine to the small
intestine can increase in some situations, passage of other
amino acids to the small intestine probably will increase
also, and the desired ratio of amino acids will not be cor-
rectly balanced; the imbalance will result in inefficient use.
Feeding diets that contain lower concentrations of crude
protein supplemented with balanced quantities of rumen-
protected amino acids should minimize excretion of nitro-
gen in the urine.
The contributions of small peptides to microbial growth
in the rumen have not been quantified in dairy cattle.
Ruminal bacteria might transport peptides more rapidly
and efficiently than single amino acids (Chen et al., 1987),
and growth and efficiency of growth of ruminal bacteria
are improved when amino acids or peptides are supplied,
as opposed to ammonia (Maeng and Baldwin, 1976a, b;
Maeng et al., 19761. Therefore, the potential exists to
improve the efficiency of microbial protein synthesis by
manipulating the quantity and composition of peptides
supplied to the ruminal microorganisms.
Few data are available to quantify the absorption and
metabolism of amino acids by splanchnic tissues of lactating
dairy cows, but the use of many amino acids by the portal-
drained viscera is substantial (Reynolds et al., 19941. Fur-
thermore, the contribution of peptides to amino acid
absorption and transport is relatively unknown (Reynolds
et al., 19941. Substantial quantities of amino acids are prob-
ably absorbed from the gut as short peptides (Webb et al.,
1992, 1993), but research is needed to provide a better
understanding of absorption and metabolism of amino
acids and peptides by tissues of lactating dairy cows. Data
on the effects of amount and composition of peptides on
ruminal microorganisms and tissues of dairy cattle could
unlock mechanisms that will improve the efficiency of
nitrogen use and decrease nitrogen output in urine and
feces.
PHOSPHORUS
In some parts of the United States and in many other
countries, the amount of waste that can be generated by
a farm operation is regulated and limited by law. For
instance, in the Netherlands in 1987, laws were enacted
that limited the amount of phosphorus that could be
applied to the land to 55 kg/hectare. That corresponded
to limiting agriculture to about three cows or 17 pigs per
OCR for page 247
Dairy CattIe Nutrition and the Environment 247
hectare (Korevaar and den Boer, 19901. Regulatory agen-
cies usually give special attention to the role of phosphate
as an environmental pollutant, because it is relatively easy
to measure and does not volatilize or leach away, as does
much of the nitrogen excreted into manure and applied
to the land. Phosphate in manure that is applied to the
land is usually adsorbed onto soil particles, so it does not
leach into water tables or into waterways; therefore, it
builds up in the soil (Pierzynski et al., 19941. It will erode
into waterways with soil and causes environmental concern
because it is considered to be the nutrient that limits growth
of most aquatic plants (Sharpley et al., 19941. From a
regulatory standpoint, it is also felt probable that if an
excessive amount of phosphate is being excreted and
applied to the land, an excessive amount of nitrogen is also
being lost to the environment.
Nearly two-thirds of the phosphorus found in common
foodstuffs is unavailable to nonruminant animals because
it is bound to the organic acid phytate. In contrast, ruminal
microorganisms effectively break down phytate, making
a greater proportion of dietary phosphorus available to
ruminant animals. In the subcommittee's model the coeff~-
cients of absorption of phosphorus from the diet are 64
percent for forages, 70 percent for concentrates, and ~
70 percent for most ofthe inorganic sources of phosphorus.
Once the phosphorus needs of cows have been met by
the diet, most of the extra phosphorus will be excreted in
the feces and urine. Morse et al. (1992) fed lactating Hol-
stein cows diets that contained phosphorus at 0.3O, 0.41,
and 0.56 percent, which supplied GO, 82, and 112 g of
phosphorus/day, respectively. On the basis of the 1989
National Research Council requirements, the cows were
fed 79, 108, and 147 percent of their phosphorus require-
ment. According to the current model in this publication,
the cows required a diet that provided 58-62 g of phospho-
rus/day. Cows fed 60 g/day of phosphorus in the diet, which
provided less than required, excreted 42.1 g of phosphorus
in feces and urine. Cows fed 82 g/day of phosphorus
excreted 50.6 g/day of phosphorus in feces and urine, or 5 g
for each 22 g of phosphorus fed in excess of requirements.
Cows fed 112 g/day of phosphorus excreted 79.9 in feces
and urine. Increasing dietary phosphorus intake from 82 g/
d to 112 g/d (a 30 g/d increase) increased phosphorus excre-
tion in feces and urine by 29.3 g/d. Wu et al. (1998) and
Satter and Wu (1999) showed that the loss of fecal phospho-
rus increased greatly once the needs of the animal were
met, which occurred at about 0.35 percent dietary P in their
experiment. They also showed that the dietary requirement
for phosphorus can be met with diets that are below the
requirement suggested in the 1989 National Research
Council publication which was 0.48 percent in diets for
cows in early lactation and 0.41 percent in diets for cows
in later lactation. Many dairy rations contain phosphorus in
excess of the needs of cows. A survey of nutritionists indi-
cated that the average concentration of phosphorus in diets
fed to commercial herds was about 0.52 percent for high-
producing dairy cows (Sansinena et al., 19991.
SUMMARY
Dairy cattle should be fed to meet but not to exceed their
nutrient requirements. Feeding diets that are deficient in
any nutrient will decrease production of milk and milk
components; however, feeding excessive amounts of a
nutrient will decrease the efficiency of nutrient utilization,
which results in increased nutrient excretion into the envi-
ronment, increased cost of milk production, decreased
profits for dairy producers, and increased costs for the
consumers of dairy products. Production of milk by dairy
cows causes losses of nutrients in feces and urine that can
not be prevented. Because nutrients accumulate on dairy
farms, nutrients should be managed to ensure efficient
nutrient cycling with a minimum impact on the
environment.
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~ 1 1
Representative terms from entire chapter:
amino acids
