CONCEPT OF AMINO ACID BALANCING IN DAIRY CATTLE

June 19, 2019

1319

CONCEPT OF AMINO ACID BALANCING IN DAIRY CATTLE
by-DR. RAJESH KUMAR SINGH, (LIVESTOCK & POULTRY CONSULTANT), JAMSHEDPUR, JHARKHAND,INDIA 9431309542, rajeshsinghvet@gmail.com

Introduction

Amino acids are the building blocks for protein, one of the most critical nutrients in the dairy cow ration. While the benefits of amino acid balancing can be great— increased milk and components, reduced ration costs and improved feed efficiency—the practice of balancing for these protein building blocks is often overlooked. Understanding the role amino acids play and why they are critical to the diet can help deliver a more precise ration for boosting performance and maintaining a healthy herd.
Protein is first limiting nutrient in cattle& buffalo diet because they are fed with poor quality roughages, which have low protein content and its low availability. Dietary protein requirements of cattle & buffalo depend upon the microbial population in the digestive system. Ruminal microbes alter the quality and quantity of dietary protein before it reaches in small intestine. The protein absorbed in small intestine is named as metabolizable protein. Metabolizable protein is efficiently utilized when there is a balance of amino acids required for the animal’s maintenance and milk production. Dietary protein degradation in rumen is about 60 to 70% which later forms microbial protein, due to which there is less chances of availability of original amino acid supplied through diet to animal. There is a possibility that better quality protein is degraded in rumen (chain of amino acids). Alternatively, there is other practical way to reach required level and ratio of amino acids, through dietary supplementation with rumen protected amino acids, so that any amino acids imbalance is corrected and overall utilization of dietary protein is improved. Amino acid nutrition of dairy cattle & buffaloes has received a lot of attention over the last few years. Two essential amino acids viz. lysine and methionine are limiting amino acids for milk protein and milk production. Lysine and Methionine are found in low concentration in feed protein and it cannot fulfill the animal requirement, secondly microbial protein is also insufficient to meet the animal’s requirements. So protected Lysine and Methionine are added in feed to fulfill the deficiency of these amino acids.
Rumen-degradable protein (RDP) is required by rumen microorganisms and amino acids (AA) are required by the cow.
Amino acids are the required nutrients, not Crude Protein, for the dairy cow.
Methionine and Lysine are the most limiting Amino acids, and Methionine is more essential than Lysine.
Balancing for Lysine and Methionine can provide significant opportunities for minimizing the risk of cows experiencing amino acids deficiencies and for reducing the need for protein supplements.
Increases in milk protein and fat concentrations observed with Lysine and Methionine balancing reflect an improved protein status that can have far-reaching effects on health and performance.
Balancing for amino acid has been a contributing factor to higher milk yields, higher milk component levels, and greater dairy herd profitability for many dairy producers

The shortage of feeds and forages is the major constraint in accelerating the growth of animal production in India . The feeding stuffs available are of poor quality and their nutrients are poorly utilized by animals. These feedstuffs are less digestible and contain lower quantities of energy, protein, minerals, and vitamins; consequently, the nutrients available to animals are further decreased. Crude protein (CP) content of these feedstuffs is low, and its utilization is further impeded due to non-availability of rumen fermentable energy source. In ruminants, a large portion of the feed protein is transformed into microbial protein and is ultimately absorbed along with escaped feed protein. Absorbable amino acids from feed origin and microbial origin constitute metabolizable protein (MP), which is in true sense utilized by the animal for maintenance, growth, and production . For many years, CP content has been used in formulating diets for lactating dairy cows because there was little information available regarding the response of dietary protein in complex ruminal microbial environment . In addition, it was long been postulated that the high quality microbial crude protein (MCP) synthesized in the rumen would complement deficiencies in the quality of dietary protein that escaped ruminal fermentation. However, for high yielding cows, microbial protein synthesis supplies a decreasing proportion of the required protein, and significant amounts of dietary protein must escape ruminal degradation in order to meet protein needs. On the other hand, the animal scientists are under strong pressure to design ways to reduce nitrogen (N) losses from ruminants in order to prevent environmental pollution. Therefore, present research works are being diverted toward improving the efficiency of N utilization by lactating cows while maintaining optimum milk production levels. The CP system does not have a provision for differentiating between the requirements of ruminal microbes and the requirements of the host animal. Therefore, supplementations based on the CP system may result in protein deficiencies in animal. Thus, time has come to replace the current protein evaluation system to MP system, which has many advantages over the old ones. The system provides a more rational description of the energy available for microbial growth (fermentable metabolizable energy [FME]) by discounting the energy content of dietary lipids and fermentation end products . Another advantage with MP system is that it provides a framework with which the net absorption of amino acids from the small intestine can be computed in relation to the animal’s requirement . MP system is also a better predictor of milk yield in lactating animals than CP . Hence, replacement of conventional CP system with MP system seems to be a better idea to define and refine protein utilization and diet formulation as this system fits well with the biology of ruminants.

Amino Acids – The Required Nutrients ————

It has been known for decades that animals require AA for the synthesis of
tissue, regulatory, protective and secretory proteins and that there are hundreds of
these proteins that must be synthesized every day. It is also well documented that the AA composition of each protein is different, that protein synthesis is a genetically determined event, and that as a result, the AA composition of a protein is the same
every time it is synthesized. Besides their role in protein synthesis, which affects
virtually every aspect of metabolism in every living cell, AA are also key regulators of various pathological and physiological processes, including immune responses, as well as being used for the synthesis of all of the other N-containing compounds in the body, which includes dozens of compounds such as hormones,neurotransmitters, nucleotides
(RNA and DNA), histamine, polyamines such as such as spermine and spermidine, etc.
These observations are mentioned to highlight the impact that AA have on overall body metabolism and the likely importance that optimizing AA nutrition has on health, fertility and production performance of animals. Finally, for nearly as long as the nutritive
significance of AA has been recognized, it has been known that some of the AA cannot be synthesized by the animal, or synthesized fast enough, from other AA, to meet requirements for protein synthesis. These AA were termed essential AA (EAA) (Rose,1938). The remaining AA that are needed for protein synthesis but can be synthesized
by the animal were called nonessential AA.

Importance of Amino Acid Balance

What this early understanding of AA nutrition and subsequent research has indicated is that: 1) AA are the building blocks for protein synthesis, 2) the ideal profile of absorbed EAA may be different for maintenance, growth, pregnancy and milk production and that as a result, the ideal profile may be different for an animal at different stages of its life cycle or at different physiological states (e.g., high vs. low milk production), and that 3) providing a more balanced profile of absorbable EAA allows meeting AA requirements with less dietary protein. The latter point has been exploited by the swine and poultry industry. By selective use of protein supplements and feed grade sources of the most limiting AA such as Lys and Met, AA requirements are being met with lower concentrations of dietary protein.

Balancing diets for AA also has the advantage of sparing dietary protein for dairy
cows, but the protein fraction that is spared is RUP, not RDP. Balancing diets for AA
provides the opportunity to supply similar or greater amounts of the most limiting AA with reduced or similar concentrations of RUP. However, because microbial protein provides about 50% of the absorbed AA requirements of lactating dairy cows, there is
less opportunity to spare as much as RUP in cows as total dietary protein in pigs or
chickens.

Limiting Amino Acids ———-

Lysine and Met have been identified most frequently as the two most limiting AA
for lactating dairy cows in North America (NRC, 2001). A variety of research studies
continue to support these early observations (e.g., Appuhamy et al., 2011, Chen et al.,
2011; Doepel and Lapierre, 2010, 2011; Noftsger and St-Pierre, 2003; Noftsger et al,
2005; Ordway et al., 2009; Socha et al., 2005; St-Pierre and Sylvester, 2005). That Lys and Met are the first two limiting AA for lactating dairy cows should not be surprising given their low concentrations in most feed proteins relative to their concentrations in rumen bacteria or in milk and tissue protein (Table 1).

Many nutritionists have questioned the possibility of histidine (His) as a potential
limiting AA. However, to the author’s knowledge, His has only been identified as first
limiting when grass silage and barley and oat diets were fed, with or without feather meal as a sole or primary source of supplemental RUP (Kim et al., 1999, 2000, 2001a,
2001b; Huhtanen et al., 2002; Korhonen et al., 2000; Vanhatalo et al., 1999). None of these diets contained corn or corn byproducts. Based on NRC (2001) predicted
concentrations of Lys, Met, and His in MP for the diets fed in these experiments,
coupled with similar evaluations of diets where cows have (or have not) responded to increased levels of Lys and Met in MP (McLaughlin, 2002), leads the author to speculate that His may become the third limiting AA in some diets, particularly where no
blood meal is being fed and where barley and wheat products replace significant
amounts of corn in the diet.

Reasons for Providing Lactating Dairy Cows with Optimum Concentrations of Lys and Met in MP

1. Reduce the risk of cows experiencing a Lys or Met deficiency, or both, and the
resulting consequences of reduced protein synthesis on health and fertility, growth
and N balance, and milk and milk component production and increase their chances
of realizing their genetic potential for milk yield and component concentrations.
Current literature is limited on the metabolic effects of specific AA deficiencies in
cows, over and beyond the effects on lactation performance, but it seems
reasonable to think that the reported effects of Lys and Met deficiencies in pigs and
chickens are also true for lactating dairy cows.
2. Take advantage of the opportunity to feed less RUP in herds where RUP is being
over-fed because of low concentrations of Met, or Met and Lys, in RUP and MP.
3. Increase efficiency of conversion of RUP and MP to milk protein and minimize
wastage of dietary N.
4. Increase income-over-feed-costs and dairy herd profitability.

Balancing Diets for Lys and Met

The following five feeding strategies have been shown to be effective in balancing diets for Lys and Met, allowing producers to realize the benefits expected of balancing diets for AA.
1. Feed a mixture of high quality forages, processed grains, and byproduct feeds that will provide a blend of fermentable carbohydrates and physically effective fiber that maximizes feed intake, milk production, and yield of microbial protein. Microbial
protein has an apparent excellent AA composition for lactating dairy cows. The
average reported concentrations of Lys and Met in bacterial true protein of 7.9% and 2.6% (Table 1) exceed the optimum concentrations of 7.2-7.3% and 2.4-2.5% that were established by Rulquin et al. (1993), NRC (2001) and Doepel et al. (2004)
(Table 2). Other than the concentrations of both Lys and Met in fish meal, the
concentration of Lys in blood meal and Met in oats, the concentrations of Lys and
Met in rumen bacteria far exceed concentrations in most other feeds.
2. Feed adequate but not excessive levels of RDP to meet rumen bacterial
requirements for AA and ammonia. Realizing the benefits of feeding a balanced supply of fermentable carbohydrates on maximizing yields of microbial protein also
requires balancing diets for RDP. Rumen degraded feed protein is the second
largest requirement for rumen microorganisms. It supplies the microorganisms with peptides, AA, and ammonia that are needed for microbial protein synthesis. The amount of RDP required in the diet is determined by the amount of fermentable
carbohydrates in the diet. Diet evaluation models differ in their estimates of RDP in
feeds and animal requirements. The NRC (2001) model typically predicts RDP
requirements of 10 to 11% of diet DM. Regardless of the model used, it is important
to use the predicted requirements ONLY AS A GUIDE and to fine tune according to
available research and animal responses. Monitor feed intake, fecal consistency,
milk/feed DM and N ratios, milk fat concentrations, and milk urea N (MUN) to make
the final decision. A common target value for MUN is 10 mg/dL, but values lower
than this is not uncommon in high producing cows with more precise feeding.
Don’t short-change the cows on RDP…superior carbohydrate balancing can be negated with an inadequate supply of RDP. Underfeeding RDP decreases
microbial digestion of carbohydrates, decreases feed intake, decreases synthesis of microbial protein, decreases production of volatile fatty acids (VFA), and decreases
milk yield. A deficiency of RDP can suppress the ability of the microorganisms to
reproduce without affecting their ability to ferment carbohydrates. This will can result in lower than expected milk/feed ratios because of lower than expected synthesis of microbial protein. Also, avoid over-feeding RDP to the point that rumen ammonia concentrations markedly exceed bacterial requirements and MUN become high. Not only does it result in wastage of RDP, but there is also good evidence that it decreases flows of microbial protein to the small intestine (e.g., Boucher et al., 2007; Peter Robinson, personal communication).
3. Feed high-Lys protein supplements, or a combination of high-Lys protein supplements and a rumen-protected Lys supplement, to achieve concentrations of
Lys in MP that come as close as possible to meeting the optimal concentration
(Table 2).
Feeding low-Lys, high-protein feeds such as corn gluten meal is NOT consistent with balancing for Lys. In similar fashion, feeding larger amounts of dried distiller’s
grains with solubles (DDGS) also compromises balancing for Lys and requires
feeding more RUP that would otherwise be needed to realize similar yields of milk
protein. There may well be times when it is economical to feed larger amounts of
DDGS, but it comes at the metabolic expense of having to feed more RUP.

4. Feed a “rumen-protected” Met supplement in amounts needed to achieve the
optimal ratio of Lys and Met in MP.
Feeding a rumen-protected Met supplement, in conjunction with one or more of the
aforementioned high-Lys protein supplements, is almost always necessary to
achieve the correct Lys/Met ratio in MP (Table 3). To achieve the desired predicted
ratio of Lys to Met in MP, and to ensure full use of the available MP-Lys for protein
synthesis, it is important to use a realistic estimate for the amount of MP-Met
provided by the Met product that you are feeding. Over-estimating the efficacy of a RP-Met supplement usually leads to disappointing production outcomes, and more
often than not, leaves the nutritionist and dairy producer believing that balancing for
Lys and Met has little value.
5. Do not overfeed RUP.

There are several disadvantages to overfeeding RUP. These include: 1) lowered concentrations of Lys and Met in MP (because most sources of supplemental RUP
contain low concentrations of Lys, Met or both, relative to optimal concentrations in
MP), 2) lowered milk production (because surplus RUP usually replaces
fermentable carbohydrates in the diet, the primary substrates for synthesis of milk components), 3) a more expensive diet (because most sources of supplemental
RUP are more expensive than most sources of nonfiber cabohydrates), and 4)
increased urinary and fecal N (because of lowered conversions of feed protein to milk protein).

Identifying the optimum concentration of RUP in diet DM is challenging. The
nutritional model that you use can be used as a guide, but it should not be used to
provide the final answer. The reason is that there are too many factors that affect
RUP requirements (e.g., intestinal supply of microbial protein, RUP digestibility,
RUP-Lys digestibility, and concentrations of Lys and Met in MP) for current
nutritional models to adequately consider and adjust requirements for. Each of these factors can have a significant effect on how much RUP is needed. Therefore, unless you are feeding an average diet to which your model validates, it is more than likely that your model will under or over estimate RUP requirements.

While disappointing, it must be emphasized that current models do not adjust MP
requirements, and thus RUP requirements, for changes in predicted concentrations
of AA in MP. This is a serious deficiency and until models are designed to predict

milk and milk protein yields from supplies of MP-Lys and MP-Met, just know that the MP requirement, and therefore the RUP requirement, for a given yield of milk and milk protein decreases with higher concentrations of Lys and Met in MP.

As a second step for identifying the optimum concentration of RUP in diet DM, it is suggested that insofar as feeding management allows, let the cows tell you how
much they need. Don’t be surprised, as a result of balancing for Lys and Met in MP, how little RUP is actually needed in the diet. Moreover, field experience indicates
that cows are more responsive to changes in diet RUP content when RUP has a
good AA balance vs. when the balance is not good. This makes sense because the
nutritional potency of the RUP is greater when it has a good AA balance vs. a poor
AA balance.

Benefits of Balancing for Lys and Met in MP

Balancing for Lys and Met in MP, using the steps as outlined, has led to many
important benefits, both in research and on-farm implementation. The benefits include:
1) increased milk yields, 2) increased concentrations and yields of milk protein and fat,
3) reduced need for supplemental RUP for similar or greater component yields, 4) more
predictable changes in milk and milk protein production to changes in RUP supply, 5)
reduced N excretion per unit of milk or milk protein produced, 6) improved health and
reproduction, and 7) increased dairy herd profitability. That these benefits to balancing
for Lys and Met in MP have been achieved supports the conclusion that while other AA may become limiting, it seldom occurs before the recommended target levels for Lys and Met are achieved.
The most understood and appreciated benefits of improved Lys and Met nutrition are affects on lactation performance and the need for supplemental RUP. Increased milk component concentrations are the most visible and generally are the quickest to
occur. It is no longer uncommon to hear reports of increases in milk protein
concentrations of 0.20 to 0.25 percentage units and increases in milk fat concentrations of 0.10 to 0.15 percentage units…often on less dietary RUP. This does not mean that responses of this magnitude are always observed, but what it does mean is varying degrees of Lys and Met deficiency exist among herds and that one can expect variable effects on animal performance when balancing for Lys and Met. Increases in milk protein percentages are the most visible of the responses to better AA nutrition, and
when observed, it should only be considered as the “the tip of the iceberg”.

Increases in milk yield will also occur. This response is sometimes more difficult
to measure because of the inherent greater variability in milk yield than milk protein concentrations on a day-to-day basis and the fact that research has shown that a smaller percentage of cows will respond with higher milk yields. Nevertheless, this is both an expected and observed response. Early studies indicated 2 to 5 lb more milk in early lactation (Garthwaite et al., 1999). More recent studies now have shown 5 to 10 lb
more milk. Increased milk yields in early lactation may or may not be accompanied by increases in milk protein percentages if levels of Lys and Met in MP are not pushed high enough. What field observations in particular have indicated is that if you see an increase in milk protein percentages, assume at least some increase in milk yield.

As mentioned earlier, a “feed advantage” to balancing for Lys and Met is the possibility for reduced RUP feeding while achieving similar or higher milk component levels and milk yields. Research and field observations alike indicate that it is no longer uncommon to see reductions in RUP of 1.0 to 2.0 percentage units of diet DM. This confirms that cows require “grams of amino acids” and not “grams of MP).

Amino Acid Requirements:—————

Dairy cows require amino acids to make milk and muscle protein, to make the protein in a growing fetus, and to make the proteins they need to maintain themselves (such as enzymes required to digest feeds). Each of these proteins is made up of a different profile of amino acids. For this reason, a cow will require different amounts of each of the essential amino acids depending on her stage of lactation, growth, and pregnancy.
Amino acid requirements can be expressed using either the factorial method or the ideal protein method. With the factorial method, requirements are based on the needs of the animal (for example, the amount of milk to be produced and its amino acid content) and the various efficiencies with which amino acids are absorbed and utilized. Unfortunately, these efficiencies are difficult to estimate. The mammary gland takes up more of some amino acids than it puts out in milk. With some non-essential amino acids, the mammary gland takes up fewer than are found in the milk produced. The pattern of amino acids needed for milk production is therefore different than the amino acid pattern of milk.
UPTAKE OF AMINO ACIDS BY THE MAMMARY GLAND VERSUS OUTPUT OF AMINO ACIDS IN MILK (G/100 G AMINO ACIDS)
Amino Acid Total Uptake Mammary Output
Arginine 8.53 3.40
Histidine 3.29 2.74
Isoleucine 8.80 5.79
Leucine 13.04 9.18
Lysine 9.14 3.40
Methionine 2.82 2.71
Phenylalanine 4.51 4.75
Threonine 4.76 3.72
Valine 10.01 5.89
Evans, 1999
Body cells use active transport mechanisms to take up amino acids. There are 3 different types of transport for amino acids: neutral amino acids (threonine, leucine, valine, isoleucine, phenylalanine, methionine, cystine/cysteine, and tryptophan), basic amino acids (histidine, arginine, and lysine), and acidic amino acids. Within an amino acid type, one amino acid can compete for and inhibit the transport of another amino acid. Because of the potential negative effects of amino acids on each other, the factorial method may overestimate production responses when there is an excess of one amino acid. For example, in one study where lysine was the first-limiting amino acid and extra methionine was supplemented, milk protein production was actually reduced (Rulquin and Verite, 1993).
For this reason, the ideal protein method (ratio approach) is more commonly relied upon to balance rations for amino acids. The ideal protein method is based on research study responses to amino acids expressed as a percentage of either metabolizable protein or intestinal essential amino acids. The relationship of amino acids to each other drives the ration rather than the actual amount of individual amino acids absorbed. According to the research of Schwab at the University of New Hampshire , 5% of the intestinal essential amino acids should be methionine and 15% should be lysine. According to research from Rulquin and Verite in France , 2.5% of the metabolizable amino acids should be methionine and 7.3% should be lysine. The NRC (2001) publication summarized a large dataset and concluded that 2.2% of the metabolizable amino acids should be methionine and 7.2% should be lysine. Without supplementation of individual amino acids, it’s hard to reach these goals. According to Sniffen et al., 2001, milk protein is reduced when methionine is less than 2.1-2.2% of metabolizable amino acids and lysine is less than 6.0-6.5% of metabolizable amino acids. Sniffen et al., 2001 analyzed the results from 21 experiments that were conducted with rumen-protected lysine and methionine and a range of concentrates and forages. For milk production and milk crude protein yield, the optimum amount of methionine was 2.07% of metabolizable protein and the optimum amount of lysine was 7.04% of metabolizable protein.
Based on their modeling work, Sniffen et al., 2001 endorsed the ratio approach to amino acid balancing. However, it was recognized that the metabolizable protein requirement must still be met and that factorial supplies of individual amino acids should still exceed factorial requirements. At this time, computerized models using both the factorial approach and the ideal ratio approach for balancing amino acids should be the most effective.