IMPORTANCE OF FEEDING PROTECTED AMINO ACIDS IN RUMINANTS
Today, the dairy sector is facing several challenges; the increase in feed raw material prices, the high volatility of agri-food products of livestock origin, a decline in meat and milk consumption and, the public view that the dairy sector has a big impact on global warming. At the same time, ruminants are experts in converting low quality roughage or by-products that are not suitable for human consumption into high quality animal protein, contributing substantially to the high demand for animal protein in human diets. We will need to increase the rate of food production to meet the needs of a growing population and for that, farming practices need to become more efficient and sustainable. There is a major opportunity for ruminants to produce more efficiently thanks to better protein efficiency and as a result reduced nitrogen (N) excretion. Although feed-efficient ruminant production is a complex system, it often starts with better N efficiency. Improvements in the efficiency of N conversion represent one of the biggest impacts on farm profitability. At the same time, this allows us to reduce methane excretion per kilogram of milk produced.
In today’s Indian animal feeding systems, protein quality and pricing are important considerations. Compared to nonruminants, ruminants require the same amino acids at the tissue level and have a similar protein metabolism (ARC, 1980). However, in ruminants, the amount and profile of amino acids accessible at the absorption site depend entirely on complex protein decomposition in the rumen, not on amino acids in the feed diet. To create microbial protein, crude protein from the feed is digested in the rumen to a combination of amino acids, ammonia, and peptides, which supplies most of the amino acids in the small intestine (Iburg and Lebzien, 2000). The status of amino acids in ruminants’ small intestines can be altered by feeding them foods of varying degradability, resulting in conditions that allow faster passage through the rumen. Because ruminal bacteria modify the amount and quality of ingested protein before it reaches the small intestine to be absorbed by the animal, the dietary protein requirements for the host animal are complicated. As a result, the protein available for absorption in the small intestine of animals is also known as metabolizable protein (MP), which is a postruminally digested protein (NRC, 2001). It bears little relation to the protein quantity and quality provided by the diet. For ruminants, microbial protein is the primary source of absorbable amino acids in the small intestine. Ruminal microorganisms, such as bacteria, protozoa, and fungi, create microbial protein. Ruminal bacteria have a nitrogen requirement for growth, which can be met by supplementing the ruminal environment with peptides, amino acids, and ammonia (NRC, 2001). On the other hand, microbial protein may not provide enough absorbable amino acids to meet the needs of quickly growing animals. Rumen microorganisms synthesize amino acids from dietary protein sources.
Protein is an important limiting nutrient in ruminant animals fed low quality forages. It becomes necessary when animal attains its optimum growth or peak production. This is because nutrient requirements of ruminants vary according to the physiological state like growth, lactation and pregnancy. Ruminant animals fed on poor quality forages with inadequate protein showed better performance with supplementation of quality protein or RPAA particularly Met and Lys.
It has two fractions: RDP and RUP/RPP. The rumen microbes breakdown the degradable protein to small peptide, AA and ammonia, which in turn, can be used by the microbes for synthesis of microbial protein. Its synthesis is limited by the rate of passage of feed from the rumen. Therefore, supplementation of RDP, RUP or AA is considered important to satisfy animal’s requirements. Supplementation of RPM increases the proportion of dietary AA that is absorbed from the intestine (Archibeque et al., 2002). They said that the absorbed Met meets a critical limitation and improves the overall use of N in the diet. There is more potential to produce profit, while minimizing undesirable environmental impacts through modification of urea kinetics.
Protein is an expensive nutrient of dairy animal diet. Improvement in protein nutrition can help in improving the economic performance of dairy farm. However, feeding a diet containing more protein is not a satisfactory solution because the breakdown of dietary protein in the rumen is one of the most inefficient processes in ruminant nutrition. In typical dairy ration, 25-30% of the feed protein reaches the small intestine for absorption. In an attempt to overcome this inefficiency, dietary protein sources that are considered to be good sources of rumen undegradable protein have been used. The other practical way to reach required level and ratio of amino acids is 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 cows has received a lot of attention over the last decade resulting in several nutritional models which allow for diet formulation on the basis of amino acids.
Reducing nitrogen losses
Depending on the animal species, ration and management, between 5% and 45% of the N in vegetable proteins is converted into meat or milk. The other 55-95% is excreted (via urine or manure) and can be used as a source of nutrients for plant production. However, the efficiency of re-conversion of the N into plant protein is limited; only a maximum of 60% of the N applied to the soil can be converted to vegetable protein and the rest will be lost. This is especially important when we consider that the estimated overall amount of N excreted by animals is comparable with the annual consumption of N fertilisers, if not higher. Strategies to reduce losses and improve the efficiency of ruminant production systems rely on an optimal supply of rumen degradable N and optimal efficiency of utilisation of absorbed amino acids (AAs). Generally, in ruminants the observed efficiency of conversion between N consumed and N deposited into protein varies between 20 and 32%, but the maximum theoretical efficiency should be between 40 and 45%. A practical objective would be to achieve around 40% conversion, and this goal can be reached by formulating for low crude protein (CP) and balancing for AAs.
Using protected amino acids
Over the last few years, tremendous research efforts have been made to refine the protein requirements of dairy cows. Our growing understanding of cow requirements has led to recognising 2 sets of protein requirements: rumen degradable protein (RDP), and rumen undegradable protein (RUP). Metabolically the cow, of course, has specific requirements for individual AAs, rather than metabolizable protein (MP). Together, the complex microbial metabolic activity in the rumen and processes in the intestines make the study of N metabolism in ruminants more challenging than in the case of non-ruminants. AAs are the building blocks of milk and body proteins and they are considered to be one of the most important nutrients in dairy cow nutrition. Many of these AAs need to be supplemented in the diet, because they can’t be synthesized quickly enough to meet the requirements of producing cows. Therefore, these amino acids are known as essential AAs. Inadequate supply of essential AAs can limit milk and milk protein yield. The essential AAs that are present in MP in the smallest supply relative to the cow’s requirements is referred to as limiting AAs. Methionine (Met) and lysine (Lys) have been recognised as the first limiting AAs for lactating dairy cows under most feeding practices. This is fundamentally true because feed proteins have lower concentrations of Met and Lys when compared to their concentrations in milk and microbial protein. Mid-range crude protein diets in Europe are not able to meet Met or Lys needs with the use of dietary feed ingredients, so the use of rumen protected (RP) supplements is required. Different technologies have been developed to protect Met and Lys from microbial degradation, allowing the RP-AA to pass to the abomasum and small intestine where they are absorbed. These protected forms help to formulate feeds more precisely.
Role of Rumen-Protected Amino Acid
In addition to its direct role in protein synthesis, methionine can be transformed to Sadenosylmethionine (SAM), which serves as a methyl group donor in various transmethylation processes in the body (Loest et al., 2002). The creation of polyamines and the methylation of phospholipids, proteins, nucleic acids, and a variety of other compounds are all SAMdependent processes. Methionine is also involved in synthesizing phospholipids, carnitine, and polyamines, among other things. Methionine also plays a role in synthesizing cysteine via homocysteine, a result of SAMdependent methylation processes and a crucial branch point between cysteine trans sulphuration and methionine remethylation. Sadenosyl methionine, a metabolite that provides methyl groups in various processes, including the de novo production of choline from phosphatidylethanolamine, is also derived from methionine. Lysine is a metabolically essential amino acid that is required for average growth. It aids in creating collagen and the production of carnitine, a nutrient that aids in the Boxidation of fatty acids and the production of energy. Supplemental lysine has also been linked to calcium absorption and preservation. There is a rising interest in improving amino acid delivery to the duodenum to precisely address the amino acid requirements for ruminant animal health and production. Although an increase in milk supply, milk protein, or milk fat has been recorded in highproducing dairy cattle fed rumen-protected methionine and lysine, the effect on growth, nutritional utilization, and blood metabolites is unknown. As a result, the purpose of this study is to see how additional rumen-protected methionine and lysine affects development, nutritional utilization, and specific blood metabolites in dairy calves fed under Indian circumstances
Degradation of protein and amino acids in the rumen
Feed proteins are hydrolyzed into peptides and amino acids by the rumen microorganisms.However, most of the amino acids are rapidly degraded to organic acids, ammonia and carbon dioxide. The ammonia produced is the primary nitrogenous nutrient for bacterial growth. Some species of ruminal bacteria use peptides directly for synthesis of microbial protein. The microbial protein alone is sufficient to meet the needs of cattle at or near maintenance. However, young growing cattle and lactating cows need bypass protein in addition to microbial protein to meet their metabolizable protein requirements.
Protection of protein from ruminal degradation
To avoid the ruminal degradation of high quality proteins and to reduce wasteful ammonia production in the rumen, it is possible to protect proteins using several procedures such as heat treatment, chemical treatment/modification, inhibition of proteolytic activity and identification of naturally protected protein sources. Heat treatment has been used to increase the undegradable protein of common feedstuffs such as soybeans and grains.
Treatment of proteins with formaldehyde is the most widely used process and has been exploited commercially. The use of these techniques improves the supply of amino acids without an increase in ammonia production, resulting in better performance by the animal.
Limiting Amino Acids
Dairy cattle have amino acid requirements for maintenance, growth, reproduction, and production (NRC, 2001). The amino acids available for digestion and absorption in the intestine come from three sources: microbial protein, undegraded dietary protein and endogenous protein from sloughed cells and secretions in the digestive tract. Ruminants have the ability to synthesize all amino acids. However, ruminants still require dietary amino acids since there is a limit in synthesizing capacity of rumen microbes (Bailey, 2000). Out of 22 amino acids, lysine and methionine are the first two amino acids that can limit production in dairy cattle on maize and soybean based diet, respectively. Recent research has indicated that histidine is probably the first limiting amino acid on grass silage based diet. Lysine and methionine are identified most frequently as first limiting essential amino acid in metabolizable protein of dairy cattle. Balancing amino acids to formulate dairy rations in a way that maximizes microbial protein synthesis. Microbial protein synthesis is important as it contains a good amount of lysine and methionine. Besides, it is economical source of lysine and methionine.
Methods of amino acid protection:
These can be divided into three main categories
- Surface coating with a fatty acid or pH sensitive polymer mixture
Surface-coating of methionine with enzyme-resistant, pH-sensitive synthetic polymer that is insoluble in neutral pH environment of ruminal digesta but highly soluble in the acidic environment of abomasum is the most effective approach. This approach provides a postruminal delivery system that is independent of enzyme, pH difference between the rumen and the abomasum. Polymer-protected methionine has high ruminal protection and intestinal release coefficient (Robert and Williams, 1997; Schwab, 1995).
- Surface coating or matrices involving fat or fatty acids and minerals
Amino acids are formulated as calcium salts or lipids which have poor solubility in the rumen. Several lipid protected methionine products have been evaluated. The greatest challenge with using lipids as the primary encapsulating material is to identify a combination of materials that provide a coating or matrix that give a reasonable degree of protection against ruminal degradation and intestinal release.
- Liquid sources of hydroxy analogs
Amino acid analogs are chemically modified molecules generated from the substitution of the á-amino group of the amino acids with a non-nitrogenous group such as a hydroxyl group. The most studied amino acids analog is Met hydroxy analog (MHA; DL-áhydroxy-ã- mercaptobutyrate) or more appropriately called 2-hydroxy-4-methylthio butanoic acid (HMB). Studies indicate that free HMB is more resistant to ruminal degradation than free methionine and ruminants have the enzymes for the conversion of HMB to methionine.
Recent research has shown that several esters of HMB enhance ruminal escape of HMB, at least in part because of their apparent ability to be absorbed across the rumen wall. The isopropyl ester of HMB has been shown to have an excellent replacement value for absorbed methionine (Schwab et al., 2001).
Advantages of protection
Post ruminal utilization of nutrients eliminates energy losses associated with fermentation and protein losses incurred in the transformation of dietary protein to microbial protein. Protection from ruminal degradation enables more amino acids to reach the intestine and therefore provide more absorbable amino acids per unit of absorbable energy. Lara et al. (2006) reported increased milk production (35.8 kg /d) and protein yield (3.16 kg/d) on addition of rumen protected methionine (RPM) and indicated that Holstein cows with a mean production of 35 kg/d milk require addition of ruminally protected methionine (16 g/d) to improve milk production. Similarly, Broderick et al. (2009) reported that supplementation of RPM and RPL enhanced the milk yield in crossbred cows. Socha et al. (2008) found an increase in milk production on abomasal infusion of methionine and lysine during peak and early lactation while there was no difference in mid lactation. Broderick et (2009) reported that supplementation of RPM in diet with reduced crude protein level resulted in increase in milk yield, milk fat and protein yield, indicating protein sparing effect of rumen protected amino acids. Thus, use of rumen protected amino acids can be used as an opportunity to reduce crude protein level of the diet and a significant amount of money can be saved. Amrutkar (2011) supplemented 5g/d of RPM and 20g/d RPL during prepartum period to crossbred cows and found that duodenal supply of methionine and lysine was increased.
However, the proportions of saturated fatty acids, unsaturated fatty acids, MUFA, PUFA in milk fat were not affected in cows fed ration fortified with RPM and RPL. Davenport et al. (1990) fed rumen protected lysine @6g/head to crossbred calves for 100 days and observed increased average daily gain in calves. Positive growth responses and increased N retention of growing ruminants were reported in several studies when lysine or methionine were infused postruminally or fed in ruminally protected forms. Besides this, methionine has a favorable role in hepatic metabolism through its capacity as a methyl donor. It plays a key role in evacuating triglycerides from the liver to peripheral tissues.Balancing the diet for methionine and lysine, the two ûrst-limiting amino acids, is now practical and easily accomplished using effective rumen-protected products. Many nutritionists are now reducing ration crude protein levels with supplementation of rumen protected amino acids, thereby, reducing the cost of the diet. Thus, rumen protected methionine and lysine present a great opportunity for economising the dairy rations and optimizing the production performance of animals.
The practical benefits of balancing Amino Acid Lysine and Methionine
- Reducing the risk of an Amino Acid deficiency (Not the crude protein but the amino acids are required nutrients for dairy cows).
- Optimizing transition cow health, increasing milk and milk component yields, and feeding less Rumen undegradable protein(RUP) to post-transition cows. Feeding less Rumen undegradable protein(RUP)not only decreases feed costs but also allows for increased carbohydrate feeding, which leads to increased synthesis of Metabolizable Protein, a protein of high quality, and increased synthesis of volatile fatty acids, important substrates for lactose and fat synthesis.
- Impact of balancing Lysine and Methionine in early lactation and transition cows has great result in terms of promoting high dry matter intake soon after calving, increase milk production and composition as well as improvement in embryo quality and reduction in early embryonic losses.
- Immune status of dairy cows is also improved due to balancing amino acid lysine and methionine. Various study suggests that there is a reduction in somatic cell count and control of mastitis by usage of rumen protected Lysine and methionine.
- Amino acid balancing helps in lowering crude protein of ration around 2% by supplementation of rumen protected amino acid and helps to obtain similar results like earlier crude protein level. Broderick and his colleagues (2008) published a study that a ration with 16.1% CP and added Rumen protected Methionine resulted in the same amount of milk as a 17.3% CP ration without RP-Met, and both rations resulted in higher milk production than an 18.3% ration.
- Ratio of 3:1 rumen protected lysine and methionine usage has great impact on feed formulation and diet plan.
- Balancing diet with rumen protected methionine and lysine equally plays critical role in buffalo as well cattle nutrition (improvement in SNF of milk).
- For milk products like chenna/paneer, khoa and dried whey, rumen protected methionine plays vital role.
Mechanism of Rumen-Protected Amino Acid
Microbial protein, rumen undegradable protein (RUP), and endogenous protein make up the majority of metabolizable protein (NRC, 2001). Various factors that impact ruminal protein degradation and microbial protein production influence the metabolizable amino acid profiles. If the protein in a diet is mostly ruminally degradable protein, for example, the supply of amino acids to the small intestine will be comparable to the amino acid profiles of microbial protein. However, amino acids delivered to the small intestine by rumen microbial protein are limited because microbial protein does not supply enough to meet animals’ precise amino acid requirements for achieving a set level of performance. Methionine and lysine appear to be the two amino acids that limit microbial protein development. Ruminal protein breakdown rates may be low, and ruminal microbial protein production may not provide the amino acid requirements of expanding tissues. As a result, the first limiting amino acids during this phase are likely to be the amino acids that are most insufficient in dietary protein. Ruminants have unique amino acid metabolic requirements for optimal development, maintenance, and productive functions. Amino acids are the only precursors to protein synthesis that are required. They also act as precursors for the synthesis of other nitrogen-containing metabolites and a source of metabolic energy when oxidized to CO2. Because free amino acids are rapidly broken down in the rumen, adding them to the diet does not always increase the absorption. However, a method of protecting amino acids from microbial degradation has allowed for the supplementation of diets with specific amino acids that will become available for absorption at the intestinal level. Amino acids absorbed in the small intestine of ruminants come from microbial protein and food protein that is not digested in the rumen. The calves cannot produce ten essential amino acids, and thus proteins digested in the small intestine must provide them. Furthermore, because a deficiency of one necessary amino acid can impede the usage of others, the proportional amounts of each essential amino acid absorbed in the small intestine should exactly meet the calves’ requirements. To enhance the overall amount of amino acids delivered to the small intestine, amino acids must be delivered in a protected form, or the proportion of rumen undegradable protein must be increased. Growing cattle, in general, have a high metabolizable protein need to achieve rapid and efficient growth. Because a single amino acid deficit might limit the usage of other amino acids that are abundant, the efficiency of metabolizable protein utilized by ruminants is strongly dependent on the profile of absorbable amino acids.
Effect of Rumen-Protected Amino Acid
Calves will consume metabolizable protein less efficiently if they do not get enough necessary amino acids in their diet. Growing calves’ forage diets are frequently lacking in metabolizable protein. Protected amino acids are given to meet the animal’s metabolizable protein demand and increase the average daily gain (ADG). Supplementing with rumenprotected amino acids can rectify amino acid deficits without increasing the amount of metabolizable protein. Alternatively, it may lower protein levels without lowering performance levels. Richardson and Hatfield (1978) found that methionine and lysine are the most limiting necessary amino acids for growing calves, which could explain why calves on pasture diets perform worse. Methionine and lysine are the first two limiting amino acids (Benefield et al., 2009). Lysine and methionine are regarded as co-limiting AAs in dairy cattle for optimal development and milk synthesis (Socha et al., 2005). This poor performance is most likely due to rumen undegradable protein’s inadequate availability of lysine and methionine. This may not be enough to meet the amino acid requirements for healthy growth, and a lack of specific amino acids may result in poor protein deposition from dietary protein. Methionine is a significant methyl donor and a Sulphur-containing amino acid. In the production of DNA, RNA, phospholipids, and proteins, methylation is an important step (Brosnan et al., 2007).
Compiled & Shared by- Team, LITD (Livestock Institute of Training & Development)
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