Background for Protein & AA Nutrition for dairy cows
By Eng. Clément Cirot – Dairy Nutritionist, Ajinomoto Animal Nutrition Europe.
cirot_clement@eli.ajinomoto.com
Milk protein (lactose, casein …) is built in the mammary gland, using amino acids (AA) as building blocks. Those AA are absorbed during digestion in the intestine and come from the truly digestible protein, called the Metabolizable Protein (MP). Milk protein has a defined and constant AA profile. Therefore the
mammary gland must be provided with these amino acids in the right amount and proportion to optimize efficiency of conversion into milk protein. However, all AA are not equally important. Some, the non- essential AA, can be synthesized by the cow from other AA found in the diet. The other ones, called essential AA, cannot be synthesized by the cows. In most diets fed to dairy cows, the most limiting essential AA for milk production are methionine, lysine and histidine. There are two sources of essential AA for the cows: the
undegraded fractions of the feedstuffs themselves (=RUP), and the rumen microbes (=Microbial protein).
consideration any other information, like rumen degradability or intestinal digestibility, which plays a huge role in the amount of protein really digested. Metabolizable Protein and AA give a better image of what happens inside the rumen, as it takes into account the different degradability and digestibility of the feeds, as well as the energy available for microbial protein synthesis.
Role of lysine in milk production, a meta analysis of trials in research stations Research often looks at amino acid response in terms of milk protein yield produced, in grams produced per day. However milk protein yield depend on two variables: milk yield (volume) and milk protein concentration (protein). Milk protein yield is the multiplication of the two. While methionine is generally recognized for increasing milk
protein concentration, what about lysine? To answer this question, Ajinomoto gathered more than 10 studies in controlled conditions where known amounts of lysine, alone or together with methionine was fed to multiparous dairy cows in early lactation, with no other diet change. From this meta-analysis we demonstrated that lysine has a beneficial effect on milk yield (see graph).
• Feedstuff Undegraded Protein, RUP: fraction of the dietary protein that is not degraded in the rumen and passes directly to the intestine. The profile and amounts of AA supplied by this fraction can vary greatly between different feedstuffs as well as digestion rate in the intestine. • Rumen microbes, microbial protein: the protein fraction of feedstuffs that is degraded in the rumen and used in the growth of rumen microbes. These are composed – like every living cell – of protein. The protein of these microbes is considered to have a constant AA profile, very close to milk AA profile, and is therefore considered almost optimal for milk production. • The sum of the digestible RUP and Microbial protein is the Metabolizable Protein. Quantity and AA profile of the Metabolizable Protein reflects the real AA available for the cow for milk protein production. Therefore it is much more precise to formulate on MP and AA
rather than crude protein (CP). Indeed CP is just chemical information (Nitrogen x 6.25) about the feed. Crude Protein doesn’t take into
PAGE 44 JULY/AUGUST 2019 FEED COMPOUNDER
• On average, when increasing supply with10g of metabolizable lysine, cows responded with +3.4% milk yield, whether or not methionine was supplemented together with lysine. • It is important to note that to obtain these results, the cows must have a good energetic status otherwise we might not see the full benefits of lysine. • When looking at the milk protein concentration, we noticed that in studies where lysine was fed alone, there was little to no change. However the milk protein concentration was increased when methionine was also supplemented. Thanks to this meta-analysis we could confirm that lysine and
methionine don’t have the same impact on milk production, even though both lead to increased milk protein yield: the lysine drives milk volume, while methionine drives milk protein concentration.
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