It is understandable how proteins—or more specifically amino acids–impact milk production, since they make up a portion of the milk protein fraction. When the supply of amino acids is inadequate, we observe not only lower milk protein yield, but also milk fat yield and milk volume suffer. However, we are now learning that simply thinking of amino acids in terms of milk production is taking a fairly narrow view of these multifunctional nutrients. A wider lens takes into consideration the cow’s metabolic need for dietary amino acids beyond serving as building blocks for proteins. Functional amino acids are those amino acids that participate in and regulate key metabolic pathways to improve health, growth, development, and reproduction, in addition to lactation.
Let’s take a look at two amino acids that we’ve likely heard about: methionine and lysine. Both are essential and must be provided in the diet for optimal production, but only methionine is a functional amino acid. A few examples of the “hot” functional aspects of methionine in the dairy cow are cell signaling (mTOR), regulation of gene expression, and modulation of immune responses.
Many of the phenotypic responses arising from the functional aspects of methionine can be seen during the transition period. Good things happen when methionine is supplied above what our nutrition models calculate is needed for maintenance, pregnancy, and production. A recently published trial from the University of Illinois is an excellent blueprint for walking through the functional roles of methionine. Mepron®, a rumen-protected methionine, was included in prefresh and postfresh rations at about 0.1% of DM. This resulted in Mepron® intakes in the range of 10-15 grams per day prefresh and 15–20 grams per day postfresh, which is equivalent to 6–9 grams of metabolizable methionine per day prefresh and 9–12 metabolizable methionine per day. The amount of Mepron® needed will vary by ration, but the important point here is that the amount of methionine needed to flip the functional switch is small, or about 10 grams.
Compared to the control ration, which was identical to the treatment ration except for the added Mepron®, cows that received additional methionine had 10% greater DMI throughout the transition period. Most of the difference in prefresh DMI occurred in the two weeks before calving, where the depression in DMI was less for the treatment cows. Keeping cows on feed as calving approaches is vitally important, since postfresh DMI is positively correlated with prefresh DMI. So, what was driving this difference in feed intake?
Two possible explanations for these results are lower circulating concentrations of non-esterified fatty acids (NEFA) and better liver function. At calving, NEFA were 25% lower in cows receiving additional methionine; NEFA are known to suppress DMI. In addition, gamma- glutamyl transferase, an indicator of liver function was 37% lower in Mepron® supplemented cows. Previous research has shown that cows with better liver function have greater DMI. A couple of other factors that may have contributed to better DMI for the Mepron® supplemented cows was lower inflammation and oxidative stress, and improved neutrophil function.
This greater DMI drove higher start-up and peak milk production. Both week 4 and week 8 milk were about 10 lbs greater for the methionine treatment. Likewise, energy corrected milk was also 10 lbs greater for the treatment ration since it generated greater yields of fat, protein, and lactose. In addition, the treatment cows exhibited a hallmark phenotypic response from the nutritional essentiality of methionine: increased milk protein concentration.
Getting back to the functional aspects of amino acids, prefresh methionine supplementation also had an impact on the placenta and growth of the neonatal calf after birth. Heifer calves born from dams that were fed Mepron® prefresh weighed 10 lbs more at weaning and were 14 lbs heavier three weeks postweaning. The in-utero effect of a nutrient on metabolism and performance after birth is known as fetal programming. This is a new area of research in dairy cattle and holds tremendous promise in unlocking the genetic potential of the calf.
Continued understanding of current research and advancements in research techniques will provide exciting new insights into the effect of nutrients on cow and fetal programming. This will remain a popular area of research in the near future for functional amino acids and other functional nutrients. Ask your nutritional consultant how Mepron® can unlock the potential of your cows and calves.