April 2013 - AFMA

or as ratios) is difficult as we have to think
multi-dimensional. The good news is that
the vast majority of diets are deficient in
both lysine and methionine. Thus, if we
begin adding lysine sources, we will typically
see an increase in milk production.
At the same time, adding methionine first
will typically result in an increase in both
milk production and milk protein concentration.
But these responses do not occur all the
time. Why? First, it appears that there is a
minimum milk protein concentration, and
that is approximately 2,8% true protein (or
about 3% crude protein). The relationship
between milk protein yield and milk yield
is nearly perfect (correlation coefficient of
0,94). This makes a lot of sense given that
several amino acids (namely methionine
and cysteine) are required in the production
of lactose.
Thus, it appears the cow may regulate
milk protein yield and milk yield very tightly
to maintain a minimum milk protein to
lactose relationship. At these low points,
the response to either lysine or methionine
could be substantial (3-10 litres milk reported).
Regardless of the starting point, it
appears that milk volume and milk protein
concentration is maximised when lysine is
supplied at 6,3 to 6,6% of metabolisable
protein and methionine at 2,35 to 2,55% of
metabolisable protein.
Several studies from the early 1990s,
and more recently research from the University
of Illinois (Loor et al., 2011), demonstrate
a health and production response.
Methionine was supplemented during the
pre-partum and fresh period. Incidence of
fresh cow metabolic disease (namely ketosis
and fatty liver) were reduced in excess
of 50%. Cows fed the methionine supplemented
diet increased dry matter intake
faster and by day seven in milk, significant
differences in milk production were reported.
Based upon this research, we are recommending
that at least 25g of metabolisable
methionine should be supplied in the diet
for pre-partum cows. Anecdotal evidence
supports improved immune response in
calves and heifers as well to amino acid
formulation.
Summary
Amino acids are not additives and should
not be thought of as such. They are critical
building blocks of proteins and enzymes,
and result in milk protein, volume, muscle
and immunity. Nutritionists must evaluate
diets for amino acid adequacy and forget
meaningless numbers such as crude protein.
The first step in amino acid formulation
is maximising microbial yield from the rumen.
This requires a good mix of fermentable
carbohydrates, physically effective NDF
and adequate degradable nitrogen to support
microbial growth. The second step is
to select the most economical sources of
by-pass amino acids. This could be from
soy-based products, blends of soy and
sunflower, etc.
And then work with your nutritionist
to evaluate the different synthetic by-pass
amino acids to achieve the desired levels
of amino acids. These levels should be:
for lactating cows, lysine > 6,1% MP and
methionine greater than 2,1% MP; for the
pre-partum cow, lysine > 6,1% MP and at
least 25g total methionine. And finally,
ingredients (such as sunflower, soy or any
maize protein product) must be valued
on an amino acid basis.
Feed science
AFMA MATRIX ● APRIL 2013 51