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Dry Matter Intake
Dry matter intake and the importance of feed intake in lactating dairy
cows. Milk yield is positively correlated to dry matter intake. For every
pound of additional intake that a cow consumes, we can expect about two
pounds of milk. There are several factors that affect intake, two of these
being dependent upon the cow. Body weight of the cow, larger cows consume
more feed. Also the milk yield, the more milk a cow gives, the more intake
she will consume. The second component affecting intake is the ration.
Moisture content has an effect through high moisture rations or those
that contain little dry matter. Mainly, this is from feeding excess silage
to cows such as corn silage which can be unpalatable when fed at high
levels of intake. The second component is the effect of the ration on
rumen pH. Remember, if excess grain is fed, rumen pH declines, passage
rate of feed in the GI tract declines and intake will decline. Too much
fat in the diet, as we talked about in the last section, can drive intake
down. If there is too little effective fiber, this can also depress intake.
Nutrient densities, if they are too low, if energy density is too low
or crude protein density is too low, this will decrease intake. And the
bulk density or how much fiber is in the diet. Remember that too much
fiber leads to filling capacity of the rumen and depresses intake and
also too little fiber and therefore too much grain can lower intake. The
third is general management, especially of the bunk. How often bunks are
cleaned or how often feed refusals are cleaned from the bunk and this
should be done daily. How often cows are fed per day, the more feedings
per day increases intake. And also how often feed is pushed up in the
bunk. Excess crowding or over-crowding can reduce intake due to social
stress or social pressure within the groups. How many hours cows have
access to feed. Ideally, cows would have access to feed 24 hours a day.
On the opposite side of cleaning the refusals, is that there is some feed
left in the bunk before each feeding to ensure that cows have free access
to feed. Behavioral characteristics within the groups. It has been shown
that if you group younger animals together, or first lactation heifers,
they will consume more feed and produce more milk versus if they are comingled
with older cows. The environment has an effect on feed intake. Higher
temperatures decrease intake, higher humidity also decreases intake. However,
even if we have high daytime temperatures, it has been shown in areas
such as Arizona, New Mexico and Texas, if we have night cooling, or low
night temperatures, we can achieve the same level of feed intake.
There are two different lines on here. One is a darker orange line that eventually meets the lighter colored line at about 19 to 22 weeks of lactation. If you use the equation that we just talked about and plugged in milk yields and body weights of cows, we would expect cows to consume on the light orange line. However, cows have suppressed intake in early lactation. Actually, there is a lag in intake and it takes about 20 weeks or so for cows to catch up to where they would be, simply based upon the milk yield they are giving. They are not eating as much feed in early lactation as we would expect from the dry matter intake equations.
We have five different levels of milk, 0, 70, 80, 90, and 100 and we predict their dry matter intake which is on the left axis. Cows giving no milk, or at maintenance, need about 10 pounds of dry matter a day to meet maintenance requirements, and all cows do, regardless of whether they are producing 70 pounds or 100 pounds of milk. Then, we have the dry matter requirement for milk yield, which are the tan bars above the dark orange. We see a cow producing 70 pounds of milk, it would be expected to consume about 36 pounds of dry matter and a cow producing 100, about 46 pounds of dry matter for milk yield plus the additional 10 for maintenance. The way that we would read this graph is for the 100 pound cow, she needs about 46 pounds of dry matter for milk and an additional 10, so a total of 56 for total milk and maintenance requirements. The blue line depicts, and the axis is the right axis, depicts how many pounds of milk we can get per pound of dry matter. You can see if a cow is producing about 70 pounds of milk, it takes about, or we could get, about 1.95 pounds of milk per pound of dry matter and up to those cows producing about 100 pounds, it increases to about 2.15. We see this small increase because these cows producing more milk are more economical, we’re spreading those ten pounds of maintenance feed costs over more pounds of milk.
So we see no cows there, but we can assume or we can predict that feed is available because it is there in the bunk.
Take a look at this bunk.
Now there is feed there, but is it truly available to the cows? And
it is not. Most of the feed is out of the reach of the cows.
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