September 5, 2017 at 3:32 p.m.

The cow days of August

By Jim Linn- | Comments: 0 | Leave a comment

According to Wikipedia, the Dog Days of Summer refer to the hottest, most sultry days of summer. Typically these days occur in the months of July and August. Again this year as last year, the dog certainly had his days in July and the first part of August. If the dog can have days, a cow should be able to have days as well. I would say the last few weeks of cool nights, low humidity and temperature days should be proclaimed the Cow Days of Summer. As I watched cows in the herds I visited the past few weeks, you can see they are enjoying the cooler weather. Cows are lying down, ruminating and even sleeping in their stalls rather than standing and panting to cool off. Feed intakes are on the increase as well as milk production and fat tests. While these are the good things about Cow Days, it is also the time when we see the latent effects of Dog Days in cows. Sore feet and foot problems are now becoming more prevalent from the increased standing in a wet environment over the last couple of months. There also are a lot more non-pregnant cows from early July breeding either from not conceiving or very early abortions. While the actual Dog Days of Summer are over, the dog's bite takes a little longer to recover from.
Feed prices and corn silage harvest are other topics of conversation during the Cow Days of August. Harvesting of corn silage will begin, if it hasn't already started in some areas, within a few days. Maximizing quality and yield will be especially important this year as the price of corn silage is directly related to the price of corn. One very quick simple method of pricing corn silage (35 percent DM) is to multiple the price for a bushel of corn by 7 (bushels of corn/ton of 35 percent DM silage) and add $5 for harvesting. Current local cash bids for corn are about $7.50, so corn silage price is $57.50/ton of harvested silage.
Because there will be a large variability in grain content of the corn silages across the region this year with drought or no drought conditions, a better way is to get a sample of the silage and estimate the grain yield based on starch content of the silage. The table below estimates the grain content of corn silage based on its starch content (DM basis).
Starch percent - corn silage Bushels corn/ton (35 percent DM) silage
20 4.1
25 5.1
30 6.1
35 7.2 40 8.2
Multiply the price of corn per bushel by bushels per ton to get the value of corn silage per ton standing in the field. For 40 percent starch, this would be 8.2 bushels times $7.50/bushel to equal $61.50/ton in the field. Ohio State researchers estimate harvest and ensiling costs increase this value by 30 percent for a final value of $79.95/ton ($61.50 x 1.3). There is definitely yellow gold out there in the fields and retaining the highest quality of silage during harvest is the best way of controlling dairy feed costs.
With high feed prices this year, economic milk production should be the goal rather than maximum milk yield or lowest cost feeding dairy cows. What is economic milk production? Economic milk is one that maximizes income over feed cost. Maintaining a good milk volume with high components while controlling feed costs is the basis for economic milk production. The amount of corn to include in the dairy ration is a good way of looking at economic milk production. There is more milk produced from the first pound of corn in the diet than the last pound. The cow and rumen bacteria optimize the use of the energy in that first pound of corn, but by the last pound they have become a lot less efficient in utilizing the energy. The efficiency of utilizing corn in the diet also is complicated by the stage of lactation.
One has to go back to 1991 to find research on milk production response to amount of grain fed when Tessmann and coworkers at Wisconsin did a very elaborate full lactation study feeding five different levels of corn in the diet. Their results are now the basis for a spreadsheet developed by Victor Cabrera, Dairy Extension Specialist at Wisconsin, to evaluate the diminishing returns (milk production) to amounts of corn fed.
The graph below summarizes the response to corn grain feeding by stage of lactation. An important point is the milk responses to grain are based on research in which alfalfa haylage was the only forage in the diet. Corn silage was not included in their diets, so it is very likely in today's feeding of high corn silage diets, the milk response to corn grain inclusion in diets would drop off faster as more corn is added to the diet. However, without or with corn silage in a diet, the principle is still the same in that there is a point in the amount of corn addition to a diet where the return in milk production is less than the price of the corn fed. With corn at $7.50/bushel and milk at $18/cwt, it takes 0.75 pounds of milk to pay for 1 pound of corn. The graph nicely illustrates in the top line the best use of feed dollars and corn is in early lactation cows. Starting in mid lactation and later (bottom two lines) there is very limited milk response to feeding corn when high quality forages are fed. Diets containing 40 percent or more high quality corn silage appear to be one of the best options for high milk production and controlling feed costs this year. You can access Dr. Cabrera's spreadsheet at if you would like more information on optimal corn feeding.
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