Determining If You Will Have Enough Forage for the Coming Year

By Gary Anderson, Animal & BioScience Specialist

Now that forage harvesting is almost complete for the year, it is time to carefully evaluate how much forage you have on hand and compare it with how much you need to feed your herd. With the drought this summer, forage is at a premium now and will only get shorter as we go through the winter.

Good silage preservation is obtained when silos are filled quickly and packed to an appropriate density. Mike Hutgens, retired from University of Illinois, has some suggestions on silage quality. The rule of thumb for packing silage is to take the weight of your tractor and divide by 800;  that gives you the number of tons per hour you can effectively pack.  The target for silage density is to have over 18 lbs of forage dry matter per cubic foot (so if your silage was 33% dry matter, that would be a target of over 54 lbs (18/.33=54) of silage per cubic foot). If you can get a grab sample from the silo face, your density is less than 15 lbs forage dry matter per cubic foot. For legume/grass silage, your target pH is in the 4.3 to 4.7 range and for corn a little lower at 3.8 to 4.2. Studies with oxygen barrier coverings on silos have been shown to reduce dry matter losses by 50% in the top meter of silage.

One of the main questions I get from producers is — “How much forage will I need for the coming year?” To answer that question, I did some calculations. I looked at average production of 3.5% fat corrected milk by 1350 lb Holsteins and calculated rations using predicted dry matter intakes and balanced rations using a low (.51 Mcal), medium(.57 Mcal) and high energy (.63 Mcal) grass/legume hay. I ended up with the amounts of hay needed per month to feed cows of differing production levels. Remember, I used a prediction equation for feed intake and actual intake by your cows is always a better estimate. I made several assumptions on these sample rations and I maximized the use of forage in the ration. I only balanced on energy so other nutrients that are commonly used that may affect forage:grain ratios were not considered. My goal was to get some average inventory numbers for feed. I need to do these same calculations for Jerseys; their intake is not just a percentage of what Holsteins eat.  If you are interested in Jersey numbers, please contact me.

With those caveats, here are my estimates of what 1350 lb Holstein cows at different levels of production will eat in tons of hay per month with forage of varying quality. You will notice that the higher the quality of the forage, the more cows will eat and the less grain you need to feed to balance a ration for their energy needs. The more cows eat, the more they produce; this is the basic physiology of bST. When I balance a ration, the first and second nutrients I look at are fiber and energy followed by dry matter. Then I look at protein and all the other nutrients.

Estimated Monthly intakes of Hay Equivalents (H.E.) for Holstein Cows Weighing 1350 lbs and Producing Various levels of 3.5% Fat Corrected Milk

Herd Production
lbs 3.5% FCM
Low Quality
.51 Mcal Tons H.E./month
Med Quality
.57 Mcal Tons H.E./month
High Quality
.63 Mcal Tons H.E./month
16000 .40 .47 .59
18000 .38 .45 .57
20000 .37 .43 .55
22000 .35 .41 .51
24000 .39 .48
26000 .36 .44
28000 .41

I did not include additional inventory for waste so please increase your total by 15-20%. 
For levels of production above with no numbers, I did not feel that I could put together a healthy ration.

For example, if I had a 20,000 lb herd and had medium quality forage, I would need .43 tons of hay equivalent (89% dry matter) forage to feed.  That would be .43 X 2000 or 860 lbs of hay equivalent per month per cow. I would multiply this times the number of milking cows times the number of months I needed to feed stored feed. If I was feeding 33% dry matter silage and no hay, I would divide the hay equivalent dry matter by the silage dry matter (89/33=2.7).  I would then multiply the 860 lbs of hay equivalent X 2.7 to get the lbs of silage per cow per month (.43 X 2000=860 X 2.7 = 2322 lbs silage per cow per month).

I have not talked about young stock or dry cows. For youngstock, you can use .22 tons of hay equivalent per animal and for dry cows, .4 tons hay equivalent.

These data give you the basic information to estimate your forage needs.  You then can compare your needs with your inventory of feed. Large round bales differ in size from farm to farm so you should get an average weight for the bales you have.  Also determine the amount of spoilage on the outer edge of your bales to determine the amount of usable feed. If your round bales are 4 ft in diameter and there is 2 inches of spoilage, that is 16% of the total volume of the bale; if they are 6 ft in diameter, the same 2 inches of spoilage is just under 11% of the total volume of the bale.  You can see the benefit of storing bales to minimize loss. Density of bunker silos can be calculated by several methods.  One of the easiest is to use a corer of known volume to determine density at different locations on the silo fact (the density is greater at the bottom of the silo so many people take samples in an X across the face to get a representative sample).  You can also mark the wall of the bunker and as you remove silage to feed, keep accurate records of the lbs removed using a mixer wagon with scales. After several days, calculate the volume of silage fed (length x wide x height = cubic feet fed) and calculate the lbs of feed per cubic foot. Doing a dry matter on silage from the mixer wagon that was representative of the whole face will let you calculate the dry matter per cubic foot. There are tables available that can give you an estimate of feed in your silo as well but actual measurements are best.  Please note that I have not included dry matter loss from stored forage. Inflating your total needs by 15-20% should help you make sure you have enough forage this coming year.