How Much Will They Eat by Mike Mehren Ph.D.

How Much Will They Eat
by Mike Mehren Ph.D.

To me, one of the hardest questions to answer is when a client asks how much will his cattle eat. The question can be about a free choice supplement such as a protein block, liquid, tub, or mineral. It might also be about a ration of hay alone, or a ration of hay, grain, and silage. There doesn’t seem to be an easy answer for any of those questions without some additional information. Even then it’s an educated guess at best.

For one thing we have to know about the animals. Say they are cows:
1. How old are they, young or smooth-mouthed?
2. What’s their body condition?
3. Have they eaten this feed before?
4. What’s their average weight? (We can have a 900 lb desert cow in decent body condition and a 1250 lb crossbred cow that should weigh 1400 lb when in average condition.
Calves will also require some more information.
1. Have they been long-hauled?
2. Were they just weaned?
3. Healthy or sick?
4. Stunted from poor feed or just young?
5. Do we expect compensatory gain (high rate of feed intake)
6. Are they with their herdmates from the ranch, or have they been put- together that day?
7. We also need to know their weight, body condition, previous feed history.
Yearlings will also have a set of questions similar to calves minus the weaning issues.
1. Have they come from a backgrounding lot using similar feeds or are they coming off range?
Environment affects feed intake.
1. Is there enough bunk space for all to eat at the same time, or are they eating hay from a feeder or bunk and some kind of concentrate from a separate self-feeder?
2. Is it hot? Cold? Wind, cold, and rain? Dust blowing into their eyes?
3. Pen surface: Well-groomed; 2 ft. deep in mud. No place to lay down in comfort.
4. Flies chasing them around the pen; stray dogs.
5. Are heifers in a pen next to a group of bulls? Heifers and steers mixed?

Water has a huge effect on feed intake. Cattle that have limited access to water due to drought, broken pipes, and water troughs that don’t work may not get enough water. Feed intake goes down dramatically in these circumstances. Highly alkaline water deters intake. I know dirty water does too, but we’ve all seen cattle drinking from the standing water in a pen or pasture. Those studies that have been conducted show a difference in water intake and performance when cattle are forced to drink ‘fouled’ water vs. clean water. I’m quite certain this was due to reduced feed intake.

The body has its own means of regulating feed intake.
The animal’s body digests and absorbs different feeds at different rates. Roughages such as hay, grass, and silage move more slowly through the animal than do grains. An animal will eat more of a high quality feed than it will one of low quality (fresh green range vs. straws and mature plants) in a given amount of time. There are also feed-back mechanisms in the brain that give the animal a sense of being full.

Certain feeds may be antagonistic to the intake of other feeds.
For instance, supplementing hay with grain has an effect on intake of the hay. The following table does an excellent job of making that point.

INTAKE OF CORN AND GRASS HAY BY COWS
LB/corn/day	Ave Daily Gain	Hay Intake, LB
0	1.32	19.3
1.4	1.75	18.0
4.2	2.0	14.1
From Johns. Univ. Tenn. 2005 Nutr. Conf.

This same thing happens when supplementing grain to grazing cattle. A small amount of grain gets a huge increase in performance because of the extra energy provided, but as more grain is fed, less grass is eaten and the benefit goes down while cost goes up. A good rule of thumb in this case
is not to exceed 0.5% of the animal’s bodyweight in grain. A 500 lb grazing calf would thus be fed no more than 2.5 lb daily of corn or other grain to maximize the advantage of extra energy.

The feeds themselves will affect intake. If the animal has never smelled or tasted silage before, it make take them awhile to start eating it. This can also occur with a mineral supplement, protein supplement, or plain old salt. Calves may not recognize the supplement container itself. This might be a liquid feeder, a creep feeder, or a block or tub. The location of the feeder may seem logical to us, but doesn’t turn out to be a place where the calves don’t want to eat. Some feeds seem to be a natural attractant. We added apple pomace to starting rations for calves, and believed that the cattle went on feed faster when it was present. Carrots are also very palatable to young animals. Calves seem to recognize the smell and taste of grass hay better than alfalfa hay when first introduced to hay.

Feed moisture also has an effect on intake. I worked with a gentleman one time that purchased corn cannery waste (21% dry matter) to feed to his cows during the winter. He called and said that the cannery was cheating him on the weight of the silage. His cows were eating 100 lb each every day and he was going broke. The cows were eating 21 lb daily of cannery
dry matter (100 lb x 21% dry matter) and I thought that 1200 lb cows could eat that much easily. I think they would have eaten more if given a chance. He had estimated that they would eat about 25 lb because that was the amount of hay he normally fed. We used some grass straw, and a little bit of alfalfa, and got cost under control.

After reviewing some of the factors that effect feed intake, it’s a wonder that our estimate ever comes close to what will really happens. Each group of animals is different. I’ve seen animals from the same herd react completely differently to the same feed, when the only difference was which pen they were in, even though the pens were side-by-side.

A feed manufacture will provide a guideline for feed intake in the instructions for feeding on the label. We estimate that cows will consume 1.5% of their bodyweight on low quality forage (less than 7.0% percent protein), but will increase intake of the forage to 1.8% of bodyweight when provided a protein supplement. Newly arrived calves will only eat 1% or less of their bodyweight when they first arrive in a pen. This will increase rapidly to 2.5 to 3.0% of bodyweight in feed dry matter once they have overcome the stress of shipping and become accustomed to the new feed. Yearlings will average about 2.4% of their bodyweight in feed dry matter while on finishing rations. Feed intake estimates are always given in pounds of dry matter. This is very important when high moisture feeds are being fed. Average feed intake means that feed intake will be low at the beginning and then peak during the middle of the feeding period and start back down as they near finish.

Michael J. Mehren Ph.D. is a livestock nutritionist whose appetite exceeds all expectations while on feed in Hermiston, Oregon. He may be contacted by Email at mehrens@eotnet.net.