To ensure constant feed availability and account for feed refusal or weigh back, you must deliver more feed to a pen of dairy cows than those cows will consume. Common recommendations in dairy circles indicate producers should expect 2 to 5 percent feed refusal or weigh back.
Efficiency in feed bunk management suggests the lower the refusal, the better, at least from an economical perspective. After all, the feedlot industry has done it successfully for years. And, when you consider the lactating cows easily will consume 50 pounds of dry matter, if you have 5 percent refusal, you are going to have to offer the cow 52.5 pounds of dry matter per day. A 5 percent refusal is equal to 2.5 pounds (50 x 0.05).
At current feed costs, dry matter of a "typical lactation diet" costs about 10 cents per pound of dry matter. This means that feeding 5 percent extra adds 25 cents per cow per day to her daily feed costs. Take that times 1,000 cows, and the arithmetic catches your eye.
So at least in an ideal situation, feeding to a clean or "slick" bunk may seem reasonable. Several studies with beef cattle have shown better feed efficiency, similar animal performance, fewer digestive disorders and more consistent feed intakes when the cattle are fed to a slick bunk. In fact, a few dairy farms have implemented a slick-bunk management scheme successfully.
However, growing animals are very different from lactating animals. If nutrient intake is restricted for a growing animal, the daily growth rate may be reduced, but the animal usually will reach the same final weight it would have if it had not been restricted. The growth just will take more days.
Compensatory growth (such as studies here at NDSU and around the country have shown) also occurs when young animals that were restricted in nutrient intake are fed more nutrients. Compensatory milk production does not occur, though, and a reduction in milk yield that occurs on any given day usually is not made up during the current or in a subsequent lactation.
The lactation/gestation cycle also means that we cannot just milk the cow longer to replace the lost milk. Therefore, managers should be very careful when applying feed bunk management data obtained from growing cattle to lactating dairy cows.
Very little data evaluating the effect of the amount of feed weigh back on dairy cow performance is available. A study conducted a few years ago compared feeding Holsteins enough so that 5 percent of the daily intake remained in the feed bunk 23 hours after the cows were fed with feeding cows the same diet but limiting it so that 2.5 percent of the amount offered was in the bunk 18 hours after feeding.
Although this was a limited study, the researchers found that dry-matter intake for high and low weigh back treatments and 4 percent fat-correct milk yields was not statistically different. The bottom line was that feeding for less feed weigh back, approximately 2 percent, compared with 5 percent, does not appear to affect milk yield and, therefore, can reduce feed costs. However, a risk exists for ruminal acidosis because it changed eating behavior.
So while feeding to an empty bunk clearly is not advantageous, having large amounts of refusals is not economical, either. Increasing the amount of dry matter refused by 1 percentage point costs 5 to 6 cents per cow per day, and that adds up.
So the question becomes: What can you do with the refused feed?
The answer depends on the quality of the refusal. In reality, you may have good-quality refusals, and then you'll have times when the refusals are garbage. Through the course of a day, the cows have sorted away the feed they don't want to eat. Maybe it is just cobs and coarse fiber, or maybe the feed has become hot, slimy and stinky - in other words, garbage.
In the case of the later, the refusals obviously should be discarded and not fed to any animals. Refusals that still have good feed quality can be remixed and fed. Some of that refused feed cost can be recovered if the weigh back eventually is consumed by some animal.
Researchers and nutrition consultants generally agree you have these options for refused feed:
- Blending it into a new total mixed ration (TMR) and refeeding it to lactating cows
- Feeding it to dry cows
- Feeding it to heifers
When blended into the TMR, the refused feed costs eventually are recovered. However, TMR weigh back has a nutrient composition that differs from the original TMR and typically is quite variable. This variation is what causes production and/or health problems. Furthermore, if the feed was refused because it was moldy or had other quality problems that caused cows not to consume it, mixing it throughout a new batch of TMR may result in less intake of the otherwise fresh feed. The result usually is less milk production, and the intended savings in feed costs are lost.
Feeding refusals to dry cows also has a risk. Because you will not know the nutrient composition of the weigh back, including it as an ingredient increases the risk of nutrient excesses and deficiencies, which could increase health disorders. For a successful lactation, much is dependent on the nutrition of the cow during the previous dry period. This is not the time in the cows" cycle to take nutritional risks.
That leaves feeding refusals to growing heifers. This presents the least risk. Feeding it to older heifers probably is the better option. The recovery value of the weigh back is not the cost of the lactating cows" TMR; rather, it is the value of the heifer feed it is replacing. A typical diet for an older growing heifer costs approximately 7 cents per pound of dry matter.
Feed costs represent the single largest variable expense of producing milk. Many dairy farms have the ability to monitor and track inventories, mixing and feeding. The economic incentives for creating a well-thought-out plan that includes feed refusal are huge. Monitoring and correctly managing weigh backs is an effective tool in controlling feed costs.