It is often considered that providing dairy cattle with unlimited access to high quality feed throughout the day is the best way to promote maximum feed intake and increase milk production. In order for cows to have unlimited access to feed however, more feed must be delivered to the cows than will be consumed. And since free-choice feed intake is not exactly equal from day to day within a cow or group of cows, we need to have some extra at the end of the day in order to assure that every cow in the group had all she wanted to eat.
While it is clearly not advantageous to feed to an empty bunk, having large amounts of refusals is also not economical. Increasing the amount of dry matter refused by one percentage point often costs 5 to 6 cents per cow per day, which amounts to approximately $20 per cow per year. When you start looking at moderate to large sized herds, this adds up fast.
Direct costs of the ration are not the only expenses associated with having excessive feed refusals. When cows are overfed a TMR with a high proportion of dry forage (such as long hay), sorting often occurs more extensively, resulting in possible health problems. Cows will select smaller particles that contain large quantities of highly fermentable carbohydrates (grains) that can result in a build-up of organic acids in the rumen and reduce rumen buffering. The combination of these changes can lead to excessive acid accumulation and a depression of pH in the rumen. Dairy cattle require physical fiber in order to maintain the forage mat in the rumen, stimulate chewing, and buffer the rumen.
Leaving the feed bunk empty is not the solution to cutting feed costs. When feed is restricted, ruminal pH can become very high. A high pH inhibits lactate utilizers, leaving the rumen ecosystem more susceptible to ruminal acidosis. During this situation, microbial balance is disrupted and cattle tend to overeat when feed is re-offered, thereby increasing their risk for acidosis by overeating a large first meal. It is often recommended that refusals for the fresh group remain around 2 to 4%, 1 to 3% for high groups, and 0.5 to 3% for late-lactation groups. In general, feed refusal should not exceed 3 to 4%. A point to note is that if feed refusals are similar in composition to feed offered, you can go for the low end numbers. If the feed refused is different from what is offered, you should go for the high end numbers. The more different in appearance and particle size that the refusals are from the offered feed, the more refusals need to be left to be certain that there was ‘quality" feed available if cows wanted more. Of note, there is actually a very limited body of conclusive research on feed refusal rates and their effects on lactation. Pushing the feed up multiple times during the day can help ensure that cows can easily reach the feed, which can encourage feed intake and fewer refusals.
So the question now becomes: "How can you use the feed refusal and not waste the feed you have?" One approach that some have taken for the lactating cow group is to remix the refusal into the new TMR batch or deliver the new TMR over the refusals. This approach is highly discouraged and can lead to problems that will cost more than the feed refusal itself in the long run. The nutrient composition of the TMR refusal is often very different from its original composition due to extensive sorting by the cows throughout the day. Further, the feed refusal may not have been consumed due to a mold or quality and palatability issue. Therefore, adding this feed into the new batch of TMR could decrease intake and further compromise milk production. A second approach, which may be more beneficial, is to feed the refusals to older heifers, steers, or other beef cattle. Refusals should never be fed to prefresh or fresh cows. Cows at this stage are vulnerable to metabolic diseases and feeding refusals that are variable in nutrient content or contain mycotoxins can impact the cow"s immune system and further exacerbate health problems for both the cow and her calf. A final option is to consider it true waste and discard all refusals. This is a more extreme alternative, but may be best in some situations. It is best to dispose feed that is spoiled, highly sorted, or feed that may cause the transmission of disease across the herd. Feed refusals can easily be disposed of by composting.