by Jim Bennett, DVM
I was talking with a client yesterday about coding cows as do not breed in his computer. He was wondering how many, or what percent of “do not breeds” he should have.
Well, of course, there is no right answer here, but since our practice maintains a database of herd information from a group of free stall farms representing about 20,000 cows, I looked up the do not breed event and found that the mean was 12.6% of average annual herd size, and the range was from zero to twenty seven percent. This does not mean that 12% is the right number for your herd. There is no right number. However coding a cow as do not breed is an important decision. She will no longer show up on lists of cows to watch for heat, enroll in timed AI programs, or to breed. In short, her days to become beef are numbered. Herds that code a lot of do not breed cows will have an artificially higher pregnancy rate than herds with few do not breed cows because dairy software systems, or at least Dairy Comp 305, take them out of the calculation once coded. But that’s not the real problem with have a lot of DNBs. The real problem is that you need replacements, and even if you have lots of them available, replacing a lot of cows with heifers results in a herd with a greater proportion of first lactation animals and a younger herd overall. As we all know, those heifers do not milk as well as mature cows, and they probably do not begin to pay for themselves until sometime well into the second lactation. So if you consistently code a lot of do not breed cows, you will have a herd that is young, and that makes it hard to make money.
On the other hand, if you hardly ever code a cow as DNB, and you almost never quit breeding cows, you may wind up spending money on semen for cows that have little chance of getting pregnant, and/or you may get cows pregnant that already have been milking for a long time, and have significantly dropped in daily milk production. These kinds of cows are also often profit robbers since a typical dairy cow drops from 0.17 to 0.20 pounds in production per day after her peak, and cows many days past peak will be producing significantly less milk. Of course, one can dry up these cows early, but then they produce no daily income at all, and long dry periods can cause health problems in the next lactation.
So while the percent DNB in any herd is a nearly meaningless number by itself, it does point us to some things do really matter.