Whether you have two cows or 2,000, there is a top and bottom half of your herd. The top half is above average in some way, the kind you want more of. The trouble is, a cow is often above average in one trait and below average in another. Sometimes the meanest cow in the herd weans the biggest calf.
If you cull strictly on disposition score, she’s gone. But her calf was 40 lb. heavier than any other in the herd and she hasn’t actually hurt anybody yet. Still, to paraphrase a credit card commercial, not having to rebuild your corral or worry about injury every time ol’ “Twister 245” goes through: priceless.
Research in Iowa and Colorado during the last decade has begun to justify culling for disposition as more than a convenience trait, when you consider the strong temperament link between cow and calf. Thousands of steers fed in Iowa during the 1990s and scored from mild to wild, show the calmest steers made $61/head more in the feedlot than their high-strung counterparts.
Colorado work backs up those feed efficiency and gain correlations, and shows 25% of the wildest scoring cattle end up as dark cutters, compared to less than 5% of other cattle. Dark cutting carcasses may be discounted by $300 or more.
Just one or two wild acting calves can excite more of your calf crop and cause the whole lot to make a bad impression on potential buyers. Worried about poor gains and discounts, they may choose not to bid. You could lose in the long run by holding onto wild cows that wean heavy calves, because your reputation is at stake.
You need a way to look at your cows that considers several relevant traits. Economically important traits must lead the way, but some, like temperament, will always be a judgment call.
The simplest approach is to work the bottom end of the herd, culling on a “strike” rule. For example, any open cow gets a strike. If you have a lot of replacements coming up, one strike might be all you allow. Producers must weigh the investment in her development, and all other traits, against the annual $300-$400 cost to keep her with no return.
Many producers elevate non-pregnancy to the level of two strikes, also culling for any combination of two other strikes. Those may be decided by such criteria as poor udder, mothering ability, thin condition, low weaning or yearling weight of progeny, multiple grid discounts of progeny, unsound feet and legs or, again, unmanageable disposition.
Of course, any one trait can get so far from optimum that you have no choice but to cull.
There are five- to seven-point rating systems devoted to most of these individual traits, from body condition score (BCS) to temperament. Using these can help you see the difference between a foul tip and a strike, but you can’t see the big picture.
The concept of a multi-trait selection index was developed as a decision-making tool more than 60 years ago. If you have dairy management experience, you’re more familiar with the idea, but even there, it is mostly associated with bull selection. Indexing does work great for choosing bulls from among various breeds, involving dozens of expected progeny difference (EPD) numbers.
But for those with individual cow-calf records, indexing the cowherd could help identify and build on the overall best cows in your herd. A computer program will help, but it takes time and effort to devise an index that fits your production scenario and goals.
Look at all the cow traits that are of economic importance to you. If you like something but it doesn’t affect profit, leave it out of the index because it will only dilute relevance and progress.
Canadian research provides the Ellerslie Index (search for it on “Ropin’ the Web at http://www1.agric.gov.ab.ca/). Its formula, “100 + (% of weight weaned - herd average) x 2 + (BCS - herd avg.) x 6,” uses the five-number Canadian BCS system, so U.S. producers would need to make some adjustments.
If you weigh cows and calves, and assign BCS numbers each fall, you could calculate such an index. In theory, most other traits relate to it, but you would need to add or subtract for disposition and postweaning value of calves. Still, these concepts can be applied to generate a single number for each cow in the herd so that ranking top to bottom will identify the best and worst.