I wanted to write a bit about culling decisions, it’s been on my mind due to a lot of discussions on sheep discussion groups I read. For this discussion, I won’t differentiate between sending an animal to slaughter versus selling it to someone else. The former is typically done when it wouldn’t be ethical to pass on a compromised animal to someone else. Selling, however, can be fine if the animal doesn’t meet our own goals, but may be a good fit in someone else’s system; as long as the perceived detractors are disclosed, and the animal is discounted appropriately. Either way, there are times when we may decide that an animal will not be retained in the herd because she’s not passing muster.

So, that said, when should we decide to cull an animal from the herd?  Books generally advise being aggressive in making culling decisions. And certainly hanging on to a underperforming animal year after year is not a good financial decision. Even good animals can have a bad year; but if a ewe is consistently lagging behind her peers in overall productivity for multiple seasons, at some point it’s warranted to replace her.

And, what about genetics? We know that many traits are heritable- twinning, temperament, feed conversion, frame size, shedding hair coat and wool characteristics, color, horns, skeletal structure, milk production, mothering instinct, growth, and even disease and parasite resistance. The thing is, most of these traits are only “lowly heritable”- meaning about 20%. It turns out that about 80% of our animals’ performance is due to management, not genes.

So, we should always put the most critical eye on husbandry practices. That is where the biggest “bang for the buck” lies in making improvements. On the other hand, if there is one underperforming animal surrounded by peers which are thriving, then we can confidently say “this animal isn’t as good of a genetic fit for this system.” How soon should we send her down the road? I would propose that some people are too quick to cull, and that this may cause setbacks in a commercial endeavor.

We have to remember that whenever we replace a mature ewe with a lamb, we are taking a two-year productivity hit right from the start. Ewes are most prolific, and productive milk-wise, from ages three to eight. So, if I replace a three-year-old with a lamb, I need to wait until the third year to see the lamb be as productive as the ewe she replaced. If we are constantly replacing middle-aged ewes with lambs, we may move the ball faster genetics-wise (remembering that genetics is only a minority component of performance), but the gain is offset by lower output during that investment period.

We have to also remember that lambs are not carbon copies of their mothers. They get only half their genes from their dams, the other half from their sires. So, if we breed a mediocre ewe to a great sire, there is potential to get some good lambs out of the equation. Thus, there doesn’t need to be an urgent rush to replace a mediocre ewe; she can hang around and produce butcher lambs, and some occasional higher quality ewelambs. When the time is right, the ewe can be replaced by a ewelamb which shows much more promise. Ideally, this is a ewelamb out of one of the top producers in the flock and a good sire. But it may even be a ewelamb out of that mediocre ewe and a great sire, one that will be an incremental genetic improvement over her mother.

The other option is to replace the ewe with one from another flock. It definitely can be beneficial to bring in new genetics, though also expensive as compared to keeping back home-bred ewes. Purchased ewes are a gamble on two fronts. Locally-born ewes have immune systems customized to the farm, passed down from their mothers. Ewes brought in from the outside are naïve to whatever disease is endemic to our herd, so they may have a rough few years adjusting. And, unless a ewe comes with performance data or NSIP metrics, it’s a crapshoot predicting whether she is any better than the ewe she’s replacing. So here again, I don’t think it’s wise to rush to replace a ewe with just another random ewe found on craigslist.

People often talk about culling based on a single trait- a ewe which shows vulnerability to hoof rot, or that has a snotty temperament, doesn’t shed perfectly, has mis-mothered once or had a single once as an adult. Though all of these things are unfavorable, if we instantly cull any animal that shows a single outstanding flaw, we may be throwing out the baby with the bathwater. We have to recognize each animal as a package of good traits and bad, and their offspring are always a grab bag of these traits. If we only focus on selecting against bad traits, and never selecting for good traits, we can end up with a herd that’s very generic; perhaps with no drastic detractors, but also no points of excellence.

This is where breeding decisions are complex. We have to weigh multiple factors against each other when deciding whether a potential replacement ewe is truly better than her predecessor, offering promise of bringing the herd forward genetically. If I have a ewe that’s excellent on many points, but doesn’t have enough milk to raise triplets, I must realize that about 20% of the time, she may pass lower milk production traits on to her lambs. But, I can breed her to a ram with strong milk numbers, improve upon those odds, and take advantage of her many strengths in the meantime. If I keep needing to supplement her lambs, eventually she’ll get bumped by a ewe which is equal in desirable traits and also has better milk scores. But there is no hurry, I can wait for the right replacement to come along.

Twinning genetics are similar, lowly heritable, but they create a little greater urgency for replacement. Every year I let that ewe stay here and single, it’s a year I might have had twins from a ewe with higher conception rates. And yet, here again, I think we must resist the urge to replace a superior singling ewe with a mediocre twinner. I think we have to insist upon always replacing a ewe with something that has strong promise of improvement. Keeping some daughters out of a singler will not make our twinning rates go down the tubes in one generation. It would take selecting singlers for multiple generations in order for the trend to “stick.”

I’ve noticed a common misunderstanding prevails about twinning genetics; and that is, that people make the “is a” mistake: they think if a lamb “is a” twin, it’s more likely to  be a twinner. In fact, it’s not the instance of the birth that gives the lamb twinning genes, it’s the mother’s overall trend for twinning, or not, which counts. If lamb A is a single, but his dam has twinned six other times in her life, I would value him more highly than lamb B, which is a twin, but comes from a mother which has singled six other times. It’s the trend which defines prolificacy, indicating the running average of how many eggs a ewe drops each breeding season.

I have a lot of customers zero-in on an individual lamb’s birth instance, and this is a mistake. Singles from yearling ewes are the most common example of a place where we shouldn’t care that the lamb is a single; as long as the ewe comes from a line of twinners. And yet, I’ve had people state emphatically, oh, I’ll never buy a ram that is a single. I see them pass over the best ram in the group for a lesser one that happens to be a twin, never asking about the twinning records of the dam and the sire’s dam.

Another mistake people make is thinking that the ram “gives” twins when he breeds a ewe. The number of conceptions is determined by the ewe, how many eggs she drops in a heat cycle, and the viability of her womb environment for keeping fetuses alive to term. Unless a ram’s sperm count is compromised such that he fails to fertilize all the available eggs, he has nothing to do with how many twins are born in a particular season. He does, however, pass on twinning genetics from the dams in his pedigree to his daughters.

And speaking of offspring, I often hear people advise that when it’s decided that a ewe is a cull ewe, the decision is made to also cull any of her daughters, past and present. I think this is also iffy logic. Here again, we have to remember her daughters have inherited half their genes from their sires. If we’ve decided a ewe has a couple of traits we don’t like, we can’t assume that all of her daughters share them or are passing them to subsequent generations, unless they are directly observable or measurable. So it can be perfectly logical to keep daughters out of a culled ewe, if we have reason to believe they are better than their mother.

Rams, however, are another story. Since there are so many to choose from, and they have so much influence over flock genetics, it’s never wise to keep working with a ram once it’s become obvious he’s inferior. I’m consistently surprised at how many buyers are price-sensitive about rams, choosing one that’s not nearly as good as another just to save fifty bucks. Choosing to spend a hundred or two more for a good ram could make a huge difference in the long-term genetic improvement of our herds. So we should always try to use a ram that’s significantly superior to our ewes, to leverage that 20% genetic puzzle piece as best we can.

All in all, this is just a meandering way of saying that I think if one has a ewe that’s had mastitis and now has a bad udder quarter, or she needs more deworming than the rest, it may make sense to keep and breed her for a few more years until the right replacement comes along. Books advise us to cull these underperformers, but we should do so prudently, so we’re sure we’re always replacing them with an improvement.