You may have heard or read, especially on Facebook discussion lists, how it’s unwise to buy a young ram lamb for breeding, before his individual growth performance can be observed. For most flocks, this is very true: you won’t know much about that ram when he is eight weeks old. All you can judge by is how heavy he is compared to his peers at that age, and maybe something about his parents based on looking at them. It may be hard to compare him if he’s a single out of a mature ewe, and his peers are twins out of younger ewes, the perception of his size will be biased. If he’s in a small flock, there is little to compare him to. The best ram of a dozen may not be a great ram, there is just no way of knowing whether he is a “big fish in a small pond.” It’s surely a gamble to buy a breeding ram from this kind of situation. Buying a ram with lower growth or prolificacy scores could set your operation back years in progress.
But, when buying from a larger NSIP flock, the situation is a little different. Now, we have data not just on that ram’s weight at sixty days. Rather, aggregated into his EBV scores are the scores of his entire extended family- parents, grandparents, siblings, cousins, aunts and uncles. And, in a large flock, that ram is now being compared against the performance of a hundred or more peers for growth to weaning or post-weaning. So, we can tell a lot about that ram at sixty days, and his genetic potential for producing great future generations. We can tell even more once his 120 day weight is taken and accounted for- now we have two data points on the growth curve, again ranked against dozens of peers, and combined with family data from several generations back and hundreds animals lateral to the pedigree.
EBVs give a much more accurate and valuable predictor of a potential breeding ram’s offering to your operation than visual appraisal of the animal and his parents ever will.