I spotted an interesting bit of data on two sibling rams that made me pause for a moment. Usually, when rams are born, they simply inherit an average of the NSIP maternal traits coming from their parents. So their scores will be identical here, and won’t typically change until those rams have female progeny, which are subsequently bred, feeding data back up the pedigree to their sires. Where the rams will differ distinctly is on weight data, once it’s collected on them, and averaged with the scores coming out of their pedigree history. But a quick glance at these twins highlights something notable in their data at four months of age:
























Why are their maternal scores different? The top ram has a slight edge in Number of Lambs Born (NLB) and Number of Lambs Weaned (NLW), but about a percent, and also a nudge higher in Maternal Weaning Weight (MWWT), or Milk.

What’s caused this is their Post-Weaning Scrotal Circumference (PSC) score. As you can see, the first ram has bigger balls. These are most obviously handy for being able to service a lot of ewes, as they carry more sperm capacity. But their hidden value is that they are also genetically associated with early maturity, which applies to both males and females. So this guy with bigger balls has a higher chance of having daughters which will mature early to lamb as yearlings, increasing their overall lifetime productivity. And these girls, while staying leaner from going into production right away, will have less fatty udders, which tend to produce more milk. A double-win for productivity and profit. No pun intended, that scrotal circumference score is literally a crystal ball, telling us what the future holds for these rams’ daughters and granddaughters.

This is a great comparison set. They are pictured above, 5007 is in the back. They are very similar-looking rams. If I were choosing one based on appearance, I’d have trouble differentiating which one is better. 5007 has an unclean brown marking on his neck, which may cause some buyers to choose the tidier, all-white sib. And 5007 here has an unsightly case of diarrhea, likely caused by coccidia. I treated the group sometime after this photo was taken, and he cleared up just fine; now probably boasting a strong immune response for the future (sheep are almost always unbothered by coccidia once they are adults). So you can imagine, on this day, a buyer would almost certainly choose the front ram, if looking was all they could do.

But interestingly, despite having scoured, 5007’s growth was stronger. 82 lbs versus 71 lbs at their 120 day weighing. (This is all on pasture grass, no creep feed or concentrates, so pretty good gains.) Of course, if a person was taking weights, just this raw data point would be a clue as to which ram was better for growth. But not many people also take scrotal circumference measurements, which means they are missing out on this important maternal data as well. In the end, my money is on 5007 as a strong sire for both growthy lambs and daughters which produce growthy lambs, and more of them. And we know increasing the number of lambs born and weaned is the surest way to increase profitability.

That’s the secret behind using EBVs, is to constantly be choosing the animals with slightly higher scores than their peers; over time, moving your bell curve to the right inch by inch. Progress is gradual, but it’s proven through research and science to be much faster than when choosing by visual appraisal alone.