While I’m on the subject of NSIP numbers… I spotted these two ewes standing next to each other in the feeder, and realized their comparison is a fun exercise in NSIP metrics. Their sizes are at two extremes in my flock. As you can see, there is a big chocolate ewe to the left, and a much smaller red ewe to the right. The big one was born in 2010, the red one in 2011. So, they are now nearly ages three and two in this photo: both fairly representing their mature sizes. 

Most people, if they had to choose between these ewes via visual appraisal, would say “oooh, so big!!” about the left one, and “aw, what a shrimp!” about the right one. The difference between them phenotypically is nearly like comparing a Great Dane to a Springer Spaniel. I bet most breeders would pick the chocolate ewe as the show winner, right?

But which one is a better producer and mother? If we look at their NSIP numbers, my bet’s on Little Red. Winking smile

ID

BWT

WWT

PWWT

NLB

NLW

MBWT

MWWT

USA HAIR

EP

TMWWT

Choc

0.207

0.911

1.327

-0.014

-0.102

-0.16

-0.997

93.91

-2.036

-0.542

Red

0.316

0.544

-0.325

0.065

0.005

-0.08

0.023

100.16

0.185

0.295

 

Good Mama, Bad Mama

I bell curve all traits across my whole flock each year. I mark in red all the scores at the low “tail” of the bell curve, and green all the scores at the high end. Black text reflects that they are somewhere in the middle “lump” of the bell curve. So, first off, we can see that Big Chocolate is one of my lowest scorers for Number of Lambs Born (NLB) and also Number of Lambs Weaned (NLW). Her USA HAIR index score is very low. This index is a composite of other scores, and tries to emphasize “pounds per ewe weaned.” All of these scores reflect an undesirable trend: she is not genetically predisposed to have multiple births and successfully bring them to weaning. And her milk supply isn’t stellar (that’s MWWT), so it’s not able to contribute to a high weaning weight.

Little Red, on the other hand, is one of my top scorers for Birth Weight (BWT). This means she has genes for being big at birth. Birth weight is statistically correlated to larger lambs at weaning, not to mention it contributes to lamb survival in pasture settings. So I want this as big as I can stand without incurring birthing problems. (Note that her Maternal Birth Weight-MBWT- is near zero. That implies she’s just average for womb environment and gestation length, which are influencers of birth weight, beyond the lamb’s own genes for birth size.)

Little Red’s above-zero MWWT score indicates she has a more generous milk supply, and probably also good mothering skills that contribute to lamb growth. Her USA HAIR index is better, reflecting my direct observation that she has weaned more pounds of lamb in her lifetime as compared to the big ewe (and this, despite the big ewe having an extra year in which to produce lambs!) This score also obviously reflects the performance of these girls’ parents, cousins, and siblings.  So not only can I observe the difference in these ewes, their correlated genetics are confirming the disparity is even greater than I might have guessed.

Adult Destinies

Where they flip in score superiority is at Weaning and Post-Weaning Weights: so far, Big Chocolate is better here. This means that Big Chocolate is more likely to produce lambs that have good growth traits on their own, assuming they have a responsible momma who can help keep them alive.

But even this has to be taken with a grain of salt. We can guess that Little Red may have genes for early maturation, so she, and her lambs, have the genes to shoot up quickly towards adult weight, and then slow down on growth after that. Big Chocolate may have genes for late maturation: her lambs get big fairly fast, but maybe only because they are going to keep on growing, resulting in very large stature as adults. So, I may not want to get too excited about the differences in number there, when I take into account adult weight.

Picking by the Numbers

If both ewes are producing a similar number of pounds of lamb, which ewe do I want to feed all winter? Little Red, of course. I’d rather not have ewes which swing so far in either direction in frame size, I’m shooting for moderation, always. Neither one of these ewes comes close to my “top” ewes. But if I could only keep one of these two girls, Big Chocolate is not the one I’d keep. With Little Red, I can pair her with a ram that has better genes for lamb growth and get immediate improvement in the resulting lambs. But no ram can help Big Chocolate bring pregnancies to fruition or make more milk! The best a good ram could do is give me daughters to keep which are better than Big Chocolate herself.

These NSIP scores will shift around as these ewes mature and more data is accumulated on their lambs, and on their mothers, sisters, daughters and cousins. Both ewes are still here because they were in the middle of the pack overall when I selected keepers for the 2013 season. So thus far, neither has gotten bumped by a high-scoring ewelamb ready to take their places. Knowing that mature ewes are generally more productive than starting over with a ewelamb, I try to only let ewelambs replace adults when there is promise of a significant jump in quality. Maybe Big Chocolate’s first two years were flukes, and she will start having triplets and redeem her record. (Though I already question whether she’ll be able to feed them!) But, she may well get ousted by a 2013 lamb, if she doesn’t knock my socks off somehow this year. Little Red, and her high performing udder, I suspect, may be here for some years to come.

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