Lamb Statistics

December 23, 2016

For anyone that doesn't know...I'm an engineer by day. That often means I'm a spreadsheet jockey. I love numbers, they always tell a story. For many years, I've been tracking data on each of my ewes. Do they have singles, doubles or triples? Do they have boys or girls? Will they be as awesome as Shirley?



I realized that my first round at judging my sheep was lacking. I was tracking the average size of their lambs.  But there were several factors that made that an inadequate judgement.


First, rams are bigger than ewes. True facts. Second, singles grow bigger than doubles who grow bigger than triples. Think of the resource management there - a single lamb gets all the milk mama produces. Twins have to share. And triples, well they certainly have to share, and since there are only two teats, they can't eat whenever they want!   Another component was the actual age of the lamb at the date of slaughter.


So I had to adjust my data to give credit to the lambs for their age. Younger lambs SHOULD be smaller than older ones. And even if triplets are smaller lambs, they still produce more meat from all three of them than one single lamb. So moms of multiples had to be given credit, too.  That gave me the following chart... 




The yellow line across the top represents Shirley, our first ewe, and one of our most productive. We said goodbye to her this year, so the line marks her productivity over her life here. The blue bars show what each ewe has already produced for us. You'll see that the blue bar for Shirley ends at the yellow line. There are factors in here that normalize their lamb weights based on their age, as well as if they were singles, triples, etc. 

For each of the rest of the ewes, the blue represents their actual production. The red shows their potential. For ewes that have lambed, the red is based on their average numbers - average number of lambs, lamb ages and weights.   Marcia, Cindy and Betty may have the opportunity to produce MORE than Shirley did for us! 


The ewes are listed here, more or less, in order of their age. You can see ladies like Applejack and Pumpkin Cake have all red bars - they haven't lambed yet at all! Their potential is based on the average of all the other ewes combined, until they have data of their own.  I use this chart to identify underproducing ewes to determine if I will cull them and make room for a better ewe. Ewes are culled for a variety of reasons, and usually need more than one to be culled. Other reasons include stillbirths, abandonment and skipping breeding seasons.  We have 21 ewes on the farm right now, and most of them are pregnant!


So that data is very ewe-centric. Focusing on the moms. But there are ways to look at the data more lamb-centric. essentially, I am trying to put together a predictive model on lamb size. Something that would help me identify or predict a lamb weight. I know it's more complicated than the chart above. Let's see what I found out...



I felt that this year's lambs were very small compared to years past, so I wanted to see. Not a direct trend, we've had smaller years in the past, and we spiked back up again in 2013, and are trending down again. Again, not this simple, let's look a little differently at this.


 If you look at the average lamb weight per year (the left axis)  compared to their age in months at the time of slaughter -there seems to be a correlation, which makes perfect sense. The younger the lamb (right axis) the smaller they would be.


That does make 2008 stand out like a sore thumb! But that's pretty easy to explain - we only had 2 lambs that year! They were both rams, twins, but they were spoiled. 


So let's see what the impact gender and number mean on a lamb's weight. 


 Look at that, I expected rams to be bigger than ewes, and I expected singles to be bigger than doubles or triples. But there is one data point that sticks out - twin rams grow larger than single ewes!   So gender certainly has an impact. We are no longer going to be banding our boys, so I fully expect the gender discrepancy to grow, as our boys will have full access to their testosterone!


One bit that isn't captured here is that bottle lambs never grow as big as mama-fed lambs. Yup, in the land of sheep, breast-fed is way better than formula! Moms who have a habit of abandoning their lambs don't get to stick around for long. But some of them do it just once on a glitch, maybe their first time, maybe one twin get separated and mom didn't bond. Now that Shirley is gone, we are going to make a habit of taking one of each set of triplets to hand-feed, as it can be too tough on mom. So that will make the triplet numbers stay small, as the hand-fed lamb will be smaller. But it's better than the alternative of losing the lamb altogether.


So it won't be as simple as using the formula below, but I may be able to better predict the size of a lamb with a few added factors put together. Below shows the weight to age data across all our lambs. Gender, multiples and bottle-babies are not identified in this data, but you can see that I could use this to predict an average weight.



Yup, there's a formula there. I'll need to figure out the possible offset based on gender and multiples, and I may do better at predicting lamb size, and maybe seeing if some mama's constantly fall below the curve, and some over, and start adjusting my flock based on the better producing mamas.

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