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More Sheep Statistics

We have completed yet another lambing season, which has been fun. A few bumps along the way. But all in all a good set of babies and happy mamas. I started tracking a lot of data on our flock. I am hoping to build a somewhat predictive model so that I have an estimate on weight, based on age and some other factors. I often have people call and ask for a lamb and want to know how much it will weigh. So I've been working on that.

But before we get to those, I've tracked some other measures for curiosity's sake.

We've slowly been growing our flock, and it shows in 2017! However, the biggest factor to having so many lambs in 2017 is that the 2016 ewes gave birth in January of 2017, and then again in November with just a few born in January of 2018.

That being said, we usually have our lambs in winter. We tried by ram management one year, to get them to be born later in the spring. What an awful time to be born - in the cold of winter! Our sheep are polyestrous, so they have cycles in different times of year. There are some types of animals that are monoestrous, so you get one shot, and they have their babies at the same time every year. We did have a big burst last year in May, which was a surprise. Though we did learn that there are benefits to winter lambing - the main one being that all the sheep are always near the barn, eating hay from the feeder. The lambs don't have to walk far to follow mom, and can nap near the barn, and mom doesn't wander off. In the spring, the babies would fall asleep in the sun, mom would wander off while grazing and when babies woke up, they couldn't find their mama! However, over ten years, this is their pattern for lambing.

So even with attempting to control their breeding by removing the ram, and bringing one in for the hopes of spring lambs, we still get our biggest lambing in winter. They seem to prefer dalliances with the boys in the fall.

As a side note, I noticed this year we seemed to have an inordinate amount of rams being born. Over time, statistically, you would expect that to be about 50%. We don't keep rams year to year, but I am trying to get some statistics on my rams based on their breed and their mothers. But clearly the biggest impact on X vs Y chromosomes would come from the rams. Which makes it difficult for me to control. We appreciate rams as they grow larger, and we have a customer base that for cultural reasons prefers intact males. Keeping all our rams intact does make it even more difficult for me to control breeding.

Though, I can see that this chart can be misleading. We only had 4 lambs born in 2008 - 2 sets of twins, all rams. 2015 seems to be an odd year, too. 2017 FELT to me like it was more biased towards rams, but looks relatively well split. 2018, again, we've only had a few lambs born so far. Although currently on the farm, we have 23 lambs, and 18 are males!

But here is the real data I have been seeking. I had to split this into 2 predictive models. The two factors that seem to have the biggest impact on weight are gender, and quantity. A single lamb will grow bigger than a twin or triple, and rams grow bigger than ewes. I do have a chart that splits out all these options, but it is way too busy. So here is the gender breakdown:

There are some outliers. It also takes the overall average age of the lamb, and predicts the average weight for all the data (That's the purple spot). And the little green bump is our average birth weights of lambs. The logarithmic curves show the predicted weight based on their age. With the data behind this graph, I can take a lamb, input their birth date, predicted process date, their gender and quantity - and predict a weight based on that information. So I can easily tell a customer that by a certain date, yes, I will have a lamb in their size range.

On average, in our flock, ewes tend to be 9% smaller than rams.

Similarly here for the singles, twins and triples.

Again, you can see outliers, and you can see that the triplets have much less data. We only have 2 ewes that have ever given us triplets, so that data is more sparse. Twins tend to be 6% smaller than singles, and triplets are 20% smaller!

The third and final factor that contributes to lamb growth is if they are bottle fed. We have even less data on that, but what we show is that bottle fed lambs are 16% smaller than their mom-fed friends.

So there you have it. This is what happens when engineers raise sheep!