Last time when we were discussing culling, we mentioned that there is a right way and a wrong way to compare the growth rates and performance of your sheep. We said you couldn’t just pick out the biggest, nicest looking lambs in the field and expect your flocks performance to improve. Those lambs are actually often the poorest performing animals. So in this article we are going to start talking about how to select your highest performing animals.
If you look at your flock of ewes and lambs and select for the best conditioned ewes, and the biggest lambs without looking at any other variables, you are actually selecting for decreased performance from your animals. Why? The biggest, most impressive looking lambs are typically singles.
These singles are produced by underperforming ewes. Those underperforming ewes are incidentally the best conditioned animals in your flock because they aren’t working very hard. You can probably see where we are going for this. Select those impressive looking large singles for a few years and your flock performance starts to decline.
So how do we evaluate which animals are actually the best performing ewes and lambs?
In addition to evaluating your ewes based on all the conditions we mentioned last time–like good udders and mothering skills (which enable them to grow good lambs)–you should use body weights. You can determine how hard an individual ewe is working for you by determining the pounds of lambs weaned as a percentage of the ewe’s body weight.
This is a very simple calculation. Weigh your ewes before breeding season and weigh your lambs at weaning. You simply take the combined lamb weight and divide it by the ewe’s body weight. For example, if 100 lb Ewe #1 weaned a 70 lb lamb, she weaned 70% of her body weight. If 120 lb Ewe #2 weaned 3 50lb lambs (150 lbs of lamb) she weaned 125% of her body weight.
Why does this calculation matter?
As a producer of lambs, your goal is to produce the most pounds of lamb from the least amount of inputs. More pounds of lambs means more profit. Ewe 2 weaned over twice the amount of lamb weight as Ewe 1. However, Ewe 2 did not eat over twice as much food as Ewe 1. Ewe 2 is working much harder for you and is therefore the more profitable ewe. When you walk through the field, Ewe 2’s triplets won’t look anywhere near as impressive as the 70 lb lamb. Nonetheless, they are genetically superior, and I should keep the triplets and send the 70 lb lamb for meat.
Now this was an exaggerated example to make a point. You probably would not need to do that calculation to know that Ewe 2 worked harder for you. But, what if you are comparing a group of ewes who all twinned? Then their performance differences won’t be as obvious, and you likely would not be able to visually see who did the best.
When evaluating ewes this way, please keep in mind that you should only be comparing contemporary age groups. Your ewe lambs are not going to perform as well as your adult ewes. Ewes between the ages of 3 and 6 are at peak performance. So don’t cull out all your young ewes because they’re ‘underperforming’ as compared to your mature (3-6 year old) ewes. Do consider getting rid of mature ewes that under perform everyone else. Or ewe lambs that underperform all your other ewe lambs.
To further complicate matters, when comparing lambs you must take into account a whole bunch of other variables.
Ram lambs grow faster than ewes, singles grow faster than twins. You cannot directly compare the lamb from an ewe lamb to the lambs from a mature ewe. Nor can you directly compare lambs that were born a month apart but weaned at the same time.
Why? Your ewe lamb is still trying to grow herself and doesn’t have the udder development of a mature ewe. A lamb born at the beginning of lambing season might be a month or more older than a lamb born at the end. This means it had a whole entire month of extra growing and will obviously be bigger when they are weaned at the same time. However, just because it is bigger does not mean its growth rate was better.
You absolutely cannot tell who is best based on just looking at the lambs standing out in your field. Fortunately, the comparison research has already been done. There are tables and calculations to allow you to adjust your lamb weaning weights to compensate for these variables. It might not be a 100% perfect system, but it is much better than the alternative of blindly guessing. By using adjusted weaning weights, you can much more accurately determine which lambs are the genetically heavier individuals. They are the ones you will want to keep.
Next time, we are going to delve into the details of how to calculate adjusted weaning weights. If you don’t want to miss out on that article, please sign up for our newsletter!
Please remember
The information provided is for general informational purposes only. All information on the site is provided in good faith, for general informational and educational purposes only and is not a substitute for professional advice. We make no representation or warranty of any kind, express or implied, regarding the accuracy, adequacy, validity, reliability, availability, or completeness of any information on this Site. Accordingly, before taking any actions based upon such information, we encourage you to consult with the appropriate professionals. We do not provide any kind of professional advice. THE USE OR RELIANCE OF ANY INFORMATION CONTAINED ON THE SITE IS SOLELY AT YOUR OWN RISK. View full disclaimer here.
