From the perspective of a long-time, full-time farmer, this article will address the topic of mature ewe size. As we seek to improve the growth and performance of our lambs, we are also producing larger adult animals. The harder we push for improved growth and performance, the faster we accelerate the trend toward bigger ewes.
Big sheep catch our attention. We may have an inborn human preference for bigger animals. The bigger sheep seem superior to the small ones. They win lots of ribbons at the sheep shows. A majority of my seed stock customers purchase the biggest animals in the group, with little regard to other information. When appearance is a top priority, as in the production of show sheep, then indeed, you need big, attractive ewes. Probably, the bigger the better.
However, if your focus is on producing meat lambs commercially, then the optimum mature size of your ewes should be considered. The objective is not to breed for bigger ewes, but to develop a ewe flock that can most efficiently convert farm resources (grass, hay, feed) into dollar bills.
We should not be seeking to maximize production. We want to maximize profit. There are three concepts involved here: production, efficiency and profit. These overlap, but they are not equivalent.
Production concerns the outputs of our sheep operation, ignoring inputs. With our ewes, we measure number of lambs born, and milk production, and lambs raised. With lambs, production involves faster growth.
NSIP and EBVs help us in breeding for increased production, but do not account for input costs. We can push production too far, to the point where diminishing returns, and unintended consequences, depress income. Production needs to be optimized, not maximized.
This is where the second concept, production efficiency, must be considered. Increasing production will require additional inputs to support higher growth and bigger size. Efficiency takes into account the additional resources needed, and can help determine optimum ewe size. A bigger ewe raises bigger lambs, but both will consume more grass and more hay. Production efficiency accounts for this, and maximizes feed and resource utilization. What size of ewes can best utilize my grass to produce maximum pounds of lamb?
The third concept in this analysis is profit, or economic efficiency. This incorporates production efficiency and also considers prices and the money involved both in farm inputs and in actual dollars in sales. Economic analysis can determine the ewe size that generates maximum profit.
Our NSIP and current EPVs do not address efficiency. They could and in the future probably will. Cattle EBVs, both dairy and beef, have EBVs that measure mature size, and Index EBVs that predict female productive efficiency. Our sheep EBVs do not.
Other countries, notably New Zealand and the United Kingdom are way ahead of us in recognizing the drawbacks to striving for ever higher production and ever bigger ewes. Recent studies looking at production, production efficiency and economics have determined that ewes are getting too big.
These studies have also discovered that the optimum ewe size for their sheep farming operations is between 55 and 65 kilo. In pounds, that translates into ewes weighing 120 to 140 pounds. Bigger ewes produce more per animal, but they consume more. With bigger ewes, stocking rates must be reduced, with fewer ewes on each acre of grass. The big ewes can produce more per ewe, but less per acre.
In recognition of this problem of big ewes having a negative overall impact on farm production and profit, farmers use their Mature Weight EBVs to assist with breeding and selection. Their current objective is to select ewes with excellent early growth, and good maternal traits, but moderate or even low mature size. Selection is for moderate mature size ewes that most efficiently convert farm resources (grass) into meat.
While we here in the US do not have the Mature Size EBV, we can still weigh our ewes. Ewe size is very strongly correlated with input costs. Efficiency of ewe production can only be discovered by accounting for inputs. Mature ewe size reflects input costs.
I would suggest the Holy Grail of sheep breeding is no longer “pounds of lamb raised per ewe”. It should be modified to “pounds of lamb raised per pound of ewe”. This new metric can also be expressed as the percentage of the ewe body weight that she produces in pounds of lamb weaned. This metric accounts for input costs of lamb production and is a very useful tool to use in our breeding decisions.
The formula itself is not complicated. Calculate the pounds of lamb weaned by each ewe, and divide by the ewe’s body weight. Various methods of calculating weights will work, as long as you’re consistent. The most common way to calculate ewe weight is at breeding, while an age adjusted 60-day weight for the lambs will work, especially if you’re already collecting this data to submit to NSIP. We, personally, use the weight of the ewe at breeding, adjusted for body condition score, and the actual weight of the lamb at weaning, adjusted for sex.
Don’t worry too much about the actual numbers. It’s how the ratio for each ewe compares to the rest of the flock that’s important. The efficiency ratio is highly dependent on management, so isn’t reliable for comparing animals between flocks, but it should give you a good indication of which ewes in your flock are the most efficient. I prefer to utilize weights over several years. This gives a more reliable estimate of true ewe efficiency. A ewe might have a great score one year, but average or below the next. With three, four, or more years of consistently good efficiency scores, a ewe proves herself superior. With multiple years of poor efficiency scores, a ewe becomes a candidate for culling.
The most efficient ewes, by this measure, are those that wean the highest percentage of their own weight. Use this formula to compare the ewes in your flock. You will find that many of your smaller ewes are most efficient at converting grass into lambs. The least efficient ewes should be culled, and replacements kept from those ewes that produce most efficiently.
An efficient flock will better utilize your feed resources and convert them into more pounds of lamb. The impact on farm profit will greatly exceed this increased output. You will be lowering costs as well as increasing production. Size does matter, and bigger is not better.
By: John Stenger, Stenger Farms, Katahdin producer
