Determining the Most Efficient Ewe Size for Your Operation

The most efficient sheep, or better yet, the most efficient flock of sheep, is what producers should strive for. But the most efficient sheep for one flock is not always the most efficient sheep for another producer's flock. So, how do we first describe an efficient sheep and then choose the size that best fits your operation?

Let's start by defining efficiency as it relates to animal production. Dr. Gordon Dickerson, a leader in defining efficiency in beef production, defined it as the ratio of total costs to total animal products from females and their progeny over a given period. He further examined efficiency from two different perspectives. One was biological efficiency, or the feed consumed to produce a product. The other was economic efficiency, which is measured by the dollars spent compared to the dollars returned.

It is well-documented that the number of lambs weaned per ewe is the most significant factor affecting profitability in an operation. But, we need to consider what size ewe will best utilize the resources available on a particular farm. Ewes need to be able to convert forage from pasture or stored feed into body condition and also produce lambs. Maximizing stocking rate on pasture is a key to determining efficient ewe sizes. Across the country, stocking rates vary significantly depending on soil productivity and rainfall. In the east, a typical stocking rate is 1,000 pounds of animals per acre. However, with excellent pasture management, this stocking rate could be doubled. Compare that to stocking rates in some western areas, where you might need five or more acres to support just one ewe.

Let's use a scenario to compare the difference in costs for maintaining a 175 lb. ewe versus a 225 lb. ewe. For many operations, producers will need to provide about four months of supplemental feed during the winter months. A 175 lb. ewe requires about 2.9 lb. of dry matter per day, and a 225 lb. ewe requires about 3.3 lb. of dry matter per day according to the National Research Council's "Nutrient Requirements of Small Ruminants." Translate that into the amount of hay that would actually be fed, and we are looking at about 0.5 lb. per day more hay for the larger ewe. This is calculated using hay at 90% dry matter and by adding a bit extra for waste. Over those four months, the additional cost to maintain the larger ewe is $4.50 for hay valued at $150 per ton. Well, that cost seems no big deal. But remember that we also have to decrease the stocking rate on pasture to account for the additional dry matter intake of the larger ewe. If we consider a full year of additional dry matter intake needs using the value of hay, the larger ewe will cost about $13.50 more to feed. Please note that this cost does not include the additional pasture acreage required to meet her feed requirements.

There are obviously some additional costs that will be needed for health care, more feeder and barn space, etc., that we have not specifically accounted for. So, let's estimate that the additional costs for that ewe are around $15 per year. If lamb prices for weaned lambs are $2.50 per lb., then the ewe will need to produce lambs that weigh 6 lbs. more as a group at weaning than the smaller ewe to justify her larger size.

What have we missed in the comparison? Larger-framed ewes are more likely to produce larger-framed lambs at birth, which could potentially increase lambing problems, which in turn can affect survivability and weaning percentages. Those larger lambs will have a higher dry matter intake than the smaller lambs. This won't make much difference for the small producer. However, if you are a large producer with 100 lambs or more, this will certainly make a difference.

What this comes down to is that each individual producer will need to determine the most efficient ewe size for their operation. Pasture stocking rates, ewe productivity, feed efficiency, and lamb values all play a part in determining what size ewe is most efficient for a particular operation. Above all, the market for your lambs should be a significant factor to consider when determining the most efficient size ewe for your operation. So, take a closer look at your farm records to sort through the pieces of the puzzle that determine what size is best for your operation.