Lambing Season Math

How many lambing seasons per ewe can you have each year?

I am frequently asked about the number of lambing seasons per ewe each year. Many times, the people who ask are surprised to learn that I have “only” one lambing season every year. Or they start the conversation by stating they want their sheep to lamb twice a year. Also, a thought often in people’s minds is to let sheep lamb every eight months or, which is the same, three times in two years. 

My one and only lambing season is in the spring, mainly in March. I let my sheep lamb in the barn. There are several benefits to once-a-year lambing as well as to lambing in the spring: 

• I lamb during a time of year that is favorable in weather since hard frost is no longer expected. The nights at or below zero-degree temperatures usually end in February. On the other hand, there is no heat and there are no flies, or other bothersome insects present at that time, which can make lambing difficult for a ewe. 

• The March-born lambs will start grazing on pasture in April, when the pasture is greening up and will have the most nutritious pasture possible available during their most rapid growth period. At no other time of the year is pasture as high in protein and energy than in the spring and early summer. 

• When the summer pasture growing slump hits, I can start reducing the size of the flock by culling the old ewes, selling the first market lambs, and having the lambs for breeding purposes picked up. 

• During the fall’s pasture growth flush, when weight gains of market lambs are lower because of the lack of energy in perennial pasture, I have very few market lambs left to fatten. 

• The ewes have ample time in late summer and early fall to regain weight and to be in good condition at breeding season in October. 

• During the winter, when the feeding cost is highest due to having to feed stored feed, I have only my ewes, my replacement ewe lambs, and my rams to feed but no market lambs. It reduces my feeding cost a lot. 

• The peak in workload is only once a year, which allows for some downtime in the fall and winter. The recovery time is particularly important as I get older. That makes the system sustainable.   

Once a year lambing in March works best for me.
Ulf Kintzel / White Clover Sheep Farm

This is what works for me. The argument against it is that lamb prices are the lowest in the summer and early fall when demand is lowest (summer) or the bulk of market lambs are entering the market (fall). I do not depend on seasonal prices since the price for my market lambs is locked in per contract and breeding stock prices do not depend on the season. But for others, selling lambs later in the winter or early spring can be more profitable if they have a good way of fattening lambs with haylage or corn silage or even grain. Stockpiling pasture in areas where the climate allows grazing well into the winter or seeding fields with triticale, Italian ryegrass, brassica and the likes for winter grazing can be an alternative to be able to supply lambs at different times of the year. Still, it would be one lambing season “only”, just at a different time.  

What are the potential downsides of having lambs just once a year? There is one I can think of, which is that lambs that are ready for the market can only be offered over a period of a few months each year. Most of the year a producer with a once-a-year lambing season will not have market-ready lambs available. That is potentially a problem for a producer who sells lambs to a vendor, a distributor or a supermarket chain. In the past, I remedied that problem in part by having a staggered lambing season: half of the flock lambed in January, half of the flock in April. This allowed me to supply lambs to a couple of vendors for a longer period throughout the year. Since my market is now mainly selling breeding stock and very few market lambs are being sold to a vendor, I no longer practice the staggered lambing seasons. However, please note, while practicing a staggered lambing season, I still let each ewe lamb just once a year. 

Where do I believe a lambing season every 8 months (or three times in two years) makes sense? It is at large farms with hundreds or even thousands of ewes that need a steady supply of lamb for large vendors or supermarket chains, where such a steady supply of lamb is absolutely needed year around to be able to secure such contracts. Such large farms with employees can set up a management system that smaller family farms often cannot without a high human toll. It is much harder for a single operator to do that over many years. 

Of course, you will need a breed of sheep that breeds out of season, meaning the ewes cycle throughout the year. Many sheep breeds only cycle in the fall and are unsuitable for such a system of three lambing seasons in two years. 

Lambing in March is in my barn.
Ulf Kintzel / White Clover Sheep Farm

Years ago, I briefly and on limited scale had ewes lambing every eight months by shortening the breeding intervals on a select number of ewes. The shorter times in between lambing did bring me initially more lambs, but it also shortened the productive life of these ewes. The time in between lambing was over the years not long enough for the ewes to recover properly. Also, the lambing percentage started dropping in subsequent lambing cycles due to the shorter recovery time. Overall, not much if anything was gained but more work was required. Also, more lambs had to be fed at a higher cost due to the seasons they were born in. Keep in mind though, my sheep are grassfed. I find it plausible that with heavy grain feeding the ewes will likely regain a good body condition quicker. But this too comes at a cost. 

Personally, I will continue having a single lambing season in March. The profit margin is highest on these spring-born lambs due to the lowest possible cost of raising them, grazing them on the most nutritious pasture of the year. Once a year lambing is in my view also the most sustainable option, both for the animals and the operator.  

What about lambing two times per ewe per year? The gestation time of a ewe is five months. A lamb needs to nurse on the mother for a minimum of two months before it can be weaned. That makes it seven months for one cycle at a minimum. Multiplied by two, you end up having a total of 14 months. That is two more months than we have in a year. In addition, ewes don’t come into estrus (heat) again for about a month to two months while nursing lambs because of high levels of a prolactin hormone, which inhibits the release of all the hormones that cause the ewe to start the reproductive cycle again. There you have two reasons why twice a year lambing per ewe is impossible.