Breeding Options for a Commercial Sheep Flock
Table of Contents
A breeding plan for a sheep flock can be compared to travel to a destination. When planning a trip a traveller will either intuitively know the roads to travel on or will consult a road map to determine the best route.
A breeding plan for a sheep flock is no different than a travel plan. It's a plan to change the genetics of a flock from its present level of performance and productivity to reach a defined target. Without a plan, animals are either brought into or leave the flock for a variety of reasons, some of which may diminish the ability of the flock to be productive and to produce offspring to meet market requirements. This can frustrate efforts to improve ewe productivity to meet market lamb requirements.
When establishing a commercial sheep flock, producers are advised to select maternal-type sheep for their ewe flock and a terminal sire to produce large numbers of lambs with desirable carcass traits. This theory makes sense.
A maternal-type ewe will excel in maternal characteristics such as:
The terminal sire will contribute the genetics for rate of gain, feed efficiency and muscularity of market lambs. This plan produces heterosis in the lambs - that is the ability of the offspring to perform above the average of the parents.
Implementing this theory can be complex and requires planning.
A typical situation is that a breeder buys 30 maternal-type ewes and a terminal ram. The ewes are bred and produce uniform, good-looking market lambs. The owner is pleased with the breeds; the lambs exhibit some hybrid vigour in performance and bring above-average prices in the market place. The owner decides to increase flock size and keeps the better ewe lambs to increase flock size to 50 ewes. When it is time to breed these ewes, there are now 20 ewes related to the current ram; thus a new ram is needed.
When buying another terminal ram, the flock owner selects a third breed. This adds complexity to the system, requiring separate breeding pastures and the resulting lambs are a different breed make-up.
The next lambing year, there are 50 ewes lambing. While the mature ewes continue to perform well, the ewe lambs don't do quite as well as expected. However, this is acceptable as they are ewe lambs and the lambs that are born perform well. The sheep business is profitable and the decision is made to keep another 30 ewe lambs.
At this point in time, there are 30 maternal-type ewes, 20 ewes that are half-maternal and half terminal-type animals, plus the additional 30 ewe lambs that are a combination of half maternal/half terminal-type animals and ¼ maternal/¾ terminal-type animals. The flock contains ewes of different breed types and future lamb crops will be less uniform.
This creates several problems:
Maternal traits tend to be negatively correlated to production and carcass traits. For example, productive maternal ewes are the result of selecting for reproductive traits such as conception rate, number born and maternal traits such as mothering ability and milk production.
It is very difficult to produce a sheep with both exceptional maternal, production and carcass traits. There likely isn't a breed that can produce as many lambs per lambing as a Romanov and is as muscular as a Texel. Thus geneticists recommend a strategy to develop a maternal ewe and a terminal sire to take advantage of concentrating maternal traits in the ewe flock and introduce production and carcass traits in market lambs through a "terminal" sire.
There are several approaches in developing and maintaining a maternal ewe flock. One approach is to purchase F1 crossbred ewe lambs from a supplier (breeder) annually to replenish the flock. An F1 female is the result of crossing animals from two breeds. The resulting F1 females have superior performance for maternal traits, which tend to low heritability when compared to the performance of either parent breed. An alternative is to generate replacement "maternal" ewe lambs on the farm through breeding a "maternal" ram lamb to the top 10% or 20% of the ewes (for maternal ability) in the flock.
A down side to this plan is the necessity to "feed out" male lambs from this mating (additional costs of production due to reduced performance and lower revenue due to carcass quality). A third option is to maintain 2 pure or straightbred flocks to generate animals for crossbreeding and developing F1 ewes.
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