By Melanie Barkley
Flock productivity is essential to the profitability of any sheep operation. Productivity can be realized through many different methods such as increased lambing percentage, heavier weaning weights, higher quality lambs or more efficient use of feed resources.
A very easy method to increase productivity in a sheep flock is through developing a crossbreeding system to take advantage of desired characteristics from two to three breeds of sheep. Combining these characteristics, or traits, not only builds improved maternal or terminal characteristics, but can also take advantage of heterosis, also known as hybrid vigor.
Heterosis, or hybrid vigor, is defined as increased productivity of the crossbred offspring as compared to the average of the parent breeds. Deb Aaron from the University of Kentucky describes this as increased vitality or “doing ability.” We also know that crossbred lambs tend to be more vigorous at birth, have a higher rate of survivability and often grow faster. In addition, crossbred females tend to mature earlier and on average are more fertile. This is particularly important for producers who wish to breed ewe lambs to produce lambs at a year of age.
Research by Dave Notter shows that crossbreeding leads to more lambs reared per ewe exposed and increased weight of lambs weaned per ewe exposed. (Notter, 1978, Breed Utilization for Meat Production in Sheep. Animal Breeding Abstracts 46: 131-143.)
Let’s take a closer look at some breeds used to produce certain desired characteristics in lambs. Breeds such as Suffolk, Hampshire, Dorper, Southdown and Texel are known for their growth and carcass characteristics. They are in general referred to as terminal breeds. Maternal breeds feature traits such as earlier maturing, increased lambing percentage, and higher wool quality. Typical maternal breeds include Border Leicester, Finn, Katahdin, Merino, and Rambouillet. However, there are some breeds that exhibit both maternal and terminal characteristics. These would include Cheviot, Columbia, Corriedale, Dorset, Montadale, and Polypay. Keep in mind that a great deal of variation can be found within each breed. There are also other breeds that exhibit terminal or maternal characteristics that could be selected to include in a crossbreeding system.
As we consider crossbreeding, we also know that crossbreeding has the greatest impact on low heritability traits. Often, crossbreeding focuses on improving traits such as reproduction, ability to withstand stress, survivability, and longevity. High heritability traits such as growth and carcass traits exhibit less improvement through crossbreeding.
When developing a crossbreeding program, there are some different options to consider. The easiest option would be a two or three-breed rotation that produces terminal lambs, or in other words all lambs produced are marketed. A two-breed cross utilizes a ram from one breed and ewes from another breed. The three-breed cross becomes more complicated because the ewes must be sorted into groups for breeding. However, the addition of the third breed essentially takes advantage of 100% of the heterosis potential in both the ewe and in the lambs.
The two breed or three breed crisscross system allows a producer to generate replacement ewe lambs from each cross. They are then backcrossed with one of the parent breeds to continue the breed rotation. In the two-breed crisscross system, replacement ewe lambs are bred to a sire from the second breed. For example, a Dorset ewe bred to a Suffolk ram would produce a crossbred ewe lamb that would then be mated back to a Dorset ram. In this manner, the two breeds continue to remain in the flock although the producer would need to maintain two breeding groups.
A three-breed crisscross system requires three different breeding groups and ewe lamb replacements can be produced through this system. This system becomes the most complicated due to maintaining three different “flocks” within a flock. Only rams would need to be purchased. Heterosis within the three-breed crisscross system runs around 87% of the potential heterosis effect, while the two-breed cross system runs around 67%.
Increasing sheep productivity can easily be achieved through a crossbreeding system. Carefully planning breed selection and breed rotations can both yield good results that improve reproductive traits, lamb survivability, ewe longevity within the flock and can also help to improve both growth and carcass characteristics.
Source : psu.edu