Sheep Breeding

Credit:Biovision-Infonet

Sheep respond very well to good care and management, so the first step to improve their health is to provide good feeding and control diseases and parasites. Only then can further improvements be made by implementing a good breeding program. 

Selection methods:

There are basically 3 ways of selecting individuals, and these can be combined

• Individual selection – on the basis of their own performance irrespective of family (or mass selection). Comparing individuals on the basis of their own performance is often called a performance test. In most situations individual selection is the best procedure as it takes account of all the additive genetic variation that is present in the population.
• Family selection – by choosing the best families as a whole and rejecting others (also called between family selection). Here selection is on the average value for the family and takes no separate accounts of individuals. Family selection may increase the rate of inbreeding so is not recommended for common use.
• Within family selection – choosing the best individuals from each family. This procedure retains at least one representative from each family for the next generation. It is most useful when differences between families are mostly due to environmental factors. Retaining at least one member from each family for the future can also be helpful in reducing problems of inbreeding.

Breeding Methodologies

Also in sheep breeding should be considered what sheep breed or crossing fits best to the circumstances at the farm. Local breeds in general are more hardy and disease resistant and used to the climate conditions, exotic breeds have higher growth rate but need better conditions (better feed quality) than the local breeds. If that can’t be offered, exotic breeds will not produce more and will need more (medical) care than the indigenous breeds. Crosses between local and exotic breeds could be a possibility to keep disease level low and collect the good genes from both breeds in the offspring. Collaborating as sheep owners in exchanging breeding rams can lead to a quick improvement the sheep flocks on individual farms. 

See also in Integrating animals into the farm – what to consider when choosing to keep animals.

Grading up

Ewes from local breeds and their female offspring are mated with rams of a more productive breed for example Dorper rams. The resulting crosses are then mated with non-related animals with the same level of cross breeding (first generation 50%, second generation 25% or 75% depending on ram used). Positive traits of the local breed (disease, parasite and drought resistance can be maintained this way. Maasai-Dorper crosses for example are most productive with 75% Red Maasai blood.

Crossbreeding

Crossbreeding refers to the crossing or mating of two pure breeds, but the term is frequently extended to include the offspring of purebred sires and crossbred females. When two purebreds are used, characteristics of the first cross animal should show:

1. Outstanding individual merit

2. Intermediate expressions between the parent types and

3. Resemblance to one or other of the parent types.

Crossbreeding of sheep is widely practiced throughout EA, especially between indigenous Red Maasai sheep and Dorper and Dorset Horn for improved performance. It should be the objective of the breeder to produce offspring superior to both parents. This is achieved when the progeny resulting from crosses demonstrate extra or improved performance above the average of the parents (heterosis or hybrid vigor).

There is no doubt that crossbreeding is an important method of commercial sheep production. The vigour, thrift and general excellence of the first cross sheep are features that are especially apparent and which can be measured accurately in terms of increased returns. As sheep production becomes more intensive for both mutton and milk production, it is likely that cross breeding and exploitation of hybrid vigour will become more popular.

Group breeding scheme without nucleus by use of reference rams

One of the main benefits from cooperation among breeders is that the animal population directly involved in a selection program is enlarged compared to what is available to the individual breeder. In order to know whether a ram used in one flock is genetically better than one of the rams in the other cooperating flocks, it is necessary to have some sort of link between the flocks. This can be done by identifying so called reference rams. These rams leave offspring in several or possibly all cooperating flocks, The offspring of the reference rams can then be compared with offspring of any other ram used in the same flock. This way the best rams in the whole of the group breeding scheme:

• Can be identified, with the help of appropriate statistical tools
• Can become available to the scheme as a whole
• Can be used to breed the next generation of males

If a community wants to upgrade and improve the quality of their herds it is recommended to seek advice from professional breeders to set up breeding schemes that fit the objectives in hand.

Nucleus group breeding schemes

These breeding methods were pioneered in New Zeeland and Australia , but successfully adopted in many countries. For such a scheme a number of flock(or herd) owners agree to cooperate by deciding on common breeding aims and pooling their animal resources. The key of such a scheme is to create a nucleus – or central flock from the best of the breeding females of each participating flock. Very good record keeping is necessary.

The nucleus flock in this case was set up from the best females from the participating flocks. Thereafter each year the poorest females (40 in this example) are culled from the nucleus flock and replaced by an equivalent number from the cooperating flocks, taking the best (8 females) from each. The best of the rams are used in the nucleus flock and the next best in the cooperating flocks.

Sheep reproductive traits

Ewes
Mature weight	90 – 300 lb.
Breeding season	early February to late June (some are poly-estrous year around, ex. Dorset)
Estrous cycle	14 – 19 days seasonally poly-estrous
Duration of estrus	24 – 36 hr. (standing heat)
Time of ovulation	24 – 30 hr. from beginning of estrus
Gestation period	145 -155 days
Breeding/year	1 – 2/yr.
Artificial Insemination	Yes Cervical or Vaginal Method Intrauterine Method (not available in Kenya)
Ewe lambs
Puberty	5 – 8 months (80 – 100 lb.)
Minimum breeding age	8 – 10 months
Rams
Puberty	6 – 8 months
Mature weight	150 – 450 lb.
Serviceability	1 ram: 30-35 ewes (60 day breeding season)
Ejaculate volume	0.8 – 1.2 ml
Sperm concentration	2000 – 3000 million/ml
Motile sperm	60 – 80%
Semen freezable	Yes