"One may consider the ancestors as thoroughbred only when all the progeny are thoroughbred."
Thaer, in 1806
One of the most valuable products of across-herd evaluation is the sire summary. A typical sire summary contains three types of information: 1) animal identification, pedigree, etc., 2) records of individual, simply inherited traits, such as huacaya or suri phenotypes, individual physical traits such as weight, testical size, bite, fleece, and other performance records, and 3) progeny performance records.
Once you have this information, you can estimate, accurately, the males' expected progeny performance in comparison with all of the other male's progeny's performance. For each trait, a mean is established for the participating studs. An individual's progeny's performance can then be compared to the mean performance for each of the characteristics; one male's cria might perform well for fineness, and another's cria might excel at density. The records for these averages also form the basis for the sire's EPDs which are recorded on the EPD summary for the male. Individual sire performance in different environments and different herds is the ultimate gauge of excellence. The more records there are of a sire's progeny, the more accurate the EPDs for the sire. A reference sire summary allows for this type of assessment.
Richard Bourdon defines nucleus schemes as, "a cooperative breeding program in which elite animals are concentrated in a nucleus herd or flock and superior germ plasm is then distributed among cooperative herds or flocks to the nucleus." There are two types of nucleus breeding schemes: closed and open. (You may find as I do that the term 'scheme" has a negative connotation, but this is the common term used by scientists to describe group breed improvement programs.) The closed system is similar to the breeding program at Accoyo. No new blood is introduced into the nucleus herd. All replacement stock is bred from the existing herd. A quality-based hierarchy is imposed. There are prepotent sires and elite dams. All replacement studs must be the product of the special sires and the elite dams. New sires should be progeny tested before being used in the general population, although this is not always the case.
Genetics from a closed nucleus system flow in one direction: from the nucleus herd out. This system is in place in the parent studs of the Australian merino industry. Parent studs sell stock to daughter studs which reproduce or multiply the genetics and distribute them to the commercial herds. In essence the daughter studs are customers of the parent studs, dependent on them for a steady supply of improved genetics. The commercial herds are the customers of the daughter studs.
In an open nucleus-breeding scheme, the genetics flow in both directions. (See Figure 12.3 above) Females and males from cooperating herds become part of the nucleus. One of the initial open nucleus herds in Australia involved 1,000,000 sheep. The success of an open nucleus breeding program is largely dependent on the initial quality of the animals that are contributed by the cooperating herds.
The dynamics of the improvement that takes place are easy to grasp. Assume that the herdsires of an open nucleus alpaca improvement program were all well chosen, progeny-tested sires. The first generation of alpaca cria born to the nucleus will all be made up of at least half of these superior genes. (Fifty percent of their genetic material will come from the superior sire.) The next generation of cria will contain at least 75% of the elite germ plasm. These results flow naturally from the use of progeny-tested males. This consolidation of superior genetics takes place without inbreeding.
Dr. Garrick, of Colorado State University, related the following example of the success of a nucleus breeding program. The intent of the selection strategy for this particular nucleus herd was to increase the percentage of lambs weaned by the flock. The nucleus managers identified all the ewes that had twins two years in a row. They only used rams to cover these ewes that were born from the mothers that had twins. The program included 1,000,000 ewes and within a few years the flock managers increased the number of weaned lambs annually by 20%. The performance improvement was even more dramatic than you might think because twinning is not a highly heritable trait.
Assuming that the initial nucleus from the cooperating herds is well chosen, gains can be quite rapid due to shorter generational intervals, selection accuracy and selection intensity as superior replacement males and dams are identified and put in service. The sires created from the nucleus are then put to work in the cooperating breeders' herds.
In spite of the initial successes of these nucleus schemes there are problems creating and maintaining them which are both practical and political. This type of program requires a common location where the nucleus can be operated as a herd in an environmentally neutral fashion. This creates considerable expense to the participating breeders. They also need to contribute their best breeding stock to the new location. This creates a problem for all but the largest operations. It would certainly be a problem in the alpaca industry which is characterized by smaller herds.
The popularity of these open nucleus schemes has waned in recent years due to the factors identified above. A new type of group improvement program has taken their place. These programs are known as sire referencing schemes. These programs are similar to the nucleus schemes but do not require the formation of central herds. Instead links are established in the members herds by the use of reference sires, hence their name sire referencing schemes.
One model for a reference sire improvement program is the assembly of a number of cooperating herds who use jointly owned males in their individual herds. (See Figure 12.4.) In another model, breeders might purchase semen from a genetics breeding operation and artificially inseminate (AI) their females. (The ARI does not permit the registration of cria from AI sires.) The process of sharing males or semen allows the owners to collectively progeny test the herdsires. The group then shares the information in a common database and a sire reference summary can be constructed. Each sire's performance can be compared to the other reference sires and the additional sires being used in the general population. The joint ownership of herdsires is the organizing principal of the Studmaster" male program.
Reference sires leave offspring in the cooperating flocks. The offspring of the reference sires can then be compared with the offspring of any other sires used in the same flock. Thus, the best males in the whole of the group breeding scheme can be identified with the help of appropriate statistical programs.
The main output of a reference sire breed improvement program is the calculation of Estimated Progeny Differences (EPDs) for the sires used by the cooperating breeders. These EPDs quantify the expected impact of each sire on the genetic merit of the flock.
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