Blood Counts

Part III - Breeding Strategies: Breeding and Genetics

As alpaca breeders, we make two basic choices in the development of our breeding programmes. Part II of these articles covered the concepts of selection, the first decision we have to make. The second and equally important choice covered in this final short series of articles concerns deciding which animal we breed with which and what system of mating we use and why.

Before we discuss this, it is useful to consider what Safley quotes as the four key points to bring about genetic change.

Selection Accuracy

If any gain is to be made, the accuracy of selection is important. The traits we wish to select for must be heritable and the alpacas we chose as parents must have high breeding value for these traits. If we wish to breed for higher clip weights, then the stud males we consider must have produced progeny with a higher average clip weight that the average of our herds. Inspection of progeny for the desired traits determines the breeding value of the male for those traits. A higher breeding value assures a higher degree of selection accuracy for the progeny.

Selection Intensity

This is the key element of the rate of genetic gain. For a given herd size, the higher the selection intensity, the fewer will be the offspring selected for transmitting superior heritable traits. Their breeding value will be high and the offspring should improve from generation to generation.

Genetic Variation

For a given trait, if there is a wide variation of this trait within a herd, then a high selection intensity will ensure rapid progress in that direction. On the other hand if the variation of this characteristic within the herd is small, then there is little potential for producing rapid improvement by utilising these progeny for the next generation. High genetic variation within a herd offers the opportunity for progress.

Generation Interval

The more rapidly one generation replaces the last, the faster the potential for gain. The generation interval is the average time taken for the offspring that replace them to be born. The generation interval is determined by the average age of the producing males and females within a herd. Female alpacas have an interval of four to six years. Males approximately five years, but this will depend on the overall age of each herd.

The interaction of these four key points together with an effective mating programme determine the direction and rate of gain within a herd. High breeding value for a selected heritable trait is the single most important factor for success.

Mating Systems

There are five types of mating systems that we will consider in this article and all have their strengths and weaknesses. What is important is to know what they are so that we can utilise the correct system in our breeding programmme. In this way we can hope to change the inheritance pattern of our alpaca herds. Nothing though is set in genetics, Mendelian laws ensure the unpredictable in individual cases. Precise predictions about the outcome of breeding plans are never possible, the expression of dominance, the negative effects of recessive genes all contribute in an area over which we have no control. What we do have control over is determining which alpaca to use and who should be mated to whom.

Random Mating

Here mates are chosen on a random basis, no choice is made and a number of unselected males are left to run within a herd of females, allowing nature to take its course. This system requires no performance record keeping and little time is spent in mating decisions. Random mating would often be used in large commercial stock herds where no average increase in a particular trait is looked for, or the sheer numbers involved make a selective approach impractical. However this approach is most useful for increasing the genetic variation within a herd, with superior progeny often balancing the 'culls'.

Using a random mating approach for progeny testing of studs is also a good method of determining their breeding value.

Like to Like, Positive Assortative Mating

There are two type of like-to-like matings. Those based on phenotype and those based on pedigree or genotype. Pedigree like-tolike mating encompasses inbreeding and line breeding, discussed a bit later. Mating the best male alpaca to the best female alpaca based on a phenotypic judgement would be a like to like mating. This inevitably encompasses some form of selection as a breeder would be unlikely to mate his worst to his worst. Large alpacas bred together and small alpacas bred together would tend to produce a herd of wide variation. Few breeders would chose this method to increase the genetic variation within a herd. They would be more likely to mate their best to their best to increase the chance of producing superior offspring. Producing an extreme individual alpaca makes good sense if the breeding goal is to produce show animals.

Like-to-like matings do not necessarily lead to a fixation of characteristics, ic homozygosity. It perpetuates a characteristic but does not fix them. Most of the benefits of a like~to-like mating will occur in the first few generation, genetic variation then diminishes, with resultant loss of possible gains.

Unlike-to-Unlike, Negative Assortative Mating

The reverse of the positive assortative mating, again based on phenotype and not pedigree. The compensation of faults or corrective matings can be utilised to help ensure they are not present in the offspring. A dam alpaca with a moderate degree of sickle hock in the hind legs would be mated to a stud who was more on the post legged side of normal. However although unlike-to-unlike matings might make parents faults disappear, subsequent generations may be likely see the faults reappear. (It is extrememely important to avoid mating alpacas with similar faults). The matings of unlikes should only be regarded as a short term expedient and breeders should move onto a like-to-like mating system as soon as possible. Just as positive assortative matings tends to increase genetic and phenotype variation in the offpsring, unlike matings tends to decrease variation.

Matings of extremes is likely to produce more intermediate types reducing the variability of the progeny. Negative assortative mating is not a good strategy for speeding up the rate and direction of genetic change. However if your breeding goal is to increase the phenotypic uniformity about some intermediate optimum this strategy can be useful.

Outbreeding

Outbreeding or outcrossing is the mating of individuals unrelated by pedigree, or more distantly related than the average for the population. As a strategy this also refers to crossbreeding or linecrossing where the sires of one line are mated to the dams of another line. The mating of suri males to huacaya dams to create suri cria is an example of crossbreeding.

The primary effect of outbreeding is an increase in heterozygosity. This has the effect of keeping bad genes in a heteroygous form where they are not expressed. They are masked. Outbreeding does not eliminate bad genes. In fact it has the effect of perpetuating them as their expression is masked, making selection against them impossible. However, if they occur at low frequencies, their impact on outbred populations is minimal.

The most important reasons for outbreeding is to add genetic variation to a herd, together with hybrid vigour. Hybrid vigour has major effects on such traits as stamina, conception rates, overall health, weaning rates. All fundamentally important economic traits are boosted by hybrid vigour from outbreeding.

Outbreeding however risks half the merit of the offspring on the selection of the next sire for the herd. If selection has already made the herd superior to the average of the breed, half of that superiority might be lost in the next generation, unless selection is as effective as what had been achieved before. Nothing is guaranteed in genetics and so the breeder who continually practices outbreedng can expect to have the merit of their herd regress towards the average of the breed. The benefits of selection disappear quickly in outbred populations once selection is no longer practised. Outbred individuals will generally have low breeding value.

Like to Like Matings Based on Pedigree. Inbreeding

Inbreeding is the mating of related animals. However, in a given population most animals will be related to some degree and so inbreeding normally relates to matings between animals that are more closely related than the average for the population. The fundamental difference between the like-to-like matings based on phenotype and that based on pedigree is that the latter are more likely to have the same genes whereas the former are more likely to have the same characteristics, irrespective of common ancestors in their pedigree.

Like outbreeding, where the primary effect is an increase in heterozygosity, inbreeding has the primary effect of increasing homozygosity. There will be an increase in the frequency of homozygous genotypes in an inbred population.

The consequence of inbreeding is the increased possibility of harmful recessive genes becoming expressed. Although it is true that harmful defects often surface in inbred populations, this is not created by the inbreeding system in itself. Inbreeding simply increases homozygosity and it does so without regard for whether the newly formed homozygous combinations contain good or bad genes. If negative recessive genes are already present in a population inbreeding will increase the chance that these will become homozygous and then express themselves with high frequency. This is further expressed in that traits of general fitness and performance also tend to suffer within the population, especially if inbreeding is not associated with selection. Inbreeding depression, if severe, must be corrected by the breeder utilising an outcross to unrelated stock. If the outcross is good, it will be possible to not lose too many of the better traits of the inbred line. The first cross progeny of inbreds are often remarkably hardy and vigorous.

It is also possible though to use inbreeding to advantage to eliminate harmful recessive genes. Inbreeding within a small population, continually selecting against undesirable traits will result in the fixing of the desirable dominant genetics and the corresponding elimination of those that are harmful.

So the positive benefits of inbreeding stem from allowing breeders to increase selection accuracy and use selection intensity to its maximum effect. Building on the desirable heritable traits and selecting gainst the harmful ones. Inbreeding exposes both the good and bad. The major negative effect is the loss of genetic variation and hybrid vigour.

This increase in homozygosity caused by inbreeding results in prepotency. An animal is prepotent if its progeny performance is like its own, or is especially uniform. Males are usually referred to in these terms as they have the greater opportunity to reveal their potency than females. An individual animal from an inbred or linebred strain will be more potent than one from a heterozygous source, even if the latter is phenotypically superior.

It is useful to be able to estimate in a broad sense, the degree of inbreeding in a herd. Inbreeding depression is unlikely to become evident in a herd if the average for the herd does not exceed 25%. Progeny carry half of the chromosomes of their parents, their brothers and sisters also carry half, but not necessarily exactly the same half. The degree of inbreeding is determined by multiplying the fraction of each parent's relationship to the animal being considered. So for a full brother and sister, each having 50% of their parents would give if bred together 0.5 x 0.5 or 0.25 or 25% inbred. A sire mated to his grandaughter would be 12.5%, a niece to an uncle would be 12.5%. Half first cousins 3.12%. This simplistic approach does however assume that the parents themselves are not inbred.

Safley quotes a rate of increase of inbreeding of 1.25% per generation for a 500 ewe closed herd using 2% of rams. The point of this is to show that in a practical sense the rate of increase is very slow. The Accoyo herd of alpacas belonging to Barreda, closed since 1946, uses over 100 rigorously selected herd sires across 1000 females. Clearly his herd is not highly inbred, but it does explain why his males breed true for so many positive traits.

Line Breeding

Line breeding is the mating of animals related to a highly regarded ancestor. It is accomplished by using parents who are closely related to this ancestor, but who are not too closely related, if at all, to each other. This differs from inbreeding primarily because it is directed towards maintaining a close relationship to the chosen ancestor, and it is therefore less intense. The focus is on the closeness of the relationship to this ancestor rather than on the intensity of inbreeding. The goal of line breeding is to perpetuate the good traits of an outstanding dam or sire and increase the number of progeny they create without lessening their resemblance to the ancestor. The success of this system depends very much on the selection process used and the size of the herd to be used. Progeny testing is again essential to cheek the potency of the animal under consideration. Occasional outcrossing to similar line bred stock can minimise the disturbance to the breeding programme. Line breeding rarely results in problems as any inbreeding is minimal.

There is no doubt that some degree of inbreeding is essential if a breeder wants to develop a a strain of alpacas with their own characteristics uniformly present though the offspring. A largely homozygous strain cannot be developed by any other method. Selection alone is not sufficient. The most significant advances made by selection are usually achieved during the first few generations after which diminishing returns set in and further progress is difficult. A change of plan to introduce line or inbreeding at this stage would perhaps then be considered. The weeding out of bad genes is fundamentally important before the fixing of the good genes can commence in any sound inbreeding programme. If initial stock is poor, selection and like-to-like breeding would be an essential precursor. There are no instant solutions.

Conclusions

So how should we proceed in the UK. The vast majority of our imported alpaca stock came from alpacas mated on a random basis. Very few South American alpaca breeders practised any form of selection except perhaps for colour. Once arriving here the majority have been bred so far on an outcross system. The results will be an increase in heterozygosity and hybrid vigour. Genes from many sources have been mixed giving us wide genetic variation.

Over the next few years, this will no doubt continue and is essential for building a strong and diverse base herd. The records kept on our pedigree Registry will become an essential tool during our researches. We must continue to improve our selection accuracy and trv and increase the selection intensity. Outcrossing to superior imported males with proven prepotency and continually selecting unrelated animals on a like to like basis for such traits as size, density, fineness, lustre colour and conformation. In this way we will build a selected herd which exhibits the traits each of us desire. Linebreeding can then be considered using the sires that exhibit the best examples of these traits thus creating lines of alpacas which are homozygous for those traits under selection. The progeny of alpacas bred in this way will have the potential to become prepotent and breed true.

Once closely bred alpacas have become consistent and uniform for the specific traits they can be outcrossed with other lines to increase hybrid vigour and increase again the gene frequency for these favourable dominant gene combinations. Like-to-like matings to produce an individual show ring champion or an outcross system in a large herd for pet breeders looking for a unique individual. Each mating plan can serve a purpose.

None of this happens quickly however. Breeding high quality animals with a long generation interval is a long term business. I always remember the Don Julio Barreda quotation when responding to a question regarding his sixty years breeding alpacas – 'it is a great disappointment that I have only completed half the job'.

But we can all start to see the fruits of a planned breeding programme where goals are known. Making informed decisions based on pedigree research, inspecting progeny, practising selection and making specific matings based on knowing to whom the resulting progeny will be bred to, will increase the probability of seeing some real results.

Chas Brooke - MileEnd Alpacas

References

I am indebted to the following authors and their excellent papers which have formed the basis of my knowledge and these short articles.

Mike Safley. Pure Blood Series.
Dr. Philip Sponenberg PhD, DVM. Jiggling Genes.
Dr. Philip Sponenbeg PhD, DVM. Breeding Strategies.
Chris Tuckwell. Genetic Improvement in the Alpaca Industry.
R. Ponzini. Breeding Plans for Tropical Sheep.
Lloyd C. Bracket. Planned Breeding.
Chris Tuckwell. Selection of Alpacas for Breeding.

Part I, Part II

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