Pigs breeding program

In spite of this, there is a growing interest in genetic improvement of welfare traits in North America and in most other countries. Therefore, several large integrators are seriously considering adapting this system. This would be a desirable change, since use of this system would enable selection for enhanced resilience using multiple resilience traits, simultaneously. As genomic tools continue to develop and improve, so does the ability to identify deleterious genetic variants within specific genes.

Using female fertility phenotypes registered at birth total number born, number born alive, mummies, and stillborn and lactation survival, several regions in the genome, as well as underlying recessive variants causing embryonic and fetal death, stillbirths or pre-weaning mortality, have recently been identified Derks et al.

Until now, deleterious recessive variants have mainly been shown to be line-specific and are, therefore, not expected to cause an increase in mortality in crossbred finishing pigs. Recessive lethal variants detected by missing homozygous haplotypes in different breeding lines. Genes for which the causative variants have been identified in italics Derks et al. Using 50K SNP genotype data as a template, the entire genome can be scanned to identify genomic regions with larger effects quantitative trait loci [ QTL ] on polygenic traits using a genome-wide association analysis GWAS.

Results obtained by Boddicker et al. At the molecular level, the favorable allele rescues the function of the GBP5 gene, thereby improving immune defenses of heterozygous animals by decreasing the efficiency of viral entry into host cells and subsequent viral replication Schroyen et al.

In an infection trial where pigs were vaccinated with a heterologous PRRSV strain, it was observed that pigs with the AB genotype had higher average daily gain and lower vaccine viral load compared to pigs with the AA genotype Dunkelberger et al.

These results suggest that certain genotypes could be more responsive to vaccination and, therefore, that genetic approaches could be used to enhance response to vaccination. Another important disease in pigs is postweaning multisystemic wasting syndrome caused by porcine circovirus type 2 PCV2 infection.

Natural polygenic variation has also been described for PCV2 host susceptibility with two major resistance loci Walker et al. For one QTL region, a missense mutation in the synaptogyrin-2 gene was associated with reduced viral load. This is an additional example of a case where part of the polygenic variation in resilience to infection could be explained at the molecular level.

Going forward, such tools can be used to improve monogenic resilience to specific pathogens or specific or general resilience to infection.

Using genome editing, additional variation can even be introduced artificially. It remains to be seen to what extent specific resistance alleles or variants improving resilience can contribute to the continuous overall genetic improvement of resilience against the entire load of pathogens changing over time and environment.

Selecting pigs to be more responsive to a specific disease can have serious drawbacks for their health or reduce their ability to defend other infective agents Nakov et al. Therefore, overall negative genetic correlations with other traits need to be monitored. Considerable natural genetic variation has been identified for a number of new resilience traits. Results from several studies show that the extent of genetic variation in resilience is most visible at the commercial production level where the level of disease challenge is greatest.

Performance data, such as variation in feed intake and reproduction records, can contribute to the genetic evaluation of resilience. Availability of genomic information at lower costs, in addition to the availability of new genetic selection tools, has increased opportunities for breeding for enhanced resilience and monitoring lethal or deleterious variants. While genetics can contribute to increase resilience of our animals, disease surveillance, biosecurity, and vaccination remain important.

Integrated approaches by geneticists, immunologists, virologists, veterinarians, and other disciplines are necessary for effective disease prevention, control, and eradication measures. The authors declare no potential or actual conflict of interest. National Center for Biotechnology Information , U.

Journal List J Anim Sci v. J Anim Sci. Published online Aug Author information Article notes Copyright and License information Disclaimer. Corresponding author: moc. Received Oct 31; Accepted Apr All rights reserved. For permissions, please e-mail: journals.

It is fairly easy to have it approach 1. There are also some lines of laboratory animals with very high average inbreeding coefficients. A few lines of beef cattle and swine that have undergone intense inbreeding for 40 to 50 years have average inbreeding coefficients of.

This takes many generations of full-sib or parent-offspring matings to accomplish. Therefore, an inbreeding coefficient over. The general formula for an inbreeding coefficient is shown in figure 1. A common ancestor is an individual that appears on both the sire and dam side of the pedigree. The calculation of an inbreeding coefficient involves several steps which need to be followed carefully.

The common ancestor is that individual that the arrows point away from. It is the ancestor that both parents trace back to. Step 4: Determine if the common ancestor in each path is inbred. If so, calculate the inbreeding coefficient of the common ancestors. The rules for determining the inbreeding coefficient of the common ancestor are no different than calculating the inbreeding coefficient of any other individual.

If the common ancestor is inbred, simply construct its pedigree and go through each step of the process as if it were the individual of interest. In this example, the common ancestor is D and its inbreeding coefficient is assumed to be 0 since neither of its parents are known.

Step 6: Calculate the value of each path connecting the sire and dam of the individual in question. Step 7: Add together the value for each path connecting the sire and dam of the individual in question. Since there is only one pathway in this example the inbreeding coefficient of X is.

The inbreeding of individual Z is the sum of the values of the three paths which is. The relationship between two animals is evaluated with the relationship coefficient. It measures the probability that two individuals have a particular gene in common because of common ancestry.

It can also be said to measure the proportion of genes two individuals have in common because of common ancestry. The relationship between a parent and offspring or between full sibs is.

The relationship is calculated as shown in figure 2. The numerator is obtained in almost exactly the same manner as an inbreeding coefficient. Otherwise the steps involved are identical.

Example 2. Therefore, individuals Z and S are expected to have. If they had been a normal sire and son, the relationship would have been. However, there was a large degree of relationship due to other sources other than them being simply a sire and son. Inbreeding depression is the decline in performance that is associated with inbreeding. Since inbreeding depression and heterosis from crossbreeding are essentially opposite effects, it is not surprising that the same traits that respond well to crossbreeding will respond adversely to inbreeding.

This demonstrates how strategically develop-ing crossbred sows can easily and repeatedly improve maternal performance. This is further demonstrated in Figure 1 with an example of Yorkshire and Landrace dams. The purebred average for Yorkshire is If a purebred Yorkshire farrows a crossbred litter, the expected average number born alive is For Yorkshire-Landrace F 1 females bred to a boar of a third breed, however, the expected average number born alive is The 0.

Figure 1. Comparison of F1 and purebred sow performance for the Yorkshire and Landrace breeds. Crossing animals that have breed ancestry in common, often referred to as backcrossing, allows for reforma-tion of some of the original undesirable gene pairs.

This reduces heterosis. For example, in Figure 2 are the expectations for average number born alive for Yorkshire and Landrace purebred females, for Yorkshire-Landrace F 1 females and for backcross females produced by mat-ing a Yorkshire boar to Yorkshire-Landrace F 1 females.

The performance expectation for backcross females is lower because of declines in heterosis. Various schemes for crossing breeds can assist produc-ers in developing a breeding program that best fits their management program and target markets. The following crossbreeding systems should be investigated for use in various pork production and marketing chains.

Perfor-mance expectations using example breeds have been calculated for each breeding system for comparison purposes. Rotational systems.

Rotational systems have been popular in the pork industry. They are easy to under-stand and require the purchase of only boars or semen. Replacement females are produced internally from each of the boar breeds used in the rotation. Rotational systems do not allow for optimal exploitation of hetero-sis, however. Table 2 shows the expectation of heterosis levels through each advancing generation of a rotational crossbreeding system.

In the first one to three gen-erations of the rotation, depending on the number of breeds involved, pigs do exhibit percent heterosis, but as the generations advance, heterosis levels, both individual and maternal, decline to an equilibrium level. Heterosis within the two-breed rotation declines to 67 percent compared with the initial cross; the four-breed rotation stabilizes near 93 percent.

A three-breed rotation is expected to maintain 86 percent of possible heterosis Table 3. Rotational systems may be simple in concept but can be difficult to implement correctly. Sow herds in rotation programs will be sired by every breed of boar in the rotation, but producers using rotational programs typically maintain only one breed of boar on the farm at a time.

This dictates that producers will breed a percentage of the sows to a boar of the same breed as their sire. This causes a reduction in heterosis and consequently a reduction in performance and vigor. The new breeding goal Saved feed is the proportion of feed intake that is not used for production of daily body weight gain and backfat thickness, therefore it optimizes the nutrient utilization by minimizing the amount of feed consumed for the same amount of meat produced.

For the maternal line, Danish Yorkshire and Danish Landrace, the new breeding goals Piglet survival , Viable piglets at day 1 and Boar fertility are added. By direct selection for piglet survival, as the percentage of viable piglets on day 21 after farrowing, it is expected to further improve the genetic progress on number of viable and robust piglets at weaning.

For Danish Duroc, the breeding goal of Survivability is included as the percentage of viable piglets on day 21 after farrowing in addition to the breeding goal Boar fertility for the number of viable piglets one day after farrowing. For feed efficiency, Saved feed, that is known as genetic residual feed intake, which reduces the feed that is not used for body weight gain and lean meat production, is going to set the pace for efficient pork production in the world.

In addition, genetic progress for piglet robustness and mothering ability will be accelerated by direct selection for pre weaning piglet survival, boar fertility, survivability and viable piglets.

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