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More Accurate Breeding for Conformation

by 5m Editor
2 November 2007, at 12:00am

By Abe Huisman, Hypor R&D. Introduction of conformation index makes breeding more accurate

An important trait for breeding animals is physical soundness. Animals need to be structurally sound to carry out their normal functions and to maximize their longevity and productive performance.

Abe Huisman, Hypor R&D

Animals that cannot maintain minimum levels of physical soundness will be culled in the selection process or will be culled relatively early from the breeding herd resulting in an adverse effect on longevity and economic losses.

Leg weakness is key reason for involuntary culling in the pig industry (e.g. Serenius, 2004; Tarrés et al., 2006). Leg weakness among pigs is thought to have a multifactorial background, which involves hereditary predisposition as well as nutritional and housing conditions.

Currently in most breeding programs, pigs that do not meet conformation standards as specified are culled based on phenotypic observation. This independent culling for conformation may undermine the efforts to improve other traits and may also have a significantly higher economic importance.

Clients expect sound and well structured animals from their genetic supplier. At Hypor, the standardized scoring of conformation has been used for many years for a variety of traits - and it has provided a valuable data resource for genetic analysis.

Variance components can be estimated and if there appears to be significant heritability for these traits, breeding values for conformation can be calculated.

This enables genetic selection for conformation which in turn can lead to improved accuracy in selection for overall conformation. Currently, subjective scores for legs, claws, ham, loin, shoulder, length and stature are collected as part of the routine data collection in the Hypor breeding program.

Dataset for Conformation Scores

Standardised data collected since 1990 from a Landrace dam line and since 2001 for a Duroc sire line were used for genetic analyses of conformation scores.

The conformation traits are all scored from one to five: For legs and claws, scoring one represents a bad score while five is excellent.

For ham, loin and shoulders one represents an extremely light animal, whereas five is extremely heavy. For length and stature the scores reflect the frame size of the animal on an increasing scale.

The average for each conformation trait is approximately three, which represents the average phenotype.

The "true type score" or breeding objective will be different in sire and dam lines. For leg and claws 5 is the true type score, while for ham, loin, length, shoulder and stature it varies per line from 3 to 5, depending on the position of the line in the crossbreeding scheme.

Table 1
Average conformation (morphology) scores as estimated from the historical dataset
Trait Sire Line
Average S.D.
Dam Line
Average S.D.
Front Legs 2.3 0.86 2.3 0.83
Rear Legs 2.4 0.81 2.5 0.75
Front Claws 2.8 0.51 2.9 0.34
Rear Claws 2.8 0.51 2.9 0.37
Ham 3.4 0.58 3.2 0.55
Loin 3.1 0.55 3.0 0.62
Shoulder 3.2 0.51 3.0 0.48
Length 3.1 0.54 3.2 0.53
Stature 3.0 0.51 3.0 0.46

Table 1 above shows the average conformation (morphology) scores as estimated from the historical dataset. From the figures it can be seen that both Front Legs and Rear Legs are scored somewhat more harshly than the other conformation traits. This is also reflected in the reasons for culling, and most animals were culled because of poor legs.

Another observation that can be made from Table 1 is that the sire line pigs score higher for Ham, Loin and Shoulder, although not statistically different.

Analysis

The model used for analysis of the conformation traits included the fixed effect of batch. To account for management, housing and seasonal effects, the effect of sex, and the effect of way of testing, where pigs were either group-housed with or without feeder stations. Also included in the model were the random components for animal genetic effect and litter effect.

Litter effect accounted for approximately one to three per cent of the total variation in these traits. The variation for most traits was very similar for the sire and the dam line. However, the variation in front and rear claws in the sire line was almost double the variation in front and rear claws seen in the dam line (Table 2). Estimated heritabilities (h²) were similar for both lines for both the leg and claw traits, whereas the heritabilities for Ham, Loin, Shoulder, Length and Stature were higher in the dam line (Table 2).

Table 2
Estimated variance components and heritabilities for the conformation traits for both sire- and dam-line
Trait Sire variance Line heritability Dam variance Line heritability
Front Legs 0.69 11% 0.62 8%
Rear Legs 0.63 7% 0.51 6%
Front Claws 0.23 4% 0.09 1%
Rear Claws 0.24 4% 0.12 4%
Ham 0.29 13% 0.27 25%
Loin 0.27 13% 0.33 24%
Shoulder 0.25 13% 0.22 26%
Length 0.26 11% 0.25 13%
Stature 0.23 9% 0.20 18%

Index

Separate conformation indices were developed for the dam and sire lines based on the desired true type for each line.

In a dam-line index, legs and claws are comparatively more critical than in sire lines, while in the sire lines, traits that determine body frame characteristics will get relatively more emphasis. Further more, the indices were fine-tuned based on the traits that have the most significant need for improvement in that breed.

Predicting ability of Index

An analysis was run to test the predicting ability of the defined indices. To investigate this 10 per cent of the conformation score data was deleted and a BLUP analysis was performed.

Animals were grouped based on index values as high, medium, and low. Average phenotypes were calculated for the traits that are included in the index. This process was repeated 10 times, results presented are the average of those 10 replicates.

Table 3 Average phenotypes based on index grouping
Dam Index
Index Front legs Rear legs Front claws Rear claws Ham Loin Shoulder Length Stature
Low -256.2 2.1 2.4 2.9 2.9 3.1 2.9 3.0 3.2 3.0
Medium 68.6 2.3 2.5 2.9 2.9 3.2 3.0 3.0 3.2 3.0
High 369.3 2.5 2.7 2.9 2.9 3.2 3.1 3.1 3.2 3.0
Sire Index
Index Front legs Rear legs Front claws Rear claws Ham Loin Shoulder Length Stature
Low -99.7 2.1 2.3 2.7 2.7 3.4 3.0 3.1 3.0 2.9
Medium 23.7 2.3 2.4 2.8 2.8 3.4 3.1 3.2 3.1 3.0
High 129.2 2.5 2.5 2.8 2.8 3.5 3.3 3.3 3.3 3.3

For the dam index, where more emphasis is put on legs and claws, it is clear that animals in the high index group have, on average, a higher score for front and rear legs. Whereas, the differences between the high and low index groups for the other traits are less obvious.

The sire index puts more evenly distributed emphasis on feet and claws and the other traits. The high and low sire index groups show a difference in favour of the high group for all traits. The differences between low and high index groups for the claw traits are not so clear. This is most likely due to the fact that the heritabilities for front and rear claws were low compared to the heritabilit ies for the other traits (Table 2). The reason for the lower heritabilities might be that the trait is less standardised. Various claw defects might be scored at the same level, while it would be more accurate to treat them as different claw traits.

Implications for the breeding program

Estimates of variance components and predicting ability show that genetic selection for conformation scores can be improved significantly through the use of conformation indices.

It has been demonstrated that both the sire and the dam index are capable of predicting which animals will get better conformation scores. Additionally, it will be possible to select nucleus replacement breeding stock much more accurately for conformation traits, since not only the animal itself, but also the relatives will play a role in determining its conformation index level.

With such methods, breeders can differentiate between a boar which is acceptable, but has very bad relatives, and a boar that gets equal scores and has relatives with excellent conformation.
The breeding value of the latter will be higher and its offspring will have higher probability of scoring better in conformation.

The presented indices and analyses show that using the conformation index can significantly improve the accuracy of selection (for conformation). Such technology will lead to a more efficient usage of selection information and a significant improvement of soundness and body structure of Hypor breeding animals in the near future.

References

Serenius, T. (2004) Genetics of sow efficiency in the Finnish Landrace and Large White populations. Doctoral dissertation. Agrifood Research Reports 58. MTT Agrifood Research Finland, Finland.

Serenius, T., Sevon-Aimónen, M.-L., Kause, A., Mäntysaari, E.A., Mäki-Tanila, A. (2004) Genetic associations of prolificacy with performance, carcass, meat quality, and leg conformation traits in the Finnish Landrace and Large White populations. J. Anim. Sci. 82: 2301-2306.

Serenius, T., Stalder, K.J. (2006) Selection for sow longevity. J. Anim. Sci. 84: E166-E171.

Tarrés, J., Bidanel, J.P., Hofer, A., Ducrocq, V. (2006) An alysis of longevity and exterior traits on Large White sows in Switzerland. J. Anim. Sci. 84: 2914-2924.

October 2007