A National System for Recording Conformation Traits

Transcription

1 Report from the working group on conformation traits A National System for Recording Conformation Traits SUMMARY A recording program for conformation traits is proposed based on the information available in the literature and the practical needs of the Canadian Swine Industry. A brief review is provided on the following aspects: 1. The need for recording conformation traits 2. Importance to producers 3. Systems used in other countries Traits measured Number of classes 4. Criteria for choice of suitable measures 5. Heritability estimates 6. Genetic correlations with production traits and longevity Correlations with growth Correlations with longevity 7. Economic values 8. Accuracy of the measurements 9. Concluding remarks 10. Proposed system of scoring 11. Time of recording 12. Steps for implementation 13. Next steps The proposed system includes scores for fore legs, hind legs and underlines. The fore legs and hind legs are scored from the distal end and sides as well as for the condition of the pasterns into five categories each. Scoring of underlines is based on the number of functional teats. Necessary steps for implementation of the scoring system and steps for use of the information for genetic evaluation are also discussed.

2 Report from the working group on conformation traits A National System for Recording Conformation Traits 1. Introduction: The need for recording conformation traits - Breeding animals must be physically sound and structurally correct to carry out their normal functions. Animals that cannot maintain minimum levels of physical soundness need to be culled earlier from the herd resulting in economic losses. - In general, the relevance of conformation traits in pigs depends mainly on their relationship with involuntary culling and on their productive value for other economically important traits. In commercial herds the conformation of sows is mainly used to predict the risk of involuntary culling. Reducing involuntary culling of sows has several advantages such as reduction in annual cost of replacement, increase of average number of piglets per litter because of decreasing number of first parity sows, reduction in number of non-reproductive days and increased opportunity for selection on other traits. - Independent culling for conformation traits has been done for many years. This is mainly based on a subjective phenotypic evaluation and a prediction about the future productive life of the individual or its female progeny. However, in many cases this phenotypic evaluation is overemphasized leading to a reduction in selection intensity for index traits. In many herds about 80-90% top indexing boars and gilts are culled on the basis of their conformation. This has resulted in reducing genetic progress by more than half in many herds, and has a tremendous effect on the overall rate of genetic improvement and economic benefits to breeders and producers. - Very often the basis for genetic improvement of specific traits is their economic value or their relationship with traits of economic importance. Conformation traits seem to have a moderate economic value compared to index traits but they have a significant impact on the economic benefits from index traits. Therefore, if proper attention is not given to the selection and improvement of conformation traits, independent culling for conformation may undermine the efforts to improve other traits that are economically more important. - Despite a long history of selection or rather independent culling for conformation, many breeders have observed limited improvement over the past years. Rather the situation has become worse. It is argued that one of the reason for this is the negative correlation with the index traits, especially growth rate. As the pigs become leaner and fast growing they seem to have more feet and leg problems 2

3 due to disproportionate growth of the bones and tendons. This may be true to some extent. Some of these negative correlations are documented in the literature. - However, this also indicates that phenotypic selection for conformation over the past years has not resulted into progress in conformation traits sufficient to overcome this negative effect of faster growth rate. If proper attention is given to selection for conformation traits, considering the negative correlation with growth traits, it should be possible to make reasonably more progress in both growth and conformation traits. - One of the reasons for the lack of genetic progress in conformation traits is the lack of a proper system for recording and genetic evaluation. Systematic selection for conformation traits has been carried out for several years in many European countries, however, in Canada the first milestone of the selection process for conformation, a national system for recording it, is still missing. - This study addresses the issue of recording conformation traits. The use of this information for genetic evaluations and selection will be discussed later when a recording system is established and some data are available to develop a genetic evaluation system. 2. Importance to producers - The first question is, is it really important to the producers? This question was asked to a random sample of 500 producers who bought gilts from the Danish Breeding System. The survey was part of an investigation to study the significance of selection for conformation and its effect on longevity of sows (Andersen and Hansen, 1996). Following are the percentages of responses of producers based upon their rating of the significance of three measures of conformation. Very important Important Not very important Not at all Length Width Legs The above survey included only linear measurements of length and width and the condition of the legs. However, it clearly shows that legs are more important to producers than length and width. - In a different study in Sweden, different reasons for culling of sows were recorded on 3990 sows in commercial systems. The study revealed that about 30% animals were culled for unsatisfactory production results (litter size), 23% for fertility problems and 11% for leg weakness. 3

4 - A more detailed investigation was done where the reasons for culling were prioritized in terms of main reason, secondary reason and so on. The following were the main reasons for culling in a smaller group of 908 sows. Reason for culling Number % Fore legs 14 2 Rear legs Claws 17 2 Udder 65 7 Productivity (litter size) Fertility problems Disease 50 6 Other reasons Total This study shows that about 25% sows are culled due to poor conformation, which is the largest factor after fertility problems and almost as significant as litter size. - Among the conformation traits, rear legs and underlines were the most important after fore legs and claws. 3. Systems used in other countries Traits measured - A number of scoring systems have been proposed and used in other countries, especially in Europe. These scoring systems are different in terms of the traits recorded, number of categories per trait and differentiation between classes. Following is a summary of the published systems. Traits Scale Country Year of beginning Nine categories with the possibility of scoring intermediate values Forelegs, hind legs, gait pattern, back and loin, hams, claws, underlines, etc. (21 conformation traits) (Appendix 1 and 2) Fore legs, hind legs, shoulder, back and loin, hams, stature, underlines (14 exterior traits) Front legs, hind legs, locomotion Fore legs, hind legs, locomotion, stance, back, underlines (Appendix 3) Fore legs, hind legs, back, overall approval Three categories (1-2-3 system) Source Sweden 1982 Van Steenbergen, (1989) The Netherlands 1982 Koning (1996) Nine categories Sweden 1993 Lundeheim (1996) Three main categories Norway 1993 Grindflek with options to record and Sehested slightly defect or (1996) severely defect Five points for approval, three for other traits Denmark 1995 Andersen and Hansen (1996) 4

5 - In the US, the NSIF guidelines (1996) suggest scoring of fore legs and hind legs in 5 categories each. Thereafter, front and rear scores are summed and the following scoring format is used: 1. Unacceptable (1-3 points). Severe structural problems that restrict the animal's ability to breed. 2. Good (4-7 points). Animals with slight structural and/or movement problems. 3. Excellent (8-10 points). No obvious structural or movement problems. (Includes even toe size, adequate length of stride, adequate flexion of hock and pastern cushion, trueness and freeness of movement.) - The scoring format for the underline soundness is as follows (NSIF, 1996) 1. Unacceptable (1-3 points). Fewer than six functional nipples on each side or one or more inverted nipples or poor spacing and prominence. 2. Good (4-7 points). Six or more functional nipples on each side with adequate spacing and prominence. 3. Excellent (8-10 points). Six or more functional nipples on each side, well-spaced and well-developed with no pin or blind nipples. - A large number of traits were recorded in most of these systems (as much as 21 traits). The most common traits were fore legs, hind legs, and underlines. Some programs have also used locomotion. - As the number of traits increases the scoring method becomes more complex and time consuming and the genetic progress in each individual trait decreases. It is important to record the minimum number of traits that are the most important, at least when the national system for conformation scoring is first established. Number of classes - The scale of recording is very important. A classification in three categories (threepoint scale) has an advantage that the scoring is clear and easy e.g. the fore leg can be classified either as buckled, sickled or normal and pasterns can be classified as high, low or normal. However, this classification does not allow much differentiation (e.g. if the fore leg is slightly buckled compared to severely buckled). The larger problem is the difficulty in the identification of genetic variability. Hence, a classification in three categories is not very suitable for genetic evaluation. On the other hand, if there are a large number of categories, it is difficult to differentiate individuals between adjacent classes and ultimately few classes end up being used. In the study by Van Steenberg (1990) there were 9 main categories with the option to record intermediate categories. Thus there were 17 possible classes. However, intermediate classes were used less than the classes with whole numbers resulting in the use of 9 main categories out of the total of 17 (Fig.1). 5

6 Percentage Category Figure 1: Overall distribution of exterior scores into different categories (source: Van Steenbergen, 1990) - This was a scientific study where the distribution in nine classes appears to be fairly normal. However, under field conditions, even nine categories may not be used properly due to the difficulty in differentiation between adjacent classes. - A five point scale is probably best in practice and also for genetic evaluations. 4. Criteria for selecting suitable measures In a systematic approach for genetic improvement, the choice of conformation traits should be based on the following criteria: Heritability estimates Economic value of the trait Correlation with other economically important traits Accuracy of measurements 5. Heritability estimates - Genetic parameters for conformation traits are not so common in the literature as those for growth and production traits. However, some of the studies have been very extensive in terms of the number of traits recorded, the number of classes within each trait and the number of records used. Estimates reported in some studies are given by Larochelle (1999) (Appendix 4). Following is a summary of the heritability estimates for important conformation traits. 6

7 Trait Range Average Fore legs Fore legs front view Fore leg bone Fore leg pasterns Fore leg claws Hind legs Hind legs rear view Hind leg hock Hind leg pasterns Hind leg claws Back Locomotion Here, the averages for individual traits should be interpreted with caution because the estimates are based on different scoring and production systems. For example, foreleg bones in the study by Grindflek and Sehested (1996) in Norway are scored on a three point scale and include males only while those by Van Steenbergen (1990) are scored in Sweden on a nine point (or 17 point) scale and include both sexes. - Among the feet and leg traits, pasterns seem to have higher heritability. For most other traits the heritability is around 15%. Locomotion has a lower heritability probably because of inaccuracy of recording. Total number of teats Most studies refer to total number of teats just after birth. The heritability estimates range from 0.7 to 0.42 (Allen et. Al. 1959; Enfileld and Rempel 1961; Skjervold 1963; Pumfrey et. al. 1980; Clayton et al. 1981). Generally, teat number is considered to be moderately heritable with a heritability of about 0.3. In a Canadian investigation, McKay and Rahnefeld (1990) have reported the following estimates for Landrace, Yorkshire and Hampshire breeds. 7

8 Breed Number of pigs Total number of teats Haritability Landrace ±.2.23 ±.02 Yorkshire ±.2.32 ± Landrace ±.3.39 ±.05 Yorkshire ±.2.44 ±.02 Hampshire ±.3.45 ±.03 The estimates in the later part of the above study might be inflated due to an influx of boars as suggested by the authors. Number of functional teats The number of functional teats is usually measured just after farrowing as the number of teats that deliver the milk. At earlier ages, the number of functional teats is the number of teats excluding inverted or deformed teats where the teat canal is not visible or apparently dysfunctional. The number of functional teats is also affected by non-genetic factors from birth to furrowing such as teat injuries. Therefore, it is expected to have lower heritability than the total number of teats at birth. Following estimates of heritability were observed by Ligonesche et al. (1995) for total number of teats and number of functional teats Inverted teats Maternal line Paternal line Total number of teats 0.25 ± ± 0.01 Number of functional teats 0.21 ± ± 0.01 If the nipple fails to protrude from the surface of the udder the teat considered to be inverted teat. The teat canal is in-wards, thus these teats are usually considered to be non functional. However, a recent study in France (Labroue et. al., 2001) has revealed that almost all of the inverted teats, become functional and give milk at the time of lactation. Therefore the inverted teats should be considered as functional teats. 8

9 6. Genetic correlations with production traits and longevity Correlation with production traits - Genetic correlations with production traits have been evaluated in a long-term study in Holland as a part of a Ph.D. dissertation (Van Steenbergen, 1990). These estimates are probably the most reliable because of the large number of observations and the number of classes used. The estimates for traits included in the current index are given below. Trait Heritability (%) Average daily gain Genetic correlation (%) Backfat Feed conversion Fore legs Front view Side view Pasterns Hind legs Rear view Side view Pasterns Claws (Ratio) Locomotion The correlations are reasonably high suggesting that selection on the index traits can significantly affect conformation and vice versa. However, the magnitude and directions of these correlations should be interpreted in relation to the scales of the measurements. The low genetic correlations may also indicate strong nonlinear relationships. Nonlinear relationships are especially possible because both high scores and low scores are undesirable, for most of these traits. A positive correlation does not necessarily mean an improvement in the production trait with an improvement in conformation. For example, the correlation between fore leg pasterns and average daily gain is 44%. This means a change in fore leg pasterns from a steep angle (score 0) to a low angle (score 9) is associated with an increase in growth rate. However, a good conformation would be the normal angle (score 4.5). Hence, if the population mean is below 4.5, improvement in conformation is associated with an increase in growth rate. However, if the population mean is above 4.5 an improvement in conformation is associated with a decrease in growth rate. - It is also interesting to note that the correlations with fore legs are positive while some of the correlations with hind legs are sometimes negative. For example, there is 9

10 a negative correlation between rear view of hind legs and average daily gain indicating that a change from O shape to X shape in the rear legs is associated with a reduction in the growth rate. However, the same change in shape of fore legs is associated with an increase in growth rate. - Therefore, the sign of the correlation and the population mean for the leg traits together determine if selection for production traits is associated with better conformation or vice versa. This situation makes it rather difficult to draw meaningful conclusions based on these genetic correlations. - However, there is evidence of negative phenotypic correlation between good conformation and faster growth rate based on the frequencies of the conformation traits in fast and slow growing animals. Grindflek and Sehested (1996) found high frequencies of weak fore leg and hind leg pasterns, uneven and small/narrow hind leg claws, X-shaped fore and hind legs, dipped back and bad locomotion in fast growing animals. In general, faster growth rate from 25 to 100 kg is associated with poor conformation. Correlation with longevity - Van Steenbergen (1990) conducted a detailed investigation on the relationship between exterior traits and longevity. Over a two-year period, over 5000 gilts and sows from different strains (Landrace, Yorkshire, Duroc and their crosses) were judged for 20 exterior traits at 24 commercial multiplier herds. Farms were visited monthly by an inspector who judged all gilts of approximately 7-9 months of age and all sows from weaning till 40 days post weaning. Sows culled for leg weakness before the fourth parity were longer and broader at the gilt stage, had less straight rear legs and more tubercles at the rear legs, walked slower and twisted more with hind quarters than animals that had produced at least four litters. - This investigation, however, did not produce any estimates of genetic correlations with longevity. - Research results from a similar study suggest that longevity is strongly influenced by exterior traits (Grindflek and Sehested, 1996). Poor locomotion and straight pasterns lead to decreased longevity. However, contrary to the common belief in Canada, they found that weak pasterns have a positive effect on longevity - According to these studies, length, width, hock joints, pasterns and locomotion are important conformation traits with significant effects on longevity. 10

11 7. Economic values - There is a scarcity of information about the direct economic value of conformation traits in the published literature. In most cases, the economic values are estimated based on relationships between individual conformation traits and longevity. Similar procedures are followed in other livestock species. Therefore, it can be assumed that the traits with the highest economic values are those that have the highest effect on longevity, as described above. 8. Accuracy of measurements - Among the important traits of conformation that are related to growth and longevity, the traits of fore legs and hind legs can be recorded clearly and easily at the time of probing. - The average estimated time for recording fore and hind legs is about 30 seconds/pig. - However, locomotion is more difficult to measure accurately. It requires a calm animal walking an even surface for some time. Therefore, it is more time consuming and difficult to record - Locomotion may be replaced by scores for fore and hind legs that can be recorded more easily and accurately - Grindflek and Sehested (1996) observed that sows with poor locomotion had 21% less chance to be used after 4 th parity than average sows. Standing under, straight fore and hind leg pasterns, and sickled hock gave the highest probability of poor locomotion. The chances of good locomotion are reduced by 39% due to the standing under condition of hind legs, 30% due to straight fore leg pasterns, 19% due to sickled hock and 15% due to straight hind leg pasterns. - These component traits of locomotion can be recorded at the time of probing in the barns. In many studies locomotion was recorded in just two categories (good or bad), which does not allow proper evaluation and use of genetic variability. That is one of the reasons for the low heritability estimates reported in these studies. The use of fore and hind leg traits can also be useful for the selection and improvement of locomotion and longevity. 11

12 9. Concluding remarks Based on the above discussion, the following conclusions can be drawn: - The most important conformation traits are fore and hind legs, locomotion and underlines - Among them locomotion is one of the most important factor determining longevity - However, locomotion is difficult to record and promises less chances of genetic improvement due to its low heritability (0.08 to 0.13) - Locomotion is mainly affected by the condition of fore and hind legs - Fore and hind legs are used in almost every system of conformation recording in Europe, US and Canada. They might be better accepted by the breeders and technicians than locomotion. - The conformation of legs can be recorded as front view (or rear view), side view, pasterns and claws. - Among these, front view and rear view, side view and pasterns have a higher effect on locomotion than claws. - Claws have lower heritability ( ) and they have not been found to affect either locomotion or longevity significantly. - Claws can be safely excluded from the scoring system to reduce the number of conformation traits - It is generally believed that sows must have functional teats to rear pigs. The role and heritability of spacing, prominence, location, etc., of teats in production has not been defined clearly by research. But, because these traits and especially the number of functional teats may have a direct influence on production they should be considered as part of a scoring system for conformation. 12

13 10. Proposed system of scoring Based on the above discussion, the system of recording of conformation traits should include the following traits: 1. Forelegs Front view (scores ) Side view (scores ) Pasterns (scores ) 2. Hind legs Rear view (scores ) Side view (scores ) Pasterns (scores ) 3. Number of functional teats The information given in Figure 2 may be used as a guide for scoring fore and hind legs. Scoring of fractional number between the categories It is very important to note that one can assign a fractional number between the categories. Scores with fractional numbers such as 3.2 or 3.7 are perfectly valid scores. There is no need to round them up to the closet whole numbers. For example, if a pig has slightly sickled fore legs and it is more likely to get a score of 3 rather than a score of 4 the score should be 3.1 or 3.2 or 3.4 depending upon the angle of the wrist. One should not round up the actual score and assign it the score of 3.0. An easier way to judge the exact value of a fractional score is to assign a value relative to other pigs in the same management group e.g. relative to a pig that has a perfect score of 3 or a perfect score of 4. The scoring of intermediate numbers will be very useful to identify small differences between animals, identify the underlying variation and do a better job on selection. 13

14

15 Figure 2: Proposed system for scoring fore and hind legs

16 Number of functional teats: Functional teats are those from which milk could be expressed at farrowing. The number of functional teats can be counted at weaning as total number of teats on both sides of the udder excluding blind and rudimentary. Inverted teats should not be excluded since they become functional and give milk at the time of lactation. Following figure can be used as guideline: 1, 2 and 3 are functional teats 4 and 5 are non-functional teats 11. Time of recording All these traits should be recorded on both boars and gilts at the time of probing and the information should be sent along with the probe records. The number of functional teats can be recorded at the time of weaning or later until the time of probing and the records should be sent early on (pre-listing of pigs) or with the probe records depending upon what is possible for each regional centre 12. Steps for implementation The recording can be done either by breeders or by technicians. In either case, it is very important to ensure the accuracy and credibility of the system. This will require an objective accreditation system just like for backfat and age and can be done with the following steps; At first, the standards of recording should be tested by technicians in the regional centres and modified if necessary; Then the scoring system should be used at the national and regional standard sessions for training the technicians. The trained technicians can then either provide training to interested breeders or do the recording themselves, depending on what each regional centre feels is best. If breeders do it, there should be monitoring and accreditation in the same way as we do for owner sampler records of backfat and age. Scores from technicians or breeders to be accredited could be compared statistically to those of a group of reference technicians.

17 The regional centres can decide what to charge for the recording of conformation traits, if the technicians do it. We could also start training some interested breeders. The records will be very useful for developing genetic evaluations. Recording number of teats The number of functional teats can be recorded at the time of weaning or later until the time of probing The records should be sent early on (pre-listing of pigs) or with the probe records depending upon what is possible for each regional centre This information can be recorded by breeders or by the technicians (need to produce extension material and do some training) The information should be recorded on all pigs, including pigs that will not be probed, as it will be useful for identifying sires who have a high percentage of progeny that are culled because they have fewer functional teats. Reports to breeders It is important to provide reports to participating breeders during the trial period (pilot evaluation). The report could contain conformation scores (possibly adjusted for age) and EBVs. One of these reports could show phenotypic averages for the herd along with regional and national averages. This will help breeders compare their herd with other herds on the program and make necessary changes to their management or genetics. The EBVs for conformation traits could be reported on the same scale as actual conformation scores after adding a mean to the EBVs (same as goat conformation system). For example, instead of zero being the average, the average could be 3 if the animals are scored from 1 to 5. EBVs would then range from 2.5 to 3.5 for most animals. This reduces the chances of independent culling on conformation traits and is ultimately useful for genetic improvement in conformation as well as production traits. 13. Next steps Genetic evaluation and selection The implementation of a genetic evaluation system of conformation would require the following steps, which would be addressed in the second part of the IRAP project once feedback and sufficient data from the proposed scoring system are available. Standardization of conformation scores based on variances within contemporary groups Single trait (or multiple trait) evaluation for conformation scores 17

18 Computation of economic values Selection index based on conformation scores Reporting Extension article to make best use of the information Monitoring genetic progress and revaluation if necessary There are several options for the computation of EBVs. For example: 1. Single trait EBVs for the 7 traits and one index value for all traits based on their relationship with longevity 2. A phenotypic combined score based on all the traits and computation of one EBV for fore and hind legs and one for the underlines Option 1: - The reporting of EBVs for many conformation traits may lead to too much selection emphasis on one or two traits and thereby reduce genetic progress. This can be even worse if it results into reduced selection intensity for production traits. One of the options is not to publish the EBVs but instead publish an index value based on the EBVs for individual conformation scores. This index will take into account the genetic correlation between the individual traits and longevity. This value can then be included in the combined index with other production traits. - This approach also provides an opportunity to monitor the genetic progress in each of the conformation scores and to change their economic values according the progress achieved after a few years and according to future needs. For example, if it is observed after a few years of selection that sufficient genetic progress has been made for fore legs, their economic values can be reduced. - Another advantage is the possibility to customize selection for specific conformation traits according to the requirements of individual herds. For example, if a herd is above average for fore leg scores but has a severe problem with hind legs, the economic values of hind leg scores can be given a relatively higher weight for faster genetic improvement without compromising progress in production traits. Option 2: - A phenotypic index based on conformation scores for feet and legs can be computed through a decision table accounting for the relationships between fore and hind legs. For example, if both fore and hind legs are O-shaped it is not so bad as O-shaped fore legs and X- shaped hind legs. - This approach provides one EBV for the whole complex of conformation scores and reduces the chances of excessive weight on individual conformation scores. 18

19 - However, this can become complicated and a consensus from breeders and geneticists may be difficult to achieve. Another significant problem is the difficulty in predicting response to selection in the component traits with this approach. Recommendations: - EBVs for individual traits and a combined index (option 1) could seem to be the most logical, but it is rather too early to make a definitive conclusion. - There are more than these two options. For example, other systems could also be used such as sum of conformation scores suggested by NSIF or other similar methods used in Scandinavian countries. - Each of these options has its own merits and drawbacks. A number of issues are involved such as the effect on the genetic progress in conformation traits, the effect on other traits, the accuracy of the evaluations, the flexibility for further improvements etc. - These issues will be addressed during the next phase of the IRAP project. 19

20 14. References Allen, A. D., Tribble, L.F. and Lasley, J. F. (1959) Inheritance of teat nipples numbers in swine and relationship to performance. Mo. Agric. Exp. Sta. Bul pp. Andersen, S. and Hensen, U. G. (1996) Selection for conformation and longevity in Danish breeding systems. Proceedings of NJF-Seminar no. 265, Denmark March 1996: Clayton, G. A., Powell, J.C. and Hiley, P. G. (1981) Inheritance of teat number and teat inversion in pigs. Anim. Prod. 33: Dyck, G. W., Swierstra, E. E., McKay, R. M. and Mount, K.(1987) Effect of location of the teat suckled, breed and parity on piglet growth. Can. J. Anim. Sci. 67: Enfield, F. D. and Rempel, W. E. (1961) Inheritance of teat number and relationship of teat number to various maternal traits in swine. J. Anim. Sci. 20: Grindflek, E. and Sehested, E. (1996) Conformation and longevity in Norwegian pigs. Proceedings of NJF-Seminar no. 265, Denmark March 1996: Koning, G. (1996) Selection in breeding programs against leg problems. Proceedings of NJF-Seminar no. 265, Denmark March 1996: Labroue, F., A. Caugant, B. Ligonesche and D. Gaudré (2001) Evolution of abnormal teats in gilts during growth and first lactation. Journées Rech. Porcine en France, 33: Larochelle, M. (1999) Selection for conformation traits, Review of literature. CDPQ. Lundeheim, N. (1996) Conformation scoring in the Swedish pig progeny testing scheme. Proceedings of NJF-Seminar no. 265, Denmark March 1996: McKay, R. M. and Rahnefeld, G. W. (1990) Heritability of teat number in swine. Can. J. Anim. Sci. 70 : National Swine Improvement Federation (1996) Guidelines for uniform swine improvement programs. Pumfrey, R. A., Johnson, R. K., Cunningham, P. J. and Zimmerman, D. R. (1980) Inheritance of teat number and its relationship to maternal traits in swine. J. Anim. Sci. 50: Skjerovold, H. (1963) Inheritance of teat number in swine and the relationship to performance 13: Van Steenbergen, E.J. (1989) Description and evaluation of a linear scoring system for exterior traits in pigs. Livest. Prod. Sci. 23: Van Steenbergen, E.J., Kanis, E. and Van der Steen, H.A.M.(1990) Genetic parameters of fattening performance in exterior traits of boars tested in central stations. Livest. Prod. Sci. 24:65-82 Van Steenbergen, E.J., Kanis, E. Koops, W. J. and Van der Steen, H.A.M.(1990) Exterior in sows: 1. Effect of parity number and association with reasons for disposal. Livest. Prod. Sci. 20

21 Appendix 1 Conformation traits and their classifications used in Sweden (Source: Van Steenbergen,1989) 21

22 Drawings to illustrate classification of 8 conformation traits used in Sweden (Source: Van Steenbergen,1989) Appendix 2 (6) Width of hams, (7) front view fore legs, (8) side view fore legs, (9) side view fore legs (10) rear view rear legs (11) side view rear legs, (12) side view hock joint (13) side view pastern real legs. 22

23 Appendix 3 Conformation traits and their classifications used in Sweden (Source: Grindflek and Sehested, 1996) 23

24 Appendix 4 Summary of heritability estimates (Source: Larochelle,1999) Source Grindflek & Sehested (1996) Van Steenbergen et. al.(1990) Koning (1996) Country Norway Holland Holland Scale 3 points 9 points 3 points Breed YY and LL YY, LL, DL, LL (Only Boars) YL, LY and commercial Number of animals tested Foreleg 0,04-0,32 0,15-0,26 Foreleg bone 0,469 0,06 Foreleg pasterns 0,474 0,31 Foreleg claws 0,042 0,09-0,15 0,05-0,21 0,08-0,14 Hind legs hock 0,04-0,21 0,13-0,16 Hind leg pasterns 0,011 0,23 Hind legs claws 0,067 0,30 foreleg wrist 0,133 0,09-0,15 0,05-0,21 0,08-0,14 Front view of forelegs 0,467 0,06 Rear view of forelegs 0,146 0,22 Locomotion 0,082 0,13 0,01-0,44 0,14-0,23 YY 24