Genetic Evaluation for Meat and Carcass Quality


Jim Brisbane
Canadian Centre for Swine Improvement,
Ottawa, Ontario, Canada

1. Introduction

Until last year, the Canadian Swine Improvement Program was managed at the national level by the federal government and EBV were supplied for only 3 traits, which were backfat, days to 100kg and litter size. Last year, administration of the program at the national level was transferred to the Canadian Centre for Swine Improvement (CCSI). Since that time, the centre has worked on the development of genetic evaluation systems for carcass and meat quality traits. This paper summarises progress to date and future plans for these systems. The data is being collected by CCSI's partners, which are the Centre de Développement du Porc du Québec (CDPQ), Ontario Swine Improvement (OSI), the Western Swine Testing Association (WSTA) and the Atlantic Swine Centre. National standards for recording data (Canadian Centre for Swine Improvement, 1996) and record formats have been established through collaboration with these groups.

2. The Carcass Trait Genetic Evaluation System

2.1 General Information

The system is a 9 trait animal model programmed using utilities from the Animal Breeders' Toolkit (Golden et al, 1992) and running under UNIX on an HP-9000 series computer. The traits used are:

1) Traditional backfat at 100kg. Backfat depth is measured by A-mode at the last rib and 11/2" in front of the hip bone. The average is taken and adjusted to 105kg using a multiplicative factor.

2,3) A-mode fat and muscle depths at the 3rd-4th last rib, each adjusted to 105kg using a multiplicative factor.

4,5) B-mode fat and muscle depths over the last 5 ribs. The fat and muscle depth above each of the 5 ribs is recorded from a longitudinal scan, and the average fat and average muscle are calculated. The averages are adjusted to 105kg using a multiplicative factor.

6) Carcass fat depth measured by the grader (Hennessy, Destron or Fat-o-meater probe at the 3rd-4th last rib).

7) Loineye area measured on the loin split at the 3rd-4th last rib (traced on acetate paper and measured against a standard grid).

8) Weight of loin lean measured by cutout.

9) Total weight of lean in the loin, ham and shoulder (3-primal lean) measured by cutout of the left side.

Trait 1 is the traditional Canadian backfat measure which is recorded on all performance tested pigs. Traits 2 to 9 are measured on a subset of this population which are generally sire line animals, and the carcass trait evaluation system is directed at these animals. Traits 1 to 5 are live-animal traits and traits 6 to 9 are carcass traits. Traits 7, 8 and 9 are in the breeding goal. The objective is to distribute EBV for these breeding goal traits, and to encourage their genetic improvement. The other traits are designed to provide a cost-effective means to increase the accuracy of EBV for the breeding goal traits.

EBV for trait 9 are measured in kilograms, but may be converted to a percentage figure which is on the same scale as the lean yield estimated by carcass grading in Canada:

Published lean yield EBV(%)= 100 x [3-primal lean EBV(kg)/standard side weight(kg)]

Genetic evaluations will be carried out separately for the Duroc, Yorkshire, Hampshire and Landrace breeds on a monthly basis.

2.2 Eligibility of Animals to Receive Carcass Trait EBV

In order to receive carcass trait EBV, an animal must either:

- have a record for at least one of the live-animal traits 2 to 5

or

- have progeny or sibs with a record on at least one the carcass traits 6 to 9

Animals which do not satisfy these criteria are served by the backfat evaluation system which produces single trait EBV for trait 1 (the traditional backfat measure which has been recorded for many years). The entire performance recorded population will continue to be probed and receive EBV for this trait, but as the carcass trait genetic improvement system develops, a growing subset of these will also obtain carcass trait EBV.

2.3 Purebred Records Available for Carcass Trait Evaluation

All records which have at least 1 measurement other than trait 1, are destined for the carcass trait genetic evaluation system. A summary of these records collected to date is given in Table 1. In future, the bulk of the records will be live animal records with traits 2 and 3 only. In the longer term, traits 2 and 3 may eventually replace trait 1 as the basic live animal measurements on the swine improvement program.

a)Hometest. Québec began collecting hometest data on traits 2 and 3 in October 1995. In future we expect hometest records to accumulate at a rate of around 13,000 per year from this province. These records will be with live-animal measures only and mostly only with traits 2 and 3. Québec is currently introducing a policy where all Durocs in the province probed for trait 1 are also probed for traits 2 and 3. This adds 7000 records per year to the carcass trait system, and most of the remaining 6000 records will be from sire line Yorkshires (in the province around 12,000 Yorkshires per year are probed for trait 1). In 1997, Québec will introduce a hometest system for recording carcass traits. The number of these records will depend on breeder demand, but will likely be at least as many as from Ontario (i.e. at least 800 per year).

Ontario began collecting hometest data on carcass traits in 1995 and on live-animal traits 2 and 3 in July 1996. In future we expect hometest records to accumulate at a rate of around 2200 per year from this province. These records may comprise around 1300 with live animal measures only (1200 with traits 2 and 3 only, 100 with traits 4 and 5) and 800 with carcass measurements.

Other provinces are just starting to collect hometest data at the moment, and will probably produce a smaller number of records than Ontario.

b) Central Test. From 1991 to 1994 Ontario collected test station data (the Ontario Pork Carcass Appraisal Project) comprising around 3000 purebred records with all traits (including full carcass cutout) except 2 and 3. In future, the accumulation of test station data will be at a much smaller rate. Currently in Québec, purebred test station records are collected at a rate of a few hundred per year, and there is no central testing in Ontario.

2.4 Fixed Effects Model

A summary of the fixed effects for each trait is given in Table 2. These were derived from univariate fixed linear model analyses of the test station records from Ontario and Québec summarised in Table 1. In Table 2, CG denotes contemporary group, which is defined as fill number for test station data and herd-year-quarter for hometest data.

2.5 Genetic Parameters

Until we are more sure of our estimates from the data, we are assuming genetic correlations are equal to phenotypic correlations. The phenotypic correlations were estimated by the correlations among the residuals from the univariate fixed effects models. The heritability of trait 1 was estimated by Li and Kennedy (1994) from the large national dataset which exists for that trait. The heritabilities of traits 6 and 7 were estimated by Kemp et al (1992). Likely values (conservative) for heritabilities of the other traits were chosen. Table 3 shows the phenotypic correlations and covariances, and the heritabilities used in the evaluation system. Parameter estimation work is ongoing, and is done on contract with the University of Guelph.

Table 1. Numbers of Purebred Records Currently Available
Source Approximate Number of records Type of record
Ontario 2975 Test station (Ontario Pork Carcass Appraisal Project data), all records with a full 3 primal cutout, all traits measured except 2,3
1150 Hometest, 700 with live animal traits only (no B-mode yet), 450 with carcass traits
Québec 475 Test station, all records with traits 1 to 7, 14% with traits 8,9
3000 Hometest, currently only live animal traits (no B-mode yet), no carcass measurements
Table 2. Fixed effects for each trait
Trait number Trait description Fixed effects
1,2,3 Weight-adjusted A-mode measures sex, prober, CG*
4,5 Weight-adjusted B-mode measures sex, prober, interpreter, CG (prober x CG for lean)
6 carcass probe fat sex, grader x CG, carcass weight
7 loineye area sex, CG, carcass weight
8 kg loin lean sex, CG, side weight
9 kg 3-primal lean sex, CG, 3-primal weight
*CG = contemporary group Table 3. Phenotypic Correlations (above diagonal) and Covariances (below diagonal) for Traits of the Carcass Quality Genetic Evaluation System. Each diagonal element contains the heritability followed by the phenotypic variance.
Live animal measures Carcass measures
Trait Trait number 1 2 3 4 5 6 7 8 9
traditional backfat (mm) 1 0.52/3.5 0.94 -0.26 0.69 -0.13 0.69 -0.44 -0.59 -0.70
3rd-4th rib fat (A-mode, mm) 2 4.5 0.40/6.5 -0.27 0.86 -0.20 0.78 -0.49 -0.52 -0.59
3rd-4th rib lean (A-mode, mm) 3 -2.1 -3.0 0.40/19.5 -0.22 0.57 -0.21 0.55 0.29 0.29
last 5 rib fat (B-mode, mm) 4 3.6 6.1 -2.7 0.40/7.8 -0.11 0.71 -0.42 -0.55 -0.65
last 5 rib lean (B-mode, mm) 5 -1.1 -2.3 11.3 -1.4 0.40/20.1 -0.21 0.46 0.37 0.30
carcass probe fat (mm) 6 4.2 6.4 -3.0 6.4 -3.0 0.38/10.4 -0.44 -0.58 -0.68
loineye area (square inches) 7 -0.65 -0.98 1.9 -0.92 1.6 -1.1 0.47/0.62 0.66 0.65
weight of loin lean (kg) 8 -0.49 -0.59 0.57 -0.69 0.74 -0.84 0.23 0.40/0.20 0.80
weight of 3-primal lean (kg) 9 -1.1 -1.3 1.1 -1.6 1.2 -1.9 0.45 0.31 0.40/0.76

2.6 Connectedness

Currently, a top priority is to establish minimum standards for connectedness. A computer routine to assess the level of connectedness in all national genetic evaluations including the meat and carcass quality systems must be developed as soon as possible. Some work in this area has been contracted to the University of Guelph. The requirement is to identify the herds which form connected groups, and the most important AI sires generating the connections within each group. Breeders in other groups would then be advised to generate a minimum number of litters from the important AI sires, or in published reports their EBV might be flagged as being from herds with low connectedness.

2.7 Current Status

In April 1996, pilot EBV were produced for Ontario test station data (sires and dams of carcasses from the Ontario Pork Carcass Appraisal Project). Currently, a trial is underway to derive improved weight adjustment factors for the live animal traits, and also the genetic evaluation data is being incorporated into a relational database at the national level. When these tasks are completed in early 1997, a second set of pilot EBV will be produced using all available data from all sources, followed by routine monthly evaluations.

3. The Meat Quality Trait Genetic Evaluation System

This system has not yet been programmed, and the data has not yet been analysed at CCSI, but some data has been collected and plans have been made for the design of the genetic evaluation system. EBV will be calculated for:

1) Loin colour
2) Loin marbling
3) Drip loss

For trait 1 the following data is being collected 24 hours post mortem on the split loin, at least 20 minutes after cutting:

-Japanese Colour Score. This is a subjective score of lightness/darkness with 13 categories from 1/2 to 61/2 in half point increments (Nakai et al, 1975). Intermediate values are favoured.

-Minolta L* co-ordinate. This measures/lightness darkness on a continuous scale using a Minolta electronic meter. The average of at least 2 measurements are taken, unless the meter has a measurement area of at least 50mm2 (e.g. the Minolta CR 310), in which case a single measure is allowed. The meter also measures red/green (the a* co-ordinate) and yellow/blue (the b* co-ordinate), but these measurements have much less relationship to the appearance of the meat.

For trait 2, data is being collected on a subjective score (Agriculture Canada, 1992) from 1 to 5 in 1 point intervals.

Trait 3 is measured as the average weight loss from 2 pieces of loin each 25mm thick stored in separate polythene bags for 48 hours at 2oC. Ultimate loin pH is also measured as a correlated trait, using a Fisher, Beckman or Cole Parmer meter at 24 hours post-mortem.

The 3 traits will each be evaluated separately. Data analysis is required to investigate the properties of the measurements. Colour may be evaluated using a 2-trait linear animal model applied to the Japanese Colour Score and the Minolta L* value. Marbling score may be evaluated using a single trait linear animal model. Drip loss may be evaluated using a 2 trait linear animal model including the pH measurement. The national standards document (Canadian Centre for Swine Improvement, 1996) gives more complete details on measurement protocols.

It is hoped that the meat quality trait genetic evaluation system will be ready for routine use by the end of 1997.

4. Summary

Within the next year, CCSI and partners hope to provide Canadian swine breeders with access to EBV, updated monthly, for 3 of the most valuable carcass quality traits, and 3 of the most valuable meat quality traits. In co-operation with the University of Guelph they hope to develop sire line indexes using these EBV. Some of these indexes will be suitable for genetic selection by most breeders, and others will be aimed at the marketing of breeding stock to commercial producers supplying pork towards specific markets. CCSI and partners are currently trying to solicit as much input as possible on the requirements of commercial producers, packers and processors. The success of the program will depend on convincing the commercial sector of the link between parent stock with good genetic indexes from the Swine Improvement Program and good carcass grading and meat quality results from the commercial progeny.

5. Acknowledgements

Various people play major roles in the development and implementation of the program, including Cathy Aker (OSI), Nicole Dion, Danielle Pettigrew and Jean Paul Daigle (CDPQ), Brian Sullivan (CCSI) and Murray Duggan (WSTA).

6. References

Agriculture Canada (1992) Publication 1879/F. Marbling Standards for Beef and Pork Carcasses.

Canadian Centre for Swine Improvement (1996) National Pork Carcass and Meat Quality Evaluation Standards Handbook.

Golden, BL, WM Snelling and CH Mallinckrodt (1992) Animal Breeders Toolkit and Reference Manual. Available by Internet from ftp://cgel.Agsci.Colostate.EDU/pub/abtk

Kemp, RA, LR Schaeffer, C Aker and R Ball (1992) Genetic and phenotypic parameter estimates for carcass traits of Ontario purebred pigs. Mimeo presented at the 42nd Ann. Meet. Europ. Assoc. Anim. Prod.

Li, X and Kennedy BW (1994) Genetic Parameters for Growth Rate and Backfat in Canadian Yorkshire, Landrace, Duroc and Hampshire Pigs. J. of Animal Science 72:1450

Nakai, H, F Saito, T Ikeda, S Ando and A Komatsu (1975) Standard models of pork colour. Bull. Nat. Inst. Animal Industry 29:69-74