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Choice Of Terminal Sire (Ai)

Peadar Lawlor, Teagasc, Moorepark Research Centre.


Introduction

"The boar is half your herd" is a long used adage of pig producers. And it is as true today as it ever was. However, few producers are giving sufficient attention to choosing this half of the herd. This could be costing you money !

Pig production is characterised by rapid turnover of stock allowing for rapid genetic improvement. This genetic improvement must be harnessed by careful selection of boars to ensure unit profitability. This is particularly true in Ireland, a country with few natural advantages when it comes to producing pigs.

This paper will consider only the terminal sire and its introduction to the herd as purchased artificial insemination (AI). AI provides unique genetic opportunities by allowing producers access to the very best or most advanced genetic material available to the industry. It is estimated that breeding companies make available the top 5-7% of their boars for distribution as AI. The selection criteria that will be discussed include: source, breed, pooled semen, health, genetic improvement and presence or absence of gene markers.

Source

The source of AI for producing finisher pigs will depend on many factors, some of which will be discussed under other headings. However, the past performance record and professionalism of a supplier can be very important. Producing quality terminal sires with important economic traits can not be done overnight. On the contrary, this is a long term process which requires dedication to detail, discipline and a considerable investment of capital.

Two breeding companies (Hermitage and PIC Ireland) are now the principle suppliers of sireline semen to pig producers in the Republic of Ireland. Appendix 1 details the types of boars available from each of these suppliers.

Hermitage recommend the use of purebred Hylean Large White semen on Landrace type sows and the use of purebred Hylean Landrace semen on Large White type sows in a rotational breeding programme. They recommend the use of selected Hylean Landrace and Large White semen when pigs are destined for plants in Northern Ireland where payment is made on P2 fat depth. Hylean 26 is recommended for use on F1 sows or in a rotational breeding system to get the benefit from hybrid vigour and improve meat eating quality. This breeder also has a pure Duroc line which is recommended to improve the eating quality of meat and hybrid vigour. They also have pietrain line for research purposes.

PIC have three terminal sire lines for use in Ireland. Their line 62 is purebred Pietrain but is halothane negative which should improve greatly their meat quality. Line 11 is a purebred Large White line and it is recommended by PIC for use when pigs are destined for plants in Northern Ireland where payment is made on P2 fat depth. PIC's line 402 is a cross between line 62 and line 11. This line is recommended by PIC for use on F1 sows or in a rotational breeding programme to produce slaughter pigs that will be paid for on the basis of lean meat percent as is the case in the Republic of Ireland. The PIC F1 (Camborough 15) is the result of a 3 way cross ((Large White x Duroc) x Landrace). This means that when mated with a PIC terminal sire the progeny of Camborough 15s will be 12.5% Duroc.

Breed

Genetic differences in pork quality among swine breeds have been known for some time. This presents the industry with an opportunity to design superior pork products for specific markets. The Duroc breed has received particular attention due to its positive contribution to the eating quality of pork (Table 1). This is thought to be due primarily to its relatively high level of intramuscular fat (marbling). A high level of intramuscular fat has been linked with improved eating quality of pork (Table 2).

Table 1. The influence of % Duroc genes on pork eating quality (MLC, 1992)

% Duroc genes

0

25

50

75

Tenderness1

4.96

5.03

5.32

5.38

Juiciness1

4.09

4.11

4.18

4.38

Flavour1

3.88

3.99

3.96

3.98

1Evaluated on an 8 point scale (lower = undesirable)

Table 2. Effect of increasing intramuscular fat % on eating quality of pork loin chops (Wood, 1993).

Intramuscular fat %

Flavour1

Tenderness1

Juiciness1

Acceptability1

1.47

2.5a

1.3a

1.7a

0.6a

2.89

2.9b

3.1b

3.2b

2.0b

4.34

2.8b

2.4c

2.5c

2.0b

1Taste panel scores on a scale from -5 to 5 with low = undesirable. a,b,cValues within columns with different subscripts differ significantly.

In 2002 we carried out an experiment in Moorepark comparing Landrace and Duroc sire line semen. The meat quality component of this experiment is not yet complete. However, Table 3 gives a summary of pig performance to slaughter. It appears (at least in this case) that selection for improved eating quality may reduce pig performance.

Table 3. Effect of Breed on grower finisher performance (Lawlor et al., 2002)

Breed

Significance

Duroc

Landrace

Days on trial

133

124

***

Intake (g/day)

1813

1829

NS

Daily gain (g/day)

655

703

***

1from48 days post-weaning to slaughter at 104 kg. *** P<0.001, NS = non-significant.

The parent sows in Ireland are generally of Landrace x Large white origin. When a third breed (e.g. Duroc or Pietrain) is used as a terminal sire, pigs can benefit from hybrid vigour (heterosis). This hybrid vigour may be seen in increased growth rate and viability of progeny. Problems with the use of Pietrains is that they were traditionally halothane positive (stress sensitive) and that their growth rate tended to slow down when they reached 70 to 80 kg liveweight. Pietrains sold by PIC (line 62) are now halothane negative. According to PIC significant improvements in growth rate with this breed has been achieved in the last five years through intensive selection for this trait (a high heritability trait). Hermitage also have a source of halothane negative Pietrains but see little benefit from using this breed.

A recent report by McCann and Beattie (2002) looked at boars of eight types (LR, LW, Dr, LR x LW, LR x Dr, LW x Dr, LR x LW x Dr, LR x LW x P). No difference in performance was seen between purebred and crossbred sires. However considerable within sire type variation was observed in this study (Table 4)

Table 4. Variation in pig production performance from weaning to slaughter (McCann and Beattie, 2002).
 

Average

Top 15%

Bottom 15%

Daily gain (g/day)

720

884

614

FCE

2.31

1.74

2.52

Pooled semen

Mixing or pooling semen from different boars is now common practice when processing semen for commercial AI. The benefits of pooling semen include:

  1. allows a large number of boar ejaculates to be processed simultaneously rather than individually thus increasing processing efficiency.
  2. reduces / eliminates inherent differences in fertility between boars.

Hermitage use pooled semen from 4 boars.

The disadvantages of pooling semen include:

  1. If a boar has a viral infection (e.g. PRRS), the virus can be shed in the semen. With pooled semen, the virus will be spread across more doses than if it were used pure.
  2. If one ejaculate is contaminated with bacteria, where this is added to a pool, the contamination is spread further.

PIC do not pool semen

Health

Purchased breeding stock can introduce new diseases and parasites into commercial herds. This is particularly important with regard to stock boars purchased but some diseases can also be carried in semen. Therefore, it is important to identify breeding companies that have implemented a comprehensive herd health program. This includes a veterinarian who makes routine on-farm inspections, conducts blood tests and other diagnostic procedures, examines animals, counsels, and makes recommendations. The breeding company should minimise opportunities for new disease organisms to enter the herd by blood testing, and enforcing strict bio-security measures.

Customers should obtain up to date veterinary reports from their AI supplier as part of their bio-security programme.

Heritability

In general, reproductive traits are considered to have low heritability, growth rate, feed efficiency traits are of moderate heritability while carcass traits are highly heritable (Table 5). This is important in terms of a selection programme for sire line stock as the economically important traits are likely to be highly heritable. A selection programme in this case will lead to fast genetic progress relative to a selection programme for reproductive traits within a dam line.

Table 5. Heritability of performance and body composition traits

Item

Heritability (h2)

Reproductive traits

Total born

0.10

 

No. born alive

0.07

 

Pre-weaning survival

0.05

 

Pigs weaned

0.06

 

Rebreeding interval

0.23

Post weaning to sale

Daily gain

0.30

 

Feed intake

0.24

 

Feed conversion efficiency

0.30

 

Days to slaughter

0.25

Carcass composition

Backfat thickness

0.41-0.52

 

Loin muscle area

0.47

 

Lean percent

0.48

Genetic improvement

Sire line AI should only be purchased from suppliers where genetic improvement programmes are utilised. This is so because the rate of genetic improvement in a commercial herd parallels the rate of genetic progress made by the supplier. Purchase of AI from the highest ranking boars available from the breeding company enables the commercial herd to approach the genetic level of the breeding company's herd.

When selecting suppliers, review their genetic improvement program. A sound genetic improvement program should include four features:

(1) accurate, complete performance records including animal identification, consistent measurement of all boars and ranking of animals within defined contemporary groups. Individual performance test results and records must be available for all pigs in a contempory group. The traits recorded should be the important economic traits.

(2) assessment of the genetic merit of economically important traits (growth rate, feed efficiency, fat depth, muscle depth and lean meat percentage) based on the individual's expected progeny difference (EPD).

Expected progeny deviations (EPDs) are estimates of genetic merit that are more powerful in driving genetic progress than selection based on individual performance records alone. EPDs are defined as the difference from the average in performance of subsequent progeny if an individual is mated to an average sow.

Some breeding companies use the term Estimated Breeding Value (EBV). The EBV is an estimate of the genetic merit of an individual. The EPD can be calculated from the EBV by halving the latter (i.e. EPD = EBV / 2).

The calculation of EPDs, the individual's performance record is used along with the performance record of other relatives, such as full sibs or half sibs, sire, grandsires, dam, granddams and progeny. All performance records are deviated from their contemporary group average and weighted by the heritability of the trait.

An EPD may have a positive or negative sign. EPDs with positive signs signify more or greater while EPDs with a minus sign indicate less or fewer. For example a boar with an EPD of -70 for daily gain if mated to average females; resulting progeny would be expected to grow at 70g/day less than the average for that line. However if the EPD was +70, the daily gain of progeny would be 70g more than the average for that line.

(3) indexes weighting EPD's of traits relative to their economic importance in commercial pork production.

The use of a selection index for the comparison or ranking of boars allows traits to be weighted on the basis of economic worth. This provides an overall single value which balances the strong and weak aspects of the traits that are considered in the index. A selection index will therefore include EPDs for all traits that are considered important in the selection process. Selection of a boar on the basis of a single trait (e.g. lean meat) is unwise. Some of these pigs will be very lean due to poor appetite and slow growth, which is obviously undesirable.

(4) selection of the highest-ranking boars based on selection indexes of EPD's (Schinckel et al., 1999)

Breeding companies should be able to describe and document their genetic selection programme.

Gene markers

Some sources suggest that major advances in biotechnology are set to bring about huge changes in animal breeding. Already several gene markers1 have been patented for pork quality characteristics and growth performance traits (e.g. carcass leanness, litter size etc.) Others are being investigated and are likely to be available in the near future. PIC now claim to be supplying boar semen to the Irish market with a gene marker for leanness. In the future it is likely that markers for disease resistance will also be available in Ireland. PIC have already identified a disease resistant marker which identifies pigs that are genetically resistant to specific strains of E.Coli (i.e. E.Coli F18; not an important disease causing strain in Ireland).

Some experts claim that in the future breeding companies will recoup the cost of R & D into these markers by charging extra for AI doses that contain them. We are in the very early stages of this technology and it will be some time before we know how effective some of these markers are under commercial conditions. Hermitage have been following a programme of parental imprinting as part of their selection procedure.

Comparing sources of boars / semen

Indexes prepared by different breeding companies cannot be compared as these indexes are probably calculated differently and the performance tests that the indexes are based on were carried out in different environments and with different diets.

The Department of Agriculture operated pig performance testing programme ceased and the test stations closed Cork (1984) and Dublin (1988). It was not until 1998 with the publication of the breed evaluation programme report (Lynch and Allen, 1998) that objective and independent information on the quality of terminal sires available in Ireland was once again available to the industry. This programme was extremely important to the industry. Its success stemmed from the fact that it tested boars from all seven of the major suppliers on the island. Semen from these suppliers was used on one source of females at Moorepark Research Centre and the progeny were then tested for growth rate, feed intake, feed conversion efficiency and carcass traits.

The results of the Breed Evaluation Programme were widely used by the industry. However, there is no way of knowing how reliable these results are 4+ years down the line. To have accurate and up to date information on the relative performance of terminal sires in the country it would be necessary for such a programme to be conducted again and at set intervals into the future. Such a programme would have to be funded by the industry, however, the investment would be very quickly recouped by producers.

Summary

Producers must select genetic stock to maximise their profits. Genetic selections in the case of terminal sires will affect profits for pigs sold one year later. Producers should select stock using the economic values that are currently available to them. Pigs in the Republic of Ireland are paid for on a weight and lean meat basis. Daily gain in Ireland is low relative to our continental competitors and it appears this trait in particular may need increased selection.

Selecting for meat quality still holds many unknown variables; and until there are price premiums or discounts for differing pork quality, there will be no rush to select genetics based on pork eating quality. However if pork producers and processors alike are serious about increasing / maintaining pork consumption among consumers, then the pricing structure for pigmeat will have to be redressed. In the past, the direction given by pork processors to breeding companies and producers alike with regard to meat quality requirements has been poor.

Acknowledgements

The direction given by Ned Nolan, Hermitage AI and Gerry Duglas PIC Ireland in the preparation of this paper is gratefully acknowledged.

Literature Consulted

Bates, R. O., Stewart, T., and Clutter, A. 1996. Selection guidelines for the seedstock producer. Pig Industry Handbook. PIH 58, 8pp.

Coffey, R., Bullock, D., Parker, G. and Laurent K. 2002. Boar selection - using expected progeny differences (EPDs). Online publication accessed on 05/03/02. http://www.ca.uky.edu/agc/pubs/asc/asc153/asc153.htm.

Lynch, P. B. 1995. Developments in pig breeding. National Co-Operative Pig Producers Society Seminar, Kilcoran Lodge Hotel, April 25th 1995. 8pp.

Lynch , P. B. and Allen P. 1998. Pig breed evaluation programme, final report to Pig Breeding Council. pp58.

McCann, M. E. E. and Beattie, V. E. 2002. The effects of sire type on reproductive and production performance and on carcass and meat quality. Report prepared for: UFU and PPDC committees.

Schinkel, A. P., Bates, R. O., Rodibaugh, D., and Safranski, T. 1999. Selection guidelines for commercial pork producers. Pig Industry Handbook. PIH 9, 3pp.

Walker, N. 2002. Carcass quality of Northern Ireland pigs compared with those originating in the Republic of Ireland and Great Britain. A report commissioned by the Department of Agriculture and Rural Development for Northern Ireland 120pp.

Line AI in the Republic of Ireland

Source

What is available ?

What is it ?

Use where ?

Benefits

Hermitage

Hylean Large White

Sire line pedigree Large white

To increase lean meat % in plants in the Republic

 
 

Hylean Landrace

Sire line pedigree Landrace

To increase lean meat % in plants in the Republic

Hybred vigour

 

Hylean 26

Hylean Large White x Duroc

To increase lean meat % in plants in the Republic

Hybred vigour, meat quality

 

Duroc

Sire line pedigree Duroc

To increase meat quality

Hybred vigour

 

Pietrain

Pedigree Pietrain

Research line

 
     

(All are selected on ADG, Intake, FCE, carcass Lean and fat)

 

PIC

Line 11

Sire line pedigree Large white

To reduce P2 in plants in Northern Ireland

 
 

Line 62

Pedigree Pietrain

To increase lean meat % in plants in the Republic

Hybred vigour, Halothane -ve

 

Line 402

Line 11 x Line 62

To increase lean meat % in plants in the Republic

Hybred vigour

     

(All are selected on ADG, Intake, FCE, carcass Lean and fat)

 

Footnotes

1 A gene marker is a segment of DNA with an identifiable physical location on a chromosome and whose inheritance can be followed. A marker can be a gene, or it can be some section of DNA with no known function. Because DNA segments that lie near each other on a chromosome tend to be inherited together, markers are often used as indirect ways of tracking the inheritance pattern of a gene that has not yet been identified, but whose approximate location is known.   Back