A Regional Integrated Pork Production System in Japan


Akira Nishids, Masayuki Jimbu, Akira Takebe,

Tomiji Akita, Tsutomu Furukawa


*Shigeru Itoh, Kamematsu Murata, Hiroaki Shimo,

Hiroshi Nishoji, Chikara Yoshida, Naoto Satoh


**Takeo Abe


National Institute of Animal Industry

Tsukuba Norindanchi, P.O.Box 5, Ibaraki 305, Japan


*Iwate Prefectural Livestock Experiment Station

Takizawa-mura, Iwate 020-01, Japan


**Livestock Improvement Association of Japan

Kameido 1-28-6, koutou-ku, Tokyo 136, Japan




A Landrace strain and two Large White strains have been developed  by  repeated  selection  in  closed  herds  based  on selection indices for desired gains at s prefectural livestock experiment station. An efficient cross breeding system has been shown to produce three-way crosses among these strains and a Duroc strain which has been established at National Animal Breeding Center as terminal sire.

Sixty-eight pig farms belonging to two agricultural cooperatives in a region, the prefectural neat processing and distribution center and a network of supermarkets have reached an agreement for the establishment of a regional integrated pork production system with the three-way crosses.

Because of high quality of the pork produced by the system, the share in the prefectural market is increasing.




A line breeding program started at Iwate Prefectural Livestock Experiment Station which is located in the north part of the main island, i. e. Honsyu, in 1970 (Mikami,lS87). The main purpose of the program was the evaluation of an closed-herd breeding scheme for the development of highly improved strains to produce economical crossbred among them.

We used the next procedures for the development of a Landrace strain.

{1) We collected animals with high performance on the traits which we were interested in.

(2) Accurate measurements of the traits were taken from each individual under a uniform environment.

(3) Breeding stock was selected based on the measurements.

(4) The herd was kept closed to be no animals and genes were introduced into the herd during the generations of selection.

(5) The generation interval was reduced as short as possible.


Explanations sre given to the each procedure listed above.

(1) It is necessary to establish a base population which has high averages and large genetic variances of the traits concerned. Large genetic vsriances would be btought in the base population by collecting characteristic  animals differing in genetical origins. If the genetic variation is large, sufficient genetic gains csn be expected. It should be avoided to introduce closely related snimsls only into the base population even if their performances sre considerably high.

(2) What we can directly messure on animals is phenotypic value, i.e. the sum of genotypic value and environmental effect. We have no way for measuring genotypic value of economically important metric characters directly. Since objective nf animal breeding is improvement of genotypic value, we have to predict it with phenotypic value. Animals which have higher phenotypic value sr' expected to have higher genotypic vslue in average. Therefore the environment aust be kept as uniform as possible for all the csndidates of breeding animals and aust let the differences in genotypic values be reflected on the differences in phenotypic values.  This effort significantly heightens the accuracy of selection.

Well adjusted measuring equipments should be used by well trained person to centrol error in measurement.

(3) The basic idea of genetic improvement by means of repeated selection is given in Fig.1. Suppose that there are data of daily body weight gsin taken from 60 boars and $0 gilts and the histogram shown in Fig.1 is obtained.  In  generation 1, the averages of .the boars  and the gilts are 700 and 600g, respectively, as shown in Fig.1 by the symbol:d. The mean of these two values: (?00+000)/2=650g; is regarded as the whole population mean at generation l. If we select the upper half of the gilts and the high@at 8 of the boars, the aesns of the selected gilts and boars become ?00 and 900g, respectively, as shown in Fig.1 with the symbol:a. The mean of these two values: (700+900)/2=800g; is the mean of the aelected population. The deviation  of  the  selected  populstion  mean  from  the  whole population  mean:  (BOO-650)=150g;  is  called  as  "selection differential". The selection differential by itself can not be the predictor of the genetic gain by the selection since our measurements are not on genotypic values but on phenotypic values as mentioned  before. Actually, from 30 to 50 percent of the selection  differential  becomes  realised  genetic  gain.  The proportion of genetic gain to selection differential is called as "heritability" and denoted as "h ". Thus, if fhc heritability of the trait in the population is 1/8, i.e. h =0.33, repeated selection is expected to bring us genetic gait of selection differential multiplied by heritability: 150x(1/3}=50g; for each one generation of' selection (Nishida and Abc,1980).

{4) Increasing  genetic  uniformity of the population  under selection will be daasged by the introduction oi' genetically unrelsted animals. If the performance of the introduced animal is low, the populstion mean is lowered.

(5) Once the base population and the detailed selection program are fixed, the expected genetic gain from one generation of selection is also nearly fixed. The rate of improvement under this  condition  can  be  accelerated  only  by  shortening  the generation interval.


[ Base population ]   Fifteen boars and sixty gilts of Landrace acre selected from National Livestock Breeding Station, some prefectural  livestock  experiment  stations  and  private  swine breeding farms on referring to performance and progeny testing records of the parents.

[ Selection ]    Selection was practiced for seven generations. About 50 litters were farrowed in each generation. The first stage selection was practiced within litter basis at 25kg of body weight. The selection criterion was the growth rate up to 25kg. One boar and three gilts were selected to be raised as candidates for replacements from each litter and additional two boars from each litter were castrated and fattened to 90kg of body weight. After the first stage selection, about 50 boars, 150 gilts and 100 castrates remained from 200 boars and 200 gilts born in 50 litters. The second stage selection was undertaken individually at 90kg of body weight.  The measurements of the following four traits were obtained (Fig.2).

(a) Average daily gain from 30 to 90kg of body weight (D.G.;g unit).

(b) Average backfat thickness probed ultrasonically at 10 points shown in Fig.2 (B. F.; cm).

(c) Average eye muscle area between the 5th and 6th thoracic vertebrae of the two castrated full brothers slaughtered at 90kg(E. M.; cm2.

(d) Average weight proportion of ham to whole carcass of the two castrates (H. R.; %).

A selection index (I) for desired gains was used as the selection criterion {Yamada et al,1975).


I = 0.012xD. G. - 5.184xB. F. + 0.276xE. N. + 0.400xH. R. The relative desired gains were assigned to 100g in D. G., -0.5cm in B. F., 5cm2 in E. M. and 0.5% in H. R.. The weighting factors in the above formula to realize the desired gains are derived as


B = P-1 G(G P-1G) -1d

where b: vector of weighting factors, P: phenotypic variance covariance matrix, G: covariance matrix between phenotypic and genotypic value and d: vector of desired gains.

Ten boars and sixty gilts were selected from 50 boars and l50 gilts based on the index value. Finally, the proportion of selection as a whole were 5% for asides and 30% for females.

The effects of selection are summarized in Fig.3. The daily gain, the backfat thickness and the eye muscle area were improved as planned but the ham ratio was slightly decreased.

[Correlated  response  ]   The correlated responses in reproductive performances and characteristics on neat qualities were investigated through all the generations of selection.

Litter size at birth and at weaning were held constant throughout the  selection program. In the generation 6, the average litter size in the first parturition were 9 at birth and 8 at weaning.  The mean weaning weight of a piglet linearly increased from 8.0 kg at generation 1 to 9.3 kg at generation 7.  This means that the selection indirectly improved the milk yield of sows.

The meat color, water holding capacity ,pH, some physical and chemical characteristics of the pork were precisely measured every generation. We did not recognize any correlated responses in meat qualities . An average reproductive performances and meat qualities were maintained from the beginning to the end of the selection program.

[  Mating  ]    For the prevention of  serious inbreeding depression, we avoided close inbreeding. On the other hand, a phenotypic assortative mating was adopted. The boars of higher selection indices were mated with the gilts of higher selection indices and vice versa, in the selected animals. The assortative mating augmented variance of the selection index in the offspring and this augmentation enabled us to get slightly larger selection differential under a fixed proportion of selection (Nishids et a1.,1977).

[ Inbreeding coefficient and coefficient of relstionship ]  The mean inbreeding coefficient (F) snd the  mean  coefficient of relationship (R) on the population incressed with generation of selection  (Fig.4).  The R exceeded 20% and approached the relstionship between half sibs, i.e. 25%, at the 7th generation. As a result, the phenotypic variations of the four traits decreased. The obtained uniformity of performance is one of the most important fruits of the selection.

This population has been recognized as an established strain by Judging coauaittee in 1982.

[ Management ]   The piglets were weaned at 5 weeks of age and each litter was raised in a pen up to 25 kg of body weight. From 25kg to 90kg, the boars and the gilts were kept separately to be 5 pigs in a pen. The two castrated full brothers of the Candidates were fattened in the same small pen. The standardized ration for performance test (TDN 70X,DCP 13X) was fed all the pigs ad libitum.

We vaccinated pigs and gave vermifuge timely according to a health control program.




We have further developed two Large White strains following the Landrace strain. The selection program started in 1980 and ended in 1988 at the same experiment station. The population sine was 8 boars and 32 gilts for each strain x generation. It was smaller than that of the previous program on Landrace. Daily gain, backfat thickness and eye muscle area were contained in a selection index as a selection criterion. For one of the strains, we used an independent culling level on stress susceptibility in addition to the selection index.

The selection was again successful. Thus the two populations have been simultaneously recognized as highly improved strains by the committee in 1S87.




An efficient cross breeding system was proposed according to the results of nicking test. The cross breeding system was for the production of three-way crosses among the three strains developed in the prefecture and a Duroc strain as the terminal sire. The Duroc strain was one of the good strain made in National Livestock Breeding Station.




In Iwate prefecture, 68 pig producers in a region belong to two agricultural cooperatives, prefectural meat processing and distribution center and a network of supermarkets have reached an agreement to  found  a regional integrated  pork production system using the three-way crosses.

In this system, the pig producers in a region, for instance in s town, are taking partial charge of the integrated system as strain maintenance farms, strain multiplication farms, hybrid(F1) sow  production  farms  and  three-way  crosses  production  and fattening farms (Fig. 5). This cooperation among the producers in a region reduces efflux of fund of the region and facilitates keeping the balance of demand and supply. The multiplication of the regional cooperating unit easily enlarges the cooperation system. Further, since this system does not require frequent introduction of pigs from other regions, spreading of the serious infectious diseases would be prevented.

In the fattening farms, they feed specially designed ration which fits the growth pattern of the three-way crosses. They have a local slaughter house in their region which can treat 200 pig in s, day. They supplied 20,000 finished pigs in a year to the slaughter house. The supermarkets sale the pork from the production system as a best brand. Because of the high quality of the pork produced by the system, the share in the prefectural market is increasing.

We are now trying to establish a closed herd breeding scheme for  the  improvement  of  economically  important  but  poorly heritable traits such as litter size (Satoh et al.,l990) and resistance to chronic disease.




1. Mikami, H. 1987. Pig breeding and development in Japan. Proceedings A Seminar on Pig Breeding and Development in Asia, El-E13.

2. Nishida, A., Nishoji, H. and Itoh, S. 1977. A comparison between selection differentials caused by post-mating cull based on performance of gilt and mean performance of pair mated. Jap. J.  Swine  Research  14(2):125-132.  (in  Japanese  with  English summary)

3. Nishida, A. and Abe T. 1980. Effects of repeated selection on population mean, heritability and distribution of breeding value. Jpn. J. Zootech. Sci. 51:485-494.

4. Satoh, M, Nishida, A. 19SO. Response to selection for litter size based on BLUP in golden hamsters. Proceedings of the 4th World  Congress  on Genetics  Applied  to  Livestock  Production. 13:329-332.

5. Yamada, Y., Yokouchi, K. and Nishida, A. 1975; Selection index when genetic gains of individual traits are of primary concern. Japan. J. Genetics. 5D(1):33-41.

Fig. 1. The basic idea of genetic improvement by repeated selection.

Fig. 2. The three traits measured at 90kg of body weight.

Fig. 3. The effects of selection.

Fig. 4. The changes in mean inbreeding coefficient (F) and mean coefficient of relationship (R).

Fig. 5. The flow of pigs in the pork production system. L: Landrace, W: Large White, D: Duroc