エンリッチド・ブロイラー生産
Rearing Systems and the Scientiﬁc Evaluationof Animal Welfare Husbandry Improved Broiler Production
小原愛 東北大学大学院農学研究科 家畜福祉学（イシイ）寄附講座 助手

Ai OHARA Assistant, Laboratory of Animal Welfare (sponsored by Ishii Corp.),
Graduate School of Agricultural Science, Tohoku University
Hello everyone. My name is Ai Ohara

ban was partially lifted. However, even before GGP

and I work as a research associate atimports were stopped, chicken meat production wasthe Laboratory of Animal Welfare

unable to keep pace with demand, and so chicken meat(sponsored by Ishii Corp.) at thewas urgently imported. As these facts show us, theGraduate School of Agricultural

Japanese chicken meat supply is not stable. Moreover,

Science of Tohoku University. Today, IImprovements in breeding chickens made in the Westwill introduce the enriched broiler

have resulted in birds that produce a lot of breast meat,

rearing system. My talk title refers to ”the Possibility ofwhich is popular in Western countries. By contrast, theAnimal Welfare husbandry for homebred breeds

Japanese favor leg meat, which tends to have a rich andTatsuno and the future”.

meaty taste. There are some differences in preference[Slide 1] Firstly I do not suppose that most of you are

between Western countries and Japan. Hence Japanesefamiliar with poultry husbandry, so Iʼd like to start bychicken breeds have been developed to suit Japanesetalking about the background to how chicken meat istastes.

produced in this country. Self-sufficiency in chicken
meat production is about 70% in Japan, which is higher[Slide 3] “Japanese chicken breeds” have beenthan either beef or pork production. The chickens

developed in Japan from pure lines. The National

produced for chicken meat are called ʻcommercial

Livestock Breeding Center has kept its own pure line

chickensʼ (CM)ʼ. In order to produce commercial

varieties, manages and breeds them, and carries out thechickens it is necessary to selectively breed the parents

entire commercial chicken production process in Japan.

stock (PS), grandparents stock (GP), great grandparents

The biggest feature of this is that it ensures traceability

stock (GGP) and a pure line for 4 generations. There areso that it is possible to ﬁnd out where and how speciﬁc

only three companies have pure lines for breeding

meat chickens were kept and who the parent birds

chicken in the world, so it is an oligopoly market. Japanwere. The chickens bred in this away are Tatsuno

continuously imports chicken strains from Europe andcommercial chickens, and the parent stock is Red

America to cover 99% of its needs for chickens. The

Cornish and White Plymouth Rock chickens. Tatsuno

subsequent generations are raised in Japan withcan answer the preferences of domestic consumerʼshatching and production performed domestically. So

demand and cope well with the Japanese climate andthe self-suﬃciency for chicken meat is about 70%, butmarket needs. They also improve the self-sufficiency

for the genetic resources that are vital to chicken

rate of domestic breeding chickens, which makes themproduction, the current situation is that Japan is almost

a risk hedge for chicken meat production. For these

totally dependent on overseas suppliers. The problem

reasons, Tatsuno is considered to contribute towards

with this is that when outbreaks of bird flu occur, it

ensuring a stable supply of safe and secure chicken

becomes impossible to import chickens breeds.

meat.
Now, letʼs make a comparison of the differences[Slide 2] This slide shows a page from the website of thebetween Japanese chicken breeds, Western chicken

Animal Quarantine Service. Recently, import poultries

breeds and “jidori” (locally produced chickens).

and their products were banned from France. Later this20

ワークショップⅢ

産業動物の福祉と経営[Slide 4] Firstly, with regard to their respective shares of

their bones cannot support the body size and weightthe chicken meat market, approximately 84% of theand the birds tend to develop lameness, a symptom ofJapanese market consists of broilers based on Western

which is limping with every step. This may become achicken breeds, 1~2% are from Japanese chicken

factor in the development of ascites, a condition inbreeds or jidori, etc., and about 15% are egg-laying

which fluid accumulates in the peritoneal cavity.

hens and their parent chickens. Also, hens that noMoreover, when their weight increases rapidly, the birds

longer produce eggs are usually turned into chicken

may not be able to move, so they sit all the time andmeat eventually. In supermarkets, this meat is sold assometimes develop dermatitis on their breasts or“oya tori” or parent chicken, while the meat offootpad. These situations influence the welfare andcommercial chicken is sold as “wakatori” or young

productivity of chicken.

chicken. In the case of broilers, the per-day increase inweight is known as the daily gain. When we compare[Slide 5] Now let us ﬁnd out and ask ourselves, ʻwhat is athe daily gain between the three breeds of chickens weproblem in the welfare of chicken? What does it meanﬁnd that for Western chicken breeds the average daily

to satisfy the requirements of livestock welfare? That is,gain is approx. 58g, growing up to 2.5 ~ 3kg in approx.

it is considered that the comfort of livestock can be

50 days before then being dispatched to market. Their

maintained by satisfying the following five freedoms.

productivity is quite high which contributes to the low

Almost all broiler producers take suﬃcient measures toprice of chicken meat. Tatsuno Japanese chicken breeds

ensure the birdsʼ “freedom from hunger and thirst,”

are bred from two kinds of parent stock, as I mentioned“freedom from discomfort” such as from overheating,before. Their daily gain is approx. 44g and they are kept

etc., and “freedom from pain, disease and injury”, sincefor around 60 days before handling. The productivity of

all these things are directly connected to productivity.

Tatsuno birds is lower than that of Western chicken

Also, “freedom from fear and suffering” can bebreeds but their production is focused more on meatsignificantly improved if supervisors treat livestock

quality. Moreover, in jidori keeping, there is a strict rulecarefully. However, hardly any measures are taken at allthat such birds must have a bloodline consisting of overto ensure the fifth freedom, which is “freedom to50% native Japanese breeds. A native breed is deﬁned

express normal behavior”.

as “a breed formed in Japan before the Meiji era, or
having been introduced to Japan before the Meiji era

Accordingly, I think that the first four freedoms are

and that has taken root in the country.” Examples

already considered, but the ﬁfth freedom is not covered.

include ʻHinai-doriʼ and ʻO-Shamoʼ. These breeds areSome additional care to allow birds to express moregenerally classiﬁed as natural treasures and we are notnormal behavior might improve these problems. For

permitted to eat them. Chickens produced by mating

chickens, pecking objects is one normal form ofHinai with Rhode Island varieties are known as Hinai

behavior. So by providing objects for chickens to peck,jidori. Since their daily gain is only around 25g, their

not only encourages them to peck but also makes themfeeing period is quite long. A great deal of time and caremore active. Some paper reported that increasingmust be devoted to making delicious chicken, so theactivity helps to develop the bones andprice of their meat is high.

cardiopulmonary system which in turn leads toimprovement in physical problems. Just as with broilers,

The daily gain is a major feature of each breed and a key

such problems have appeared in the domestic

point within the production system. It is also said that

production of Tatsuno breeding chickens. But thethere is a deep relationship between the daily gain andTatsunosʼ daily gain is less than that of Western chicken

the birdsʼ level of welfare. When the daily gain is large, itbreeds, so it seems Tatsunos are suitable candidates formeans that the growth speed of muscle (meat) is fast.

the chicken welfare rearing system.

But generally the growth speed of their bone andcardiopulmonary system is not as fast as muscle. So[Slide 6] We carried out an environmental enrichment

Workshop Ⅲ Welfare and Management of Farmed Animals

21

experiment in which we placed things in the house thattriggered normal behavior. In this context, normal
behavior essentially means ʻnatural habitsʼ. And in thecase of chickens this means pecking things, roosting
when going to sleep, etc. So we conducted acomparative experiment between an ordinary rearing
group provided with only a waterer and a feeder, andan enrichment test group provided with additional hay
bales and perches, [slide 7]. The experiment results
however showed no significant differences in thedispatch weight of the daily gain, bird productivity, or in䇼㪪㫃㫀㪻㪼㩷㪈䇽the number selected for dispatch or the number ofdead or diseased birds.
[Slide 8] However, regarding breast inflammation,
which is considered a problem, the results show amarkedly lower incidence of the problem among malechicks in the test group. [Slide 9] Also, with regard to
footpad inflammation, the number of chicks that did
not have this problem was larger among the females inthe test group. [Slide 10] As for a summary and future
research plans, we will be analyzing video recordings of䇼㪪㫃㫀㪻㪼㩷㪉䇽the birdsʼ behavior and verifying the availability ofenrichment materials. In addition, we are planning tocomprehensively examine enrichment testing bycalculating the ratios of pseudo eosinophils andlymphocytes, which are indicators of physiologicalstress.
From the results of all of these things, during the next
fiscal year we are aiming to build up a Japanese-styleanimal welfare animal husbandry system for meat-use
chickens through the use of improved enrichment䇼㪪㫃㫀㪻㪼㩷㪊䇽

materials and an objective evaluation of the breedingenvironment.

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ワークショップⅢ

産業動物の福祉と経営䇼㪪㫃㫀㪻㪼㩷㪌䇽䇼㪪㫃㫀㪻㪼㩷㪐䇽䇼㪪㫃㫀㪻㪼㩷㪍䇽䇼㪪㫃㫀㪻㪼㩷㪈㪇䇽䇼㪪㫃㫀㪻㪼㩷㪎䇽䇼㪪㫃㫀㪻㪼㩷㪏䇽Workshop Ⅲ Welfare and Management of Farmed Animals

23