http://course.sdu.edu.cn/976

Chapter 8 Guinea Pigs (荷兰猪，豚鼠)Ⅰ Main strains and stocksⅡ UsesⅢ BehaviourⅣ AnotomyⅤ Physiologic features

Ⅵ Breeding and reproductionⅦ Feeding and

wateringⅧ Germ free and SPFⅨ Techniques

Wild guinea pig• The domesticated guinea pig is related to

the wild guinea pig, Cavia aperea, which is widely distributed throughout Argentina, Uruguay, Brazil and Peru.

HISTORY AND ORIGIN

Wild guinea pig• The first reports of domestication of the

guinea pig were around 1530, when Pizarro conquered Peru. The rodents were used for food and religious sacrifices.

• In South America, its natural habitat, it may be raised for food.

• 达·芬奇《最后的晚餐》 1495年Paintings such as the last supper have included the guinea pig as main course meal

• Origin of the guinea pig is unclear. • Origin of “guinea pig" name is vague.

– Common name is "cavy". – suggest: “guinea” ----trading ships may have

travelled via Guinea in West Africa, or via Guiana

• Adult females called sows, and adult males called boars. Parturition referred to as farrowing.

• Europe • In the Sixteenth Century, Dutch sailors

introduced guinea pigs into Europe, where they were bred for show and as pets.

• One of the earliest recorded uses of guinea pigs for research was in 1780, when Lavoisier used them to measure heat production.

• Other early uses of the guinea pig in research included investigations of anaphylactic shock, vitamin C deficiency and tuberculosis.

• 1770's: reached the United States used as a pet and as a research animal.

Taxonomy

• Kingdom - Animal • Phylum - Chordata• Class: Mammalia• Order: Rodentia• (single row of upper and lower paired incisors

which grow continuously; no canine teeth)

• Family: Caviidae• Tailless South American rodents with (1) one pair of

mammae and (2) four digits on front feet and three digits on hind feet.

• Genus: Cavia，豚鼠属• Species: Porcellus,土拨鼠

– South American cavy; possibly ancestral to the domestic guinea pig

• The guinea pig is in the order Rodentia, the largest mammalian order, which includes rats, mice and squirrels.

• Guinea pigs are placed in the suborder Hystricomorpha, along with chinchillas and porcupines, and in the family Caviidae.

• The Caviidae, which include the capybara, are herbivorous South American rodents characterized by a stocky body, vestigial tail and long gestation.

ⅠMain strains and stocks• Coat characteristics are the basis for

classifying guinea pigs by variety, since body conformation and size are very uniform for all varieties.

• The most common pet varieties are the English Shorthair and the American Shorthair.

A. ENGLISH• a. Short, smooth, straight hair (3.8 cm) • b. Solid colors: albino, black, agouti,

sandy, red, chocolate, cream, etc.• c. Bicolored and tricolored animals

also.

• Most inbred and outbred laboratory guinea pigs are the English variety.

• Lab stocks-outbred– Hartley, also known as the Dunkin-Hartley,

an outbred shorthair albino;

• Lab strains-inbred– Although a considerable amount of

research was conducted in the past using inbred strains, only two inbred strains are readily available today: Strain 2 and Strain 13.

• Lab stocks-outbred – the NIH Outbred, a multi-colored

guinea pig;– and the hairless, euthymic guinea pig.

• Mutant Stocks/Strains:– a. Complement 4 Deficient (C4D/N):

in 1970 NIH – b. Waltzer (Wz)– c. Hairless and Immunodeficient

Mutant

B. ABYSSINIAN• a. Short, rough hair that radiates

from multiple centers on the body to form rosettes or whorls.

• b. Variety of colors.

C. PERUVIAN• Has long silky hair up to 15 cm (6 in)

long.

• Pigmentation: 15 loci are known to influence coat color in guinea pigs.

• Most are single gene mode of inheritance. – a. Agouti locus (A) – (1) black or brown pigment – (2) Light-bellied agouti allele (A) – (3) Non-agouti allele (a): – Eliminates the Phaeomelanin band from

individual hairs and animals are therefore black (or brown, or variation).

– b. Brown locus (B): – c. Color, or albino locus (C)

Ⅲ. BEHAVIOR• 1. Diploid chromosome number is

2N=64, one pair of sex chromosomes– 31 pairs of autosomes.

• 2. Docile and shy, easily handled– Popular as pets– Seldom bite or scratch– Easily alarmed, injuries of young, orthopedic,

abortion when startled,

• 3. Social animals.– Tolerate close physical contact with each

other at rest, communal, amicably– Rarely climb or jump. Short legs, tailless– Male-dominated social hierarchies, a new

introduce, fighting barbering

• 4.Most active in the morning and evening– Feeding: Generally occurs during daylight

hours especially at dawn and dusk– Crepuscular animals

• 5. Preyer reflex: – Cocking of the pinna of the ears in response to

sound. • 6. Communication

– Scent, Auditory: – (a) “chutts” - brief vocalizations, single or paired– (b) "chutter" - 2 to 4 components – (c) "whine" - during flight, discomfort – (d)Also whistle, tweet, purr, drr, scream, squeal.

• 7. Rigid habits and dislike change. – Any change in food or water may cause a

guinea pig to stop eating or anorexia.– Environmental alterations, such as a change

to wire bottom caging, may result in injury.– Tend to be messy, scattering feed,

bedding and feces• 8. The development of human allergies

to guinea pigs is not uncommon

• 1. Feet: Forefeet have 4 digits each, Rear feet have 3 digits each.

Upper surface of right manus

Upper surface of right pes

ⅢⅢ.. ANOTOMYANOTOMY

• 2. Large tympanic bullae– easier to access internal structures of the ear.

• 3. Thymus– surrounds the trachea. – incontrast to rats, mice, deep within the thoracic cavity, overlying the heart.

• Thymus: Present in immature animal, Gradually involutes as the animal matures. In immature animals it is on each side of the ventral cervical midline.– Guinea pig (also ferret, monkey and man) is

considered a corticosteroid-resistant species because steroid treatment does not readily affect lymphocyte count or thymus. (Other species respond with decreased thymus weights and lymphocyte counts).

• 4. The pharynx has a unique anatomy– The soft palate is continuous with the base of

the tongue and has a hole in it, called the palatal ostium.

– The only opening from the oropharynxto the remainder of the pharynx.

• 5. Lung– Right, four lobes. – Left, three lobes.

MICE

• 6. Adrenal glands– Bilobed and large compared to most rodents.– They are situated cranial to each kidney.– In this image, in which the animal's head is to

the left, the kidney is obscured by renal fat, but the left adrenal gland is indicated by an arrow.

• 7. Gastrointestinal– Monogastric, but a lower intestinal tract typical

of herbivores.– The large intestine occupies most of the

abdominal cavity– the cecum, identified by the arrow, contains

up to 65% of the total gastrointestinal contents.

• 8. Coprophagic– Eat feces directly From the anus or from the cage floor.

• They have marking glands located circumanally and on their rump and are often seen walking or sitting with the glands pressed against a surface

A. Osteology• Dental formulas• Monophyodont, one permanent set of teeth.• Unique for rodents, have premolars.• All the teeth are hypsodont, or open rooted.• 2(I 1/1 C 0/0 PM 1/1 M 3/3) = 20

MICE

哺乳动物的牙齿

• 哺乳动物的牙齿是区别于其它脊椎动物（鱼类、两栖动物、爬行动物、鸟类）的最重要特征，只有哺乳动物的牙齿是“异齿型”。

• 门齿用来切割植物，犬齿用来杀死猎物，臼齿用来咀嚼食物，牙齿构成可判断食性。– 食草:犬齿消失，门齿发达，臼齿整齐；– 食肉:犬齿发达，门齿细小，臼齿参差不齐；– 杂食:各齿优势持平；啮齿类，上下颌一对门齿无齿根，终生继续生长。无犬齿。

• 人的齿式：2.1.2.3/2.1.2.3, 32颗最后4颗臼齿 “智齿”,30多岁才长出来

A. Osteology

• Vertebral• Guinea pigs have 7 cervical, 13-14

thoracic, 6 lumbar, 2-3 sacral and 4-6 coccygeal vertebrae.

• Vertebral formula:• C7 T13-14 L6 S2-3 Cy4-6

D. Skin and derivatives• Hair

(1) Consist of coarse large guard hairs surrounded by undercoat of fine hair.

(2) Each hair follicle has associated sebaceous gland

(3) Pelage Variations: • a.Rough (R) locus:

is characteristic of the Abyssinian breed

• b.Long Hair (l)

• Teats• Both the male and female have teats. The

female has a single pair of inguinal mammary glands.

E. Gastrointestinal system(2) Stomach, glandular stomach (3) Small Intestine: About 125 cm in lengthCommon bile duct enters duodenum 1 cm

caudal to pylorus.• (4) Cecum:• a. Occupies left side of abdominal cavity • b. Large thin-walled sac 15-20 cm long• c. Accounts for about 15% of body weight.

• (5) Liver: 6 lobes• (6) Pancreas:

– Divided into cranial and caudal lobes; Pancreatic duct enters duodenum 7 cm distal to common bileduct.

• (7) 4 pairs Salivary Glands

G. Reproductive system• Vaginal closure• The female guinea pig (sow) can be

distinguished from the male by a shallow, U-shaped break in the ridge between the urethral orifice and the anus. This break is covered with a vaginal closure membrane which is only open during estrus and parturition.

• Everted penis• Sexing is more easily accomplished by

applying gentle pressure to evert the penis of the boar, or male.

• The mature boar has extra-abdominal paired testes, which lie in the scrotal pouches and open inguinal canals.

• Penile styles• The os penis, or baculum, is found within

the dorsal surface of the entire length of the glans. The intromittent sac, unique to hystricomorph rodents, is in the ventral aspect of the glans.

• When the penis is erect, the intromittentsac everts, revealing two keratinaceous, horn-like styles attached to its caudal end.

• Female and male reproductive tracts• male, large vesicular glands, that are

bilateral, smooth and transparent. • female, uterine horns.

• Accessory glands• In addition to vesicular glands, the male

accessory sex glands include the paired coagulating glands,

• prostate gland• paired bulbourethral glands.

Ⅴ. Physiologic features

• 1. Hematologic characteristics– White Blood Cells – (1) Neutrophils 38%– (2) Lymphocytes 55% – (3) Monocytes 3%– (4) Others 4%

• Blood Pressure: systolic rarely greater than 100 mm Hg.

• 2. Kurloff cells• One of the unique features of guinea pigs

is the presence of Kurloff cells. • Kurloff cells are mononuclear leukocytes

with intracytoplasmic inclusions. • They are found in highest numbers in the

placenta and may have a role as a killer cell.

• 3. the guinea pigs are a source of serum complement that has high activity;

• auditory research;• teratology and toxicity research; • gnotobiotic research.• The guinea pig is also being used as a

model for spontaneous diabetes mellitus• Complement 4 deficiency and

cryptosporidiosis

• 4. Similarity to humans• Guinea pigs and humans share

several features, including– a need for dietary vitamin C,– similar placentation and hormonal

control of pregnancy,– delayed hypersensitivity reactions,– susceptibility to tuberculosis.

• 5. Unique features• Other unique physiological features are

listed here. Guinea pigs are subject to lethal bronchial constriction (bronchiolar smooth muscle contraction) in response to histamine administration.

• They also have a relatively high incidence of anaphylaxis when injected with small amounts of antigen.

• 6. Guinea pigs tolerate cold better than hot temperatures

• 7. Significant weight losses by transportation and handling– (up to 50g) within 24-48 hours. – This weight is regained rapidly if

conditions are stabilized– may alter experimental data.

• 8. Undesirable characteristics • Guinea pig features that may make them

undesirable for research include higher maintenance costs than smaller rodents and the fact that only a few inbred strains are available.

• Also, blood collection and intravenous injections are difficult in guinea pigs due to lack of easily accessible peripheral veins, and they have a relatively high susceptibility to infection.

• 1. Mating• (1) Males

– a. Fertile matings before 8-10 weeks of age b. Usually mated at 3-5 months (450-600 gm) c. Efficient reproduction until 27-30 months of age.

(2). Females:– a. First estrus as early as 4-5 weeks of age

b. Usually mated between 2.5-3 months of age, or when reach 350-400 gm.

Ⅵ. Breeding and reproduction

• 2. Continuously polyestrouswithout significant seasonal variations.– Estrous cycle 15-17d– Has distinct signs of estrus

(vaginal membrane opening) – lasts 9-11 hours – Postpartum estrus: Occurs with a 12-15

hours– Gestation: 59-72 days; mean = 63 days

Ⅵ. Breeding and reproduction

• Vaginal membrane: – (a) Opening precedes estrus– (b) Open for about 2 days during cycle. – (c) Open for average 11 days during 1st

cycle; 5 days on future cycles– (d) Closure occurs after ovulation.

• 3. Breeding systems:• (1). Monogamous pairs: • (2). Polygamous Mating

– Used for outbred production – One boar mated with 4-6 sows.

• 4. Litter size– Outbreds: Average litter size 3-4– Inbreds: Average litter size 2-3– Weaning 21 d or 180 g weight

• 5. Placentation• Placentation in the guinea pig is discoid

and hemomonochorial. • 6. Gestation is between 59 and 72 days,

with an average of 68 days; gestation length varies inversely with litter size.

• 7. Newborns• Each newborn weighs between 60 and

100 grams, with individual birth weights inversely proportional to the litter size.

• A birth weight of less than 50 grams usually results in death of the piglet, and litters of more than five piglets are generally stillborn.

• Photo-newborns• The young are precocious. They are fully

haired, with teeth, eyes and ears open. • They are able to eat solid food in the first

week of life; therefore, hand-rearing is not as difficult as in altricial species.

• Young pigs are weaned between 14-28 days, or when a weight of 180 grams is reached.

• 7. Breeding Colony Mortality:– a. Abortions in one report of 8.3%– b. Stillbirth– c. Should weigh 165-240 g at 21 days

• 8. Sexing– a. In young guinea pigs, females exhibit a

"Y"-shaped fold in the genital area. – b. Young males have a slit in the genital

area.

• 1. Have an usually high requirement for certain amino acids (arginine, methionine, and tryptophan) – Requirements can be met by providing 18-20%

protein diet usually of plant origin.• 2. Roughage: Crude fiber should be 13.5%

– Many breeders advocate feeding hay• Decrease boredom and "barbering"

Ⅶ. Feeding and watering

• 3. Dietary requirement Vitamin C – a. Resembles human, require an

exogenous dietary source of Vitamin C (ascorbic acid).

– b. Are unable to convert glucose to ascorbic acid because they lack the microsomal enzyme L-gulonolactoneoxidase.

L-古洛糖酸内酯氧化酶

葡萄糖 抗坏血酸

– c. Ascorbic acid required to: • (1) Prevent scurvy• (2) Maintain natural disease

resistance• (3) To maintain blood complement• (4) Essential of collagen

• d. Deficiency results in:• (1) Formation of defective collagen • (2) Hemorrhages in various tissues

(3) Delayed wound healing• (4) Impaired bone and tooth formation.

• e. Daily Ascorbic Acid requirements: – (1) Immature guinea pigs: 0.5 mg/100 g

body weight – (2) Maintenance (over 300 g BW): 6 mg – (3) Breeding females: 20 mg

• f. Supplementation with ascorbic acid in drinking water or Green Vegetable Supplementation– Carrots, cabbage,

• 5. Diet:• (1) Green grass and vegetables

(2) Are especially fond of alfalfa• (3) Gustation:

– (a) Avoid sweet foods; (b) Reject overly bitter, salty, or chemically pure diets

– Acute hemolytic anemia in response to excess dietary cholesterol (versus cardiovascular lesions in most animals).

• 6. Antibiotic Therapy– (1). Many antibiotics apparently cause

an alteration in the intestinal flora which leads to diarrhea or death within 3-5 days.

– (2). "Toxic" antibiotics include:a. Penicillin b. Bacitracinc. Erythromycind. Clindamycin

a. Lincomycinb. Chlortetracyclinec. Oxytetracyclined. Streptomycin

• (3). "Safe" antibiotics include: – a. Chloramphenicol palmitate（棕榈酸）: 60

mg orally daily for 5-7 days – b. Chloramphenicol（氯霉素） succinate（丁二酸盐）: 10-30 mg/kg BID IM

– c. Sulfamethazine（磺胺类药）: 4 ml of 12.5% solution/500 ml of drinking water for 1-2 weeks

– d. Cephaloridine（头孢噻啶）: 10 mg/day

Table 8.1 Biologic and reproductive data for guinea pigsAdult body weight: Male

FemaleLife spanBody temperatureHeart rateRespiratory rateFood consumptionWater consumptionBreeding onset: Male

FemaleEstrous cycle lengthGestation periodPostpartum estrusLitter sizeWeaning ageBreeding durationChromosome number(diploid)

900-1200 g700-900 g4-5 y37.2°-39.5℃230-380 beats per minute42-104 breaths per minute6 g/100 g/d10 mL/100 g/d3-4 m (600-700g)2-3 m (350-450g)15-17 d59-72 dFertile2-514-21d18-48m64

Ⅱ. Uses

• Guinea pigs have contributed to 23 Nobel prizes for medicine or physiology

• Studies on guinea pigs led to the discovery of: – Vitamin C – The tuberculosis bacterium– Adrenaline.

A. Early Uses

• 1905年，德国医学家。以举世瞩目的开拓性成绩，问心无愧地摘走了诺贝尔生理学及医学奖。

• 从古至今，鼠疫、伤寒、霍乱、肺结核等夺去了人类无数的生命。第一个发现传染病是由病原细菌感染造成的人就是罗伯特·科赫，堪称世界病原细菌学的奠基人和开拓者。

罗伯特·科赫

培养出的纯种结核菌制成悬液,通过注射豚鼠的腹腔实验,4～6周后豚鼠即死于结核病。他用实验证明结核菌不论来自猴﹑牛或人均有相同症状。阐明了结核病的传染途径。1905年发表了控制结核病的论文。

• 1901年获首次诺贝尔生理学或医学奖。德国细菌学家,免疫学家。发现白喉抗毒素。

• 百白破.当时白喉流行,严重威胁儿童生命。• 他用以毒攻毒的中医理论进行研究：

– 首先给豚鼠注射白喉杆菌，得上白喉病，然后药物治疗。结果，数百只豚鼠死掉了，但有两只侥幸存活。把比上次剂量更大的白喉杆菌注射给这两只豚鼠，仍安然无恙。

– 进行了一系列实验之后，贝林决定将实验转向临床治疗阶段。血清疗法的创始人之一 。 儿童的救星

– 第一次世界大战期间,他研制的破伤风免疫血清应用於战伤,他又被誉为“战士的救星”。

贝林

• Guinea pigs were used in development of:– Vaccines for diphtheria, TB – Replacement heart valves– Blood transfusion,– Kidney dialysis– Antibiotics– Anticoagulants– Asthma medicines

• B. Guinea pigs and isolated tissues– In research and testing to develop new

medicines.– Such as guinea pig lung and intestine are

extensively used in research to develop new medicines.

– beta blockers to treat high blood pressure – drugs to treat stomach ulcers– the anti-nausea drugs used by cancer

patients

– The identification of enkephalins. – Study the 'little brain' in the gut, the

workings of nerve circuits. – The information gathered from

these studies is being used to develop computer models.

C. Allergies and respiratory diseases

• The extreme allergic reaction, anaphylactic shock,

• More readily and strongly than most other species.

• Cavia>Rabbit>Dog>Mice>Cat>Frog– Airways are sensitive to allergens, so it has

been widely used in asthma studies, inhaled medications

• They are also used in the testing of vaccines against anthrax

• Currently an important area of biodefenceresearch, and new medicines to treat drug-resistant tuberculosis.

D. Nutrition research• （1）Scurvy

– the oldest known disease caused by a poor diet

– In the 1740s, British sailors, muscle weakness, bleeding under the skin and at the gums, and loss of teeth.

– Later, research on guinea pigs showed that scurvy was due to a lack of vitamin C.

• Vitamin C was discovered using guinea pigs in 1907.

• Most other animals synthesise their own vitamin C.

• （2）Need high levels of– AA,– folic acid, – thiamine, – arginine and potassium

• Useful in nutrition studies• （3）Most of plasma cholesterol in LDL• Useful in the study of cholesterol and

lipoprotein metabolism.

E. Hearing• The structure of ear is similar to that of

humans, and can be exposed and studied easily.

• Display the Preyer reflex used in checking for deafness, in which the outer ear moves in response to a whistle.

• Hair cells are sound-sensing cells that are important in hearing.– In 2003, The first successful attempt to

regenerate hair cells in the inner ear of a mammal was achieved in guinea pigs.

http://tupian.hudong.com/s/%E5%86%85%E8%80%B3/xgtupian/1/3

• 中华耳鼻咽喉科杂志–耳蜗微窥镜应用的初步报告

• 实验方法：10只豚鼠，取单侧耳作耳蜗微窥镜检查，左、右各5耳。

• 手术全身麻醉：氯胺酮70 mg／kg肌肉注射，戊巴比妥钠30 mg／kg皮下注射，将豚鼠固定于操作台上。

• 耳后背侧进路，显微镜下钝性分离皮下组织，暴露听泡．

• 电钻磨开听泡外后壁，小心保护中耳结构，暴露耳蜗底回及圆窗，于近圆窗龛1-1.2 mm处以三棱钻开窗(直径约0.8 mm)

• 电钻磨开听泡外后壁，小心保护中耳结构，暴露耳蜗底回及圆窗，于近圆窗龛1-1.2 mm处以三棱钻开窗(直径约0.8 mm)

• 见外淋巴溢出后，将窥镜沿开窗处插入鼓阶，进入鼓阶的最大深度为4 mm，从窥镜所连接的监视器上观察鼓阶内结构、并摄像。

• 螺旋器（spiral organ）又称柯蒂（Corti）氏器为听觉感受器。由基底膜蜗管面的上

皮细胞所特化，主要由支持细胞和毛细胞构成

微创、保留残余听力的人工耳蜗植入术

F. Safety testing• The long gestation period of 59-62 days

and mature central nervous system at birth means that guinea pigs are important in safety testing– Particularly to prevent birth defects.

• The similarity of their immune system• Their skin sensitivity

– Led to their widespread use to test for allergic skin reactions.

• This use of guinea pigs to test for skin allergies has now been largely replaced by the milder local lymph node assay (LLNA), which uses mice and fewer of them.

• Developed by British scientists, the LLNA was recently endorsed by international validation bodies.

• In 1999, about 18,000 such tests were carried out on guinea pigs in the UK, mostly for non-medical products. This number fell to under 200 in 2004.

• 27,101 experiments using live guinea pigs took place in the UK in 2004.– Representing less than 1% of total animal

research • The use of guinea pigs has fallen by over

three-quarters since 1988, mostly due to a reduction in their use in safety testing

一、动物实验的重要性

Total number of animals used in 2005(EU-25) is 12.1 MioBirds

Pig

Mouse

Rabbit Guinea pig

Rat

Fish

Other species

Total number of animals used in 2002(EU-15) is 10.7 Mio

Infectious Disease

• In 1882, the German scientist Robert Koch used guinea pigs to discover that TB was caused by the bacterium Mycobacterium tuberculosis– immune defence system resemble to human– the sensitivity of the guinea pig to infections– to study infectious diseases.

Immunologic studies• Guinea Pig used extensively for

immunologic studies because the cervical thymus is easily removed

• 2-3 mon, 350~400 g

Ⅷ. GERM FREE GUINEA PIGS• 1. Not commercially available• 2. Impractical to maintain breeding

colonies because enlarged cecumcontributes to poor breeding performance

• 3. Usually obtained by hysterotomy of conventional animals.

• 4. Germ-free neonates are marked by precocious behavior requiring little or no hand feeding, easily reared to maturity.

• 5. First germ-free pigs derived by cesarean section in 1895 (Nuttall and Thierfelder).

青霉素

豚鼠肠道菌代谢

过敏

• 6. Germ-Free vs. Conventional• (1) Cecal distension

– a. Conventional animals' cecum is 15% of body weight, 30% in germ-free.

– b. Same weights as conventional when corrected for increased cecal size.

– c. Predisposes to cecal rupture, herniation, torsion, and uterine prolapse.

– d. Anal and rectal prolapse has increased incidence of about 5%.

• 2. WBC: – Total WBC: 1900 in germ-free vs. 5 -12,000

in conventional• 3. Immunoglobulins:

– a. Gamma globulins same until 8-10 weeks of age, then decrease in germfree to 20-50% of normal.

– b. Hemolytic complement activity same.

• 4. Pregnancy– a. Frequent in germ-free, but rarely reach

term– b. Sows abort; prolapse uterus, often death– c. Cecal distention postulated as cause of

reproductive problems

• 5. Germ-free are slower to develop signs of scurvy.

• 6. Miscellaneous Abnormalities– a. Enlarged gallbladder– b. Decreased muscle tone– c. Thin gut wall– d. Reduced lymphoid tissue

• 7. Germ free guinea pigs uses– Germfree animals are useful as a “culture

medium” for infective agents which otherwise cannot be grown in the laboratory.

– Have more pronounced reaction than conventional counterparts

Ⅸ. Techniques

• A. Handling• easy to handle.• must be supported

when lifted • One hand is placed under the trunk while

the other supports the rear limbs.

B. Identification• Permanent methods include color pattern

records, ear notching and tattoos.• An ear tag, as shown here, is another

acceptable identification method;however, guinea pigs that are group housed may have the tag chewed off.

• Dyes and markers can be used for temporary identification.

C. Blood collection• Cranial vena cava• Blood is sometimes collected from the

cranial vena cava of the guinea pigs, as shown here.

• Other sites for collecting small amounts of blood include the orbital sinus, the marginal ear vein.

C. Blood collection

• Cardiac puncture• Cardiac puncture as a method of survival

blood collection carries a high risk in guinea pigs as it requires anesthesia;

• Hemorrhage into the pericardium also may result in death due to cardiac tamponade.

E. Drug administration

• IM injection• Intramuscular (IM) injections may be given

in the quadriceps muscle, as shown here, to avoid the sciatic nerve.

• IP injection• Intraperitoneal (]P) injections can be made

safely into the lower, left quadrant of the abdomen.

• The guinea pig is tilted with its head toward the floor, to shift the abdominal organs cephalad and help prevent inadvertent injection into the intestine.

• SC injection• Subcutaneous injections can be made by

tenting the skin in the neck area.

• IV, marginal ear vein• Intravenous injection into the marginal ear

vein is possible, but difficult due to the small size.

• Other sites are the saphenous vein and the lingual vein.

• IV, dorsal penile vein• Intravenous access is also possible into

the dorsal penile vein;• however this is a painful procedure and

premedication is necessary.

F. ANALGESICS, ANESTHETICS• Signs of pain• Analgesics should be administered when pain is

observed or expected. • Clinical signs include decreased activity, restlessness,

abnormal gait or posture, rough haircoat, altered patterns of vocalization, and reduced food or water intake.

• Specific signs of pain in the guinea pig may be quite subtle and pain detection is based on a subjective judgment of change from usual behavior in response to a stimulus.

• It is most humane to assume that procedures which cause pain in humans may do so in the guinea pig.

• Analgesics• Analgesic drugs used in the guinea pig

include– buprenorphine (0.05 mg/kg SC at 8 hour

intervals), – morphine (10 mg/kg SC or IM every 4 hours) – meperidine (20 mg/kg, IM or SC, every two-

three hours).

• Pre-anesthetics Guinea pigs can be sedated or preanesthetized using ketamine (50-100 mg/kg IM) or diazepam (5 mg/kg IM or IP).

• Atropine (0.05 mg/kg SC) should be used to decrease bronchial and salivary secretions.

• Anesthesia in the guinea pig is difficult for several reasons,

• including variability in response to various drugs and difficulty monitoring depth of anesthesia;

• postoperative complications also are common. • To attain a surgical plane of anesthesia, a

combination of ketamine (25-40 mg/kg) and xylazine (5-12 mg/kg) can be given IM or IP. Pentobarbital sodium (25-35 mg/kg, IP) is sometimes used to produce surgical anesthesia, although the higher dose rates normally needed are associated with high mortality in guinea pigs.

• Fentanyl-droperidol (Innovar-Veto, Pitman-Moore Inc.) should not be used in the guinea pig at anesthetic dosages, because it has been shown to cause muscle necrosis at the injection site.

• Methoxyflurane• Methoxyflurane is the inhalant anesthetic of

choice for the guinea pig. Anesthesia can be induced in a chamber and maintained with a nose cone.

• Endotracheal intubation is very difficult in the guinea pig due to the small size of the trachea and difficulty in visualization.

• Ether is not recommended; in addition to being flammable and explosive, it is irritating and unpredictable in the guinea pig.

• Post-anesthesia• To prevent hypothermia, an anesthetized

guinea pig should be kept warm on a heating pad and 10-15 ml of warmed lactated ringer's solution can be infused subcutaneously.

• Turning the animal every 30 minutes helps to prevent hypostatic pulmonary congestion.

G. Euthanasia• Guinea pigs may be euthanatized in a

carbon dioxide chamber that is pre-charged prior to use.

G. Euthanasia

• An alternative method is intravenous or intraperitoneal injection of pentobarbital sodium (1 50 mg/kg).

• Intracardiac injection can be used if the animal is already under anesthesia.

• Objectives • Upon completion of the class, you

should be able to:• · describe the unique anatomical and

physiological features of the guinea pig including normal behavioral and reproductive characteristics.

• · state several uses of the guinea pig in research and some diseases in which the guinea pig is the animal model of choice.

• · describe common techniques used on the guinea pig in the laboratory including proper restraint, handling, injection sites, and blood collection sites.

• · state the preferred analgesics, anesthetics, and methods of euthanasia for the guinea pig.

• GOAL– To provide the viewer with information on the

origin, biology, anatomy and biomethodologyof the guinea pig and some uses of the guinea pig in research.

• OBJECTIVES Upon completion of the program, you should be able to:– 1. recognize the common strains and varieties

of guinea pigs. –2. describe normal behavior of the

guinea pig.

–3. describe unique anatomical and physiological features of the guinea pig.

–4. state the age at first breeding for the sow and boar, the gestation length and the weaning age or body weight of the guinea pig.

– 5. state five uses of the guinea pig in research and state the characteristics that make the guinea pig a useful animal model.

– 6. describe the proper technique to handle and restrain the guinea pig.

– 7. identify preferred sites for parenteralinjections and blood collection in the guinea pig.

– 8. list two drugs which can be safely used to anesthetize the guinea pig and state their advantages over other drugs.

– 9. describe signs of pain in the guinea pig.

– 10. list three drugs which may be used as analgesics in the guinea pig.

– 11. describe two humane ways in which guinea pigs may be euthanatized.