Cull guinea pigs: carcass and non-carcass traits in males and females compared to their fattening counterparts.

Culling of guinea pigs can provide a large number of animals per year for meat production, but little information is available in the scientific literature on the carcass characteristics and non-carcass components of these animals. The objective of this study was to evaluate the carcass and non-carcass characteristics of cull guinea pigs in comparison to their fattening counterparts. Forty-eight fattening (3 months-age, 24 females and 24 males) and forty-eight cull (14 months-age, 24 females and 24 males) guinea pigs were slaughtered and carcass yield, linear measurements, tissular composition, and non-carcass components were evaluated. In general, cull guinea pigs had higher carcass, tissue, and non-carcass component weights. Cull male and both female guinea pig groups had similar carcass yields. Cull animals had higher carcass and hind leg lengths, lumbar and thoracic circumferences, and carcass compactness than their young counterparts. However, a sex effect was found for leg compactness depending on whether they were fattened or cull. Tissue percentages values were similar between fattening and culling animals of the same sex. However, females had a higher percentage of fat tissue than males. Fattening females had the best muscle to bone ratio, followed by cull males. The non-carcass elements were more represented in fattening animals than in culls, probably due to an allometric growth of the viscera in relation to the rest of the body. In commercial and cooking terms, this information is valuable for producers and researchers who need to understand the factors that influence carcass characteristics of guinea pigs.

Effects of feeding flaxseed on performance, carcass trait, and meat fatty acid composition of Guinea pigs (Cavia procellus) under northern Peruvian condition.

A study was conducted to determine the effects of flaxseed supplementation on performance, carcass traits, and hindleg fatty acid composition of guinea pigs. Sixty male and female weaned guinea pigs (1 month old, five animals/cage) were blocked by sex and bodyweight and randomly fed 0 (control) or 100 g/kg flaxseed concentrate diets (15 g/animal) plus ad libitum fresh alfalfa for 30 days. Results showed that flaxseed supplementation had no influence on animal performance. However, final body weight (P = 0.035), total feed intake (P = 0.019), and body weight gain (P < 0.001) were higher in male than female guinea pigs. Similar results were also observed for carcass composition (i.e., hot, chilled, and reference carcass weights). Inclusion of flaxseed reduced saturated (P < 0.001), mono-unsaturated (P = 0.004), and increased (P < 0.001) polyunsaturated (PUFA) fatty acid concentrations in hindlegs. Concentrations of linolenic acid and n-3 PUFA increased (P < 0.001) by 49.7 and 37.1%, respectively as a result of flaxseed inclusion. It was concluded that feeding flaxseed to guinea pigs at 100 g/kg of the concentrate diets improves meat PUFA concentrations with no adverse effects on performance or carcass composition.

Cortisol during adolescence organises personality traits and behavioural syndromes.

Despite the growing evidence for the importance of developmental experiences shaping consistent individual differences in behaviour and physiology, the role of endocrine factors underlying the development and maintenance of such differences across multiple traits, remains poorly understood. Here, we investigated how an experimental manipulation of circulating glucocorticoids during early adolescence affects behavioural and physiological variation and covariation later in life in the precocial cavy (Cavia aperea). Plasma cortisol concentrations were experimentally elevated by administering cortisol via food for 3 weeks. Struggle docility, escape latency, boldness, exploration and social behaviour were then tested three times after individuals attained sexual maturity. In addition, blood samples were taken repeatedly to monitor circulating cortisol concentrations. Exogenous cortisol affected mean trait expression of plasma cortisol levels, struggle docility and escape latency. Repeatability of cortisol and escape latency was increased and repeatability of struggle docility tended to be higher (approaching significance) in treated individuals. Increased repeatability was mainly caused by an increase of among-individual variance. Correlations among docility, escape latency and cortisol were stronger in treated animals compared to control animals. These results suggest that exposure to elevated levels of cortisol during adolescence can alter animal personality traits as well as behavioural syndromes. Social and risk-taking traits showed no correlation with cortisol levels and were unaffected by the experimental manipulation, indicating behavioural modularity. Taken together, our data highlight that cortisol can have organising effects during adolescence on the development of personality traits and behavioural syndromes, adding to the increasing evidence that not only early life but also adolescence is an important sensitive period for behavioural development.

Could an increase in airway smooth muscle shortening velocity cause airway hyperresponsiveness?

Airway hyperresponsiveness (AHR) is a characteristic feature of asthma. It has been proposed that an increase in the shortening velocity of airway smooth muscle (ASM) could contribute to AHR. To address this possibility, we tested whether an increase in the isotonic shortening velocity of ASM is associated with an increase in the rate and total amount of shortening when ASM is subjected to an oscillating load, as occurs during breathing. Experiments were performed in vitro using 27 rat tracheal ASM strips supramaximally stimulated with methacholine. Isotonic velocity at 20% isometric force (Fiso) was measured, and then the load on the muscle was varied sinusoidally (0.33 ± 0.25 Fiso, 1.2 Hz) for 20 min, while muscle length was measured. A large amplitude oscillation was applied every 4 min to simulate a deep breath. We found that: 1) ASM strips with a higher isotonic velocity shortened more quickly during the force oscillations, both initially (P < 0.001) and after the simulated deep breaths (P = 0.002); 2) ASM strips with a higher isotonic velocity exhibited a greater total shortening during the force oscillation protocol (P < 0.005); and 3) the effect of an increase in isotonic velocity was at least comparable in magnitude to the effect of a proportional increase in ASM force-generating capacity. A cross-bridge model showed that an increase in the total amount of shortening with increased isotonic velocity could be explained by a change in either the cycling rate of phosphorylated cross bridges or the rate of myosin light chain phosphorylation. We conclude that, if asthma involves an increase in ASM velocity, this could be an important factor in the associated AHR.

Growth performance and reproductive function impairment of glyphosate-based herbicide in male guinea pig (Cavia porcellus).

Glyphosate formulations, widely applied non-selective systemic herbicides, are progressively becoming the most controversial pesticides on the market due the adverse effects they pose to humans and environment. The information on these potential hazardous effects to the handlers of the pesticide remains obscure. This study investigated effects of glyphosate-based herbicide on growth performance, seminal parameters and hemato-biochemical profiles in male guinea pig. Forty sexually mature male guinea pigs weighing between 393.3 and 418.4 g were divided into four groups of 10 animals each and orally administered 0, 186, 280 and 560 mg/kg body weight of WILLOSATE daily for 60 days. Daily feed intake and body weight gain were recorded. At the end of experimental period all animals were humanely sacrificed, and blood samples and vital organs were collected for appropriate analysis. Results showed a significant decrease (p < 0.05) in body weight gain (-102.2%), final body weight (-9.8%) and feed intake (-13.1%) of animals following sub-chronic exposure of WILLOSATE. The weights of the liver and kidney increased significantly (p < 0.05) by 25.4% and 28.8%, respectively, while testicular weights decreased (p < 0.05) by 24% with increasing doses of WILLOSATE. A decrease in sperm motility (-67.9%), viability (-52.7%) and concentration per vas deferens (-40.7%), and an increase in sperm major (28.1%) and minor (45.3%) morphological aberrations were recorded in WILLOSATE - exposed guinea pigs when compared to controls. There was a dose-dependent increase (p < 0.05) in MCV and WBC and a decrease in Hb content and RBC, as well as serum content in total protein (-11.8%). The serum content of cholesterol (37.8%), urea (87.1%), creatinine (22.4%), ALAT (74.2%) and ASAT (88.7%) were significantly higher in treated groups compared to controls. These results point toward the toxic effects of WILLOSATE on vital organs and reproductive function of the body at high doses and long-term exposure.

Effects of nutritional quality during early development on body weight and reproductive maturation of guinea pigs (Cavia aperea f. porcellus).

In many species, somatic and reproductive maturation are sensitive to seasonally-fluctuating environmental conditions such as food quality. The protein content of the diet during early development has been considered to be particularly important, a low-protein diet during gestation and lactation typically delaying growth and reproductive onset. To investigate the effects of maternal and early postnatal diet quality on body weight and puberty of male and female domestic guinea pigs, we fed F0-mothers either a low-protein (14%, LQ-group) or a high-protein diet (23%, HQ-group) during gestation and lactation. Their male and female offspring received the same respective diets until six weeks of age; afterward they were switched to an intermediate control diet. Body weight of F1-subjects was significantly affected by the dietary treatment. Reproductive parameters were only affected in F1-females but not in F1-males. We conclude that in guinea pigs, growth is sensitive to the quality of the maternal and early postnatal diet, and that reproductive maturation is more sensitive in females.

A comparison of the growth performance, carcass traits, and behavior of guinea pigs reared in wire cages and floor pens for meat production.

To achieve efficient production of guinea pigs for meat, it is essential to determine the most suitable housing system. A total of 220 guinea pigs were maintained in either wire cages (n = 11, 10 animals per cage) or floor pens (n = 11, 10 animals per pen) containing a deep litter of woodchips, both housing systems having the same dimensions (2 × 1 × 0.4 m). Growth traits, food intake and feed conversion ratio were recorded weekly and expressed as the difference between the two groups. After 77 days, the animals were slaughtered, and carcass traits were evaluated. Growth performance and carcass trait parameters, as well as mortality and behavior trends, were not affected by the housing system type. Nonetheless, the use of wire cages is recommended for raising guinea pigs since water, urine and feces pass through the wire floor, resulting in cleaner animals.

Estimation of the selenium requirement of growing guinea pigs (Cavia porcellus).

The aim of the study was to determine the selenium (Se) requirement of guinea pigs as a species unable to synthesize ascorbic acid. Forty-nine male guinea pigs (average weight 208 +/- 3.5 g) were divided into an initial status group and six experimental groups. The animals received a Se deficient Torula yeast based basal diet (<0.02 mg Se and 26 mg alpha-tocopherol/kg) or a Se addition of 0.05, 0.10, 0.15, 0.20 and 0.25 mg/kg diet as sodium selenate for 10 weeks. There was no significant difference in weight gain (final weight 643 +/- 21 g) between the groups and no clinical symptoms of Se deficiency occurred. With the exception of the testes, there was an increasing Se concentration in liver, plasma and haemolysate dependent on supplementation level. Glutathione peroxidase was determined in the plasma and Se dependent glutathione peroxidase (GPx1) in haemolysate, liver, kidney, heart and lung. Thioredoxin reductase (TR) activity was measured in liver, kidney and heart and deiodinase activity in the liver. A phospholipid hydroperoxide reducing activity with Se influence was determined in liver, kidney, heart, testes and brain. With the exception of GPx1 activity in heart and haemolysate and TR activity in the kidney, all enzymes already reached their maximal activity at 0.05 mg Se/kg diet. The activities of GPx1 and TR were used as parameters for broken line analysis and a Se requirement of 0.080 mg Se/kg diet was derived as sufficient for growing guinea pigs adequately supplied with vitamin E.

Guinea pig for meat production: A systematic review of factors affecting the production, carcass and meat quality.

In developing countries, interest in guinea pig farming is growing exponentially because it provides a regular source of high quality animal protein for domestic consumption. Guinea pigs (Cavia porcellus) are prolific animals, grow and are capable of reproduction on a flexible diet, and are adaptable to a wide range of climates. This article mainly reviews findings on guinea pig meat production, including factors affecting raising guinea pigs, carcass and meat quality. We also present some studies that describe biological and pathologic effects on carcass component composition. During the last decades no standard procedure has been established for guinea pig carcass evaluation, which makes very difficult any comparison of results with other studies around the world. Herein we highlight a variety of factors that significantly affect carcass and meat quality. Some of these factors are production systems, environmental and genetic factors, management systems, the diet and health status, age, sex and reproductive management.

The use of ultrasound to assess fetal growth in a guinea pig model of fetal growth restriction.

Fetal growth restriction (FGR) is a common and potentially severe pregnancy complication. Currently there is no treatment available. The guinea pig is an attractive model of human pregnancy as placentation is morphologically very similar between the species. Nutrient restriction of the dam creates growth-restricted fetuses while leaving an intact uteroplacental circulation, vital for evaluating novel therapies for FGR. Growth-restricted fetuses were generated by feeding Dunkin Hartley guinea pig dams 70% of ad libitum intake from four weeks before and throughout pregnancy. The effect of maternal nutrient restriction (MNR) on dams and fetuses was carefully monitored, and ultrasound measurements of pups collected. There was no difference in maternal weight at conception, however by five weeks post conception MNR dams were significantly lighter ( P < 0.05). MNR resulted in significantly smaller pup size from 0.6-0.66 gestation. Ultrasound is a powerful non-invasive tool for assessing the effect of therapeutic interventions on fetal growth, allowing longitudinal measurement of fetuses. This model and method yield data applicable to the human condition without the need for animal sacrifice and will be useful in the translation of therapies for FGR into the clinic.

Normal development of refractive state and ocular dimensions in guinea pigs.

PURPOSE: This study investigated changes in refraction, corneal curvature, axial components and weight of posterior sclera in guinea pig eyes during the normal development from birth. METHODS: Sixty-four guinea pigs were assigned to eight groups (n=8 each). Each group underwent a series of ocular measurements at one of the eight time-points (0, 1, 2, 3, 5, 7, 9 and 11 weeks), including refraction (streak retinoscopy), corneal radius of curvature (CRC; keratometry), anterior segment length (AS: corneal thickness and depth of the anterior chamber), thickness of the crystalline lens (CL), vitreous chamber length (VC; all A-scan ultrasonography) and dry weight of a circular 6mm diameter punch in the posterior sclera (electronic balance). Results of all the measurements were statistically compared between right eye and left eye, male and female and among different age groups. Artifacts of retinoscopy due to small eye artifact were also estimated at different ages. RESULTS: The refraction in guinea pig eyes was +5.22+/-0.23 D (Mean, SE) at birth. This value decreased rapidly during the first 3 weeks followed by a slow decline. The overall decrease in refraction was highly significant from birth to 11 weeks (p<0.001 one way ANOVA). The small eye artifact was approximately 4.00 D at birth, which reduced to 2.76 D at 11 weeks. The guinea pig eyes were emmetropic by 3 weeks of age when the small eye artifact was taken into account. The CRC (3.24+/-0.01 mm at birth), AS (1.20+/-0.01 mm at birth), CL (2.72+/-0.03 mm at birth) and VC (3.28+/-0.01 mm at birth) increased within the first 3 weeks despite a transient decrease in the CRC within the first week. The increase in CRC, CL and VC continued after 3 weeks, however, the AS remained constant after this age. The increase in VC was better correlated to the decline of hyperopia (R(2)=0.70) than the other components (R(2)=0.33-0.39). Dry weight of the posterior sclera increased linearly from birth (p<0.001 between any two close time-points from 3 to 9 weeks) and had a moderately linear correlation with the VC (R(2)=0.60). There were no significant differences between the right eye and left eye or between male and female in all the measurements. CONCLUSIONS: In guinea pigs, the hyperopia present at birth rapidly reduces to emmetropia within the first 3 weeks of age. The emmetropization process in guinea pigs is mainly related to the increase in the vitreous chamber length. This relationship in guinea pigs is similar to that in chickens, tree shrews, primates and humans. The axial development of the vitreous chamber in guinea pigs appears to be associated with tissue growth of the posterior sclera.

Within-litter differences in personality and physiology relate to size differences among siblings in cavies.

Many aspects of an animal's early life potentially contribute to long-term individual differences in physiology and behaviour. From several studies on birds and mammals it is known that the early family environment is one of the most prominent factors influencing early development. Most of these studies were conducted on highly altricial species. Here we asked whether in the highly precocial cavy (Cavia aperea) the size rank within a litter, i.e. whether an individual is born as the heaviest, the lightest or an intermediate sibling, affects personality traits directly after birth and after independence. Furthermore, we investigated whether individual states (early growth, baseline cortisol and resting metabolic rate) differ between siblings of different size ranks and assessed their relation to personality traits. Siblings of the same litter differed in personality traits as early as three days after birth. Pups born heaviest in the litter were more explorative and in general more risk-prone than their smaller siblings. Physiological state variables were tightly correlated with personality traits and also influenced by the size rank within litter, suggesting that the size relative to littermates constitutes an important factor in shaping an individual's developmental trajectory. Our data add valuable information on how personalities are shaped during early phases of life and indicate the stability of developmentally influenced behavioural and physiological traits.

[Acute toxicity of LDS, a molluscicide, to non-target organisms].

OBJECTIVE: To evaluate the acute toxicity of 10% LDS, a new molluscicide, to non-target organisms. METHODS: Based on "Chemical pesticide environmental safety test evaluation standard", an acute toxicity test was carried out with Coturnix coturnix japonica (quail), Apis mellifera L (bee), Bombyx mori (silkworm), and Brachydonio rerio (zebra fish) , and the skin stimulus test was also performed with guinea pig. RESULTS: The quails had no toxic symptoms while the maximum poisoning concentration of LDS was 200 mg/kg (no toxicity). LC50 of bees was 2.68 x 10³ mg/L (low toxicity). After 96 hours, no silkworms died in each group of different concentrations of LDS while the most concentration was 6.00 x 10² mg/kg, but there were some toxic symptoms such as inappetence and inactive in the high concentration group as compared to the blank control group (low toxic). LC50 (96 h) of zebra fish was 6.16 mg/L (medium toxicity). CONCLUSIONS: LDS has no toxicity to Coturnix coturnix japonica, low toxicity to Apis mellifera L and Bombyx mori, and medium toxicity to Brachydonio rerio. Compared with niclosamide ethanolamine salt, the toxicity to the fish is lower, and therefore, it is more suitable for the field application.

Labeling of pyramidal and nonpyramidal neurons with lectin Vicia villosa during postnatal development of the guinea pig.

Labeling of cortical neurons with a lectin, Vicia villosa (VVA), was investigated in guinea pigs aged 1 day old to adult. Lectin histochemistry revealed a perineuronal sheath, which outlined the cell bodies, apical dendrites, and axon initial segments, in distinct populations of pyramidal and nonpyramidal neurons. Their laminar positions were segregated, with the pyramidal neurons confined to layer 5 and the nonpyramidal neurons distributed mainly in layers 3-5. The VVA-labeled substance(s) was detected at the interfaces between neurons and cellular elements present in the perisynaptic region, including glial processes and fine axons. However, it was excluded from synaptic clefts of presynaptic terminals. Double immunohistochemistry revealed that most of the VVA-labeled neurons were also labeled perineuronally with a monoclonal antibody, Cat 301, and vice versa. Dendritic patterns of the VVA-labeled pyramidal neurons were studied further by intracellular injection of Lucifer yellow into fixed slices. Apical dendrites had a considerable thickness before arborizing into a few daughter branches in layer 3 or 4, suggesting a morphological resemblance to intrinsic, bursting pyramidal neurons defined physiologically in vitro. During postnatal development, there was a global spatiotemporal pattern in the onset of VVA labeling of the cortical neurons. The labeling progressed from medial and posterior cortical areas, which are closely related to the hippocampal formation, to more lateral and anterior areas, which are less closely related. The labeling patter thus tends to follow the order of the phylogenetical development of the isocortex.

Neuropeptide Y immunoreactivity in cutaneous sympathetic and sensory neurons during development of the guinea pig.

Different levels of the cutaneous vasculature are innervated selectively by subpopulations of sympathetic neurons distinguished by the presence or absence of immunoreactivity (-IR) for neuropeptide Y (NPY). This study used multiple-labelling immunohistochemistry to examine the appearance of NPY-IR in neurons innervating cutaneous vessels in the ear pinna of embryonic, fetal, and neonatal guinea pigs. NPY-immunoreactive axons were detected in the ear bud at embryonic day 25. However, these axons lacked IR for tyrosine hydroxylase (TH) and often ran in bundles with substance P (SP)-immunoreactive axons close to the epidermis. Many neuronal somata in the cervical dorsal root ganglia (DRG) at late embryonic stages contained NPY-IR with or without SP-IR, but no NPY-IR was detected in DRG or subepidermal axons by late fetal stages. IR for calcitonin gene-related peptide increased in DRG neurons from midfetal to late fetal stages, after the decrease in NPY-IR. Populations of TH-IR neurons with or without NPY-IR were present in the superior cervical ganglion (SCG) from midembryonic stages. TH-immunoreactive axons were not detected in the ear pinna until midfetal stages, when axons with TH-IR and NPY-IR innervated proximal arteries and TH-immunoreactive axons without NPY-IR innervated distal vessels. Vasoactive intestinal peptide-IR was detected transiently in most fetal SCG neurons with TH-IR and NPY-IR but was not detected in cutaneous axons. These results demonstrate that selective expression of NPY by subpopulations of sympathetic neurons occurs prior to innervation of their targets. This suggests that target contact is not required to establish appropriate patterns of expression of peptide neurotransmitters by cutaneous sympathetic neurons.

Development of convergent synaptic inputs to subpopulations of autonomic neurons.

Visceromotor neurons in mammalian prevertebral sympathetic ganglia receive convergent synaptic inputs from spinal preganglionic neurons and peripheral intestinofugal neurons projecting from the enteric plexuses. Vasomotor neurons in the same ganglia receive only preganglionic inputs. How this pathway-specific pattern of connectivity is established is unknown. We have used a combination of immunohistochemical, ultrastructural, and electrophysiological techniques to investigate the development of synaptic inputs onto visceromotor and vasomotor neurons in the celiac ganglion of guinea pigs. Functional synaptogenesis occurred primarily from early fetal (F30-F35) to midfetal (F36-F45) stages, after the neurochemical differentiation of vasomotor and visceromotor neurons but before establishment of their electrophysiological phenotypes. Intestinofugal inputs were detected only on presumptive visceromotor neurons located primarily in medial regions of the ganglion. The number of ultrastructurally identified synaptic profiles increased in parallel with functional synaptogenesis, especially in medial regions, where dendritic growth rates also were higher. However, the expression of immunoreactivity to choline acetyltransferase in the terminals of inputs was very low until late fetal stages, after functional transmission already had been established. These results show that peripheral intestinofugal neurons directly establish appropriate functional connections with their target visceromotor neurons simultaneously with the development of functional preganglionic inputs to both visceromotor and vasomotor neurons. It seems likely that synaptogenesis occurs independently of the neurochemical differentiation of the target neurons but is closely related to the pathway-specific dendritic development of those neurons.

Follicular development in the immature guinea-pig.

A method for making statistical comparisons between populations and types of antral follicles within the ovary of the immature guinea-pig is described. This was used to demonstrate that atresia in the antral follicles first appeared at around 14 days of age, but that the population of healthy antral follicles remained remarkably consistent throughout the second half of the prepubertal period, since neither the total number of healthy antral follicles nor the proportion of atretic follicles changed significantly. However, the maximum diameter of the antral follicles gradually increased with age, from 400 micron at 7 days to 1000 micron at 28 days, 4 days before the vagina first opended. Because the percentage distribution of all types of follicles was so consistent at any age, although individuals showed substantial differences in the numbers of follicles within each ovary, it is suggested that mechanisms operate which regulate the total population of antral follicles within the ovary.

Changes in the concentration of follicle-stimulating hormone in plasma during development in the guinea-pig.

The concentration of FSH in the plasma of guinea-pigs from day 50 of gestation to day 45 of postnatal life was assayed by a radioimmunological procedure utilizing a cross-reaction with the NIAMDD S6 antiserum to rat FSH. At 68 days of gestation the mean plasma FSH concentration of female foetuses was greater than that of the males, although the concentrations in the two sexes were similar on day 50 of gestation. Maternal levels remained consistently low throughout gestation. Postnatally there were no marked changes in plasma FSH levels through to maturity, although a transient rise in the male occurred over the first 3 days after birth. Gonadectomy on days 0, 5, 10, 15, 25 or 35 of postnatal life, or when adult, resulted in a significant increase in plasma levels of FSH within 10 days. The rise in plasma FSH concentration was greater in males than in females at all ages, although, a larger increase was observed in females spayed at 5 or 10 days of age than at other times.

Changes in the concentration of luteinizing hormone in plasma during development in the guinea-pig.

The concentration of LH in the plasma of guinea-pigs from day 50 of gestation to day 45 of postnatal life was assayed by radioimmunoassay utilizing a cross-reaction with anti-ovine LH antiserum. The effect of gonadectomy in infancy and in the adult upon the plasma concentration of LH was also studied. The LH concentration in the plasma of male or female foetuses was high immediately prenatally and fell at birth. High levels of LH were again detected in male, with a lesser increase in female, guinea-pigs over the first 10 days postnatally. Maternal plasma concentrations of LH remained consistently low. Removal of the gonads on days 0, 5, 10, 15, 25 or 35 of postnatal life, followed by blood collection at autopsy 10 days later, caused a significant rise in plasma LH content at all ages. The rise in plasma LH after gonadectomy in adults was less marked in male than in female guinea-pigs.

Isolation of an insulin-like growth factor II cDNA from guinea pig liver: expression and developmental regulation.

Insulin-like growth factor II (IGF-II) cDNA was isolated from adult guinea pig liver by polymerase chain reaction (PCR) screening. A cDNA sequence was obtained corresponding to part of the preproIGF-II, including the signal peptide, the mature IGF-II and 37 amino acids of the acid carboxy-terminal E-domain. Amino acid sequence prediction, based on the cDNA clone, showed that mature guinea pig IGF-II has a high homology with both human and rat IGF-II, 100 and 94% identity, respectively. Levels of IGF-II mRNA in guinea pigs of different ages were analyzed by solution hybridization/RNase protection assay using part of the isolated IGF-II cDNA as a probe. There is a marked developmental regulation of IGF-II after birth. IGF-II mRNA levels were high in fetal livers, and decreased 15- to 30-fold in adults. As in man, but in contrast to rats, adult guinea pigs have significant levels of IGF-II mRNA in the liver. In fetal guinea pigs, the expression of IGF-II mRNA was 5-, 2- and 70-fold lower in kidney, skeletal muscle and brain cortex, respectively, than in liver. IGF-II mRNA levels in kidney and skeletal muscle of fetal guinea pigs were 5- and 4-fold higher, respectively, compared with adults. Similar sizes of IGF-II mRNA transcripts could be observed on Northern blots in newborn rats and in fetal guinea pigs. Our conclusions are that the mature IGF-II peptide in the guinea pig is 100% identical to the mature peptide in the human.(ABSTRACT TRUNCATED AT 250 WORDS)