Polyphasic growth-weight response in the guinea pig.

An assessment of the growth rate pattern based on longitudinal weight data of guinea pigs was conducted over the presumptive preweaning and early postweaning period. The study covered the minimum of 44 and maximum of 53 days with means calculated for 3-day intervals involving 13 litters and a total of 40 young. Initial analysis showed males heavier than females at birth and both sexes being inversely proportional to litter size at birth. At the end of the experimental period the males were still heavier than the females but their weight distribution peaked in litter of three while the females were heaviest in the largest litters of five and lightest in the litter of one. Phasic linear regression line analysis revealed 4 litters with a triphasic growth outline and 6 litters with quadrophasic growth outline. Final assessments indicate that the total period of 53 days manifests a quadrophasic growth outline while, in contrast, the period specifically involved with the process of lactation and weaning displays a definite diphasic growth spectrum and is comparable to the tri- or quadrophasic spectrum occurring in the albino rats, rice rats and hamsters.

Growth in the myopathic Syrian hamster (Cricetus auratus).

The objective was to assess the effect of the hereditary myopathic disease (muscular dystrophy) on 4 growth parameters: body-weight, head-body length, skull weight and cranial length in the Syrian hamster over a 4-13 month period. A control colony of 34 males and 32 females was compared to a muscular dystrophy colony consisting of 37 males and 27 females. The monthly means of the 4 growth parameters were computed and full data were used for computations of analysis of variance with regression of each group, sex and growth parameter. Intersex and intergroup comparisons of the same parameters were made using analysis of covariance. In the controls, the male bodies were heavier and longer than the female bodies; males grew over the total period. In dystrophic hamsters, males were heavier than females, but females were longer. In both control and dystrophic hamsters, female skulls were longer and heavier. In all parameters the means of the control colony were greater than those of the dystrophic colony relative to age. The disease factor in the muscular dystrophy colony adversely influenced all 4 growth parameters.

Variation in the growth of the preweaning Syrian hamster (Cricetus auratus).

An assessment of the growth rate spectrum based on a longitudinal weight study of golden hamsters was undertaken over the preweaning period. The period covered 23 days with data probes at 24-hourly intervals and encompassed 16 litters providing a birth number of 120 young and a weaning survival number of 82. Subsequent analysis directed initially at the pooled or averaged data showed sex differences with males gaining weight faster than females. Further analysis showed the total period to have three definitive break-points and therefore four phases of growth activity. The segmented linear regression line calculations showed that the phasic duration of males in the second and third phases were two days later than the females. Following data-analysis adjustments and taken into account aberrations of the sample, final indications pointed to the preweaning hamster growth spectrum as quadrophasic, exhibiting a stable first phase, a second and third phase terminating earlier in females and a final weaning weight being heavier in males. The growth curves demonstrated a 'U' shaped outline and formed an integral part of hamster preweaning precocity.

Postnatal somatometry of the rat facial skeleton.

Growth of the rat facial skeleton over a 40 day period from birth was examined relative to 8 length and 4 width parameters of animals subject to somatic growth retardation experimentally induced by overtaxing the maternal lactational capacity by means of excessively large cross-fostered litters. Least squares regression lines were calculated for the preweaning period (day 1-20); the postweaning period (day 21-40) and the total period (day 1-40), thereafter being recalculated into segmented regression lines relative to the physiological growth phases. Specific phases of growth activity were noted throughout the 40 days with those in the preweaning period showing a marked consistency concomitant with the maternal lactational ability and subsequent emergence of biological weaning. A consistent phasic growth spectrum with definitive breaks in continuity supports the original postulate (Brody, 1927) that growth curves consist of phases of exponential activity delineated by changes in growth rate. Due to the inclusion of both control and experimental samples, the breakage points of the phases marking the change of growth rate different and were therefore reciprocated by alterations of phasic duration. Phasic growth occurred in the postweaning period with some degree of variance which did not permit an assessment of the causation factors with sufficient validity. The postweaning period of the experimental sample exhibited varying degrees of growth recovery (catch-up) in the majority of the facial parameters. Covariance analysis of the parameters in most instances showed that the parameters, as defined, and the bone units incorporated within them manifested a characteristic growth response in each sample irrespective of the modifying influence of the environmental factors.

Cranial postnatal growth of the rat relative to environmental variance.

Neurocranial growth during the first 40 days of postnatal development was biometrically investigated relative to the specific parameters of calvarium length and width; basioccipital length and width; basisphenoid length; biparietal width; frontal bone length and cranial vault length. Specimens were obtained from rat litters subject to moderate nutritional suppression by raising the litter numbers above the norm via the cross-fostering technique and causing the overtaxing of the lactational capacity. Alterations in growth rate occurred throughout the pre- and postweaning periods with clearly demarcated phases of growth. Male and female growth in the preweaning period was uniform within each litter type but the phasic growth changes in the experimental litters differed from the control litters with regression line breakage emerging at different points and altering the phasic lengths. The preweaning phasic spectrum in both control and experimental litters was evidently linked to the maternal lactation capacity--relative to quantity and duration. Weaning was insidious in both litter types but occurred earlier in the experimental litters although the continuity of growth was maintained up to the end of the definitive preweaning period (day 20). The definitive postweaning period (day 21-40) showed considerable heterogeneity--unsatisfactory scatter--with differing regression line breakage points and phasic lengths. Analysis based on the total period (day 1-40) brought compensatory adjustments and indicated more acceptable phasic patterns in the postweaning period with confirmation of catch-up growth in the experimental litters. Allometric analysis of the parameters revealed varying rates of growth, line breakage points and differing phasic lengths indicating that each neurocranial parameter and the skeletal unit forming it had an individual characteristic response spectrum mostly attributable to the functional matrix with emphasis on the capsular rather than the periosteal.

Postnatal skull growth of the rat relative to environmental variance.

Rat growth during the first 40 days of postnatal development was examined relative to cranial length, facial height and bizygomatic width of animals subject to nutritional suppression induced by increased litter size during the preweaning period. The postulate (Brody, 1927) that growth curves consist of phases of exponential activity delineated by alterations in the growth rate thus inducing breaks in the continuity was confirmed in the skull. The preweaning and postweaning periods showed three clearly demarcated phases of growth within each period. Breakage points of the phases--alteration in growth rate--differed between the control and experimental litters thus changing the length of the specific phases. Within the preweaning period of both types of litter the phasic characteristics appeared directly linked to the maternal capacity--quantitatively and in duration, while the latter part of the preweaning period and the postweaning period remained within the province of external or non-maternal food supplies. The postweaning of the experimental animals exhibited catch-up growth phenomena in all parameters with a slight variation relative to catch-up growth phenomena in all parameters with a slight variation relative to the sexes. In general terms, analysis of the total period of investigation indicated that growth within the preweaning period was more active although sexual dimorphism was not significant. In addition, relative growth (allometric) analysis of the three parameters showed varying growth rates, breakage points and hence phasic lengths indicating that irrespective of environmental factors that each parameter and the bone units incorporated in it manifested a response as a whole which was characteristic of the parameter.

Growth variability in the rat.

Growth of rats during the first 40 days of postnatal life was investigated in relation to the parameters of head-body length, weight and cranial length on the basis of standard growing litters of 6 young and experimental litters of 12-14 young--the latter exhibiting a range of differences attributable to nutritional suppression. A characteristic triphasic growth spectrum manifested in all the parameters of both sexes and litter type within the preweaning period (day 1-20) of development. In the postweaning period (day 21-40) three phases of growth were also detected during analysis. Growth was shown to be at its greatest potential during the preweaning period but did not exhibit any sexual dimorphism in either type of litter. Differences in growth potential existed between the standard litter and the experimental litter but these did not detract from the overall triphasic pattern apart from slight alterations in the individual phasic length. Analysis of the postweaning period of development showed that growth was considerably slower compared to the preweaning period with sexual dimorphism appearing in the parameters. In addition, relative growth (allometric) analysis of the three parameters indicated that the growth rates differed throughout the whole of the developmental period (day 1-40) irrespective of the conditions imposed on the litter types indicating that each parameter possessed an individual growth response.

Aspects of skull and dentition morphology of the mink (Mustela vison).

The skull morphology of the mink (Mustela vison Schreb) based on a sample of 97 (56 male and 41 female) mink, ranch bred and aged between 7 months to 2 years has been examined to provide the characteristic features of an inbred colony whose ingress into the natural environment by escapes of releases has led to a viable feral population. Behavioural adaptation including breeding of the feral group is confirmed and the need for a cranial morphological base line is therefore paramount if cranial morphological adaptations arising from the feral group are to be compared in the future. Morphological details have been recorded by various drawings, and the characteristics which form part of the species key were noted as: postorbital constriction marked, minimum width behind postorbital processes less than width of interorbital space, tympanic bullae are flattened and broad with anterior edges merging with adjacent bones, length of tympanic bullae greater than width, maxillary molar large with inner lobe expanded lingually until much greater than the outer buccal lobe. Sexual dimorphism was indicated from the skull measurements but was not significant due to the preponderance of immature adults present in the sample.

Hydrocephalus in the laboratory rat.

The state of hydrocephalus is applied to all conditions in which the intracranial volume of cerebrospinal fluid is abnormally large in relation to the volume of the brain. Increase in volume of cerebrospinal fluid raises the pressure and results in brain tissue atrophy and enlargement of the cranial vault. The condition can be hereditary or acquired and commonly arises from congenital malformations, inflammatory processes or expanding lesions such as tumours. The laboratory rat has an incidence of hydrocephalus of about 0.3% but no satisfactory indication of hereditary linkage. A small breeding unit of laboratory rats consisting of 2 males and 3 females produced 32 offspring of which 13 exhibited varying degrees of hydrocephalus. Examination indicated that the hydrocephalus was congenital in type, that 11 of the 13 hydrocephalic rats were proven males, that the remaining 2 were likely to be male, that female young were unaffected and that the incidence of the condition was 40.62%. Craniofacial examination showed that the cranial vault enlarged due to intracranial pressure and that the facial and basal components were mainly unaffected. The olfactory aspect of the frontal bone bulged slightly outwards, medial walls of orbits were laterally displaced, parietal and interparietal showed distention and their related sagittal and coronal sutures unfused and open to 1 mm in places. The basioccipital width showed a significant increase to the normal state. It is postulated that this particular congenital hydrocephalus in the rat is a normal autosome mutation, sex limited to males and one in which both males and females could transmit the trait to male progeny.

Biology of the rice rat (Oryzomys palustris natator) in a laborabory environment. X. Postweaning growth of the skull.

A survey of skull development of the rice rat (Oryzomys palustris natator) covering a period of 21 days to 16 months involving equal numbers of males and females (108) was undertaken using various skull parameters. Sexual dimorphism in relation to body weight and length emerged before that of the skull which was only clearly marked by 2 months. A number of the skull parameters by virtue of their individual growth potential did not show sexual differences in size for a long time, whereas others were clearly marked. Once the differences between the sexes had been established they were maintained. One parameter - lenght of cranium - represents those parameters which show changes and it was found that the male rat continued to show a steady linear increase in length up to 16 months, whereas the female cranial length shows a deceleration with termination around 12 months. The skull differences are mirrored in the weight and length findings and it suggested that the earlier sexual maturity of the females is compensated by an earlier cessation of growth compared to the males which mature later and have a correspondingly later cessation.

Biology of the rice rat (Oryzomys palustris natator) in a laboratory environment. VII. Pre-weaning growth of the body.

Body growth using weight and length parameters have been examined following the introduction of the rice rat to laboratory conditions and a history of breeding covering some 15 generations. The pattern of growth shows a characteristic enphasic form which appears to be determined by the interplay of the external environment and the genetic endowment. The external environmental factors include the waxing and waning of the lactational performance of the mother and the intake of solid food, resulting in the first phase being mainly controlled by the maternal environment, the second phase being mainly controlled by a lessening maternal environment + external (solid food) environment + some genetics, the third phase being influenced by external environment + genetic endowment.