THE INFLUENCE OF AGE , LIVE WEIGHT AND GENDER ON THE MORPHOMETRICAL ASPECTS OF THE GOAT BRAIN DURING EARLY POSTNATAL DEVELOPMENT

Monterde. J. GoO A. J. Gonzalez. A. M. Galisteo. E. Agliera: Thelnf/uenceofAge. Li"e Weight And Gender 011 The MOlphollletrical Aspects of The Goat Brain During Ear/r P05111awl Det·elopment. Acta vet. Brno 1998.67: 145-151. The study assessed the effects of age. gender and liver body mass on brain morphometric variables during the early postnatal life. The brains of 44 Florida Sevillana kids (22 female. 22 male) were processed using routine laboratory techniques in order to determine size (linear dimensions). weight and volume. The animals were analyzed at the age of 30.45.60 and 75 days. Over the age-range studied. morphometric variables were found to increase. Analysis of covariance showed that in fact age onl) exerted a significant intluence on brain weight and length: live weight. however. was the main factor of variation for all morphometric parameters except hemisphere width and height. Differences between sexes showed significantly greater intluence of males than of females on brain weight. hemisphere weight and hemisphere length. Bruin morphometry. det·elopmem. growth. width. height Both brain morphometry and craniometry have been the subject of a great deal of controversy, particularly when used in research aimed at correlating brain size with alleged functional aspects. Broadly speaking. the development of the mammalian brain shows that evolution has demanded a considerable increase in the surface area of the brain: the brain is known to develop from smooth surface vesicles which. in the course of growth, fold in upon themselves due to the spatial limits of the cranial cavity (Hofman 1985, 1989). Much more open to debate is the influence of indi vidual factors. such as sex, age or body weight, on the brain growth (Mayhew etaI.1990, 1996). This paper was prompted by an outstanding group of animals in terms of the great number of animals, the homogeneity of breed and the sequential grouping by age, even though it was limited to the early postnatal development. Kids belonged to a batch used for experimental carcass research by the University of C6rdoba Animal Production Department. and were kindly donated by that department for present research purposes. The principal aim of this study was to chart the evolution of the morfometric variables (weight. volume and linear dimensions) of goat brain during early postnatal development. A further essential aim of the study was to examine the correlation between these morphometric parameters and growth factors (age and weight) for each sex. Addre"s for Correspondence: J. G. \l\)nt~rJl! DepartJnll!llto de AI1.ttomia) Anatomia PatoI6gi-:,\ CornpJrad.l"> Facultad de Ve(('rinaria Calk \kJinJ. Alahara "in :\0 C6rdob.l [-l-005, E..,pai'la Pholl(,: +J...\. 95721 866.1 Fa\.: +.1...j. 95721 8666 E-mail: an I gallloj 0 U('ll.e~

Both brain morphometry and craniometry have been the subject of a great deal of controversy, particularly when used in research aimed at correlating brain size with alleged functional aspects.
Broadly speaking.the development of the mammalian brain shows that evolution has demanded a considerable increase in the surface area of the brain: the brain is known to develop from smooth surface vesicles which. in the course of growth, fold in upon themselves due to the spatial limits of the cranial cavity (Hofman 1985(Hofman , 1989)).Much more open to debate is the influence of indi vidual factors.such as sex, age or body weight, on the brain growth (Mayhew etaI.1990(Mayhew etaI. , 1996)).
This paper was prompted by an outstanding group of animals in terms of the great number of animals, the homogeneity of breed and the sequential grouping by age, even though it was limited to the early postnatal development.Kids belonged to a batch used for experimental carcass research by the University of C6rdoba Animal Production Department.and were kindly donated by that department for present research purposes.
The principal aim of this study was to chart the evolution of the morfometric variables (weight.volume and linear dimensions) of goat brain during early postnatal development.A further essential aim of the study was to examine the correlation between these morphometric parameters and growth factors (age and weight) for each sex.

Materials and Methods
This study was made using the brains of 44 Florida Sevillana kids (H err era et al. 1991)  Following slaughter in an abattoir.brains were removed through a cranial opening and immediately weighed to the nearest decigram on an electronic balance.Brain volume was measured by liquid displacement, using a graduated cylinder containing an isotonic tluid.Brains were subsequently fixed in 10% formol, in which they remained for at least two months prior to processing.After this period.brain weight and volume were measured again to assess possible changes induced by the fixation process.
The following linear dimensions were then measured: length at pyramids (i.e.length from frontal pole to decussatio pyramidum).maximum width (maximum distance between temporal lobes of both hemispheres), and maximum height (maximum distance from the basilar surface to the dorsal surface).
The two cerebral hemispheres were separated by a midline slice through the corpus callosum.For each hemisphere, the forebrain was separated from the midbrain at the level of the colliculus rostralis.Only one of the two hemispheres was used for the present study, and was selected at random for processing; the other was kept in solution.
The weight.volume.length and width of each hemisphere were measured using the routine techniques described earlier.Hemisphere height was the same as the brain height already measured.

Statistics
Means and standard deviations for each variable were calculated using routine statistical procedures.Variance was analyzed using a two-way analysis of variance (ANOV A) to test for the main effect of age and sex, and Scheffe's multiple range test to compare group means. .Given the interrelation of age and sex with body weight, an analysis of covariance (ANCOV A) was performed 111 ordeno ascertain the true intluence of these factors on each variable.A simple ANCOVA model was used, taking regression with respect to live weil!ht.
Finally.correlation coefficient~ between different variables and simple linear regression equations were calculated as a f~nction of age and live weight.
In all c~m'pansons, the null hypothesis was rejected at a level of significance of 0.05.
(s.~.ls~;~Ustlcal tests were performed using the General Linear Models Procedure of Statistical Analysis System

Results
Brain weight and volume were slightly modified by the fixation process.Modifications are shown in Table 2, which also indicates the shrinkage/swelling correction factor applied (i.e. the ratio of "fresh" data to "preserved" data).Figures for brain weight and volume in the remaining Tables are those obtained after fixation (i.e. after shrinkage/swelling).Findings obtained for each variable by the total batch are summarized in Table 3.This table show means and standard deviations (in brackets) by sex and by group for each of the variables studied: brain weight (BW); hemisphere weight (HW); brain volume (BV); hemisphere volume (HV); brain length (Bl); hemisphere length (Hl); brain width (BWd); hemisphere width (HWd); brain/hemisphere height (HH).This Table highlights those cases in which ANOV A revealed significant differences due to age or sex; age-related differences are further broken down into specific inter-mean differences as revealed by Scheffe's multiple-range test.An analysis of covariance was performed to determine the effect of age, sex and live weight on morphometric variables, considering regression as a function oflive weight.Sexgroups (male and female) and the age-groups described earlier were used for this purpose (Table 4).
The analysis of covariance revealed a clear influence of sex on brain weight, hemisphere weight, brain volume and brain length.An ANCOV A was therefore perfonned for each sex, in order to ascertain the effect of age by measuring regression with respect to live weight (Table 5).The following conclusions can be drawn from the results obtained: 1. Live weight was the main source of variation for practically all the variables studied.2. Age exerted a significant effect on brain weight and length.3. Sex mainly affected brain weight, hemisphere weight, brain volume and brain length.Separate analyses of covariance traced these effects -with the exception of brain length -to males.
Only hemisphere width and height appeared not to be influenced by any of the three factors (weight, age and sex).
The present study also recorded carcass weight and head weight.Since these three weight parameters are closely inter-related (Table 6), live weight was treated as influencing factor; the effects of this factor on brain growth are equally applicable to carcass weight and head weight.Correlation coefficients for total variables studied are also shown in Table 6.Various regression models were tested; those which best fitted the results of the present experiment were simple linear regressions (Table 7).
In the case of age, significant regressions were recorded for brain weight (BW), brain length (BL).All morphometric variables showed significant or highly significant regression for live weight.with the exception of hemisphere width and height.

Influence of fixation on morphometric variables
Brain measurements are modified by the fixation process.A number of authors have reported that formol causes shrinkage of tissues (B auc hot 1967;Sass 1982;U Y lings et al. 1986).Nevertheless.morphometric data always refer to fixed brains, due to the practical difficulties involved in handling "fresh" brains.
In the present study.and as evidenced by the correction factors shown in Table 2, shrinkage through fixation was negligible.These correctors could.if required.be used to relate morphometrical data to live-brain data.

Influence of age and live weight on brain growth
One of the main purposes of this study was to correlate brain growth, in morphometric terms.with the general growth of the animal.To that end.experimental animals were grouped sequentially by age, in order to chart the effects of age on morphometric development of the brain.Live weight.one of the main indicators of general somatic growth, was also recorded.
There is evidently a close relationship between age and body weight during growth; increase in weight with age is so significant that it is generally used as a measure of the normality of growth.It would consequently appear reasonable to assume that age and body weight would prompt similar variations in morphometric data.This would undoubtedly have been the case if the age groups studied had been separated by intervals sufficiently wide to ensure a similar differentiation in live weight distribution between age groups.However, in the present study the interval between age-groups was so narrow that there was no clearly differentiated distribution of live ISO weight.This is seen in the oscillation of body weight (within normal levels) shown in Table I. although body weight increases progressively with age, there is some overlap of ranges for each group.
This may account for potential interference between factors: the effects of one factor (e.g.age) may increase, mask or cancel out the effects of another (e.g.live weight).It is thus necessary to identify these effects in order to ascertain the real influence of each factor on growth.
Discriminant analysis of age and live weight as sources of variation in brain development yielded some interesting results.Although both factors are closely related, they are open to differring interpretations.Age represents a chronological development closely linked to the maturation ofbrain structures and circuits.At the same time, body weight represents somatic growth. of which brain growth is equally a part.
Since results here were expressed in terms of age groups.age was taken as the factor of variation for the first analysis of \'ariance (Table 3); Results of analysis of covariance for variables studied as a function of age, sex and live weight (Table 4) showed that in fact age only exerted a significant influence on brain weight and length.Weight, however, was found to influence brain weight (P<O.OOI), hemisphere weight (P< 0.05), brain volume (P < 0.001), hemisphere \'olume (P < 0.00 I), brain length (P < 0.0 I) and hemisphere length (P < 0.00 I).Weight was thus the main factor of variation for all morphometric parameters except hemisphere width and height.Variations in brain weight and length were attributable both to live weight and age.F values for age and live weight express their relative importance: 2.86/25.50for brain weight and 2.91/8.12for brain length.Live weight thus exeI1s greater influence than age, the difference being almost ninefold in the case of brain weight and threefold in that of brain length.
As Table 6 shows, carcass weight and head weight were both closely related to live weight.The effect ofli\'e weight as a factor influencing variations in brain morphometry is therefore also applicable to carcass weight and head weight.
Results of ANCOV As, correlations and regressions suggest that, irrespective of live weight, increasing age is accompanied by increasing brain weight and, to a much lesser extend, brain length.This correlates with the need for cerebral structures to develop and mature with age, regardless of the space available, which is fundamentally determined by live weight.

Influence of gender on brain growth
Differences between sexes were highlighted by both the analysis of variance (Table 3) and that of covariance (Table 4) performed.Both analyses for the total number of experimental animals showed significantly greater influence of males than of females on brain weight, hemisphere weight and hemisphere length.
The ANCOV A performed to separate the effect of gender from the effect of live weight yielded similar results, suggesting that the interaction between sex and live weight was negligible.
ANCOV As were performed for each gender in order to identify the factors giving rise to the differences mentioned above (Table 5).The results showed a highly significant effect of age and live weight on brain weight, hemisphere weight and hemisphere volume, but only in males.The strong influence of age, and particularly of live weight, recorded in males only is striking.Possible genetic or hormonal causes may be adduced to account for the fact that inter-sex differences for these variables are determined by males.However, a reasoned explanation of the causes, rather than mere speculation on a number of possibilities, lies beyond the scope of this paper.
from the Sevilla Provincial Council Animal Health and Production Service (Spain).Kids (22 male.22 female) were divided into four age-groups as follows: group I. 8 females and 8 males.30 days old. group II. 4 females and 5 males.45 days old. group III.7 females and 6 males.60 days old. group IV. 3 females and 3 males.75 days old.Table I shows live weight.carcass weight and head weight, by groups and as batch totals.

Table I
Data for Ih'e weight, carcass weight and head weight by group and for total batch divided by gender

Table 2
Effects of fixation on brain weight and brain volume, with corresponding corrector factors

Table 3 !
\lean and standard deviation (in brackets) for morphometric variables (all animals)

Table 4
Analysis of covariance for variables studied as a fundion of age, sex and live weight Re~ression con,idered as a function of li\'e weil!ht.**:F values statistically significant for P~O:05.P~O.OI and P~O.OOI.respecti\,elyTable 5Analysis of covariance for variables for which intersex differences were found *. t".***.***: F values statisticaly significant for P~O.OI and P~O.OOI.respecti\'ely

Table 7
Simple linear regression analysis