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Ovine prenatal growth, its mathematical description and the
effects of maternal nutrition
J. J. ROBINSON I. McDONALD
Rowett Research Institute, Bucksburn,
Aberdeen AB2 9SB (Scotland).
are made different of that have
Summary. Comparisons eight types equation
among
been used to describe the of the foetus in the last 12 weeks of The
growth sheep gestation.
to the because it sensible extra-
is others estimates on
Gompertz equation preferred provides
to 25 after and its can be in
polation days mating parameters interpreted simple biological
terms. A standardised form of the can be in foetal
Gompertz equation employed comparing
growth patterns between species.
Reviews are presented of the literature on the effects of maternal nutrition on foetal
in and and the are discussed in
growth early, middle late pregnancy respectively, findings
relation to estimates of foetal and rate at each derived from a
weight specific growth stage,
Gompertz equation fitted to foetal data.
The lack of a model for foetal has contributed to
satisfactory development disagree-
different effects on different foetal
ment on whether maternal under-nutrition has organs
and effects and that a of
tissues. It is concluded that there are differential recent extension
a
the to embrace the allometric clearer and more
Gompertz equation relationship provides
of than the
generally applicable model for describing the growth foetal constituents does
allometric itself.
equation by
Introduction.
are of limited value as a substitute for
Mathematical basic
equations very biologi-
at conditions. with
cal data unless can least three should the
they satisfy (i) They agree
data, to limitations the of the latter. should
subject only imposed by variability (ii) They
tenable outside the of the data. It should be to
yield extrapolations range (iii) possible
interpret the parameters of the equation in simple biological terms.
Many published equations describing pre-natal growth are concerned only to
and can
the first of these do little more than convenient des-
satisfy conditions, provide
the When all three conditions are the
of data. satisfied, however,
criptions equation
to the identification and of from
can be a aid interpretation differences one set
powerful
can more be into models
of data to and of and
another, safely incorporated growth
the whole Graham et al., In the
production involving reproductive cycle (e. g. 1976).
a
we number that have been used to
describe
paper compare of equations pre-
present
in we review the evidence on the of
natal growth sheep, modifying effects maternal
we discuss
on foetal and some of these effects in the
nutrition of the
development light
preferred equations.
to from
foetal time
Equations relating weight conception.
all the data on foetal in have been confined to
Nearly published growth sheep the
so it has to a
final 12 out of the total 21 weeks of and been fit great
gestation, possible
some of which are shown in table 1. The
variety of equations, extrapolative capabilities
of with as in the
each used the values of the constants
equation, given original publica-
it a 25
tion, have been tested to estimate the of foetus at from
by using weight days
On the basis of a review of the literature et at., and of
conception. (Robinson 1977),
and this is of
additional observations Robinson, data), weight the
(Rhind unpublished
order of 0.25 g. The estimates from the in table 1 were 273,
equations respectively
-
and 102 from
- 5.5, 0.36, 3.7, 1.6, 0.29, 0.33 the
g. Apart Gompertz equations, only
the law an estimate of the correct order of
« self-adjusting power » gave magnitude.
of
A of the the is in
further comparison extrapolative qualities equations given
which shows how estimated 1 dy varies with the
figure 1, the specific growth t,
rate, y dt ,
foetal It is that a
decreases at rate
age. generally accepted specific growth decreasing
with for the equation, which has
increasing gestational age. Except Gompertz by
definition an specific growth rate, only the self.adjusting power
exponentiallydecreasing
law exhibits a of the the of
curve even correct over whole
approximately shape gesta-
in
and the latter is anomalous the in that the rate
tion, very early stages specific growth
tends to as decreases towards zero.
infinity gestational age
the of
law satisfies the first and second our criteria
Although self-adjusting power
for a as as it is inferior
almost well does the the third
growth equation Gompertz, by
in for of the
criterion, that there is no interpretation the values para-
simple biological
an
meters b and c. Those for the have such as has
a, Gompertz equation interpretation,
been described and Barton Laird and et al.
by Laird, Tyler (1965), (1966), Robinson
and we therefore that the is to be more
(1977), may argue Gompertz equation likely
useful in the of data than of the other examined. One
analysis growth any equations
little known transformation of can to ovine
the be used set the
relatively equation pre-
natal growth pattern in the context of that for other species.
As described Laird there is a standard form of the Gompertz equation
by (1966),
within n
can a useful basis for of foetal both
which provide comparisons growth patterns
and linear transformations of both the
between species. By axes, equation
= - of the transformed
can be to the standard form In Y e-0,1266T. In terms
changed
In the new
and time all data then fall on a curve.
weight scales, Gompertz single growth
scale, Y, each foetal is as a fraction of the value.
weight weight expressed asymptotic
is 0 to the time of maximum
The time scale determined two T = corresponds
by points ;
foetal rate, and T = -1 to the time at which foetal is half
growth corresponds weight
= is a considerable
of that at T 0. 0.368 and There
(Values of Y are respectively 0.184.)
to events
of between in the values of T which the
degree agreement species correspond
of in have combined results
and as can be seen in table which we
conception birth, 2,
given by Laird (1966) and more recent measurements.
Nutrition and early foetal growth.
The tiny absolute foetal growth rates in very early pregnancy would appear
to to in the nutrition of ewe and effects of
unlikely be vulnerable changes the any
nutritional on birth such as those shown Black
change subsequent weight, by Speedy,
and Fitzsimons are to be indirect and mediated effects on condi-
(1978), likely by body
tion. rates are 100 even as late
day
Conversely, specific growth very high (16 p. per
as to
and make the vulnerable sudden stress. Most nutritional
day 40) may embryo any
studies have focussed attention on survival rather than on growth and it has been
that losses accentuated increased
are condition,
suggested embryo by poor body by
duration
of and also the
under-feeding by over-feeding during pre-implantation phase.
reviewed the results and that induced seldom
Edey concluded losses
(1976) nutritionally
exceed 15
p. 100.
is to to
There increasing evidence that during the 0 16 the
suggest period days
of the is influenced endocrine in
growth embryo by factors, particular the circulating
levels of blood progesterone (Wintenberger-Torres, 1967 ; Lawson, 1977), and that
these an alteration in the amino-acid balance of uterine fluid
may operate through the
and Whether or not these endocrine
(Ménézo 1976). changes
Wintenberger-Torres,
can be linked to nutrition or stress rise to enhanc-
directly nutritionally imposed giving
ed adrenal activity Smith and Gunn, remains to be
(Doney, 1976) proved.
have been few at of
There attempts direct measurement effects of early maternal
nutrition on foetal Foote and Price did not difference
Hulet, detect
weight. (1969) any
in foetal at 21 or 30 between ewes
weight days offered 75 p. 100 and others offered
150 100 of their
maintenance from onwards.
p. requirements Simi-
energy conception
larly, EI-Sheikh et al. and Foote et al. found no effect of nutrition
(1955) (1959) of plane
on foetal or at 40 was an on
weight crown-rump there effect
length days, although
chorion weight.
Nutrition during the second and third months of pregnancy.
the end of this the rate of the
By period specific growth foetus has fallen to under
6 100 absolute rates are to
Although increase the
p. per day. growth beginning rapidly,
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