ON THE THYROID MORPHOLOGY AND THE LEVEL OF
MILK YIELD AMONG THE PROGENY OF GOITROUS

AND APPARENTLY NORMAL COWS
Vappu Kossila

Department ofAnimal Husbandry, University ofHelsinki

Received July 6, 1969

Thyroid activity as well as disposition to a goitrous condition are obviously influenced
to a certain degree by hereditary factors.

Individual variations have been observed in the activity and weight of the thyroid
in the same breed of dairy cows. The thyroxine secretion rate (TSR) (Hamblin et al.
1958, Premachandra et al. 1958b) and the level of protein bound iodine (PBI) in serum
(Kossila 1963) were found to vary considerably in individual cows during the same
season. In the same herd, a number of cows had enlarged thyroids while others had
thyroids normal by weight even though all of them had been given the same kind of
feeds (Kossila 1967). According to Schultz (1962), goiter in cattle might be due to a
recessive gene and the condition is not linked with sex.

Significant daughter-dam correlations in respect of the FBI level in winter (r = 0.59),
and seasonal differences in the PBI level (r = 0.73), have been noted by Okamoto et al.
(1963) in cattle. Premachandra et al. (1958a) observed a significant difference in the
TSR in two lines of New Hampshire fowls, selected for three generations on the basis
of their response to feeding thiouracil by variation in the average thyroid weight. The line
with a high thyroid enlargement had TSR 1.02 pg/100 g body weight L-thyroxine, and
the line with the low thyroid enlargement had TSR 2.98 p,g respectively. At present there
is fairly little direct evidence to demonstrate the extent to which endocrine characteristics
pass from dam to daughter in cows. However, according to Turner (1968b) a faster
improvement in dairy cattle would be achieved if the breeding animals (especially the
bulls) were selected on the basis of their hormonal secretion rates, for instance, on the
basis of their TSR. Since the most convenient and reliable methods applied to the esti-
mation of the TSR require the use of 1131,I 131

, and the health regulations today prohibit the
utilization ofmeat from animals treated with this isotope, large scale TSR studies in cattle
meet with particular difficulties. The in vitro uptake by erythrocytes of the 1131-L-triiodoI131-L-triiodo-

https://www.c-info.fi/en/info/?token=jyAyh4DcAMeAyo1q.3f_4QfSxsrHMF1TfOSGOpQ.tCKhOUWCXGiLYlufGQAHiwN860EXPEFqQ_PB428I_-qoWtucw6KFv9LFpje3Fnvf3ts2KGD5Yqvaz-Nybc12pDnoTMs0wRStD7bbkrUPqx3IcbfOtBgXVrac48664VuG90bVlezGGR778HfCA8Gs6M5os-gbU8r0tL8b


214

thyronine is probably not sensitive enough for this purpose, neither is the FBI level in
serum. Since the weight and histological characteristics of the thyroid can be estimated
sufficiently accurately only after the death of the animals, they are not very suitable for
this reason. Besides, the thyroid structure depends largely on certain nutritional factors,
and the structural changes occurring in it are not necessarily associated with corresponding
changes in the TSR.

An attempt has nevertheless been made in this study to ascertain the extent to which
the weight and the epithelial tissue content of the thyroid of so-called normal, slightly
goitrous, and goitrous dam-cows are manifested in their daughters. Attention has been
paid also to the milk yield of the cows, since the thyroid is one of the endocrine glands,
whose function is important in maintaining the milk yield at an optimal level (Turner
1968a).

Material and methods

The thyroids were obtained from cows discarded from the Ayrshire herd of the Viik
Experimental Farm during the years 1958—66. The feeding and management of this
herd has been recently described in detail (Kossila 1967, pp. 32—36).

The percentage of epithelial tissue (E %) in the thyroid specimens was estimated
histoquantitalively by the method of Uotila & Kannas (1952). The accuracy of this
method has been discussed by Tala (1952). The absolute amount of epithelial tissue con-
tained per thyroid gland in grams (Eg) was calculated on the basis of E % and the wet
weight of the gland. The Eg is not influenced by the age of the cow, but it is slightly
affected by the body size (Kossila 1969b). Furthermore, especially in growing (<6O
months old) cows, theEg seems to be a better indicator of goiter than the thyroid weight
(Kossila 1967).

The body weight, corrected for the stage of gestation and/or for the degree of fatness,
was used in this study as an indicator of the body size of the cows, because it was previously
noted that the weight (Kossila 1967, p. 73) and the Eg (Kossila 1969b) of the thyroid
gland, as well as the milk yield (writer’s observation), were more closely correlated with
the corrected body weight than with the live weight of the cows at slaughter. The method
used in estimating the corrected body weight has been explained previously in greater
detail (Kossila 1967, p. 37—39). The relative thyroid weight (BRT = bovine relative
thyroid weight) was obtained by calculating the thyroid weight in grams per 100 kg
corrected body weight. The mean daily fat corrected milk (FCM) yield in kg during the
productional life time of the cow was used as an indicator of the lactational performance.
The age of the cow was also noted, since it is known to affect, among others, the thyroid
weight.

The data, consisting altogether of 51 dams, of which 26 had one daughter, 19 two

daughters, 4 three daughters, and 2 four daughters, i.e. altogether 84 daughters (heifer-
daughters were omitted from this study), was first divided into three groups according to
the thyroid weight of the dam (Table 1). Group I consisted of 29 dams whose thyroids
weighed less than 30 g (apparently normal), group II included 17 dams whose thyroids
ranged from 30 to 50 g (slightly goitrous), and group 111 5 dams with thyroids heavier
than 50 g (goitrous).



215

Table 1. The mean values and standard deviations of the thyroid weight, the BRT, the Eg, the corrected body
weight, age, and the FCM yield of three groups (apparently normal I, slightly goitrous 11, goitrous III) of dams

and in the corresponding groups of their daughters.

Group N Thyroid BRT1 ) Eg 2 ) Corrected Age, FCM3 )

weight, g body months yield, kg
weight, kg

Dams
I 29 24.17 ± 3.14 4.55 ± 0.55 4.81 ± 1.46 497 ±4l 85.6 ± 21.8 14.64 ± 1.36
II 17 38.13 ± 5.82 7.42 ± 1.78 5.37 ± 1.68 507 ±47 107.7 ± 35.4 13.93 ± 1.97
111 5 61.22 ± 5.06 11.46 ± 1.48 6.96 ± 4.88 517 ±37 119.2 ± 35.0 13.48 ± 1.18

II ± 111 22 43.38 ± 11.35 8.34 ± 2.41 5.73 ± 2.68 510 ±45 110.3 ± 34.8 13.83 ± 1.80
I±II ± 111 51 32.46 ± 12.32 6.19 ± 2.49 5.21 ± 2.10 502 ±43 96.2 ± 31.5 14.29 ± 1.65

Daughters
I 42 21.07 ± 5.10 4.18 ± 1.00 4.13 ± 1.06 474 ±49 61.8 ± 24.6 15.06 ± 2.38
II 32 24.51 ± 7.90 4.92 ± 1.26 4.81 ± 1.59 462 ±53 59.8 ± 24.3 13.78 ± 1.98
111 10 31.58 ± 10.21 6.29 ± 2.55 5.61 ± 1.83 489 ±54 64.0 ± 26.9 13.94 ± 1.95

II ± 111 42 26.20 ± 8.90 5.25 ± 1.73 5.00 ± 1.66 469 ±54 60.8 ± 24.7 13.81 ± 1.95
I±II ± 111 84 23.63 ± 7.66 4.71 ± 1.50 4.57 ± 1.44 471 ±5l 61.3 ± 24.5 14.42 ± 2.21

N = Number of cases.
*) 2) 8 ) Abbreviations explained in the text.

Histologically the goitrous thyroids resembled struma hypoepithelialis, medio- & macrofolli-
cularis (ref. Uotila 1957) i.e. colloid goiter. This type is apparently less severe than the
struma hyperepithelialis micro- & mediofollicularis (parenchymatous goiter).

Statistical calculations were done according to Croxton & Cowden (1955).

Results and discussions

The following values, the thyroid weight in g (x,), the BRT-value (x IA ), the Eg-
value (x1B), the corrected body weight in kg (x 2A ), the age in months (x 3), and the
FCM yield in kg (x 4) obtained for the dams in groups I, II and 111, and correspondingly
for their daughters, are presented in Table 1. Also the results obtained after combining
groups II + 111 and all three groups, are given in Table 1. The dam-daughter correlations
obtained for the said factors have been summarized in Table 2.

Thyroid characteristics. Results in Table 1 indicate clearly that the
characteristics of the thyroids of the daughter-cows exhibited trends similar to those of
their dams. The dams as well as the daughters in group I had the lowest thyroid weights
and BRT- and Eg-values, and those in group 111 the highest values, correspondingly.
However, as a whole, the dams had considerably higher thyroid weights and BRT- and
Eg-values than their daughters.

There are a number of factors largely or entirely independent from those inherited
from the dam (effect of sire, nutritional conditions prevailing during the intrauterine



216

Table 2. The dam-daughter correlations in respect of the thyroid characteristics, body size, age, and
FCM-yield of the cows.

Group N Thyroid BRT Eg Corrected Age FCM
weight body yield

weight

I 42 0.13 0.07 0.27 0.22 0.25 0.42**
II + 111 42 0.40** 0.41** 0.24 0.07 0.15 0.22

I + II + 111 84 o.47*** o.49*** 0.30** 0.13 0.16 o.3s***

N = number of dam-daughter pairs
***

=
p <O.OOl

*� = P < 0.01

growth and development as well as later in life, the environmental climate, season ofbirth,
diseases, age at death, etc.) that may cause variations in the characteristics of the thyroid
in the offspring. Some of these factors have been considered in this paper.

Goiter was found in a number of animals slaughtered before the year 1960 from the
Viik dairy herd. This condition was believed to be primarily due to the marginal or low
iodine content of the ration (Kossila 1967, p. 89, 98). In these conditions several dam-
daughter pairs developed goiter while others remained apparently normal. Some examples
of this are given below.

Dam Daughter

Thyroid BRT Age in Name Thyroid BRT Age in
Name weight, g months weight, g months

Joiku 62.20 12.30 125 »Oikku 41.00 9.21 45
Pikku 52.50 11.41 41

Juhla 33.705.03 122 Mallu 26.704.62 70
Ohra 25.005.30 43

Maissi 20.503.88 108 Faija 16.603.61 50
Eini 14.473.63 44

* cow treated with KI by mouth three weeks prior to slaughter.

The results in the above compilation indicate clearly that the thyroid weights and BRT-
values ofthe daughters resembled those oftheir dams; the somewhat lower thyroid weights
in the daughters were apparently due to their ages being lower.

Furthermore, when supplemental iodine, in a form of iodized mineral salt mixture,
was given to the dam during the entire period of gestation, the weight of the thyroid in
the offspring (daughter) tended to become smaller. This phenomenon is demonstrated
in the examples given below.



217
Dam Daughter
Name Thyroid BRT Age in Name Thyroid BRT Age in

weight, g months weight, g months

Makea 46.00 10.70 112 Oikea1 34.65 7.30 65
�lmelä 16.23 3.89 53
�Jalna 17.20 4.51 29
�Korea 3 17.10 3.81 38

Maikki 34.90 5.51 103 Alli 27.30 5.62 55
�Juuri 18.753.77 42

Milli 31.005.27 137 Oili 1 18.503.74 41
Eeli3 19.004.75 30

�Juuli 14.302.73 38

Aamu 28.405.26 108 Haamu3 22.454.17 67
�UIa3 13.902.67 45
�Mummu 11.753.46 31

� the dam received supplemental iodine during the period of gestation from which the daughter
was born.

1 sire R-Jaarli 2 sire V. Aito 3 sire L. Nerokas

The differences in age of the daughters of the same dam in the above compilation are not
large enough to account for the differences noted in their thyroid weights. Moreover, if
the diet contains apparently enough iodine but hardly any goitrogenic substances, the
effect of age on the weight of the thyroid becomes less evident in cows (Kossila 1969a).

Body weight, age, and milk yield. In the present data the body weight
and age of the dams were higher than those of the daughters, whereas the FCM yield
was nearly the same in both (Table 1).

The body weight and age of the dams were the lowest in group I and the highest in
group 111, whereas those of the daughters were the lowest in group II and the highest
in group 111. The FCM yield of the dams and the daughters was highest in group I,
whereas the FCM yield of the dams was lowest in group 111, but that of the daughters
lowest in group 11.

It was previously noted in the same herd (writer’s observation) that the FCM yield
was positively correlated with the corrected body weight of the cows. In order to eliminate
the effects on milk yield of the variations in thebody weight, the FCM yield was computed
to correspond to 500 kg corrected body weight. The results thus obtained for all groups
of dams and, respectively, for the daughters are summarized in the following compilation.

Group Mean daily FCM yield in The difference in favor of
kg/500 kg corrected body wt. the daughters

Dams Daughters kg %

I 14.73 15.87 + 1.14 7.74
II 13.74 14.92 + 1.18 8.59
111 13.04 14.28 + 1.25 9.59

II + 111 13.56 14.73 + 1.17 8.63
I + II + HI 14.24 15.31 + 1.07 7.51



218

According to the above results, the FCM yield per 500 kg body weight has decreased
uniformly from group I to 111 in the dams (by 1.69 kg) as well as in the daughters (by
1.59 kg) the milk yield being consistently higher in the latter. The difference in the FCM
yield in favor of the daughters would obviously have been even larger than indicated by
the above figures, if the daughters had been as old as their dams, because the level of
milk production in the said herd has tended to increase up to the sth 6th calving, i.e.
up to the age of 85—95 months (Kossila & Taskinen 1969), and the mean age of all
daughter cows was only 61.3 months (Table 1).

In addition to the possible effect of the sire, the higher FCM yield of the daughters
may also have been due to a more efficient thyroid function resulting from the normaliza-
tion of the thyroid gland (ref. Kossila 1969a).

Thyroid characteristics versus milk yield. The weight of the
thyroid and the Eg- and the BRT-values were the lowest, and the FCM yield per 500 kg
corrected body weight was the highest in the daughters of group I, whereas the reverse
was true in the dams of group 111 (Table 1). In fact, the larger the thyroid weight, the
Eg-, and the BRT-values, the lower the FCM yield per 500 kg corrected body weight.
A significant negative correlation between the Eg value and the FCM yield was noted
earlier in more heterogenous cow material of the same herd, but only, when goitrous
individuals were included in the data (Kossila 1969b); the thyroid weight, in turn, was
not significantly related to the respective FCM yield (Kossila 1967, p. 73).

Dam-daughter correlations. The dam-daughter correlations, calculated
in respect of the thyroid weight, the Eg, the BRT, the corrected body weight, the FCM
yield, and age at slaughter, have been summarized in Table 2. The coefficients of the
correlations were obtained separately for group I, for groups II -f- 111, and for the entire
material, i.e. for groups I -f- II -f- 111, but not for the groups II or 111 the data being too
limited.

The dam-daughter correlations in respect of the thyroid weight and the BRT (the
effect of body size on the thyroid weight eliminated in BRT) were non-significant in group
I (r = 0.13, r = 0.07 respectively) but significant in groups II + 111 (r = o.4o***,
r = o.4l***) and in the entire material (r = o.47***, r = o.49***). The dam-daughter
correlation in respect of the Eg was significant only in the entire material (r = 0.30**).
When the effect of body weight on the Eg value was eliminated by means of calculating
the Eg as corresponding to 500 kg corrected body weight, the dam-daughter correlation,
r = 0.31**, obtained for the entire material was only slightly closer compared to the
previously presented respective correlation, in which the body weight has not been taken
into consideration. It seems that the dam-daughter correlations in respect of the thyroid
weight and the Eg value were not appreciably influenced by the body weight of the cows.

According to earlier observations (Kossila 1967, p. 76 —79, 88—89), even in conditions
in which the iodine intake was apparently marginal or low, the Eg value was not appreci-
ably influenced by the age of the cow. The thyroid weight and the BRT value, on the
other hand, increased significantly with age in full-grown but not in growing cows( <6O
months old). Furthermore, in the latter the Eg value was superior in revealing the tendency
towards goiter when compared to the thyroid weight. The BRT-value of the dams in the
present data was significantly correlated with age in group I (r = 0.41 **), in groups
II -f- 111 (r = 0.38**), and in groups I -f- II -f- 111 (r = o.4B***), whereas the BRT



219

value of the daughters was not significantly influenced by age (r = 0.18, r = 0.03, and
r = 0.24). It seems quite possible that the dam-daughter correlations obtained in respect
of the thyroid weight and the BRT-value (Table 2) are somewhat influenced by age,
whereas those obtained in respect of the Eg are not.

The dam-daughter correlations in respect of the corrected body weight and age of
cows were closer in group I (r = 0.22 and r = 0.25) than in groups II -j- 111 (r = 0.07,
r = 0.15), or in the entire material (r = 0.13, r = 0.16) (Table 2), but nevertheless non-
significant, suggesting that probably neither the body weight nor age had played a marked
role in dam-daughter correlations concerning thyroid characteristics.

The dam-daughter correlations in respect of the FCM yield were significant in group
I (r = 0.42**) and in the entire material (r = 0.35**) but non-significant in groups
II + 111 (r = 0.22) (Table 2), i.e. in groups consisting of slightly goitrous and goitrous
dams (Table 1).

Conclusions

The results of this study indicate that the tendency towards goiter was transferred
from the dam to the daughter and that in favorable nutritional conditions (after addition
of supplemental iodine) this tendency diminished suggesting that severe inherited enzyme
defects were apparently not involved. It would rather seem that the goitrous individuals
had been less efficient in maintaining a positive iodine balance during certain phases of
their life than the nongoitrous ones.

The FCM yield ofcows in the present data was in inverse relation to the thyroid weight,
the Eg, as well as the BRT values.

Summary

The thyroid morphology and the level FCM yield were studied in 84 dam-daughter
pairs discarded from the Ayrshire herd of the Viik Experimental Farm. Data was divided
into three groups according to the thyroid weight of the dam: less than 30 g in group I,
from 30 to 50 g in group 11, and 50 g or over in group 111.

The following mean values were obtained for the dams and their daughters: thyroid
weight in grams: I 24.17 and 21.07, II 38.13 and 24.51, 111 61.22 and 31.58; thyroid
weight in grams per 100 kg corrected body weight (BRT): I 4.55 and 4.18, II 7.42 and
4.92, 111 11.46 and 6.29; absolute amount of epithelial tissue contained per thyroid in
grams (Eg); I 4.81 and 4.13, II 5.37 and 4.81, 111 6.96 and 5.61; corrected body weight
in kg: I 497 and 474, II 507 and 462, 111 517 and 489; age in months: I 85.6 and 61.8,
II 107.7 and 59.8, 111 119,2 and 64.0; mean FCM yield in kg during productional life-
time; I 14.64 and 15.06, II 13.93 and 13.78, 111 13.48 and 13.94; FCM yield in kg per
500 kg corrected body weight: I 14.73 and 15.87, II 13.74 and 14.92, 111 13.04 and
14.28.

The lower thyroid weight in daughters was apparently due to their lower body weight
and age as well as to the higher iodine content of the ration.

The dam-daughter correlations in respect of the thyroid weight, the BRT, the Eg,
the corrected body weight, age, and FCM-yield were: I 0.13, 0.07, 0.27, 0.22, 0.25, and



220

0.42**, II + 111 0.40**, 0.41**, 0.24, 0.07, 0.15, and 0.22, I + II + 111 o.47***,
o.49***, 0.30**, 0.13, 0.16, and o.3s***.

The results of this study indicate a) that the incidence of goiter was higher in the
progeny of goitrous than in that of normal dams, b) that the incidence of goiter in the
daughters decreased ifthe goitrous dam received supplemental iodine during the gestation
period from which the daughter was born, c) that a heavier thyroid weight resulted in a

lower FCM yield.

Acknowledgements. This study has been subsidized by a grant from the August and
Aino Tiura’s Foundation.

REFERENCES

Croxton, F. E. & Cowden, D. J. 1955. Applied general statistics. 2nd ed. Pitman, London. XVI + 843
pp. Chapt 21.

Hamblin, F. 8., Johnston, J. E. & Schrader, G. 1958. PBI and 1181I181 extrapolation technique as methods
of determining thyroid activity in dairy cows. J. Dairy Sci. 41: 728.

Kossila, V. 1963. Effects of season and stage of lactation on protein bound iodine and total cholesterol
in serum of dairy cows. J. Sci. Agr. Soc. Finland 35: 81 —91.

—»—- 1967. On the weight and basic structural components of the thyroid in dairy cattle. Acta Agr.
Fennica 109.2.

—»— 1969a. On the development of the thyroid weight in the dairy herd of the Viik Experimental
Farm. J. Sci. Agr. Soc. Finland 41: 149—-153.

—»— 1969b. Simple and partial correlations between the epithelial tissue content of the thyroid, the
body weight, age, and level ofmilk yield in Ayrshire cows. Ibid. 41: 154—159.

—»— & Taskinen, P. 1969. Sources of variation in the birth weight of Ayrshire calves. Ibid.
41: 180—190.

Okamoto, S., Goto, I. & Koga, O. 1963. Statistical studies on the inheritance of heat tolerance in dairy
cows. Sci. Bull. Fac. Agric. Kyushu Univ. 20: 211 —215. (ref. Anim. Breed. Abstr. 32: 473, 1964).

Premachandra, B. N., Pipes, W. G. & Turner, C. W. 1958a. Thyroxine secretion rates of two strains
of New Hampshire chickens selected for high and low response to thiouracil. Poultry Sci. 37: 399.

—
»
—

—»— —»— 1958b. Variation in the thyroxine secretion rate of
cattle. J. Dairy Sci. 41: 1609.

Schulz, K. C. A. 1962. The inheritance of the suspectibility of gongenital goitre in Africander cattle in
South Africa. Proc. 2nd Congr. S. Afr. genet. Soc. 90—93.

Tala, P. 1952. Histoquantitative studies on the effect of TSH and thyroxin on the morphology of the
thyroid gland, with special reference to standardisation of TSH. Diss. Helsinki. Acta Endocrin.
X, Suppl. 9.

Turner, C. W. 1968a. What causes high production? Story of the role of the thyroid glands in milk secre-
tion. Mo. Agr. Exp. State Bull. 871.

—»— 1968b. (Personal communication) Department of Dairy Husbandry, University of Missouri,
Columbia Mo. U.S.A.

Uotila, U. 1957. Thyreoideas histofysiologi. Nord. Med. 57:809.
—»— & Kannas, O. 1952. Quantitative histological method of determining the proportions of the

principal components of the thyroid tissue. Acta Endocrin. 11: 49—60.



221

SELOSTUS

EMÄ-TYTÄR TUTKIMUS KILPIRAUHASEN MORFOLOGISISTA PIIRTEISTÄ JA
MAITOTUOTOSTASOSTA VIIKIN AYRSHIRE KARJASSA

Vappu Kossila

Helsingin yliopiston kotieläintieteen laitos

Tutkimusaineisto käsitti 84 vuosina 1958—66 Viikin Ayrshire karjasta poistettua emä-tytär paria..
Tutkimuksessa tarkasteltiin erityisesti kilpirauhasen morfologisia ominaisuuksia sekä maitotuotosta.
Aineisto jaettiin kolmeen ryhmään emien kilpirauhaspainon mukaan seuraavasti: I alle 30 g normaali,.
II 30—50 g lievä struuma ja 111 yli 50 g selvä struuma.

Seuraavat keskiarvot (Taulukko 1) saatiin emille ja tyttärille vastaavasti: kilpirauhasen paino g:
I 24.17 ja 21.07, II 38.13 ja 24.51, 111 61.22 ja 31.58; kilpirauhasen paino grammoina 100 kg tiineys ja/tai
lihavuuskunto korjattua elopainoa kohden: I 4.55 ja 4.18, II 7.42 ja 4.92, 111 11.46 ja 6.29; epiteelisolu-
kon määrä grammoina per kilpirauhanen: I 4.81 ja 4.13, II 5.37 ja 4.81, 111 6.96 ja 5.61; korjattu elo-
paino kg: I 427 ja 474, II 507 ja 462, 111 517 ja 489; ikä kuukausina: I 85.6 ja 61.8, II 107.7 ja 59.8,
111 119.2 ja 64.0; keskim. päivässä tuotannollisina elinaikana tuotettu 4 %:ksi muunnettu maitomäärä
kg:na: I 14.64ja 15.06, II 13.93 ja 13.78, 111 13.48 ja 13.94; vastaava maitotuotos kiloina 500 kg korjat-
tua elopainoa kohden: I 14.73 ja 15.87, II 13.74 ja 14.92, 111 13.04 ja 14.28.

Tyttärien alhaisempi kilpirauhaspaino on johtunut osittain niiden pienemmästä ruumiin koosta ja
alhaisemmasta iästä sekä myös runsaammasta jodimäärästä ravinnossa verrattuna emiin. Tyttärien kor-
keampi maitotuotos on saattanut johtua isän vaikutuksen ohella myös kilpirauhasen normalisoitumisesta.

Tutkimuksessa laskettiin emä-tytär vuorosuhde seuraavien tekijöiden välille; kilpirauhasen abso-
luuttinen ja suhteellinen paino, epiteelisolukon määrä grammoina per kilpirauhanen, korjattu elopaino,
ikä ja maitotuotos (Taulukko 2), jotka koko aineistossa (I + II + 111 ryhmät) olivat vastaavasti seuraa-
vat: o.47***, o.49***, 0.30**, 0.13, 0.16 ja o.3s***.

Tutkimuksessa kävi ilmi, että a) struumalehmien jälkeläisillä kilpirauhanen painui enemmän kuin
normaalilehmien jälkeläisillä, b) jälkeläisten kilpirauhaspaino laski kun jodipitoista rehusuolaseosta oli
annettu struumalehmälle sen tiineyden aikana josta ko. jälkeläinen syntyi, c) mitä painavampi kilpirauha-
nen oli sen alhaisempi oli maitotuotostaso.