SOME QUANTITATIVE DATA ON THE ROLE OF THE RUMI-
NANT PROVENTRICULI IN THE DIGESTION AND ABSORP-

TION OF NITROGEN-FREE ORGANIC MATTER

L. Paloheimo, A. Mäkelä and M.-L. Salo

Department of Animal Husbandry, University of Helsinki

Received April 25, 1955

A critical review of earlier investigations

The earliest ideas regarding absorption from the ruminant stomach were based
en anatomical findings. The enormous extension of the mucous membrane of the
proventriculi led investigators to the view that absorption of digested food must
occur in these compartments of the digestive apparatus (7, p. 66; 10, p. 145; 14,
p. 189). Kühn (1.e.), referring to the rich network of blood capillaries in the laminae
of the omasum, ascribes to this stomach a special absorptive capacity. On the other
hand, Colin in 1873 (ref. 8, p. 187) on anatomical grounds denies any absorptive
power to the proventriculi. He refers to the cutaneous and stratified character of
the epithelia concerned and does not admit for them any greater absorptive capacity
than for the epidermis of the skin. Ellenberger (1, p. 863) also denies that the
proventriculi have any noteworthy absorptive capacity. The reason alleged by him
is rather curious: »Wenn daselbst lebhafte Aufsaugung stattfände, dann würde
wegen Eintrocknung des Inhaltes das Wiederkauen unmöglich werden.» As for the
omasum, Ellenberger refers to his own experiments, which had given negative
results. According to Mangold (8, 1.e.) these experiments were made in vitro with
fragments of mucous membrane. Adopting Colin's and Ellenberger's line of reason-
ing, Mangold emphasizes the absence of absorptive power in the mucous membrane
of the proventriculi. He postulates that the water-soluble substances formed in the
proventriculi are absorbed by the portal blood only on reaching the small intestine.

Trautman (15, p. 178), re-examining the histology of the mucous membrane
of the proventriculi, admits the possibility of a remarkable absorptive capacity.
In his experiments a rapid absorption of some alkaloids was established. Phil-
i.ipson and McAnally (12, p. 199) were the first to give evidence of the absorption

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SOME QUANTITATIVE DATA ON THE ROLE OF THE RUMINANT 71

of volatile fatty acids from the proventriculi. In their experiments sheep with
both rumen and abomasal fistulae were used. In the abomasum the concentration of
volatile fatty acids was found to be insignificant and did not increase significantly
after feeding, while in the rumen the concentration was considerable. It was con-
cluded that at least the bulk of the acids were absorbed from the proventriculi.
Later the same authors (ref. 13, p. 17) showed »that blood draining the rumen,
reticulum, omasum, and caecum carried a higher concentration of volatile acids
than peripheral blood.» Taking into consideration the volume of blood draining
the rumen and reticulum, and the gross area of the surface of these compartments,
Barcroft, McAnally and Phillipson (ref. 13, 1.e.) established that in sheep from
1 to 5 g of volatile acids, expressed as acetic acid, were absorbed from the rumen
and reticulum per hour.

Using the iron of the food as tracer and taking samples from the rumen contents
of sheep at different intervals after feeding, Rathnow (ref. 6, p. 255) found that in
3 hours 32 %, in 6 hours 48 %, and in 9 hours 59 % of the dry matter of hay was
digested.

Hale, Duncan and Huffman (3, p. 953) criticize the use of iron as tracer and
are of the opinion that Rathnow's method is not reliable for determining rumen or
total digestion coefficients. By a somewhat similar technic, but using lignin as
tracer, these authors (ibid.) studied the digestion of alfalfa hay in the rumen of the
cow. (Although the term »rumen» is used, rumen together with reticulum must be
meant.) They used a cow with a rumen fistula, the rumen being evacuated before
the first feeding with the hay to be examined. Then followed a preliminary feeding
period of at least 12 days, and at the close of this period, 14 hours after a certain
meal, the rumen contents were removed, weighed, sampled for chemical analysis,
and replaced in the rumen. This procedure was repeated twice for each level of
feeding (10, 20, or 30 lbs hay per day). Using the same hay, digestion trials for
determining the coefficients of total digestion were performed with other cows. On
the basis of the increase in the percentage of lignin, the »coefficients of rumen
digestion» were calculated and compared with the »coefficients of total digestion».
It is, however, apparent that these two groups of coefficients are incommensurable.
The latter coefficients express the percentages of the different food constituents
absorbed from the alimentary tract or disappeared in the form of CH4 and C02

during passage. »The coefficients of rumen digestion», however, cannot reveal the
amounts of food constituents absorbed from the rumen or disappeared from it
in the form of gases. It is evident that the percentage of lignin in the rumen contents
14 hours after feeding is appreciably higher than in the food ingested, not only
because a certain amount of food constituents have been absorbed from the rumen,
but also because the products of digestion have been transferred from the rumen-
reticulum to other compartments of the digestive tract. These transferred products
of digestion may be included in the part of the food digested in the rumen, but this
concept of digestion is not the same as in the usual digestion trials. It is evident,
too, that the undigested particles transferred have not the same lignin content as
the contents remaining in the rumen. On the contrary, it is probable that these



particles have on the average a lower content of lignin because the more tender
parts of the hay and easily suspended particles may be transferred sooner than the
coarser fragments. Thus it is not surprising that in some cases in the experiments
of Hale et al. the digestibility of protein in the rumen appears to be nearly 100 %

(in one case 99.5 %) of the total digestibility of the protein. Errors of the same kind
must also be included in the figures pertaining to other food constituents. Later
the named authors (4, p. 733) have criticized their method described above, but
they still maintain that »it is unlikely that any appreciable passage of plant particles
not yet thoroughly subjected to the disintegrative action of the rumen would take
place». This statement, however, can hardly be valid. In their following paper
(5, p. 747) they describe investigations made with two rumen fistula cows. The
method used was in principle the same as in the experiments related above. Samples
were removed from one of the cows at 6 and 12 hours and from the other cow at 14
and 24 hours after feeding. A period of from 1 to 2 weeks was allowed between the
removals of rumen contents to ensure complete resumption of the normal function
of the rumen. Alfalfa hay was used also in these experiments. In the interpretation
of their findings the authors are this time more cautious than in their previous paper.
But much of the criticism directed above at the earlier experiments of Hale et al.
must also be applied to their later investigation and especially to the interpretation
of its results. Moreover, the terms used are highly misleading: they still speak of
»rumen digestion coefficients» and of disintegration of alfalfa hay in the rumen.
Both expressions are alike misleading. However, because the inaccuracy of the
method used tends to give, in our opinion, too high »rumen digestion coefficients», the
figures relating to the disappearance of cellulose from the rumen in all probabilitv
have the right tendency. They give the impression that during the first 6 hours
after feeding the disintegration of cellulose is rather slight. During the following
6 hours it is most intensive and from the 12th to the 24th hour almost negligible.
To the question of the absorption of the products of digestion from the rumen the
investigations of Hale et al. do not give any answer.

Gray (2, p. 15) has also used the lignin ratio method in investigating the
extension of the digestion of cellulose in the rumen of sheep. The number of experi-
mental animals was four. Gray determined not only the digestibility in the rumen
but also the total digestibility and the digestibility in the omasum, abomasum, small
intestine, caecum, and colon. The technic used by him differed in principle from
that of Hale et al. The sheep were fed for some weeks on a constant ration composed
of wheat straw and alfalfa hay. Then the animals were slaughtered, samples of
ingesta taken from different compartments of the digestive tract, and cellulose and
lignin determined from the samples. The principle in determining the digestibility
in different compartments was the same as is generally used in determination of
total digestibility. For instance, in determining the digestibility in the rumen-
reticulum, Gray compared the cellulose-lignin ratio of the food with the correspond-
ding figures of the ingesta in the omasum. However, as a considerable absorption
of volatile fatty acids probably occurs in the omasum and as the omasum functions
as a filter press, the figures proposed by Gray as rumen digestion coefficients must

2 L. PALOHEIMO, A. MÄKELÄ and M.-L. SALO



SOME QUANTITATIVE DATA ON THE ROLE OF THE Rl VNT 73

be somewhat too high if these coefficients are to be understood in the same way
as the usual coefficients for total digestion. As the absorption from the abomasum
is minimal and as the separation of solid and fluid fractions of the ingesta brought
about by the omasum is reversed in considerable degree in the abomasum, it is
possible, using the figures presented by Gray, to compute the digestion coefficients
for the proventriculi as a whole. Thus it appears that there disappeared in the
proventriculi 40—45 % of the cellulose of the food eaten, which makes 67—75
% of the total digestibility of this component. But there is still one obscure
point in Gray's experiments. It is evident that the results obtained are in some
degree influenced by the time elapsing between the last feeding and the slaughtering
of the animal. In our opinion slaughtering should take place in the middle of the
period between two feeding times. On this point Gray gives no information, but
one must suppose that he has arranged his experiments in the said way.

Marshall (9, p. 1) has used Gray's technic in investigating the digestion
of the pentosans in hay by two sheep. The digestion in the proventriculi was about
30 %, which makes about 67 % of the total digestion of pentosans. As the author
mentions that the rumen contained much recently ingested material, one may
conclude that the slaughtering did not take place in the middle of the period be-
tween two feeding times.

Own experiments

In their investigation on the rate of passage of food in the digestive tract of cattle,
Paloheimo and Mäkelä (11, p. 165) have determined the percentage of lignin,
N-free organic matter, and X-free non-lignin organic matter in hay and in the
corresponding ingesta of the abomasum. The animals, 14 cows and 5 young bulls of
about 7 months old, were fed with hay (mainly timothy) thrice daily during a period
of 10 days. The individual animals received the same amount of hay at every
feeding time (three times daily) and the feeding intervals were uniform. After 10
days the animals were slaughtered 4 hours after the last feeding and the contents
of the different parts of the alimentary tract were measured and examined. The
experiments were spread over a longish period and for this reason the quality of
the hay was not quite the same for the different animals. The method of lignin
determination used by us gives, when applied to hay, lignin which is indiges-
tible in ruminants.

As one may see, the results of our experiments make it possible to calculate the
digestibility of N-free organic matter and N-free non-lignin organic matter in the
proventriculi according to the principle used by Gray. In table 1 the results for
individual animals are shown. One sees that, although the hay eaten by individual
animals was not of exactly the same quality, the results are fairly uniform. As
the amount of ingesta in the abomasum is always relatively small, it is presumable
that the sample taken from this compartment cannot always be representative of
the material transferred from the proventriculi. This inaccuracy, however, seems
not to have had any greater detrimental effect on the results of the experiments.



L. PALOHEIMO, A. MÄKELÄ and M.-L. SALO74

Table 1. Digestibility of N-free organic matter and of N-free non-lignin organic matter in the provent
riculi and in the whole digestive tract of cows and young bulls.

Digestibility of Digestibility of N-free
Animal Hay dry- N-free organic matter non-lignin organic matter Ratio

matter ; a: b
... a) in the b) in the a) in the b) in the
, proventri- whole proventri- whole

culi digestive culi digestive
% tract % tract

%

Cow 1 10.67 52.23 60.52 57.47 66.60 0.86
» 2 4.14 56.26 62.94 61.89 69.31 0.89
)> 3 2.48 57.74 63.29 63.59 69.61 0.91
»> 4 2.48 52.87 67.93 58.18 74.72 0.78
»> 5 6.30 56.46 64.81 62.61 71.93 0.87
» 6 6.76 50.55 57.47 56.67 64.44 0.88
»> 7 3.38 53.70 61.37 60.19 68.81 0.87
» 8 3.38 49.37 56.96 55.34 63.83 0.87
» 9 6.00 56.43 63.23 62.37 69.87 0.89
» 10 6.00 57.13 64.64 63.21 71.46 0.88
» 11 4.08 53.39 62.14 59.14 88.86 0.86
» 12 4.08 57.61 66.03 63.64 73.04 0.87
»> 13 2.40 48.31 63.53 53.51 70.38 0.76
» 14 2.40 53.01 62.65 58.81 69.41 0.85

Young bull 1 3.49 55.37 60.68 58.91 65.15 0.90
»> 2 4.12 59.57 60.22 63.80 64.59 0.99
» 3 3.53 54.74 63.11 58.12 67.99 0.86
»> 4 3.77 57.99 61.40 61.98 65.95 0.94
» 5 4.26 55.92 60.52 59.48 64.93 0.92

As the lignin is considered to be indigestible, it follows on arithmetical grounds
that the ratio between the digestibility in the proventriculi and the total digesti-
bility must be the same independently if the calculation is made on the basis of
N-free organic matter or on the basis of N-free non-lignin organic matter. The table
shows that of the total amount of N-free non-lignin organic matter digested in the
whole digestive tract, 76—99 % is digested in the proventriculi. If the cows Nos.
4 and 13 are left out, the limits in the cows are 85 and 91 %. The average for the
cows is 86 % and for the heifers 92 %. The ratio in question seems to be indepen-
dent of the amount of hay eaten.

The amount of dry matter in the ingesta of the abomasum was determined in
the ordinary way, without taking into consideration the volatile fatty acids. As the
amount of these substances in the ingesta of the abomasum is very small, the
inaccuracy caused by this omission must be negligible. According to some later
studies by one of us (Mäkelä) the total of volatile fatty acids, both free and bound,
calculated as acetic acid, in the contents of the abomasum varied in 5 cows and
2 calves from 0.17—0.98 % of the drv matter.



SOME QUANTITATIVE DATA ON THE ROLE OF THE RUMINANT 75

As hay contains only a small amount of lipids in proportion to carbohydrates, the
fraction »N-free non-lignin matter» amounts to almost the same as carbohydrates.
Thus the figures pertaining to the first-named fraction must be nearly the same as
those pertaining to the carbohydrates.

The terms »digested» and »digestibility» are used in this investigation in the
same sense as in the usual digestion trials. Hence the percentage of N-free non-
lignin organic matter digested in the proventriculi means the relative amount of
the fraction in question which disappears from the alimentary tract during the
sojourn in the proventriculi. As the main part of what disappears is absorbed in
the blood vessels and a smaller part is removed as gases, the results of our investi-
gation strongly support the view that in cattle the carbohydrates are digested
mainly in the proventriculi and their degradation products are absorbed principally
from these stomachs.

Summary

Fourteen cows and five young bulls were fed with hay uniformly during 10 days.
After slaughtering, the ingesta of the abomasum were removed and sampled. From
the hay, from the contents of the abomasum, and from the feces lignin, N-free
organic matter, and N-free non-lignin organic matter were determined. Using the
lignin ratio principle, the digestibility of the two N-free fractions was calculated
both for the proventriculi and for the whole digestive tract. It appeared that of
the total amount of the N-free non-lignin organic matter digested in the whole
digestive tract, 76—99 % was digested in the proventriculi. If the results for two
of the cows are discarded, the limits in the cows are 85 and 91 %. On the basis
of this investigation it can be concluded that in cattle carbohydrates are digested
mainly in the proventriculi and their degradation products are absorbed principally
from these stomachs.

REFERENCES

(1) Ellenberger, W. 1890. Vergleichende Physiologie der Haussäugethiere I. Berlin.
(2) Gray, F. V. 1947. The digestion of cellulose by sheep. The extent of cellulose digestion at succes-

sive levels of the alimentary tract. J. Exp. Biol. 24.
(3) Hale, E. B. & Duncan, C. W. & Huffman, C. F. 1940. Rumen digestion in the bovine with

some observations on the digestibility of alfalfa ha)-. J. Dairy Sei 23.
(4) Hale, E. B. & Duncan, C. W. & Huffman, C. F. 1947 a. Rumen digestion studies I. J. Nutrition

34.
(5) Hale, E. B.& Duncan, C. W. & Huffman, C. F. 1947 b. Rumen digestion studies 11. Ibid.
(6) Jarrige, R. 1953. I. utilisation des glucides alimentaires par les ruminants. Ann. de la nutrition

et de l'alimentaticn 7.
(7) Kühn, Julius. 1873. Die zweckmässigste Ernährung des Rindviehes. Dresden.
(8) Mangold, E. 1929. Handbuch der Ernährung und des Stoffwechsels der landwirtschaftlichen

Nutztiere 11. Berlin.



(9) Marshall, R. A. 1949. The digestion of pentosans in hay by sheep. Brit. J. Nutrition 3.
(10) Müller, C. F. 1876. Die Rindviehzucht. Berlin.
(11) Paloheimo, L. & Mäkelä, A. 1952. The rate of passage of food in the digestive tract of ruminants.

Maataloustiet. aikak. (J. Scient. Agr. Sec. Finland) 24.
(12) Phillipson, A. T. 1947. Fermentation in the alimentary tract and the metabolism oi the derived

fatty acids. Nutrition Abstr. Rev. 17.
(13) Phillitson, A. T. & McAnally, R. A. 1942. Studies on the fate of carbohydrates in the rumen of

the sheep. J. Exp. Biol. 19.
(14) Schmidt-Mülheim, Adolf 1879. Grundriss der speziellen Physiologie der Hanssäugetiere. Leipzig.
(15) Trautman, A. 1933. Beiträge zur Physiologie des Wiederkauermagens VI. Arch, für Tierer-

nährung und Tierzucht 9.

SELOSTUS:

ERÄITÄ KVANTITATIIVISIA TIETOJA MÄREHTIJÖIDEN ESIMAHOJEN OSUUDESTA
TYPETTÖMÄN ORGAANISEN AINEEN SULATUKSESSA JA IMEYTYMISESSÄ

L. Paloheimo, A. Mäkelä ja M.-L. Salo

Kotieläintieteellinen laitos, Helsingin Yliopisto

Neljätoista lehmää ja viisi nuorta sonnimullia ruokittiin 10 päivän aikana määräsuuruisilla heinä-
annoksilla. Teurastuksen jälkeen juoksutusmahan sisältö punnittiin ja siitä otettiin näyte. Heinästä,
juoksutusmahan sisällöstä ja sonnasta määritettiin ligniini, typetön orgaaninen aine sekä typetön
ligniinivapaa orgaaninen aine. Ligniiniä johtoaineena pitäen laskettiin mainittujen typettömien frak-
tioiden sulavuus sekä pötsissä että koko ruoansulatuskanavassa. Tutkimuksessa kävi ilmi, että koko

ruoansulatuskanavassa sulaneesta typettömästä ligniinivapaasta orgaanisesta aineesta oli esimahoissa
sulanut 76 —99 %. Jos kaksi lehmistä jätetään laskuista pois, saadaan lehmille raja-arvot 85 ja 91 %.

Tämän tutkimuksen perusteella voidaan päätellä, että naudalla hiilihydraattien sulatus ja hajoamis-
tulosten imeytyminen tapahtuvat pääasiassa esimahoissa.

L. PALOHEIMO, A. MÄKELÄ and M.-L. SALO