Anatomy, Development, and Functions of the Bovine Omasum1

ANATOMY, DEVELOPMENT, AND FUNCTIONS BOVINE OMASUM 1

OF THE

1¢. B. BECKER, S. P. MARSHALL, AN]) P. T. DIX At~NOLD Department of Dairy Science, :Florida Agricultural Experiment Station, Gainesville SUMMARY

Numbers of laminae and their arrangement varied significantly among omasums of different cattle and between the upper and lower portions of the omasums of 85 among 86 organs examined. Pedunculated shape of, and partial blockage by the first-order laminae at the reticulo-omasal orifice, and their extension generally across to the suleus omasi, tend to allow mainly small feed particles to enter, and divert them between the laminae. From ingesta samples air-dried, some reduction in size of particles was found in the omasum to under 1 mm in diameter. Digestion and solution of fine ingesta caused rapid removal of fine particles in the abomasum. Significant differences were found in numbers of laminae among animals and between upper and lower portions of the omasum (P < .01). Volume of the full omasum increased to 60 times between 10 and 150 days of age. Moisture contents of omasal contents decreased markedly from those of the rumen and reticulum, without respect to age in these calves.

Preliminary studies (3) in 1937 of bovine stomach contents indicated that the omasum tended to reduce the size of forage particles passing through it. Further investigation of normal stomachs led to the offering of forage and concentrates to calves when one day old (4). Winters et al. (19) showed a photomicrograph of the developing stomach of a 29-dayold bovine fetus that weighed 0.28 g. Stomach compartments were differentiating visibly in a 59-day-old Jersey fetus (4, 5). The net empty omasum increased from an average of 12.8% of total empty stomach weight in five calves at birth, to 30% in 24 mature dairy cows. Chauveau (7) described the omasum as ovoid, the anterior face being against the diaphragm and posterior part of the liver, with the lesser curvature against the reticulum and tureen. Free borders of :[2 to 15 large laminae advanced near the lesser curvature wall. Laminae of lesser widths occurred between the large ones. Very attenuated ingesta filling spaces between the laminae contained little liquid. He stated that feeds were reduced by trituration and attenuation in pressing between the laminae. Sisson (13) reported that about 100 folds of laminae of five orders from the dorsal and side walls occupied much of the omasum, and that food in thin layers pressed into spaces between the laminae is ground down by rounded horny papillae on them. The omasum has slow rhyth:Received for publication May 27, 1963. Florida Agricultural Journal Series No. 1678.

Experiment

Stations, 835

mic contractions, and the reticulo-omasal orifice relaxes briefly at the instant of reduced omasal pressure (12, 18). Relaxation of the reticulo-omasal orifice when the omasum dilates indicated nerve control (12). An aspiratory action facilitates entrance of food into the inter-]aminal spaces where omasal contractions express excess moisture and retain coarse particles for further h i t u r a t i o n before passing to the abomasum. Ewing and Wright (9) fed corn stover to a steer, slaughtered it, and separated diluted contents of the several digestive organs through a 2-ram sieve. They dried, weighed the fractions, and calculated the proportions of comminution that took place in each part. These were: ~'umen, reticulum and by mastication 58.5%; omasum 10.9%; abomasum 11.2%; small intestine 5.1%; large intestine 4.5%; and 9.8% remained in the feces. A preliminary Florida report (5) also showed that a limited amount of comminution occurred in the omasum. The bovine stomach was devoid of living protozoa (17) or aerobic bacteria (6) at birth. Calves acquire them later from the food or environment. With 26 calves, Swanson (15) noted that 18 ruminated in the first 2 wk; seven in the second 2 wk, and the last calf soon thereafter. Less time was used in rumination per pound of feed eaten by them as ages advanced. The omasum in calves developed rapidly between seven and 30 days of age (11). After surgical removal of the omasum from several kids, feed in their abomasums was coarser than in control animals of similar age (16).

836

R. B. B E C K E R , S. e . M A R S H A L L , AND P. T. D I X A ~ N O L D

~XPEglMENTAL PROCEDUR~ Fifty-two Jersey male calves of known ages and variously fed in the station herd were sacrificed when no longer needed in other investigations. Samples of ingesta were obtained from each part of the stomach and separated as described below. Sixteen other male Jersey calves received colostrum and reconstituted skimmilk up to 60 days of age, mixed concentrates ad libitum up to 4 lb daily, and free access to chopped alfalfa hay until sacrificed. They were killed at predetermined ages to observe stomach development and function. The stomach was separated into compartments by clamps; volume and specific gravity were measured by water displacement and weight. The p H of stomach contents was measured with a Beckman glass electrode p H meter. Moisture contents of ingesta were determined on sanlples in a vacuum oven at 100 C. Additional ingesta samples were air-dried and separated through standard soil sieves into five fractions. Detailed observations were made of anatomy. RESULTS

General observations. The omasum is located on the right side of the abdominal cavity, against the diaphragm, with the long axis almost vertical. I t is connected medially by a short neck with the reticulum at the termination of the esophageal groove, and by a large open orifice below, with the anterior part of the abomasum on the medial face. The greater curvature is against the right abdominal wall between the eighth and tenth ribs. The primary laminae tend to be pedunculated at the top insertion, and partially occlude entrance of ingesta during contractions. This arrangement also allows mainly fine feed particles to gain entrance between them, and to follow somewhat the periphera of the passageways between the laminae. I t facilitates passage downward in thin layers. Also, large particles tend to be prevented from entry, except whole or coarsely cracked hard grains. The primary laminae extend from the greater inside curvature to full length of the organ and extend almost, if not entirely, to the medial wall or sulcus omasi. A varying number of unguliform horny papillae arise mainly from the anterior free margins of the primary laminae, their tips extending outward and downward toward the interior of the omasum. A few were on margins of the esophageal groove. The tips become cornified at an early age. Their numbers ranged between 6 and 28 in 67 animals, mainly between six and ]7, the mode being eight horny

papillae. They were not aeveloped sufficiently to identify in some young calves, or were accidentally severed in others when separating the stomach compartments. Their function may be to retard regurgitation of omasal contents. Secondary laminae are inserted between the primary laminae at 0.7 to 1.0 cm below the opening, the third order usually 1.2 to 2.0 cm below, the fourth order at 2.4 to 3.3 cm. The fifth order may start as a ridge at any distance from the entrance. As the laminae extended downward in the cavity, some of them united and terminated in a single lamina, but others sometimes arose from the omasal wall. No regularity was observed in arrangement of the five orders of laminae. Also, some laminae ter~ninated before reaching the omaso-abomasal outlet on the medial face below. No laminae were attached to the short sulcus omasi between the entrance and outlet. Rounded hard papillae studding the sides of the laminae were large in diameter near the entrance, and reduced gradually in size toward the outlet. A few appeared to be arranged in rows toward the outer curvature. Slight ridges resembling fifth-order laminae sometimes arose on the sides of larger laminae. Numbers of laminae. Laminae were counted in 86 omasums from calves and yearlings. The omasums were cut horizontally into upper and lower portions. No regularity was found in numbers or arrangement of laminae in omasums from different animals, or in their distribution in the upper and lower portions. There were more fifth-order laminae, and fewer of the first order in the upper portion than in the lower part. Only one organ among 86 had an equal number in the two portions. The range and average numbers are listed in Table 1. TABLE 1 Numbers of laminae in the upper and lower portions of 86 omasums Order of laminae First Second Third Fourth Fifth Total First Second Third Fourth F~th Total

Range

Average

Upper portion 8 to 18 11.49 4 to 16 10.71 12 to 29 20.57 21 to 49 39.94 36 to 94 69.92 89 to 192 152.52 Lower portion 12 to 29 20.44 6 to 20 12,68 7 to 27 15.48 15 to 48 31.80 20 to 80 57.0'8 93 to 182 137.4.8

Standard deviation 1.83 1.97 4.04 5.59 11.72 19.39 3.57 2.6'2 4..17 6.45 12.9'8 18.95

FUNCTIONS

OF

THE

O1V!ASUI~

837

:FIG. 1. A. The omasum is somewhat ovoid, located toward the right eighth to tenth ribs. B. Anterior insertions of primary laminae partly occlude the reticulo-omasal orifice, except when relaxed, as after slaughter. C. A horizontal cross-sectlon of the omasum shows four orders of laminae with ingesta between them. A few fifth-order laminae are visible. D. Horny papillae on this first-order lamina are larger toward the top, and decrease in size gradually downward. A l t h o u g h t h e r e were common similarities i n i n t e r i o r s t r u c t u r e of the omasums a m o n g the 86 animals, yet they also differed considerably. Only 2 % of the v a r i a t i o n in total n u m b e r s of l a m i n a e was associated with increased age of

the calves; this was n o t significant. A n a l y s i s of v a r i a n c e showed t h a t the differences a m o n g a n i m a l s were statistically significant ( P < 0.01). Differences in n u m b e r s of l a m i n a e in the u p p e r a n d lower p o r t i o n s were real, usu-

838

R. B. BECKER, S. P. M A R S H A L L , AND P. T. D I X ARNOLD

ally more being in the upper portion. Not all Jersey males had more laminae in the upper than in the lower portion, but this occurred frequently enough to be a true biological characteristic. Typical appearance of the omasum is seen in five views in Figure 1 and Figure 2. Initiation of omasal function. Twenty-seven calves were sacrificed under 3 wk of age. Two calves under 24-hr-old had licked mixed concentrates and one had at least 63 particles between the laminae. Three among eight calves had no feed in the omasum at I wk or younger. Some dry feed had reached the omasum in six among nine calves at 8 to 14 days. Only four among ten calves between 15 and 20 days old had no feed in the omasum. This organ was functioning in every calf slaughtered at 3 wk or older. Fineness of feed in the oma~um. Representative samples of ingesta were taken from between the laminae of 68 dairy calves sacrificed between 30 and 227 days of age. The limited amounts in calves under 30 days old were needed for other studies. Samples were airdried and separated into five fractions with standard soil sieves, and weighed. A few whole grains or coarsely cracked corn particles were present in the omasal contents of calves so fed. This doubtless affected weights of samples from a few calves. It is recognized that portions of feed in each compartment were reduced by absorption of end-products (fatty acids, moisture, gases, etc.). These reductions must be borne in mind, particularly in the changed proportions in the

FIG. 2. This omasum was opened vertically along the sulcus omasi or free passageway, and the orifice slit for a wider view of the interior. Large unguliform papillae with cornified tips are on the upper insertion of some first-order laminae. Second-order laminae insert farther below the entrance. Free borders of the first-order laminae extend medially across the inside cavity.

abomasal samples. Part of the smaller particles would have disappeared by solution, fermentation, and digestion. Weights of the several fractions were computed to a percentage of the sample from each organ, and are shown in Table 2. Development of the omasum. Jersey male calves were sacrificed at certain ages in groups of four animals. The average volume, with standard deviations, of the omasums with contents were: ten days, 44 ml -----8; 30 days, 102 ml ± 15; 90 days, 1,292 ml ± 205; 120 days, 2,441 ml ± 348; and 150 days, 2,643 ml ± 331. This was a volume increase of 60 times in 140 days. The average dry matter of the ingesta in the rumen was 17.2%; in the reticulnm 13.1%, and 22.6% in the omasum. Omasal ingesta ranged in p H from 5.2 to 6.8. No relationship was seen between p H or dry matter percentages of the ingesta and age of the calves within these groups. A separate report will deal further with these animals. DISCUSSION

Description of the omasum in Table 1 showed the wide range of variation which occurred in this organ among animals of the same species. No two organs were alike. Differences were wider than indicated previously. Feed particles are softened by saliva and other fluids in the rumen. Activities of bacteria and of protozoa cause some weakening of cellular plant tissues of the ingesta, as was seen microscopically by Uzzell et al. (17), rendering them easier to be fractionated. This tended to confirm the statement by Chauveau (7) in 1857 that contractile pressure tends to crush feed particles while passing downward between the papillated laminae. Other workers (1, 2, 13, 18) believed that the horny papillae had a triturating action, but this could not be confirmed by inter-stonmch manipulation, since the latter interfered with normal contractions. To explain such reduction it is not necessary to assume trituration by contraction of alternate laminae. Structure of the retieuto-omasal orifice tends to prevent entry of coarse feed particles, as indicated in Table 2, from the greatly reduced percentages of particles exceeding 1 mm in diameter on the air-dry basis. This size may be closely akin to the 2-mm size used in the moist separation of corn stover particles by Ewing and Wright (9) at the Texas station. I t confirms also the observations with kids by Trautmann and Schmitt (16) that the omasum functions either to prevent entry of coarse

FUNCTIONS OF THE OMASUI~

839

TABLE 2 Proportion of weighed alr-dry particles of different sizes in ingesta from stomach compartments of 68 dairy calves between 30 and 227 days old Diameter of air-dry particles Compartment Rumen Retieulum Omasum Upper portion Lower portion Abomasum ~

Above 5 mm 2.54 2.35 .13 .09 .65

5 to 3 mm

3 to 2 mm

2 to ] mm

Percentage by weight of air-dry particles 9.55 20.12 35.14 8.50 17.94 33.95 .83 .65 2.48

5.95 5.88 7.39

25.73 25.40 24.58

Under I mm 3.2.6.5 37.26 67.36 67.98 64.70

Enzymatic digestion removes substantial proportions of smaller particles. Also, some fine particles go into solution, and slightly increased moisture contents may swell some particles larger.

f e e d particles or to reduce t h e i r size d u r i n g passage t h r o u g h this organ. The omasum f u n c tions in p a r t to reduce p a r t i c l e size of some feeds as they pass d o w n w a r d t h r o u g h this o r g a n p r e p a r a t o I T f o r digestion by enzymes. ACKNOWLEDG~IEI~TS Many persons helped toward this investigation over several years. These included D. A. Sanders, E. J. Becket, H. F. Burner, E. tI. Uzzell, It. L. Somers, J. M. Wing, and others. C. d. Wilcox made the statistical analyses of laminae numbers. Photographs were taken by R. 'J. Sneeringer. Appreciation is expressed to each of them. REI~ERENCES (1) BXLC~, C. C. Movement of Digesta Through the Digestive Tract. I n Digestive Physiology and Nutrition of the Ruminant, ed., D. Lewis. p. 23. Butterworth's, London. 1961. (2) BALOl:i, C. C., KF~LY, A., AN]> H~IM, G. Factors Affecting the Utilization of Food by Dairy Cows. 4. The Action of the Reticulo-Omasal Orifice. British J. Nutrition, 4: 207. 1951. (3) BI~CKE~, R. B. Certain Points in the Physiological Processes of the Cow. J. Dairy Sei., 20: 408. 1937. (4) B~CK~R, R. B., A N D ARNOIA), P. T. DIX. Early Development and Function of the Bovine Stomach. Proc. Assoc. Southern Agr. Workers, 49: 78. 1952. (5) B~CK~, R. B., AI~NOI~, P. T. DIx, Am) MAI~S~IALL, S. P. Development of the Bovine Stomach During Fetal Life. J. Dairy Sci., 34: 329. 1951. (6) BUTNm%H. F. A Comparison of the Aerobic Mierofiora in the Stomach of Calves at Different Ages. M.S. thesis, University of Florida. 1947. (7) C ~ u v ~ , A. Traite d'Anatomie Comparee des Animaux Domestiques. p. 367. J.-B. Baillieres, Paris. 1857.

(8) DUKEIS, It. H. The Physiology of Domestic Anlma]s. 7th ed. Somstoek Publishers Assoc., Ithaca, N. Y. 1955. (9) EWlNG, P. V., AND WI~IGttT, L. H. A Study of the Physical Changes which Take Place in Cattle During Digestion. J. Agr. Research, 13: 639. 1918. (10) L~wvis, ]). Digestive Physiology and Nutrition of the Ruminant. Butterworth's, London. 1961. (11) MARSFIALL, S. P., ARNOLD, P. T. DIX, AND BECKF~, R. B. Postpartum Development of Bovine Stomach Compartments and Observations on Some Characteristics of Their Contents. J. Dairy Sci., 33:379. 1950. (12) SC~ALK, A. F., A m A]~ADON, R. S. Physiology of the Ruminant Stomach (Bovine). North Dakota Agr. Expt. Sta., Bull. 216. 1928. (13) SISSO~r, S. The Anatomy of the Domestic Animals. 2nd ed. W. B. Saunders Company, Phfladelphla. 1914. (14) SMITH, F. A Manual of Veterinary Physiology. Alex. Eger, Chicago. 1916. (15) SWANSON, E. W , A m HAI~RIS, D., Jl¢. Development of Rumination in the Young Calf. J. Dairy Sci., 41: 1768. 3958. (1G) TRAVT~AN~, A., AND SC~MIT% ft. Experimentel]e Untersuchungen zur Frage der Psalterfunktion. Deutsch. Tier~irzt. Wochenschr., 12: 177. 1935. (17) U z z ~ b , E. M., BECKFA% 1:~. B., AND JONES, E. R., JR. Occurrence of Protozoa in the Bovine Stomach. J. Dairy Sci., 32: 806. 1949. (18) W r e s t , J. Die Physiologie und Pathologic der Vormagen beim Rinde. 1~. Sehoetz, Berlin. 1926. (19) Wr~EU, L. 1VL, G ~ N , W. W., AN]) CoYS~)eK, R. E. Prenatal DevelOpment of the Bovine. Minnesota Agr. Expt. Sta., Teeh. Bull. 151. 1942.