Ultrasonographic examination of the reticulum, rumen, omasum, abomasum, and liver in calves

: This article describes the ultrasonographic findings of the reticulum, rumen, omasum, abomasum, and liver of calves from birth to 100 days of age. Reticular motility is used to exemplify how the forestomach function in calves progresses and gradually approaches that of adult cattle. The ultrasonographic examination of the esophageal groove reflex and the investigation of factors affecting esophageal groove closure are described. The ultrasonographic findings of the forestomachs and abomasum of calves with ruminal drinker syndrome are discussed. The article concludes with the description of the ultrasonographic examination of the liver. This article describes the ultrasonographic findings of the reticulum, rumen, omasum, 29 abomasum and liver of calves from birth to 100 days of age. Changes in ultrasonographic 30 appearance, location and size of these organs during the first 100 days are outlined. Reticular 31 motility is used to exemplify how the forestomach function in calves progresses and gradually 32 approaches that of adult cattle. The ultrasonographic examination of the esophageal groove reflex and the investigation of factors affecting esophageal groove closure are described. The 34 ultrasonographic findings of the forestomachs and abomasum of calves with ruminal drinker 35 syndrome are discussed. The article concludes with the description of the ultrasonographic 36 examination of the liver.


Ultrasonographic findings of the reticulum
The reticulum is rarely visualized in the first 2 weeks because it is very small and not close enough to the ventral abdominal wall to be within reach of the ultrasound beams. 5,9,11 From the third week, the reticulum can always be visualized in the sternal region. The spleen or the liver is often seen between the ventral abdominal wall and the reticulum until the age of about 80 days (Fig. 1). After the age of 100 days, the reticulum is always adjacent to the ventral abdominal wall. The reticular wall appears as an echoic line as described in mature cattle. 12 Because of its gaseous nature, the reticular content is not usually visible or it may appear as hypoechoic, cloudy, ill-defined material near the reticular wall. Small projections indicating the mucosal folds and the reticular honeycomb pattern are only seen in exceptional cases.
Reticular contractions are biphasic similar to those seen in adult cattle. 12 During rumination, contractions are triphasic as seen in adult cattle. The contraction preceding the normal biphasic contraction serves to transport the cud into the esophagus, from where it is propelled to the mouth and chewed. The frequency of reticular contractions increases significantly in the first 100 days of life; there were 0.9, 1.0, 1.2, 1.4 and 1.4 contractions per minute at the age of 20, 40, 60, 80 and 100 days, respectively. 9,11 The reticulum cannot be visualized in pre-weaned calves during and 30 min after ingestion of milk because it is displaced craniodorsally by the expanding abomasum and becomes obscured by the lungs. 6,7 The content and shape as well as the motility of the reticulum do not change during suckling. Likewise, the ultrasonographic appearance of the reticulum does not change during and after eating hay and grass silage but the frequency of contractions and the interval between contractions changes significantly. 6,8 During feeding, the mean number of contractions of 10 calves during a 9-min measuring period was 18.5, which was a significant increase from 11.1 before and 11.5 after feeding. Because of the increased rate of contractions, the interval between contractions was significantly shorter (P < 0.01) during eating (21.7 sec) than before (41.1 sec) and after eating (37.3 sec). The reticular contraction rate of 1.2 ± 0.23 per min in calves before feeding was very similar to the rate in resting cows of 1.2 ± 0.13 per min 12 but slightly higher than the rate of 0.9 ± 0.19 per min in pre-weaned calves. 6,7 During feeding, the increase in the frequency of reticular contractions was greater in ruminating calves than in cows; in the former it almost doubled from 1.2 to 2.1 contractions per min and in the latter it increased from 1.2 to 1.6 contractions per min. 12 The mean duration of the first and second contraction was 2.5 and 3.9 sec in calves, which were similar to the values of 2.8 and 4.2 sec measured in resting cows 12 and 2.4 and 4.9 sec in pre-weaned calves. 6,7 Ruminating calves, pre-weaned calves and cows differed with respect to the speed Formatiert: Schriftfarbe: Hellblau, Durchgestrichen Formatiert: Schriftfarbe: Hellblau, Durchgestrichen of the first reticular contraction; it was 7.0 cm/sec in cows, 8 3.5 cm/sec in ruminating calves and 1.7 cm/sec in pre-weaned calves. 6,7 The approximately 4-fold increase from pre-weaned to ruminating calves to mature cows is an impressive illustration of the gradual reticular development in growing cattle.

Examination of the rumen
The rumen is examined at the 6th to 12th intercostal spaces (ICSs) and the flank on both sides. 11 Each ICS and the flank are scanned from dorsal to ventral with the transducer held parallel to the ribs. The size of the rumen is determined by defining the dorsal and ventral visible margins of the rumen by measuring the distance from each margin to the dorsal midline using a tape measure. The size is then calculated by subtracting the distance of the dorsal margin from the distance of the ventral margin. The location of the longitudinal groove is identified to determine the size of the rumen sacs. The dorsal rumen sac extends from the dorsal visible margin to the longitudinal groove and the ventral sac extends from the longitudinal sac to the ventral visible margin of the rumen. The thickness of the ruminal wall is best measured using a 13-MHz transducer.

Ultrasonographic findings of the rumen
The rumen can be visualized from the first day of life. 11 It is adjacent to the abdominal wall in the caudal abdomen and further cranially the spleen is seen between the abdominal wall and the rumen. The wall of the rumen is visible as an echoic line, and three layers including the serosal, muscular and mucosal tunics can be clearly differentiated using the 13-MHz transducer. On the first day of life, the rumen content is anechoic with hyperechoic stippling and a small dorsal gas cap almost always can be seen. After the first day, most calves have reverberation artifacts dorsally (Fig. 2), indicating a gas cap, and an ingesta phase ventrally.
The transition between the two phases is characterized by the abrupt disappearance of the reverberation artifact. Because of their gaseous nature, the ingesta and the ventral fluid phase cannot be seen. The ultrasonographic appearance of the rumen does not change in pre-weaned calves during and after the ingestion of milk 7 and in ruminating calves during and after eating hay and grass silage. 8 The rumen is visible only from the left side on day 1 but from both sides thereafter. The longitudinal groove appears on the left as a mucosal fold, separating the dorsal and ventral sacs of the rumen, but the actual groove develops later (Fig. 3). Because of superimposition of the lung and spleen, the distance between the dorsal visible margin of the rumen and the dorsal midline is largest in the 7th ICS (Fig. 4). It becomes smaller further caudally and is smallest in the 12th ICS. In the flank, the distance between the dorsal midline and the dorsal margin of the rumen increases. In contrast, the distance between the dorsal midline and the ventral visible margin of the rumen does not change much.
In each ICS, the overall size of the rumen increases progressively with age (Fig. 5). The most pronounced increase occurs after weaning, which was between days 60 and 80 in a study at our clinic. The same is true for the size of the dorsal and ventral sacs of the rumen. Until day 40, the dorsal and ventral sacs are similar in size, and after day 60, the ventral sac is slightly larger. The length of the rumen also increases gradually; on the first day, the rumen does not extend beyond the last rib but can be seen in the flank region from day 20. The cranial dorsal blind sac of the rumen cannot be seen in the newborn but it appears as a semicircular structure between the reticulum and the ventral sac of the rumen from day 20, similar to descriptions in adult cattle. It contracts immediately after the biphasic reticular contraction.

Examination of the omasum
The omasum is examined on the right side from all ICSs from dorsal to ventral with the transducer held parallel to the ribs. 7,11 The dorsal and ventral visible margins and the size of the omasum are determined analogous to the method used for the rumen.

Ultrasonographic findings of the omasum
The omasum can always be seen from the right side. 11 It is medial to the liver dorsally and usually medial to the small intestines ventrally, and only occasionally directly adjacent to the abdominal wall. In the first few days of life, the omasum can occasionally also be seen from the 7th to 10th ICSs on the left side. It is seen on the right side from the 6th to 9th ICSs and occasionally from the 10th ICS. The best images are obtained at the 8th or 9th ICSs. In the newborn calf, the omasal wall usually appears as a completely circular line (Fig. 6). The omasal contents are echoic in these cases and the omasal leaves are seen as fine echoic lines.
After a few days, the omasal contents can no longer be seen because of their gaseous nature, as described in adult cattle. The omasal wall then appears as a semi-circular to circular echoic line (Fig. 7). Sometimes the origin of the omasal leaves can be seen as echoic projections protruding into the omasal lumen. The ultrasonographic appearance of the omasum remains unchanged in suckling calves during the ingestion of milk 7 and also in ruminating calves when they eat hay and grass silage. 8 The dorsal visible border of the omasum has a caudodorsal course (Fig. 8). It is furthest from the dorsal midline at the 6th ICS and moves progressively closer to the dorsal midline toward the 10th ICS. The visible omasal size measured at the 8th and 9th ICSs increases in the first 100 days, whereas the size measured in the 6th and 7th ICSs does not change appreciably ( Fig. 9). The visible omasal size is largest in the 8th ICS and smallest in the 6th ICS.
Typically, omasal motility cannot be detected.

Examination of the abomasum
The abomasum is scanned from the 5th to the 12th ICSs and the flank on both sides starting at the ventral midline and progressing laterally and dorsally with the transducer held parallel to the ribs. 7,11 The location and size of the abomasum and visibility of its wall, folds and content are assessed before and after the ingestion of milk. The abomasal length is measured in the ventral midline. Video recordings can be made of the abomasum slightly to the left of the ventral midline during and after the ingestion of milk to document filling of the abomasum and clotting of the milk. The time between the start of milk intake and the appearance of the milk in the abomasum can be measured using a stop watch.

Ultrasonographic findings of the abomasum
The ultrasonographic appearance of the abomasum strongly depends on the time of milk intake. In the newborn calf, the abomasum is the largest organ and dominates the abdominal cavity. It is visible at the 5th to 12th ICSs and from the ventral flank. The content is heterogeneous and hypoechoic with hyperechoic stippling (Fig. 10) and often contains hyperechoic particles of varying size reflecting clotted milk. The abomasal wall appears as a fine echoic line and the abomasal folds are often distinct. From day 80 onward, the pyloric part of the abomasum can often be seen on the right side parallel to the fundic part of the stomach. The pylorus usually is oval to circular in cross section and has a characteristic spoke wheel appearance. 5 The influx of milk is readily seen and first appears as a cloud-like hyperechoic mass. This expands to fill the entire abomasal lumen and is seen as homogeneous hyperechoic content ( Fig. 11). In contrast to cow's milk, milk replacer appears heterogeneous and hyperechoic. 13 The mean interval between the start of nursing and the ultrasonographic appearance of milk in the abomasum varies from 10 to 25 sec (range of individual examinations 5.9 -68.0 sec).
After the influx of milk, the abomasal content usually appears as homogeneous, and rarely heterogeneous, hyperechoic material, and the abomasal folds are seen as distinct, undulating, echoic folds. Toward the end of nursing, the first signs of milk clotting can usually be seen in the form of consolidation of the hyperechoic material. The homogeneous echoic content changes and forms a hypoechoic peripheral zone with hyperechoic stippling and echoic milk coagula. The abomasal milk content first forms a large homogeneous clump and distinct moving echoic stippling is seen in the peripheral fluid zone. A dorsal gas cap is sometimes seen after nursing as evidenced by reverberation artifacts on ultrasonograms. Distinct changes in the abomasal content are seen 15 min after milk intake (Fig. 12). The content becomes heterogeneous and the abomasal folds usually can no longer be seen. The clotted milk appears as hyperechoic clumps 6,7,14,15 surrounded by a small rim of hypoechoic fluid. The clots usually measure more than 5 cm in diameter. Thirty minutes after milk intake, the abomasal folds are once again distinct. The visible clots are still the same size but they start to disintegrate and to become less distinct and overall less echoic, and the peripheral fluid rim becomes larger. By two hours after milk intake, the clumps are much smaller and their size varies from 1 to 5 cm.
The amounts of solid and liquid contents are about the same. The pylorus is much more difficult to identify after feeding than before but is always located in the right hemiabdomen.
Of 29 calves fed milk replacer, eight had no ultrasonographic signs of curd formation 2 hours later. 16 On the first day of life, the abomasum is visible on both sides of the ventral midline but it extends more to the left than to the right. 13 11 Extension to the left varied from 8.9 to 15.1 cm and to the right from 3.1 to 17.1 cm before feeding (Fig. 13). After feeding, extension to the left and right varied from 8.9 to 23.2 cm and from 3.4 to 19.8 cm, respectively. Similar measurements were made on days 20 to 60 and the visible extension of the abomasum to the left was greater than that to the right (Fig. 14). From day 80 (the calves were weaned at day 60), abomasal extension to the left was smaller because of the expanding rumen. The visible extension to the right changed little in the first 100 days.
The mean visible abomasal length varied from 12.9 to 23.8 cm before feeding (Fig. 15) and changed little in the first 60 days. On day 100, the abomasal length was significantly greater (P < 0.05) than on day 1. With the exception of day 20, the visible abomasal length was greater before feeding than after feeding (P < 0.05).
Ultrasonographic measurements of abomasal dimensions ( width, length and height), location and emptying rate were made in suckling calves before and after they were fed different Formatiert: Schriftart: Fett, Schriftfarbe: Rot volumes of milk replacer or oral electrolyte solutions. 14 All three abomasal dimensions increased during feeding, and after suckling, the abomasum was symmetrically located about the ventral midline. There were strong linear relationships between ultrasonographic and ingested volumes.
In contrast to feeding milk, the ultrasonographic appearance of the abomasum was the same before, during and after feeding hay and grass silage. 8 Ultrasonography was used to examine the effect of erythromycin, neostigmine and metoclopramide on abomasal motility and emptying rate in suckling calves. 17 Six Holstein calves were examined 1 h before until 3 h after being fed milk replacer (60 ml/kg). The calves received six treatments of varying doses of the three drugs given 30 min before feeding. A high dose of erythromycin (8.8 mg/kg) increased the frequency of abomasal luminal pressure waves and the mean abomasal luminal pressure and decreased the half-time of abomasal emptying by 37%.

Ultrasonographic monitoring of the esophageal groove reflex
The term esophageal groove reflex refers to the reflex spiral contraction of two muscular folds forming the lips of the groove and simultaneous relaxation of the reticulo-omasal orifice and the omasal canal creating a bypass from the esophagus to the abomasum. 18 As a result, the ingested milk bypasses the reticulorumen and flows directly into the abomasum. The functioning of the esophageal groove reflex is easily monitored during suckling using ultrasonography; a functional reflex is confirmed when milk is seen entering the abomasum during milk intake. 7,14,19 Complete or partial failure of the reflex can result from unnatural housing and feeding management 18 or from neonatal disorders such as diarrhea. Milk given to a calf by tube feeding is deposited into the reticulorumen. 20,21 When a healthy calf nurses, about 10 % of the ingested milk reaches the reticulorumen 22 from where it is actively transported through the omasum into the abomasum within three hours without adversely affecting the forestomach system. 23 Milk remaining in the rumen for an extended period of time undergoes bacterial lactose fermentation leading to a disorder referred to as ruminal drinker syndrome. 24 Fermenting milk in the rumen of these calves can be detected ultrasonographically. 6,25 Examination of the esophageal groove reflex techniques, at all milk temperatures and with all milk replacer concentrations. It should not be concluded from these findings that feeding technique has no effect on esophageal groove closure. More likely, occasional deviation from the optimal feeding technique, for instance the feeding of cold milk, does not adversely affect esophageal groove closure but can lead to digestive disorders if the suboptimal feeding management persists.

Ruminal drinker syndrome
Ultrasonographic examination of the reticulum is well suited for the differentiation of healthy calves and calves with ruminal drinker syndrome and to visualize the milk in the reticulorumen of the latter. In ruminal drinkers, the reticular wall appears as an echoic line 25 as described in healthy calves 7 but the two groups of calves differ with respect to the reticular content. Reticular content is not seen in healthy suckling calves 7 but appears as hyperechoic and heterogeneous material in ruminal drinkers (Fig. 16). Reticular folds are distinct in ruminal drinkers 25 and the honeycomb structure of the mucosa is often clearly visible (Fig.   17). Reticular contractions are biphasic as seen in healthy calves and the parameters of reticular contractions are similar 25 to those seen in healthy suckling calves. 7 Of note, reticular motility does not appear to be affected by the acidic and liquid content, although generally acidic rumen content has an adverse effect on forestomach motility in calves. 27,28 Ultrasonography is very useful for the detection of milk in the ventral sac of the rumen in The parenchymal pattern of the liver consists of numerous fine echoes homogeneously distributed over the entire area of the organ (Fig. 18). 9 . 19). The distance of the dorsal visible margin of the liver from the dorsal midline decreases caudally because the liver becomes less obscured by the lung. The distance between the dorsal visible margin of the liver and the dorsal midline was greatest at the 5th ICS and shortest at the 11th ICS. The ventral visible margin had a similar course; it was furthest from the dorsal midline at the 5th ICS and closest to the dorsal midline at the cranial flank. The visible size of the liver is largest at the 8th to 11th ICSs and is considerably smaller cranially and caudally (Fig. 20). There is no measurable increase in liver size in the first 60 days, and the size is smaller at 80 and 100 days than in the first 60 days. The thickness of the liver increases until day 40 and changes little thereafter until day 100 (Fig. 21). The maximum thickness is measured at the 8th and 9th ICSs.
The caudal vena cava is triangular in cross section attributable to its location in the sulcus of the vena cava of the liver (Fig. 18) 9,10 but occasionally is round to oval. The vein is always seen in at least one ICS, most commonly at the 9th to 12th ICSs, but is not seen cranial to these ICSs because of superimposition of the lungs. The mean circumference of the vein of newborn calves is largest at the 10th and 11th ICSs and varies from 3.8 to 4.3 cm. The circumference increases slightly and is largest at 6.5 cm at 40 days.
The portal vein is circular or oval in cross section and has stellate ramifications branching into the liver parenchyma (Fig. 22). 9,10 The wall is more echogenic than the wall of the caudal vena cava, and the portal vein is seen at more ICSs than the caudal vena cava because of a more ventral position and less superimposition of the lungs. It is always seen at the 7th to 11th ICSs. Compared with the caudal vena cava, the portal vein is always more ventral and closer to the diaphragmatic surface of the liver. The diameter of the vein varies little in the first 100 Kommentiert [UW3]: Very nice article, do you think it could be pertinent to make a conclusion that insists on the interest of ultrasound for non-invasive assessment of GI tract in calves. I found a lot of new information in that article and I will make a particular referenc to it in my editorial fort he issue. Ultrasonography can be an excellent alternative to invasive processes to assess the GI tract for experimental studies in calves. I mean that with ultrasound use we could improve animal welfare of many experimental studies avoiding (or decreasing) many pain associated procedure. This article is I think a key article for not only veterinarians but also for animal scientists and people working on calves nutrition. An amazing source of information! Formatiert: Überschrift 1 Legend to Figures   Fig. 1 There are no post-suckling measurements at examinations 5 and 6 because the calves had been weaned. * Difference between before and after feeding (P < 0.05; paired t-test). a Difference between examinations 1 and 6 (P < 0.05; paired t-test). For key for the examination numbers see