“Hardware disease” is the common term for traumatic reticuloperitonitis (TRP) and is caused by cattle ingesting metal or other objects, which then perforate the reticulum. This disease mostly occurs when (dairy) cattle are fed mixed feed that has metal (or plastic) incorporated accidentally. Cattle are notoriously careless feeders when eating prepared mixed feed and often eat foreign bodies (Dyce et al., 1996). Grazing cattle are much more careful and less likely to eat metal objects.
In addition to abomasal displacement, TRP remains one of the most significant internal disorders of cattle. Incidence of hardware disease was reported to be as high as 80 percent in the 1950s but more recently reported incidence rates are around 2 to 12 percent (Braun et al., 2018).
Pathology of hardware disease
When metal perforates the reticulum, it can go in a few different directions. Most perforations occur in the lower part of the cranial wall, but some of them occur laterally in the direction of the spleen or medially towards the liver (Radostits et al., 2007). The pericardium can also be perforated, causing pericarditis.
When a metal object does not perforate the serous surface of the reticulum, it does not cause any detectable illness and might be fixed for long periods before slowly corroding away
It is important to realise that when a metal object does not perforate the serous surface of the reticulum, it does not cause any detectable illness and might be fixed for long periods before slowly corroding away (Radostits et al., 2007).
Clinical signs and diagnosis
TRP can present as either acute or chronic; in textbooks, clinical signs are always segregated into acute and chronic symptoms of TRP.
Acute TRP can cause local or diffuse peritonitis. Acute hardware disease tends to cause distinct signs that include anorexia, decreased milk production, fever, ruminal atony and tympany, abdominal pain, arched back and abdominal guarding, and a tense abdomen (Braun et al., 2018). Also, a short audible grunt is often seen as a typical sign of acute TRP. These clinical signs are caused by peritonitis. In its acute stage, peritonitis causes ruminal atony and abdominal pain.
Chronic hardware disease tends to show many less distinctive signs, and it is important to realise that acute symptoms only last for a short period
Chronic hardware disease tends to show many less distinctive signs, and it is important to realise that acute symptoms only last for a short period (up to a couple of days). Often, when a veterinarian examines a cow, acute symptoms have waned.
In a study by Braun et al. (2018), 503 cows were diagnosed with TRP, and the authors described their clinical signs. Diagnosis was specific and based on ultrasound, radiography, laparorumenotomy and/or post-mortem testing. As these cases were all admitted to a teaching hospital, the clinical exam was carried out in the same way every time, reducing the chance of missing certain clinical signs.
The most common clinical findings were:
- an abnormal general demeanour (87 percent)
- reduced or absent rumen motility (72 percent)
- a minimum of one positive foreign body test (58 percent)
- poorly digested faeces (57 percent)
- decreased or absent intestinal ruminal motility (50 percent)
- reduced rumen fill (49 percent)
- fever (43 percent)
- spontaneous signs of pain (39 percent), such as arching of the back in 18 percent, bruxism in 20 percent and grunting in 2 percent
In addition, 30 percent of the cattle had watery to loose faeces, 21 percent had bradypnoea, 14 percent had a fuller than normal rumen, 14 percent had abnormally thick faeces and 10 percent had ruminal tympany. Rectal examination showed distension of the rumen in 19 percent, and eating and rumination were also decreased (Braun et al., 2020).
This list shows that, in practice, clinical signs are variable and non-specific.
Anatomy and physiology of the reticulum and rumen
The anatomy and physiology of the reticulum and rumen are described in the next half of this article. A better understanding of how local or diffuse peritonitis can influence the normal physiology of these forestomachs can help when diagnosing hardware disease.
Together, the rumen and reticulum form a large vessel. An adult bovine rumen can hold 100 to 175 litres of content; most of this content is semi-fluid ingesta. The first two stomachs combined are often called the reticulorumen compartment. In this compartment, food is reduced by microbial fermentation. Some of the simpler products produced in this compartment (such as the volatile fatty acids) are immediately absorbed in the rumen, while others are digested and absorbed lower in the digestive tract (Dyce et al., 1996).
The reticulum lies cranial to the rumen under ribs six to eight and mainly to the left of the median, although ventrally it passes across the midline and lies above the xiphoid process of the sternum. It reaches from the cardia to the most forward part of the diaphragm and occupies the full height of this shallow part of the abdomen. The rumen in the adult cow is very large and reaches from the cardia to the pelvic inlet (Dyce et al., 1996).
The rumen and the reticulum are divided by a series of pillars that project internally; they communicate over the U-shaped ruminoreticular fold. The ruminal pillars divide it into the dorsal and ventral major sacs, and there are also a couple of smaller caudal sacs. Communication with the oesophagus and omasum takes place through either end of the reticular groove (the oesophageal groove in the unweaned calf). The lining of the reticulum has a honeycomb structure, with mucosal ridges outlining “cells”; the “cell” floors have low papillae. The rumen has papillae, the size and density of which depend on age, diet and location (Dyce et al., 1996).
The bovine food cycle
The motility in the reticulorumen has three different patterns in adult cattle: the primary cycle, the secondary cycle and rumination.
The main aim of the primary cycle is to mix food in the reticulorumen. It starts with a biphasic contraction of the reticulum. Both reticular contractions force food dorsally and caudally into the rumen, though the second contraction is much stronger than the first. After this, the dorsal ruminal sac begins to contract as the ventral sac relaxes, thereby causing digesta to move from the dorsal to the ventral sac. Subsequently, contractions of the caudoventral, caudodorsal and ventral ruminal sacs force digesta back into the reticulum and cranial ruminal sac. After a brief pause, the contraction sequence is repeated (Radostits et al., 2007).
The motility of the reticulorumen results in the layering of the ruminal content, with fibrous material floating on top of a fluid layer
Content of the reticulorumen gets moved into the omasum and abomasum during each contraction of the reticulum. Heavy grain and food particles (2 to 4mm) pass through the reticulo-omasal orifice into the omasum and abomasum. The motility of the reticulorumen results in the layering of the ruminal content, with fibrous material floating on top of a fluid layer (Radostits et al., 2007).
The frequency of the primary cycle in a healthy cow is variable and can be determined from information acquired between cycles. The frequency can be as high as 60 cycles per hour but is less when a cow is ruminating or lying down. The strength and duration of the cycle depends more on the ingesta present in the reticulorumen than the frequency of the cycle (Radostits et al., 2007).
The secondary cycle only involves the rumen and is focused on ensuring the cow can eruct gas. This contraction occurs independently of the primary cycle and occurs about every two minutes (Radostits et al., 2007).
Rumination is a complex process and tends to start half an hour to an hour after feeding. It takes place for 10 to 60 minutes at a time, and cows can ruminate for up to seven hours a day (Radostits et al., 2007). As the different contraction cycles are variable and inconstant, it is advised to auscultate and assess the rumen for two to five minutes at a time.