4| DISCUSSION
To the best of the authors’ knowledge, this is the first description of
an outbreak of abomasal bloat (emphysematous abomasitis) in a dairy goat
flock in Latin America. Likewise, based on an epidemiological
investigation combined with pathological, microbiological, and molecular
diagnosis, it was possible to identify the agents and associated factors
involved. Therefore, we emphasize the importance of a broad diagnostic
approach in order to elucidate and resolve health conflicts within rural
establishments.
According to Panciera et al. (2007) and reviewed by Burgstaller,
Wittek, and Smith (2017), abomasal bloat syndrome can be multifactorial,
and the pathophysiology primarily involves excess fermentation of
high-energy gastrointestinal contents in the abomasum (from milk, milk
replacer, or high-energy OES), as well as bacterial activity releasing
fermentative enzymes leading to gas production and bloat. In addition,
such a progression would also be enhanced by any factor that slowed
abomasal emptying or caused paralytic ileus. Regarding the bacterial
etiology, in agreement with the current report, the most frequently
isolated bacterial pathogens include C. perfringens type A andC. ventriculi species (DeBey et al., 1996; Vatn et al., 2000;
Edwards et al., 2008; Van Kruiningen et al., 2009; Leite Filho et al.,
2016). Additional bacterial pathogens isolated from calves affected with
abomasal bloat include α streptococci, other streptococci species,E. coli , C. fallax , and C. sordellii (Roeder et
al., 1987; Vatn et al., 2000).
The pathogenic role of C. perfringens type A was first
demonstrated by intraruminal inoculation of such bacteria in neonatal
calves, resulting in anorexia, depression, abomasal bloat, diarrhea, and
death (Roeder et al., 1988). Clinical severity is associated with the
production of lethal toxins as the major cause, namely alpha (CPA;
necrotizing and hemolytic action), although other toxins such as
enterotoxin (CPE; enterotoxic), beta2 toxin (CPB2; enterotoxic and
cytotoxic) and beta-like toxin (NetB; enterotoxic and cytotoxic) can
also be produced by this agent (Freedman et al., 2015). Interestingly,
this agent has also been reported in cases of gas gangrene in horses
and, more recently, in cattle (Peek et al., 2003; Pires et al., 2017).
Lastly, Khan et al. (2020) reported a greater prevalence of
pathogenic C. perfringens type A in kid goats when compared to B
and D types.
While C. perfringens has been associated with food poisoning in
humans, the role of C. ventriculi as a primary agent in
gastrointestinal disorders (e.g., emphysematous gastritis) is
well-described in humans (Freedman et al., 2015; de Meij et al., 2017;
Singh, 2019). In addition, it is found in patients with gastric ulcers
and delayed gastric emptying, but it is also considered a normal
commensal microbiota, and it was also found in our control kids in the
current report. Therefore, it is considered to be opportunistic when the
environment becomes conducive to its growth (Crowther, 1971; Al Rasheed
and Senseng, 2016). Although the pathogenic role of C. ventriculiis not clear, the local accumulation of acetaldehyde and ethanol formed
from carbohydrate fermentation by the organism could induce stomach and
duodenal injuries. Furthermore, the carbon dioxide production from
glucose fermentation and pyruvate metabolism results in abdominal
distention, as previously reported in some human patients (Tolentino et
al., 2003).
Regarding the diagnosis, confirmation of C. ventriculi infection
is feasible by molecular or histology/cytology methods, since this
microorganism cannot be detected by classical culture techniques, which
in most cases reveal negative results (DeBey et al., 1996; Vatn et al.,
2000; Edwards et al., 2008; Lam-Himlin et al., 2011; de Meij et al.,
2017). In this sense, concerning C. ventriculi detection, it is
important to highlight two facts. Firstly, the diagnosis of such an
agent must be associated with pathological findings, as its finding by
chance does not point toward a clinical risk to the animal. Secondly,
the smears evaluation in combination with histopathology of the abomasum
is a strongly suggestive diagnostic method, as carried out in this
study. Morphologically, the main differential diagnosis in this case is
the presence of bacteria of the Micrococcus genus; these are
smaller (0.5 μm) and tend to form tightly packed clusters, a feature not
seen with C. ventriculi (Lam-Himlin et al., 2011).
Concerning the presence of S. cerevisiae in the milk replacer
used to feed the kid goats, S. cerevisiae fermentation products
have been extensively used in the dairy industry with beneficial effects
on production parameters (Poppy et al., 2012), modulation of the immune
system (Zaworski et al., 2014), improvement in rumen fermentation,
stability of the gut microbiota (Brewer et al., 2014), and reduction of
diarrhea in calves (Alugongo et al., 2017). Although there are several
positive arguments regarding the introduction of such yeast into the
ruminant diet, disturbances in gastric emptying associated with milk
accumulation may have provided an opportunistic and deleterious growth
of the S. cerevisiae within the kids’ abomasum. They also ferment
sugars, releasing ethyl alcohol and carbon dioxide similar to C.
ventriculi . Corroborating this line of thought, there was a lot of
yeast in the cytological smears of the kids affected by abomasal bloat.
Therefore, more attention should be paid when adding yeasts to the diet
of young ruminants.
Regarding the possible associated factors with the occurrence of
abomasal bloat, our results are in agreement with the findings from most
worldwide reports, where high infection rates were related to microbiota
imbalances and poor hygiene. All environment/food samples (100.0%; 7/7)
collected in this case were positive for the 16S rRNA gene related toClostridium spp. Likewise, the use of a milk substitute instead
of natural goat milk can be closely related to the disturbance in
abomasal emptying. The large volume of milk ingested in a short time,
high osmolarity, and the high temperature of the milk replacer
associated with kid management are other strong reasons already verified
in previous reports (DeBey et al., 1996; Van Kruiningen et al., 2009;
Burgstaller et al., 2017).
Other important management findings highlighted is this study is the
offering of ad libitum concentrate to the kids and their behavior
to look for such food immediately after milking management. This can
have favored the development of an environment with a large amount of
milk and soluble carbohydrates contained within the abomasum. As already
known, a high protein and carbohydrate concentration in the gut triggers
the growth of C. perfringens , increasing the risk of
enterotoxemia (Riddell and Kong, 1992; Roberfroid et al., 2010). Quinnet al . (2011) also described various predisposing factors for the
occurrence of enterotoxemia, like changes in diet, low proteolytic
efficiency in neonates, trypsin inhibitors in colostrum, malnutrition,
inefficient pancreatic secretion, no established intestinal flora,
carbohydrates engorgement, and intestinal hypomotility (Sato et al.,
1978).
Few reports on treatments of abomasal bloat have been described.
However, most therapies included antibiotics (primarily penicillin and
ampicillin), rumen “tonics” (including a wide variety of medicaments),
non-steroidal anti-inflammatories (primarily flunixin meglumine),
relieving the distension via a tube or trocar, Clostridial antitoxin,
and fluid therapy as reviewed by Shoemaker et al . (2008). In the
authors’ experience, the earlier the clinical signs (abomasal bloat) are
identified, the better the animal’s prognosis.
Lastly, regarding prophylaxis, the high frequency of C.
perfringens type A detection in several reports on abomasal bloat and
gas gangrene in ruminants, reinforces that such an agent should be part
of the routine clostridial vaccines. Reversed genetics have demonstrated
that alpha toxin is the main virulence factor for C. perfringenstype A causing gas gangrene, and that vaccination with alpha toxoid
could protect animals against this agent (Awad et al., 1995).
Unfortunately, only a few vaccines against clostridial diseases for
ruminants contain C. perfringens alpha toxoid in Brazil (Pires et
al., 2017). Therefore, it is important to look for this information at
the time of purchase and immunization of the flock. In the current
report, pregnant goats were vaccinated with a commercial vaccine
containing alpha toxin, so it is believed that since there was no
colostrum management program, the kid goats could be receiving low
quality colostrum and immunization was not occurring efficiently. In
this sense, the importance of quality plans for colostrum management in
dairy farms is also emphasized.
In conclusion, an outbreak of abomasal bloat affected a dairy goat farm
throughout the kidding season. The disease affected suckling kid goats
among one and three months old with an acute clinical course of 6–12
hours until death. There was a mortality rate of 30% (66/221), and the
agents C. perfringens type A and C. ventriculi were
identified as the main ones involved with possible participation ofS. cerevisiae . Among the possible associated factors, the
erroneous use of milk replacer associated with errors in kid management
favored decreases in abomasal emptying with local dysbiosis and clinical
signs. Among the prophylactic measures, hygiene care, proper use of milk
replacer, vaccination plan containing C. perfringens alpha toxoid
associated with a good colostrum management were suggested.