Diet and anal-sac impaction in dogs

Abstract

Diet and anal-sac impaction in dogs.

Full text

Dier-en-Arts 2019; Nr 12: 312-313.
Anton C. Beynen
Diet and anal-sac impaction in dogs*
*Based on article in Dutch (1)
Main points
Progressive, inflammatory anal-sac disease in the dog involves anal-sac blockage followed by
infection and abscessation within one or both sacs. The condition may be initiated by fecal
impaction of the anal-sac duct, or more specifically by the blocking of its opening to the anal orifice.
Symptoms of anal-sac disease are, amongst others, tenesmus, licking or biting the anal area,
“scooting” and perianal discharge. Therapy consists of expressing the anal-sac contents, and
administration of antibiotics as appropriate. Repeated recurrence may be an indication for anal
sacculectomy.
Among the dogs that are presented to a veterinary practice, the prevalence of anal-sac disease is
about 5% (2-5). In one study there was no clear breed predisposition (3), but in dogs that underwent
sacculectomy, Labrador-type dogs were overrepresented (6). One to three weeks prior to the
diagnosis of anal sacculitis (with impaction), 75% (225/300) of the dog patients had mild, short-
lasting (1-2 days) diarrhea (7).
A study found that sixty percent (180/300) of the anal-sac patients received an all-meat diet (7),
which implies zero consumption of crude fiber. There is no published research on the influence of
diet on the prevention of (recurrent) anal-sac disease in the dog. To promote anal-sac emptying
and/or to prevent anal-duct blockage, a fiber-rich diet is often recommended (8, 9).
It is plausible that fecal impaction of the anal-sac duct is combated by short, rectal-transit time,
enhanced innervation of the rectum and surrounding tissue, and increased laxity of rectal contents.
That means that the diet should accelerate passage, and increase volume and water concentration
of rectal contents. On closer examination, a fiber-rich diet can be further specified to a complete dry
food with ± 5% cellulose (± 5% crude fiber) and ± 5% beet pulp. Efficacy of the proposed fiber-rich
diet in preventing (recurrence of) canine anal-sac impaction can only be tested by controlled
research.
Anal-sac content
The numerous glands of the dog’s two anal sacs are located in the connective tissue near the fundus.
The glands empty into the sac’s lumen. Anal-sac contents contain about 88% water, 11.5% organic
and 0.5% anorganic matter (10). Healthy dogs display an extreme individual variation in the
appearance of their anal-sac fluids (11-16). The color varies from yellow to gray to brown, and the
consistency from watery to mucous to doughy. The secretion contains mucin rich in sialic acid and
other anti-microbial proteins, namely lysozyme, immunoglobulin A and lactoferrin (14, 15). Gram-
positive cocci belong to the normal flora within the anal sacs (7).

The degree of malodorousness of the anal-sac contents differs between animals (16). The volatile,
organic components mainly consist of short-chain fatty acids (C2-C6) and trimethylamine (17).
Gender and estrous stage had no effect on the volatile compounds (17), while anal-sac secretions of
estrous versus disestrous bitches were not more attractive to male dogs (18). Secreting anal-sac fluid
into the anal channel probably serves to scent mark an individual’s territory via feces.
Experimental anal-sac blockade
The canine anal sac has one duct to the anal channel. In experiments with healthy dogs, the duct of
one sac per animal was ligated. McColl (19) attempted to induce anal-sac fistulas as model for
humans with perianal fistulas. Halnan (20) tested whether the symptoms of canine anal sacculitis
would develop. In 14 dogs, McColl found swelling of the blocked anal sacs, but no anal sacculitis
within 20 weeks. Halnan saw swelling in all 8 experimental dogs, and within a week also sacculitis in
four animals. The studies suggest that many dogs are resistant against infection development in a
blocked anal sac, but there are susceptible animals also.
An older theory (21) advances that blocking of the anal-sac drain, by impaction of feces (and
secretion), causes swelling of the sac, followed by sacculitis and empyema. When individually-
determined susceptibility to infection is taken into consideration, the theory is not rejected by the
two experiments (19, 20). The theory is corroborated by the statement (7) that in canine anal
sacculitis the removed, abhorrently stinking anal-sac contents invariably contained a plug.
Required dietary effects
There are no experimental data on how diet may affect anal-sac impaction in the dog. Only
reasoning can lead to a possible diet composition for the prevention of (recurrent) anal-sac disease.
It is plausible that fecal impaction of the anal-sac duct is combated by short rectal transit time,
enhanced innervation of the rectum and surrounding tissue, and increased laxity of rectal contents.
That means that the diet should accelerate passage and increase volume and water concentration of
rectal contents.
The three requirements match the observation (7) that an all-meat diet increased the risk of anal
sacculitis (with impaction). Compared with a dry food, an all-meat diet decreased the passage
velocity of chyme in dogs (22). The fiber-free, all-meat diet possibly also decreased the volume of
rectal contents. That suggestion is supported by the likenesses of all-meat and deep-frozen foods.
The latter foods are meat-based and (very) low in carbohydrates and fiber (23). Per unit of energy
intake, four deep-frozen versus four dry foods reduced feces weight in dogs by on average 54% (24),
possibly associated with less filling, and thus less distension of the rectum.
Dietary fiber and feces
Chyme passage, fecal volume and water content, are all influenced by the amount and type of
dietary fiber, or the indigestible carbohydrates in the diet. Three fiber sources are exemplary:
cellulose, beet pulp and psyllium. Cellulose is insoluble and non-fermentable in the dog’s gut. Beet
pulp holds about 20% pectin, a soluble, viscous, fermentable fiber. Psyllium hulls contain about 60%
soluble, non-fermentable arabinoxylans that appear as a gel in feces (25).

In dogs, higher dietary levels (≥ 5% in dry food) of cellulose (26, 27), beet pulp (28, 29) or psyllium
seed (30, 31) accelerate chyme passage and increase both feces volume and defecation frequency.
The studies also showed that cellulose lowers water content of feces to a limited degree, whereas
beet pulp and psyllium seed have a clear increasing effect. That would mean that only dietary
cellulose makes firmer stools.
Diet proposal
The three required diet effects and the reported fiber effects are possibly reconciled by a
combination of insoluble and soluble fibers. Dietary cellulose and beet pulp demonstrably speed up
chyme passage and may enlarge the volume of rectal contents. Beet pulp may raise the amount of
water in rectal contents, and cellulose, as bulk-forming fiber, may innervate the rectal area. In
stating those fiber effects, it is assumed that greater volume and water concentration of feces go
hand in hand with greater volume and water concentration of rectal contents. A dry food containing
about 5% cellulose and 5% beet pulp is realistically feasible and theoretically effective. With psyllium
seed or hulls at the same, high inclusion level, the food would be too expensive.
Dietetic food and supplements
A production information text for dog owners clarifies about the dietetic food concerned that the
bulk-forming effect of the insoluble fiber component promotes natural expressing of the anal glands
(32), but presumably the anal sacs are meant. The dry, dietetic food declares vegetable fibers as
second ingredient, beet pulp as twelfth ingredient and psyllium husks and seeds as sixteenth (33).
The dietary content of crude fiber is 11.1% (33), which probably for the most part represents
cellulose.
Some dietary supplements, in the form of treats and powders, claim the support of healthy anal
glands by promoting their natural emptying (34-38). Soft chews for anal-gland support are offered
with guaranteed success within 3-5 weeks (34). According to a paper backing the formulation, post-
marketing surveillance indicates that 85.7% of pet owners reported measurable effectiveness (39).
The soft chews contain pumpkin seed powder, granulated pumpkin seed and apple pectin cellulose
powder as active fibrous ingredients (40). They provide, as based on the dosing advice (41), a total
amount of fiber that is equivalent to ± 0.07% in a dry food (Note 1), which is negligible.
Note 1
The active, fibrous ingredients per soft chew (4 g) are 158 mg pumpkin seed powder, 68 mg
granulated pumpkin seed and 34 mg apple pectin cellulose powder (40). Taking into account that
pumpkin seed contains about 29% total fiber (42), one soft chew provides 100 mg fiber. For dogs
weighing 26-50 pounds, the daily dosage is two soft chews (41). A dog weighing 38 pounds (17.2 kg)
would consume 200 mg fiber per day. That intake is equivalent to 0.07% in dry food for a 17-kg dog
consuming 16.7 kg dry food/kg body weight, or 284 g food/day.
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