Constipation in dogs: diagnosis and management

Introduction

Constipation in dogs has been defined as infrequent, difficult and painful elimination of dry and hard stools, but without permanent loss of functional capacity. When they do not pass any stools, it is called obstipation, which always requires veterinary attention. Repeated episodes of obstipation may lead to megacolon.^1,2

Aetiopathogenesis

The large intestine is responsible for absorbing water and electrolytes from faeces and for their retention until voiding. There are two types of contraction in the colon:

• The haustral contractions, which are continuous and mainly serve to maximise the faeces’ exposure to the digestive mucosa to absorb more water; and
• And there are mass movements, whichonly occur a few times a day and propel the stools toward the rectum, for defaecation.
   

These movements cause the internal anal sphincter to relax, which, when followed by the external sphincter, normally leads to defaecation. Unlike the internal sphincter (innervated by the autonomic nervous system), the external anal sphincter is innervated by somatic fibres, which means defaecation is under voluntary control. Under normal conditions, the voluntary and sustained contraction of this sphincter causes mass movements to cease in 10–30 minutes, so the rectum relaxes, the internal sphincter contracts again and the urge to defaecate subsides.²

Causes of constipation

Any situation that increases the time stools remain in the colon can potentially cause constipation.

The most common causes of constipation in dogs include:

• A diet with insufficient fibre and too much indigestible material (e.g., bones).
• Lack of exercise.
• Clinical conditions that course with weakness and dehydration.
• Intra- or extraluminal obstruction of the colon or rectum.
• Hip fractures.
• Perineal hernia.
• Neurological alterations.^2,3

Constipation in dogs: clinical evaluation

The diagnostic assessment of dogs troubled by constipation should include a complete physical examination, with a special focus on the abdominal cavity searching for any masses that could cause the constipation. In males, it is essential to perform a rectal examination and assess the size of the prostate. Similarly, the anus and perianal region should be examined to rule out any perianal hernias or fistulas.

As for diagnostic tests, abdominal X-rays should always be taken in two positions to assess the degree of distension of the colon and for the presence of any foreign bodies or masses that could hinder defaecation. If the ratio between the maximum diameter of the colon and the length of the seventh lumbar vertebra is greater than 1.5, then the patient has megacolon.³

Radiographic findings may indicate the need for an abdominal ultrasound. Additionally, in recurrent cases where the cause cannot be determined, it is advisable to perform a colonoscopy in search of any intraluminal obstructions.²

Patients with constipation may return completely normal laboratory results (haematology, blood chemistry and urinalysis) or they may reveal changes related to the underlying cause.

Constipation in dogs: treatment

MILD/MODERATE CONSTIPATION

These cases are usually treated with a combination of laxatives, enemas, prokinetic agents and dietary changes.

SEVERE CONSTIPATION

It may be necessary to administer fluids and manually remove stools under general anaesthesia. Patients with megacolon may also require surgery.^1–3

ENEMAS

Enemas, either with a commercial solution or simply warm water (5–10 mL/kg) + a 50% lubricant solution, can be used to facilitate the expulsion of stools.

• If using a commercial enema, always exercise precaution when using products with sodium phosphate (especially in small dogs) because of the risk of severe hyperphosphataemia, hypocalcaemia and death.
• Dioctyl sodium sulfosuccinate (5–30 mL depending on the patient’s size) or mineral oil (5–30 mL) based enemas are another option, but they should never be used together as sulfosuccinate promotes systemic absorption of the oil.
• Lactulose (5–10 mL/kg diluted to 30% in water) can also be used as an enema.
• Soaps or potentially irritating substances should not be added to the enema.
   

LAXATIVES

• Laxatives are only recommended for use in well-hydrated patients.
• Oil-based laxatives may interfere with nutrient absorption, so they are not recommended for long-term use. Therefore, it is preferable to use osmotic laxatives such as lactulose (0.5 mL/kg/8–12 hours).
• As we mentioned earlier, high fibre diets are also advisable and the administration of prokinetics should be considered, if necessary.³

Conclusions

The incidence of constipation in dogs has declined because increasingly more owners are turning to suitable commercial diets and fewer are feeding their dogs lots of bones. However, trends such as BARF diets could see an upturn in the number of dogs with constipation visiting our clinics. Regarding the treatment of severe constipation, the anecdotal use of Coca-Cola® to soften faecalomas has been described in human medicine. Although there is nothing published on this matter in dogs, it could be an option in cases that do not respond to the usual management. 

References

1.     Washabau RJ. (2013). Constipation. In Washabau RJ, Day MJ (Eds). Canine and Feline Gastroenterology. Elsevier: 93-99.

2. Foley P (2017). Constipation, Tenesmus, Dyschezia and Fecal Incontinence. In Ettinger SP, Feldman EC, Cote E. (Eds). Textbook of Veterinary Internal Medicine. 8th Ed. Elsevier: 633-638 

3.     Ludwig L. Constipation/Obstipation and Megacolon. (2020). In Cohn LA, Côté E, (Eds). Clinical Veterinary Advisor Dogs and Cats. Elsevier: 764-772.