ANYONE WHO LISTENED IN
ON CECILIA VILLAVERDE’S
WEBINAR series13 on the
management of cat and dog urolithiasis
a few weeks back will now have a
complete appreciation for the way in
which diet can be used to manipulate
the urinary environment… and realise
it’s not always easy to make the “right”
recommendation.
Five key factors (including qualities
of the stones and
characteristics of
the urine) should
be taken into
account when selecting an appropriate
food: solubility, the presence of
precursors, the inhibitors present,
urinary pH and urine-specific gravity.
For me, this really points out the
importance of knowing which stone
type, or mix of stone types, you’re
dealing with.
Cecilia reminds us that the relative
importance of diet is stone-dependent.
The formulation of a diet alters its
influence on the urinary environment
and of course, what we’re all searching
for in practice is proven effect. Let’s
understand each of the above five
factors so we can confidently affect the
most appropriate nutritional solution.
Solubility in water
Reflecting on the calls to our
nutritional helpline, some don’t realise
that only one stone type (namely
struvite) is consistently proven to
be soluble, and therefore able to be
dissolved medically in the bladder.
Solubility is of course advantageous
for the patient, the owner and often
the clinician when our urinary case
doesn’t present as an acute blockage
and therefore surgical emergency. A
non-invasive approach is less traumatic
for all involved.
As an exception to the solubility rule,
certain protocols have been written for
urate stones but these are fruitful in
about 30% of canine cases only, with
a significantly longer dissolution period
than for struvite. Other stone types,
including calcium oxalate, calcium
phosphate, cystine and silica aren’t soluble.
Precursors
and inhibitors
When considering
diet (and
communicating
its importance
to owners), it’s easy to take the reductionist route and
recommend a “low mineral” or even
“low ash” diet.
While this may have been considered
an appropriate approach a few
decades ago, we now know things
aren’t so simple in the real world.
Urinary diet formulation relies on a
meticulous balance which factors in
the interactivity of minerals presented
to the pet’s body. Whether an element
is considered a nutrient (essential or non-essential), levels of dietary
inclusion, bioavailability (influenced by
digestibility) and the passage of any
precursor or inhibitor to the urinary
space all need considering.
Thereafter the interaction between
electrolytes is key. We should be
mindful that the promotors of some
crystal and stone types are claimed
inhibitors of others (depending on
which reference you read).
This again highlights the importance
of knowing which stone type we’re
dealing with and for me, increases my
awareness of the complexity of urinary
diet formulation.
The take-home message here is
that a patient with recurrent calcium
oxalate stones shouldn’t be simply
asked to restrict dietary calcium. We need to recognise not only
the essential nutritional role
of calcium, but the many
interactions which Cecilia
called out in her webinar.
Urinary pH
This factor is well
recognised to be of
critical importance in
the management of
struvite stones, given that magnesium and ammonium
phosphate are considerably
less soluble at an alkaline
pH.7 This relates of course to the strength of
molecular bonds between
our precursors and their
interactivity with free
hydrogen ions.
As a general rule, other
stones are reported at either
acidic pHs or in neutral
urinary solutions. Let’s
remember, however, that
calcium oxalate, a stone type
equally prevalent to struvite
in many regions, can form
at any physiological pH.13
Some epidemiological
studies describe urinary
acidity as a risk factor,
related to the buffering action of the
body. After endogenous bicarbonate
stores are exhausted to counter this
acidity, phosphate is drawn from bone
stores and calcium is mobilised with it,
predisposing calciuria.
Finding the “best pH” for
minimising calcium oxalate remains
a controversial topic in the eld of
veterinary nutrition, but considering
calcium oxalate is an “idiopathic
disease”13, the focus is on manipulating
as many factors as possible to extend
the “stone-free” periods between
bouts.
Urine-specific gravity (USG)
We’re now acutely aware that
in uencing USG is the most important
strategy when it comes to the
management of all uroliths, hence: it’s
all in the ow!
By diluting urine the likelihood of
contact between crystal precursors
is minimised, simply meaning
precipitation is less likely. In diuresing
the cat or dog, we lower USG and
increase the frequency of urination,
offering a further advantage; with
regular bladder “flush-out” there is
less time for these lasting precursor
interactions to occur.
Regardless of the crystal or stone
type, achieving a low USG is the
name of the game. Cecilia’s targets are
<1.030 for the cat and <1.020 for the
dog13, which in effect is an intentional
polydipsic-polyuric state.
Remember to communicate this
intent to pet owners who by re ex
will need not only to have multiple,
well-placed fresh water sources about
the house but clean the cat’s litter trays
more often, or take their dog out for
more frequent toileting breaks.
Lowering USG can occur by means
of simply increasing water intake
(feeding wet diets or soaking dry
kibbles in water to create a soup-like meal), adding salt to a diet (within
safe levels and being mindful of
recognising patients with salt-sensitive
hypertension once again, according to reference) or less commonly,
lowering protein may be trialled. The rst two strategies are more commonly
employed in newer formulations.
What’s the solution?
Let’s remember that not all urinary
claims are created equal. While foods
which are available on supermarket
shelves can often have a “urinary
health” message on the bag, there
are many manners in which this can
be justified to the owner and verified
in either a laboratory or in animals
themselves.
One newer approach is to consider
a diet’s relative super-saturation (RSS)
measure. This figure (a mathematical
ratio calculated as a result of pooled
urine analyses) tells us how likely a diet
is to create a urinary environment in
favour or ideally unlikely to precipitate
a particular crystal type, when fed
exclusively.
RSS measures are diet-specific and
crystal/stone-specific, but in using this
technology and incorporating all of
the above five factors, a diet can be
formulated to help support patients
with multiple urolith types, namely
struvite and calcium oxalate – our
most common presentations in clinical
practice.
Clinical diets formulated with the
RSS method of verifcation in mind are
classed as “formulated for a particular
nutritional purpose” (that is, covered
by what we call a PARNUT5).
Once again, it’s important that our
clients realise this; that a veterinary
diet requires an accompanying
professional recommendation from the
practice team, and that the after-care
monitoring and follow-up is key to maintaining their pet’s urinary health.
These diets should be fed exclusively just like an elimination
diet to render their desired effect
and never, ever forget to fill up that
water bowl!
- With thanks to Erica Moorhouse,
RVN, for proof reading.
References and further
reading
- Albasan, H., Lulich, J., Osborne,
C., Lekcharoensuk, C., Urlich L. and
Carpenter, K. (2003) Effects of storage
time and temperature on pH, specific
gravity, and crystal formation in urine
samples from dogs and cats. Journal of the
American Veterinary Medical Association 222
(2): 176-179. - Bartges, J. and Kirk, C. (2012)
Nutritional management of lower
urinary tract disease. In: Fascetti, A.
and Delaney, S. (eds), Applied Veterinary
Clinical Nutrition, 1st edition Wiley-
Blackwell, Chichester, pp269-288. - Buranakarl, C., Mathur, S. and Brown,
S. A. (2004) Effects of dietary sodium
chloride intake on renal function and
blood pressure in cats with normal and
reduced renal function. American Journal
of Veterinary Research 65: 620-627. - Caney, S. Cortadellas, O. Dhumeaux,
M. and Nickel, R. (2014) Practical
Management of Urinary Tract Disease.
Veterinary Focus special edition, Royal
Canin, Aimargues, France. - F.E.D.I.A.F. (2011) Code of Good
Labelling Practice for Pet Food. [Online]
Available from: http://ec.europa.eu/
food/food/animalnutrition/labelling/
docs/pet_food_code_20102011_en.pdf
[accessed 16/06/16]. - Greco, D. S., Lees, G. E., Dzendzel, G. et al (1994) Effects of dietary sodium
intake on blood pressure measurements
in partially nephrectomized dogs.
American Journal of Veterinary Research 55:
160-165. - Hesse, A. and Neiger, R. (2009) A
Colour Handbook of Urinary Stones in Small
Animal Medicine. Manson Publishing,
London. - Koehler, L. Osborne, C., Buettner,
M., Lulich, J. and Behnke, R. (2015)
Canine Uroliths: Frequently Asked Questions
and Their Answers. [Online] Available
at: http://www.cvm.umn.edu/depts/
minnesotaurolithcenter/prod/groups/
cvm/@pub/@cvm/@urolith/
documents/asset/cvm_asset_388871.
pdf [accessed 9th May 2015]. - Krieger, J. E., Liard, J. F. and Cowley,
A. W. (1990) Hemodynamics, uid
volume, and hormonal responses to
chronic high-salt intake in dogs. Am J
Physiol 259: H1,629-H1,636. - Lulich, J. Osborne, C. and
Sanderson, S. (2005) Effects of dietary
supplementation with sodium chloride
on urinary relative supersaturation with
calcium oxalate in healthy dogs. American
Journal of Veterinary Research 66 (2): 319-
324. - McNeill (ed) (2014) Veterinary Focus:
Lower Urinary Tract Disease, Buena
Media Plus, Boulogne, France. - Moore, A. (2007) Quantitative
analysis of urinary calculi in dogs and
cats. Veterinary Focus 17 (1): 22-27. - Villaverde, C. (2016) Deconstructing
Urolithiasis: One stone at a time [two-part
webinar series], Royal Canin UK, 24th
and 31st May 2016, accessible online:
https://attendee.gotowebinar.c…
register/8836271750277033986 and
https://attendee.gotowebinar.c…
register/909459218058925570.
