m=male, f=female

Discussion

Contrary to the opinion, we found in literature, that bladderstones in guinea pigs are very rare, in own examinations over a period of 8 years urinary calculi in 20 guinea pigs were proved. In a retrospective study Peng et al. examined systematically the organs of deceased or euthanized guinea pigs of a breeding farm. This way they could find urinary calculi in 5 female and 1 male of 170 (96 female, 74 male) guinea pigs. This would correspond to an incidence of about 1.3 - 5.2% and lies in a range comparable to the dog. Fundamentally it is to notice in the assessment of the incidence of urolithiasis, that spontaneously left stones very rare are remarked by the owners of the animals. So these calculi are not correctly recordable.

Urinary calculi shall be found frequently in elder female guinea pigs. In own investigations the part of female animals is 75% (15/20), Peng et al. report about 5 female and one male guinea pig with urolithiasis. In dogs the risk of the male animal of getting urinary calculi is twice the size as the risk of females. Also in rabbits there are in female animals less stones found, probably because during pregnancy and lactation the greater need for calcium reduces the building up of stones. On the other side female animals shall of anatomic reason more often come down with infections of the urinary tract with the result of "inflammation stones". The average age in the own examinations was 4.6 years (min 2, max 8) (Hamel 4,5 - 7, Peng 3 years).

ventrodorsal x-ray , female guinea pig, 6 years, urethral calculus

The owners of only 6 sick guinea pigs in the own studies reported on haematuria, which in literature is described as pathognomonic for infections of the urinary tract, especially for urolithiasis in guinea pigs. In at least six guinea pigs with unspecific anorexia, urinary calculi were diagnosed after palpation of the cranial perivaginal region. In two animals a frequent production of soft faeces was noticed, this was caused perhaps by stone caused tenesms. Three cavy owners noticed stone caused swellings of the urethral mouth of their female guinea pigs. The ostium urethrae externum leads cranial of the vaginal opening, and it is normally covered by the praeputium clitoridis. In nine of the 13 animals with uroliths was, caused by the size of the stones, the orificium urethrae externum clear recognizable shifted to cranial and ventral.

Urethral stones of 3 guinea pigs were removed with a "sharp spoon" or "foreign body pliers". Alternative a break up of the stones could happen by ultrasound treatment at a frequence of 30 khz.

extirpation of an urethral stone, female guinea pig, 2 years old

The consistence of the stones was found by infrared spectroscopie. It is of interest, that in these examinations all stones consisted of two and more minerals. Against this in dogs more than 60%, in humans only 28% of the stones are monomineralic. The components of stones agree with those, described in literature, similar to rabbits, minerals containing calcium are predominant. 18 out of 20 uroliths contain a share of calcium carbonate of 66,7% (min 40%, max 90%), 12 of 20 a share of calcium phosphate of 25,8% (min 5%, max 80%), 3 of 20 a share of calcium oxalate of 20%(min 5%, max 40%). The buildt up of these 3 most important components of urinary calculi is favoured by a too good supply of minerals. Meyer et al. prove, that calcium and phosphate at a high percentage are absorbed (80 +- 8%, 50 +- 17%). Excess amounts of calcium and phosphor are renal excreted with the risk of building up concrements. Calcium oxalate is only found in 3 guinea pigs, 2/3 of human uroliths consist of calcium oxalates (whewellite and weddelite). Surprising is the great share of struvite in 10 of 20 guinea pigs (average 42,5%, min 35%, max 50%). All concrements with a share of struvite were found in the urethra near the ostium urethrae externum.

urethrotomie, urethral calculus, guinea pig, 6 years old

To what extent ascending infections are responsible for the beginning must be found in other examinations. Pure struvite- stones in humans are only buildt up by infections. For the beginning of these "infection- stones" urea splitting bacteria must be present. Kunstyr et al. (corynebacterium) and Okewole et al. (streptococcus pyogenes) report of uroliths caused by infections of the bladder. Different informations have been given to the incidence of infections of the bladder of guinea pigs. So Wood finds cystitis in 19 out of 500 guinea pigs of a breeding farm (incidence 0,6%). Because only female animals are affected, she assumes the influence of female hormones or pregnancy. Peng et al. find cystitis in 19 of 170 sections (incidence 11,2%). 17 of the 19 guinea pigs are female (89,4%).