Studies on bovine urolithiasis

Weaver, Anthony David (1971) Studies on bovine urolithiasis. PhD thesis, University of Glasgow.

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Abstract

Ovine urolithiasis is alleged to be associated with intensive feeding of concentrates, a type of husbandry which has similarities to methods of-rearing male sheep in Scotland, and which may become increasingly common in intensive feeding systems in ruminants in Britain. Part I of the thesis reviews the literature, in particular the predisposing factors, urine composition, and renal pathology. In Part II various surveys revealed that obstructive urolithiasis was uncommon in Britain except in Scotland, where the incidence varied from 1-10% principally among housed male sheep, and where, since cases were often fatal, the economic loss was significant. In determination of the liability of ovine urinary pH to change under different conditions of storage, samples kept in screw-topped containers to exclude air underwent no significant pH change in 24 hours. In catheterised samples taken at monthly intervals for seven years, from healthy Cheviot and Half-bred ewes, a seasonal variation was shown in urinary pH, which, except in a few summer months, was acidic, a finding contrary to most textbook statements. Urinary pH was significantly correlated (p< 0.01) with urinary potassium concentration. Studies on four housed Blackface rams (half-brothers) showed that their urinary pH was generally alkaline. Urinary mineral concentrations, especially magnesium, were higher than in grazing ewes. The urinary phosphorus concentration of one tup was significantly (p < 0.01) less than in the others. Feeding experiments were carried out on 172 Blackface sheep to determine the incidence of clinical (obstructive) and subclinical urolithiasis (presence of calculi). Seven animals developed a fatal obstruction with calculi, a further three had non-fatal obstruction, and 92 sheep had renal calculi. No calculi developed in six male lambs fed a mixture grossly inadequate in calcium (0.7 g daily) and adequate in phosphorus (3.81 g), for 120 days. Two clinical cases of obstruction by calculi developed and four others had renal calculi when ten castrated lambs were fed a high calcium (2.90%) and phosphorus (1.70%) concentrate mixture with roots and wheat straw. Kidneys of obstructed sheep demonstrated hydronephrosis and pyelonephritis. Other sheep showed early foci of pyelonephritis. Experiment 2 employed a feed composition known in the United States to be calculogenic but, despite a subsequent increase of the potassium acid phosphate concentration in the mixture from 2.14 to 4.28%, no animal developed obstruction. Eight of 30 sheep had calculi at slaughter. On a relatively normal and narrow range of Ca and P intakes, differing quantities of concentrates and roots had no effect on the development of urolithiasis. Nineteen of 42 sheep (45%) contained calculi, including three fatalities. Liveweight increase was unrelated to the presence of renal calculi. The calcium intake was then varied in 42 castrated lambs (1.51 g to 25.60 g daily), while the phosphorus intake was low (1.9 -2.4 g). While 71% of the animals had calculi, the incidence was unrelated to calcium intake. The previous experiment was repeated with ram lambs, and initially twelve were killed after 135 days of hay feeding alone, seven of which contained renal calculi. After 96 days of concentrate feeding, renal calculi were found in 22/27 sheep, including two animals with fatal urinary obstruction. No significant differences in plasma mineral values were demonstrable between calculus-containing and other sheep. The pathological features of obstruction were similar to those in the natural disease. Microcalculi were demonstrated in renal collecting tubules. Pyelonephritis was common in obstructive urolithiasis and was considered sometimes to result from ascending infection from a urethrotomy wound, and sometimes from blood-borne infection. Glomerulonephritis and chronic interstitial nephritis were rare. Intracytoplasmic PAS-positive globules occurred in the proximal convoluted tubules of sheep with renal calculi. On biochemical analysis, ovine urinary calculi consisted of triple phosphate, together with some calcium phosphate and in two cases with calcium oxalate and carbonate. X-ray crystallography showed that some calculi were amorphous in structure while others were struvite (magnesium ammonium phosphate) or newberyite (magnesium hydrophosphate-trihydrate). The results are discussed in Part III. As struvite is an important crystalline component in ovine calculi in Scotland, urinary pH is likely to be a significant factor in its production. From the results of these experiments it appears unlikely that extreme Ca and P intakes, high K2HPQ4, or a high root intake are significant in producing an increased incidence of calculi in indoor sheep. Since animals developed calculi on hay feeding alone, it appears that factors such as climate, genetic profile, or elements such as K and Na may explain certain discrepancies in these results in Scottish sheep.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: William Weipers
Keywords: Animal diseases
Date of Award: 1971
Depositing User: Enlighten Team
Unique ID: glathesis:1971-73872
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jun 2019 08:56
Last Modified: 14 Jun 2019 08:56
URI: http://theses.gla.ac.uk/id/eprint/73872

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