Review of macro mineral metabolism and male castration on obstructive urolithiasis in small ruminants

Obstructive urolithiasis is a prevalent and economically significant urogenital disorder in small ruminants, particularly in male and wether lambs. This review examines the multifactorial etiology of urolithiasis, emphasizing the roles of macro mineral metabolism and male castration practices. The condition arises from the supersaturation, crystallization, and aggregation of minerals in urine, often exacerbated by dietary imbalances, water intake, urinary pH, and anatomical predispositions. Common calculi types include struvite, calcium phosphate, calcium oxalate, and silicate stones, with high-grain diets, low calcium-to-phosphorus ratios, and inadequate water intake identified as major contributors. The influence of macro minerals such as potassium, sodium, chloride, sulfur, calcium, and magnesium on urinary mineral concentration and acid-base balance is explored through the dietary cation-anion difference (DCAD) framework. Manipulation of DCAD via anionic salts like ammonium and calcium chloride can effectively reduce urine pH, minimizing stone formation risk. This review also highlights the significant impact of early castration on urogenital development, particularly the reduction in urethral diameter due to testosterone deficiency, which increases susceptibility to obstruction. Despite established preventative strategies, including dietary modifications and delayed castration, obstructive urolithiasis remains a complex challenge. The review emphasizes the need for further research, particularly within South African feedlot systems, to optimize prevention strategies involving castration timing and mineral nutrition. Improved understanding of DCAD manipulation and mineral metabolism will contribute to enhanced animal welfare and feedlot productivity.