Effects of Tetracycline on Ruminal Activity and Blood Calcium in Sheep

The objective of this study was to assess the effects of tetracycline administration on the frequency of ruminal contractions and serum calcium concentrations. Rumen contractions were monitored by auscultation in 23 sheep prior to the administration of oxytetracycline and recorded every 12 hours for 84 hours after the intramuscular injection of the antibiotic. The blood for calcium analyses was collected by venipuncture of the jugular vein before and at 24, 48, 72, and 96 hours after the administration of oxytetracycline. The serum calcium concentrations were determined by atomic absorption spectrophotometry. The analysis of variance (ANOVA) was used to analyse the time effect of tetracycline treatment on the rumen contractions and serum calcium concentrations. There was a significant decrease (P < 0.01) in ruminal contractions following the application of oxytetracycline, with a maximum decrease at 24 hours following oxytetracycline application and a return to the initial rumen contraction frequency by 60—72 hours following the oxytetracycline application. The oxytetracycline administration resulted in a serum calcium decrease from 2.42 mmol.l^–1 to 2.26 mmol.l^–1 24 hours after the administration (P < 0.01). In conclusion, the administration of tetracycline in sheep can be associated with a decline in ruminal motility potentially causing production losses, particularly in lactating ewes. Despite the resulting transient production decreases, oxytetracycline remains the antibiotic drug of choice for the treatment of bacterial infections in small ruminants, including foot rot especially.