Effects of naloxone on calcium turnover in cows affected by milk fever

Milk fever is a metabolic disorder of calcium homeostasis that affects abou t 2 to 6% of postpartum cows. Current therapy is based on the administratio n of calcium gluconate. On the basis of the clinical signs, and given that endorphins increase at parturition, we supposed that endogenous opioid pept ides (EOP) could be responsible for this pathology. In this study, cows wit h milk fever were administered the opiate antagonist, Naloxone (Nx; experim ent 1) or Nx with calcium salts (experiment 2). In experiment 1, Nx induced the recovery of affected cows. The effects of Nx therapy, expressed in ter ms of proportion of recovered cows, of cows recovering in less than 30 min and cows requiring repeated treatments, were not statistically different th an those obtained by means of calcium administration (17/17, 100%; 10/17, 5 9% and 7/17, 41% vs. 33/35, 94%; 22/35, 63% and 11/35, 31%, respectively; N S). In experiment 2, a significantly higher ratio of cows recovered in less than 30 min in the group of animals treated with Nx in association with ca lcium salts, compared with the group of cows treated with the calcium tradi tional therapy (106/118, 90% for calcium-Nx treated cows vs. 34/62, 55% for calcium-treated cows). Moreover, in the group of cows treated with calcium -Nx, the number of cows requiring repeated treatments was significantly red uced and no unrecovered cows were observed. The results support the idea th at high EOP levels interfere with inward movement of calcium through the ce ll membrane and with calcium activity. The association of calcium and Nx at low dosage is a safe method to treat milk fever in cows and reduces muscul ar complications.