Effects of Routinely Oxytocin Injection to Induce Milk Ejection on Some Reproductive Parameters of Crossbred Cows in the Tropics of Veracruz

The objective was to assess the effects of routine intramuscular injection ofoxytocin in crossbred milked cows in days to first service (DPS), number of services per conception (SC), percentage of abortions (PA), cumulative percentage of pregnant cows(PAVG) length of the embryo (LE), serum cortisol concentrations and milk production (PL). Cows were milked twice daily and randomly assigned to: (i) Received a routine intramuscular injection of oxytocin (10 IU / milking Injected Group, n=31) or (ii) not receive injection (Control group, n=29). Pregnancy diagnosis and measurement of the embryo was performed by ultrasonography 33(±4) days after artificial insemination. At 152.2±10 days in milk, several blood samples were taken before and after injection of the two groups of cows (Control, n=8 and Injected, n=7). The serum was processed and cortisol concentrations were determined by radioimmunoassay. Statistical analysis was performed using ANOVA and chi-square. The Control cowshad lower (P=0.05) percentage of abortions (3.8%) than Injected cows (PA=23%). The PAVG was higher (P=0.01) in Control group. Embryos from Control cow (19.0±2.0 mm) had greater (P=0.0001) length than those of Injected cows (14.22±1.4 mm). There were no differences (P=0.10) in DPS, SC and PL. Cortisol concentrations were higher (P=0.0003) in Injected cows (33.4±2.8 ng / ml) than Control cows (11.6±2.4 ng/ml) cows. In conclusion, routine intramuscular injection of oxytocin increased serum cortisol concentrations and affected some reproductive profiles; we suggest not using intramuscular injection of oxytocin routinely.