R. Bras. Zootec.01/Aug/2016;45(8):478-82.
Behavior affected by routine oxytocin injection in crossbred cows in the tropics
The objective of the study was to determine the effect of routine intramuscular injection of oxytocin to induce milk ejection on behavior assessed in terms of stress and rectal temperature in crossbred cows (Bos indicus × Bos taurus) in the tropics of Veracruz, México. Immediately after calving, cows were milked twice a day (n = 210) and randomly assigned to receive at each milking: 10 IU (0.5 mL) of oxytocin intramuscularly (n = 70); 0.5 mL of saline solution intramuscularly (n = 70); or no injection (n = 70). The following behavioral indicators of stress were observed: trampling, kicking, tail movement, failure to eat, jumping to avoid injection, vocalization, urination, and defecation. After milking, rectal temperature (RT) was measured. Statistical analysis was performed using ANOVA and chi-square. There were no differences in terms of behavioral stress indicators or rectal temperature in cows injected with oxytocin or saline solution, but both groups had greater behavioral indicators of stress and RT compared with non-injected cows. Cows injected with oxytocin or saline solution manifested a higher percentage of animals that trampled (96.8%), kicked (32%), ceased eating (61.2%), moved the tail (81.2%), jumped (20.9%) and avoided the injection (78.2%), compared with non-injected cows. Cows injected with oxytocin and saline solution had higher rectal temperature (39.13±0.08 ºC) compared with non-injected cows (38.96±0.12 ºC). All injected cows had higher behavioral indicators of stress measurements and rectal temperature regardless of the solution, suggesting that cows injected routinely and intramuscularly do not become habituated to this, even though some cows were injected more than 600 times throughout lactation.