ABSTRACT.To evaluate the effect that immunocastration has on behaviour, testosterone and cortisol levels of feedlot Holstein bulls, 720 intact animals aged between 7 and 8 months, weighing 232±1.19 kg were randomly assigned to two treatments: immunocastration using the Bopriva vaccine and a placebo (360 animals per treatment). The bulls were slaughtered at day 239 of treatment. Animals were vaccinated on days 1, 21, 101, and 181, and on those same days testosterone levels were measured; while cortisol, glucose and creatin kinase measurements were done on day 181 and during exanguination at slaughter. Sexual, aggressive and social behaviours were evaluated and it was found that intact bulls showed a higher average of head butts, mounting, threats, flehmen sign and sniffing (P<0.05), no differences were found for vocalisations, lowering of the head and grooming (P>0.05). Testosterone levels in intact bulls remained at 0.47ng/mL throughout the study, however, by day 181 differences (P<0.05) were observed in immunised bulls, with values of 0.22ng/mL. At slaughter, testosterone levels were 0.21 ± 0.06 ng/mL in immunocastrated bulls and 0.54 ± 0.06 ng/mL in the placebo group. The use of immunocastration with Bopriva has shown to be effective to reduce testosterone, sexual and aggressive behaviours on Holstein bulls.
Se compararon los resultados económicos de la engorda entre animales enteros y animales inmunocastrados con la vacuna anti GnRH, Bopriva. Se incluyeron 510 novillos Holstein entre 7 y 8 meses de edad con peso inicial de 220±1.19 kg. 269 novillos fueron vacunados y 241 no recibieron tratamiento. El grupo vacunado recibió cuatro inmunizaciones: 24 horas después del arribo a la engorda y 21, 101 y 181 días después de la primera vacunación. Los animales en el grupo control recibieron un placebo. Los efectos del tratamiento sobre peso de la canal caliente, peso de la canal fría, el espesor de la grasa dorsal, la grasa pélvica, renal y cardiaca, área del ojo de la costilla y marmoleo fueron analizados utilizando un modelo lineal que incluyó la media general, el efecto fijo de tratamiento, el efecto aleatorio de corral dentro de tratamiento (error experimental) y el componente aleatorio de animal dentro de corral (error de muestreo). La utilidad de cada grupo fue obtenida restando el costo total al ingreso total. A excepción de peso de la canal fría y marmoleo, con las variables estudiadas se estimaron rendimiento final al corte y grado de calidad. El peso promedio de las canales del grupo vacunado fue superior (P
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