Interpretative Summary: Zinc injection as a novel castration method in beef bulls: effects on performance, behavior, and testosterone and haptoglobin concentration
By: Megan LaFollette
In March 2018, Journal of Animal Science published an article that investigated the use of a zinc injection as novel castration in beef bulls. In the United States, 15 million beef bulls are castrated to reduce aggression, prevent breeding, and improve meat quality. Unfortunately, castrating bulls results in stress and pain which reduces performance and welfare. Currently, beef bulls are primarily castrated using either surgical or band castration, without clear preference. An alternative to traditional castration methods is using an injectable product. Zinc acetate neutralized by L-histidine is an approved potential injectable product for investigation in beef bulls by the FDA, but its efficacy is unknown. This study’s objective was to determine the effects of feedlot cattle castration and castration method on growth performance, behavior, and serum testosterone and haptoglobin concentration.
In this study, 180 crossbred beef bulls were split into 3 treatment groups: zinc injection, band castration, or intact bulls. During feedlot processing, zinc injection cattle were given 1 mL of Zn solution into each testis while band castration cattle were banded. Banded cattle did not receive a growth promoting implant. Each treatment group had 6 pens and 10 cattle per pen for a total of 60 cattle per treatment. Before splitting into treatment groups, bulls were blocked by bodyweight (337 ± 10.9, kg). A subset of 54 animals (3 per pen) had behavior evaluated via accelerometers, testis width and scrotal circumference measured, and blood drawn to determine serum haptoglobin and testosterone. During slaughter, testes were collected from 7 zinc injection cattle and 6 intact bulls for final testes weight and histopathological evaluation. Bodyweight and feed consumption were also recorded.
Results showed that castration method (zinc, band, or none) impacted growth performance, haptoglobin concentration, and behavior. Both zinc injection cattle and intact bulls had higher performance as shown by higher final bodyweight, average daily gain, and gain to feed ratio than banded cattle. All treatments had similar dry matter intake. Zinc injection cattle had higher serum haptoglobin on days 1-7 than intact bulls or banded cattle which may indicate stress and pain due to inflammation. For behavior, both zinc injection cattle and intact bulls had higher motion index and step count which may be a result of increased aggressiveness from testosterone levels. However, all treatments had similar overall standing time and lying bouts.
Results showed that castration method impacted behaviors related to pain, testicular histopathology and serum testosterone. Indications of pain behavior (increased standing and lying, decreased steps) were seen between day 1-3 post injection for zinc injection cattle and between days 10-12 banded cattle. When evaluating testicular function, histopathological evaluation revealed that zinc injection testes were degenerative and reproductively nonviable. Intact bull testes were normal. However, both zinc injection cattle and intact bulls had similar levels of serum testosterone. After day 14, banded cattle’s serum testosterone levels were not detectable.
Overall, this study suggests that zinc injection has minimal efficacy as a castration method for feedlot bulls since it did not remove testicular function and endogenous male androgens. However, zinc injection did appear effective for sterilization since it appeared to cause the testes to be reproductively unviable. Overall, zinc injected cattle appeared more similar to intact bulls than banded cattle.
To view the article in full, "Zinc injection as a novel castration method in beef bulls: effects on performance, behavior, and testosterone and haptoglobin concentration," visit the Journal of Animal Science.