Comparative Investigation of
GnRH
‐Immunocastration and a Phytogenic Feed Additive on Reproductive Parameters, Testicular Echogenicity and Behavioural Activity in Young Holstein Bulls
Nurdan Coşkun, Oğuz Kaan Yalçin, Murat Yüksel, Cafer Tayyar Ateş, Hasan Basri Dingil, Fikret Karaca ABSTRACT
Managing aggressive behaviour in bulls often involves a trade‐off between handling ease and the anabolic benefits associated with endogenous testosterone production. This study compared the effects of GnRH‐immunocastration and a phytogenic feed additive on reproductive parameters, testicular echotexture and behavioural activity in young Holstein bulls aged 12–15 months. Bulls were allocated to either an immunocastration group (IC, n = 6) or a phytogenic feed additive group (PFA, n = 7). The IC group received two subcutaneous injections of 1 mL Bopriva (400 μg GnRH‐protein conjugate) at a three‐week interval, whereas the PFA group received 50 g/day of a phytogenic feed additive throughout the 90‐day experimental period. Evaluations included scrotal circumference (SC), serum testosterone concentrations, ultrasonographic testicular echotexture assessed by mean grey value (MGV) and behavioural observations. Repeated measurements obtained throughout the study were analysed using linear mixed models. Significant group × time interactions ( p < 0.001) were observed for SC, testosterone concentrations and MGV. In the IC group, testosterone concentrations and SC progressively decreased beginning on Day 15, while MGV values declined from Day 30 onward. In contrast, the PFA group maintained relatively stable testosterone concentrations and ultrasonographic echotexture throughout the observation period. Qualitative behavioural observations indicated reduced mounting attempts and restlessness in both groups during the follow‐up period. Immunocastration induced marked suppression of reproductive parameters and alterations in testicular echotexture in young bulls. Under the conditions of this study, supplementation with the phytogenic feed additive was associated with relatively stable reproductive parameters, while qualitative reductions in behavioural activity were also observed. Further studies including untreated control groups and quantitative behavioural scoring systems are warranted.