Grouping previously unknown bucks is a stressor with negative effects on reproduction

Abstract

Grouping previously unknown animals produces social stress, which might have negative effects on reproduction. The aims of the experiment were to determine if grouping unknown bucks (1) triggers a stress response and produces changes in body weight; (2) affects scrotal circumference, testosterone concentration, and semen quality; and (3) has differential effects between resident and introduced bucks. One group of nine Saanen bucks was transported and introduced (introduced bucks, group IG) to a group of eight Saanen bucks (resident bucks, group RG). On day 0, cortisol concentration and rectal temperature were determined, and from day -7 to day 29, body weight, scrotal circumference, and testosterone concentration were recorded and semen quality was determined. The stress response was different between groups: on several moments on day 0, resident bucks had greater cortisol concentration (P < 0.0001), while introduced bucks had higher rectal temperature (P = 0.02). Body weight decreased similarly in both groups from day -7 to day 2 (P < 0.0001), but on day 29, IG bucks were lighter than RG bucks (P = 0.05). Also, the reproductive response differed between groups: introduced bucks had lower scrotal circumference (P < 0.01), lower testosterone concentration (P = 0.02), and lower percentage of motile spermatozoa in the ejaculate (P = 0.05). It was concluded that grouping unknown bucks was stressful and negatively affected the reproduction, being more serious for the introduced than the resident bucks.

Bull-bull mounts in Holstein bulls: a survey of its incidence, possible causes, and consequences in Uruguayan bull’ breeders

“…In the same sense, in goats, it has been shown that mixing bucks provokes a marked increase in the number of aggressive (Sánchez-Dávila et al, 2018) and sexual interactions (Ungerfeld et al, 2013) in the group. This is also accompanied by increases in cortisol concentration (Giriboni et al, 2015;Sánchez-Dávila et al, 2018), and negatively affects testosterone production, testicular size, and seminal quality for at least 20 days (Giriboni et al, 2015). Although in this survey the seminal quality was not evaluated, some breeders mentioned the negative effect of mounting between bulls on it, as well as on libido, affecting directly even in marketing (return of bulls).…”

Reproduction in Small Ruminants (Goats)

“…Previous studies have evaluated the social hierarchy in rams raised in pairs, identifying that the dominant males exhibit a greater sexual precocity and a greater reproductive capacity compared to the subordinate males. A negative influence on testosterone production has also been reported, due to the stress of the grouping of bucks [34][35][36].…”

“…Among the responses at the physiological level present in male goats in stressful situations is the secretion of glucocorticoids (GC), which exert a negative feedback effect on the hypothalamic-pituitary-gonadal axis, reducing the synthesis of GnRH and together thereby inhibiting the synthesis of gonadotropins and sex steroid hormones [34,39]. This endocrine mechanism aims to stimulate the body to respond to stressors, such as loss of appetite, suppression of the immune system, energy mobilization, vasoconstriction, and loss of erection and receptive sexual behaviors [42].…”

Progesterona y respuesta de estrés: mecanismos de acción y sus repercusiones en rumiantes domésticos. Revisión

“…En muchas situaciones vinculadas a la producción animal, las respuestas indicadoras de estrés no logran modificar la situación que las generó (25) . Esto sucede, por ejemplo, luego del destete, en que los animales no logran juntarse nuevamente (26) , durante el transporte en que el animal no puede evitar su traslado, o durante el reagrupamiento social (27) , en que el animal debe adaptarse a convivir con nuevos individuos previamente desconocidos. En estos casos, las respuestas son costosas para el animal, pero no se modifica la situación, por lo que el resultado final es deletéreo en lugar de ventajoso.…”

“…In many situations related to animal production, the response is not enough to modify the situation (25) . This happens, for example, after weaning, in which animals fail to reunite again (26) , during the transport in which the animal cannot avoid its transfer, or after social grouping, as animals must adapt to live with new previously unknown individuals (27) . In these cases, the responses are expensive for the animal, and does not end changing the situation, so the result is deleterious rather than advantageous.…”