Behavior, physiology, and performance of bulls mixed at the onset of finishing to form uniform body weight groups

Abstract

In some production settings, beef bulls are mixed at the beginning of the finishing period to obtain homogeneous groups to facilitate finishing and to produce more homogeneous carcasses. Given the stress induced by mixing, we questioned whether this practice was profitable. Sixty-four young bulls were finished in groups of four over 8 mo. They were either mixed or unmixed and had either homogeneous vs. heterogeneous BW at the beginning of finishing. Behavioral traits (social behavior following mixing and general activities during the finishing period), stress measurements (cortisol concentration, adrenal weight, catecholamine-synthesizing enzyme activity, and pain sensitivity), and production traits (growth rate, homogeneity, feed efficiency, and carcass measurements) were evaluated. Bulls reacted to the mixing with increased frequency of social interactions (agonistic interactions: 17.9 in mixed vs. 1.2 in unmixed bulls, P < 0.001; sexual interactions: 9.6 vs. 1.7, P < 0.001; nonagonistic interactions: 5.25 vs. 3.1, P < 0.05). Agonistic and sexual interactions were more frequent between bulls of homogeneous BW (P < 0.05). Throughout the finishing period, the synchronization of activity tended to be lower between mixed bulls (P = 0.09). At slaughter, the activity of tyrosine hydroxylase, a catecholamine-synthesizing enzyme, was increased in mixed bulls (1.52 vs. 1.16 nmol.h(-1).mg(-1), P < 0.05), which may indicate chronic stress. No differences were noted in ADG or carcass traits among treatments. The variability of BW within groups increased in groups that were initially homogeneous, whereas it decreased in groups that were initially heterogeneous. In conclusion, mixing young beef bulls at the beginning of the finishing period did not have detrimental effects on health and production, but mixing induced stress, perhaps due to decreased cohesion within groups. Thus, we failed to confirm the proposed benefit of mixing bulls to homogenize their BW at the onset of finishing because BW homogeneity within groups was not maintained throughout the finishing period.

Scientific Opinion on the welfare of cattle kept for beef production and the welfare in intensive calf farming systems

“…However, in heifers, there was no habituation in terms of elicitation of agonistic interactions after regrouping (Raussi et al, 2005). After mixing, agonistic behaviours were more frequent in homogenous groups of bulls (in terms of weight) than in more heterogeneous groups (Mounier et al, 2005). This also led to more cohesive behaviours in a food competition test, less fear responses during separation and lower cortisol levels during pre-slaughter handling (Mounier et al, 2006) in the unmixed groups, whilst homogeneity of body weight could not be maintained throughout the finishing period (Mounier et al, 2005).…”

“…After mixing, agonistic behaviours were more frequent in homogenous groups of bulls (in terms of weight) than in more heterogeneous groups (Mounier et al, 2005). This also led to more cohesive behaviours in a food competition test, less fear responses during separation and lower cortisol levels during pre-slaughter handling (Mounier et al, 2006) in the unmixed groups, whilst homogeneity of body weight could not be maintained throughout the finishing period (Mounier et al, 2005). From a health perspective, mixing of animals has disadvantages compared to all-in all-out systems as this may prolong disease outbreaks and increase the exposure to pathogens.…”

Effect of concentrate feeder design on performance, eating and animal behavior, welfare, ruminal health, and carcass quality in Holstein bulls fed high-concentrate diets1

“…To analyze the general activity (standing, lying, eating concentrate and straw, drinking, and ruminating) in the pen and social behavior (nonagonistic, agonistic, and sexual interactions) of animals, a scan sampling procedure was used. Records correspond to total counts of each activity in a pen (Mounier et al, 2005). Animal behavior was recorded on d 1, 3, 5, 8, 14, and 26 and every 28 d throughout the study from 0830 to 1100 h by scan sampling as described by Rotger et al (2006), Robles et al (2007), Mach et al (2008), and Marti et al (2010).…”

Indicadores Conductuales y Fisiológicos para Evaluar el Transporte de Novillos al Rastro y su Relación con el pH de la Carne

“…La mayor frecuencia de interacciones afiliativas en los bovinos durante los viajes pudo ser consecuencia de la ausencia de mezcla social, que favoreció el mantenimiento de la cohesión y estabilidad del grupo (Millman y Los encuentros antagónicos pueden causar estrés y un incremento de las concentraciones de cortisol sérico (Mounier et al, 2005), aspecto presente en este estudio. Se ha sugerido que las manifestaciones conductuales de los animales ante un agente estresante están de manera estrecha asociadas con el incremento de cortisol, debido a que sus receptores se encuentran localizados en regiones específicas involucradas con la regulación hormonal (hipotálamo e hipófisis) y, en particular, con el sistema límbico, que juega un papel relevante en las conductas emocionales.…”

“…Los cambios fisiológicos observados (Cuadro 4) que no comprometieron el metabolismo proteico, ni los constituyentes celulares sanguíneos, indican que los novillos mantuvieron la homeostasis por factores relacionados con su buena condición física y adaptabilidad (Cockram et al, 2004), el diseño del vehículo (Lambooij et al, 2012), las condiciones del viaje, la ausencia de mezcla social (Mounier et al, 2005) y, posiblemente por otros factores que requieren ser evaluados en estudios posteriores. De igual manera, los niveles sanguíneos de βHB encontrados, acordes con los parámetros basales para la especie (Kaneko et al, 2008), sugieren que los bovinos requieren varios días de ausencia de alimento para experimentar ayuno fisioló-gico (Tadich et al, 2003).…”