The aim of this study was to assess individual differences in temperament and stress response and quantify their impact on feed efficiency, performance, and methane (CH4) emissions in beef cattle. Eighty-four steers (castrated males) (Charolais or Luing) were used. Temperament was assessed using two standardized tests: restlessness when restrained [crush score (CS)] and flight speed (FS) on release from restraint. Over a 56-day period individual animal dry matter intake (DMI) and weekly body weight was measured. Ultrasound fat depth was measured at the end of 56 days. Average daily gain (ADG), feed conversion ratio (FCR), and residual feed intake (RFI) were calculated. After the 56-day test period, animals were transported in groups of six/week to respiration chamber facilities. Blood samples were taken before and 0, 3, 6, and 9 h after transport. Plasma cortisol, creatine kinase (CK), glucose, and free fatty acids (FFA) were determined to assess physiological stress response. Subsequently, CH4 emissions were measured over a 3-day period in individual respiration chambers. CS (1.7 ± 0.09) and FS (1.6 ± 0.60 m/s) were repeatable (0.63 and 0.51, respectively) and correlated (r = 0.36, P < 0.001). Plasma cortisol, CK, and FFA concentrations increased after transport (P = 0.038, P = 0.006, and P < 0.001, respectively). Temperament (CS) and CK concentration were correlated (r = 0.29; P = 0.015). The extreme group analysis reveals that excitable animals (FS; P = 0.032) and higher stress response (cortisol, P = 0.007; FFA, P = 0.007; and CK, P = 0.003) were associated with lower DMI. ADG was lower in more temperamental animals (CS, P = 0.097, and FS, P = 0.030). Fat depth was greater in steers showing calmer CS (P = 0.026) and lower plasma CK (P = 0.058). Temperament did not show any relationship with RFI or CH4 emissions. However, steers with higher cortisol showed improved feed efficiency (lower FCR and RFI) (P < 0.05) and greater CH4 emissions (P = 0.017). In conclusion, agitated temperament and higher stress responsiveness is detrimental to productivity. A greater stress response is associated with a reduction in feed intake that may both increase the efficiency of consumed feed and the ratio of CH4 emissions/unit of feed. Therefore, temperament and stress response should be considered when designing strategies to improve efficiency and mitigate CH4 emissions in beef cattle.

In beef cattle, feeding behaviour and activity are associated with feed efficiency and methane (CH4) emissions. This study aimed to understand the underlying traits responsible for the contribution of cattle behaviour to individual differences in feed efficiency, performance and CH4 emissions. A total of 84 steers (530±114 kg BW) of two different breeds (crossbreed Charolais and Luing) were used. The experiment was a 2×2×3 factorial design with breed, basal diets (concentrate v. mixed) and dietary treatments (no additive, calcium nitrate or rapeseed cake) as the main factors. The individual dry matter intake (DMI; kg) was recorded daily and the BW was measured weekly over a 56-day period. Ultrasound fat depth was measured on day 56. Based on the previous data, the indexes average daily gain, food conversion and residual feed intake (RFI) were calculated. The frequency of meals, the duration per visit and the time spent feeding per day were taken as feeding behaviour measures. Daily activity was measured using the number of steps, the number of standing bouts and the time standing per day. Agonistic interactions (including the number of contacts, aggressive interactions, and displacements per day) between steers at the feeders were assessed as indicators of dominance. Temperament was assessed using the crush score test (which measures restlessness when restrained) and the flight speed on release from restraint. Statistical analysis was performed using multivariate regression models. Steers that spent more time eating showed better feed efficiency (P=0.039), which can be due to greater secretion of saliva. Feeding time was longer with the mixed diet (P<0.001), Luings (P=0.009) and dominant steers (P=0.032). Higher activity (more steps) in the pen was associated with poorer RFI, possibly because of higher energy expenditure for muscle activity. Frequent meals contributed to a reduction in CH4 emissions per kg DMI. The meal frequency was higher with a mixed diet (P<0.001) and increased in more temperamental (P=0.003) and dominant (P=0.017) steers. In addition, feed intake was lower (P=0.032) in more temperamental steers. This study reveals that efficiency increases with a longer feeding time and CH4 emissions decrease with more frequent meals. As dominant steers eat more frequently and for longer, a reduction in competition at the feeder would improve both feed efficiency and CH4 emissions. Feed efficiency can also be improved through a reduction in activity. Selection for calmer cattle would reduce activity and increase feed intake, which may improve feed efficiency and promote growth, respectively.

Respiration chambers are considered the ‘gold standard’ technique for measuring in vivo methane (CH4) emissions in live animals. However, the imposed isolation required may alter feeding behaviour and intake, which ultimately impact CH4 emissions. The aim of this study was to assess the impact of isolation within respiration chambers on feed intake and CH4 emissions with two different diets and breeds of beef cattle. In addition, a routine stressor (transport) was used to examine the relationship between individual stress responsiveness and changes in feed intake during isolation. Eighty-four steers (castrated males) (569 ± 5.7 kg bodyweight, BW) were divided into two groups and each group fed with one of two basal diets consisting of (g/kg dry matter, DM) either 50 : 50 (Mixed) or 8 : 92 (Concentrate) forage to concentrate ratios. Within each basal diet there were three supplementation treatments: (1) control, (2) calcium nitrate, and (3) rapeseed cake. The stress biomarkers plasma cortisol, creatine kinase (CK), and free fatty acids (FFA) were determined before (0 h) and after (30 min, 3 h, 6 h and 9 h) a 30-min journey, when steers were transported to the respiration chamber facilities. Methane emissions were measured over a 3-day period using individual respiration chambers. Dry matter intake (DMI) was assessed within the group-housed pens (4 weeks before entry to training pen), in the training pens and the chambers. Cortisol, FFA and CK increased (P < 0.05) after transport confirming a stress response. DMI (g/kg BW) decreased (P < 0.001) during isolation in the training pens (14.7 ± 0.28) and the chambers (14.3 ± 0.26) compared with that of the same animals in the group pens (16.8 ± 0.23). DMI during isolation decreased more in those animals which had an increased (P < 0.05) stress response during transport as measured by cortisol, FFA and CK. With the Mixed diet, the decline in DMI was estimated to result in an increase in CH4 (g/kg DMI) (r = 0.25, P = 0.001), which did not occur with the Concentrate diet. According to the results of this experiment, the stress associated with isolation reduces the DMI resulting in an increase in g CH4/kg DMI in fibrous diets. Habituation to isolation needs refinement in order to reduce the impact of stress on intake and therefore achieve more accurate estimates of CH4 emissions. Alternatively, modelling CH4 estimations according to behavioural and physiological changes associated with isolation stress would improve accuracy of CH4 estimations.

No abstract