Exposure to negative stimuli or stress can manifest in general changes in cognitive processing. This study aimed to investigate if a spatial maze task could be used to identify stress-induced differences in the cognitive performance of sheep. Two negative stimuli were used to test the hypothesis. For a negative pre-treatment (‘dog’ pre-treatment), sheep were moved individually to a holding yard at the beginning of the maze where they were exposed to a dog for 3min, for 5 consecutive days. Alternative to the dog pre-treatment, sheep were moved in small groups to the same holding yard, for the same amount of time, where they received a feed reward (‘food’ pre-treatment). For a during-test stimulus, white noise was played as sheep moved through the maze (‘noise’ treatment). Sixty-four male castrated lambs were allocated to one of four groups: dog and noise, food and noise, dog and no noise, or food and no noise. Sheep traversed the maze on 3 consecutive days and the total time to complete the maze, the number and the duration of errors made were used to assess cognitive performance. Maze results were analysed using GLMM, LMM and linear contrasts. The noise increased both total time (140s vs. 105s, P=0.043) and error time (67s vs. 56s, P=0.044) on day 1. The dog pre-treatment increased error time compared to the food pre-treatment (81s vs. 41s, P=0.041) and tended to increase the number of errors made on day 1 (1.5 errors vs. 1.2 errors, P=0.057). Neither noise nor dog pre-treatment influenced cognitive performance on days 2 or 3. Results suggest that both stimuli affected cognitive performance in the maze by impeding initial problem solving. The maze used demonstrates the ability to identify differences in cognition.

In this study we test the hypothesis that selecting sheep for a low behavioural reactivity to stressful situations will improve their metabolic efficiency, and thereby feed efficiency, during a controlled trial in an animal house. Twenty-four Merino wethers were used, 12 each from lines selected for high (HBR) and low (LBR) behavioural reactivity to stressful stimuli (human presence and social isolation). The sheep were habituated to the experimental procedures for 10 days, followed by 45 days during which voluntary feed intake was measured so that total daily energy intake was quantified. The sheep were weighed twice weekly before daily feeding. Feed efficiency was determined by measuring net feed intake, average daily weight gain and body condition score. Our hypothesis was not supported by the results of this study. There was no difference between LBR and HBR sheep in average daily weight gain or body condition score. The net feed intake of HBR sheep was lower than that of LBR sheep (P = 0.02), indicating that under the conditions of our experiment, HBR sheep were actually more feed efficient than LBR sheep. This study was carried out on sheep with steady intakes and in familiar surroundings. It is possible that LBR sheep may be more efficient than HBR sheep in more stressful situations.

Metabolic rate and energy consumption increase through the activation of the hypothalamic-pituitary-adrenal axis when an animal is exposed to a stressor. Residual feed intake (RFI) as a measure of efficiency has been shown to be related to exogenous adrenocorticotropin hormone (ACTH)-stimulated cortisol concentrations, which is indicative of the relationship between an animal's response to stress and the efficiency with which the energy is used for growth and production. In this study, we tested the hypothesis that sheep with low post-ACTH serum cortisol concentration relative to the other sheep in the flock have lower RFI values and lower cortisol concentrations following insulin-induced hypoglycemia. Adrenocorticotropin hormone (2.0 μg/kg body weight)-stimulated cortisol concentrations were measured in 100 sheep. The extreme responders were selected (n = 12 high cortisol, n = 12 low cortisol), and feed efficiency and body composition parameters were measured. A second ACTH challenge and an insulin challenge were administered. More efficient sheep (more negative RFI value) were found to have lower (P < 0.05) cortisol concentrations following both an ACTH challenge and an insulin challenge. Low-cortisol sheep (low response to ACTH or insulin) were found to have a lower (P < 0.05) proportion of fat tissue in comparison to the high-cortisol animals. These data clearly indicate that an animal's response to exogenous ACTH or insulin-induced hypoglycemia as a stressor is related (P < 0.05) to efficiency of energy use when measured as RFI. These data have important implications in enabling identification of animals that are superior in terms of feed efficiency and for understanding the physiological mechanisms underlying efficiency of energy use.

Deficits in selective attention have been associated with poorer driving ability in older drivers. Along with declines in selective attention, Alzheimer's disease (AD) patients also show deficits in effectively integrating stimulus features processed within distinct cortical areas due to the disruption of corticortical connections. This study examined the relative contribution of selective attention and sensory integration processes to on-road driving in healthy elderly and patients with very mild dementia. Forty-one healthy elderly and twenty-three early AD patients were administered two visual search tasks identical in selective attention demands but differing in demands placed on cross-cortical interactions: Subjects were required to integrate a target's motion with either a) its luminance contrast (black or white) or b) its isoluminant color (red or green). Because luminance and motion are both processed within the dorsal stream while color is processed within the ventral stream, motion/color integration places greater demands on cross-cortical interactions than motion/luminance integration. Step-wise regression analyses were performed separately for each group on task summary measures (slope, search accuracy, overall response time) as predictors of subjects' performance on a standardized road test. Road test error rates were higher in AD than healthy elderly drivers. While healthy elderly performed comparably on the two search tasks (indicating intact sensory binding), AD patients displayed a selective decrease in search accuracy in the motion/color task (indicating an additional decline in cross-cortical sensory binding). Slopes of both tasks and motion/luminance search accuracy were significant predictors of road test score for healthy elderly, whereas motion/color slope and search accuracy were significant predictors of road test score for AD patients. These results provide confirmation of a sensory binding deficit associated with neocortical disconnectivity in AD, and suggest that the relative contribution of selective attention and sensory integration deficits to driving performance differs across healthy elderly and AD patients: In healthy elderly, selective attention measures most strongly predicted driving performance, whereas cross-cortical binding measures were more sensitive driving predictors in AD patients. Computerized tasks designed to specifically assess these distinct processes may therefore prove particularly effective in differentially predicting driving risk in aging and AD.

An animal's response to a stressor is to increase metabolic rate, and thus energy consumption through the activation of the hypothalamic–pituitary–adrenal axis. Changes to energy use by an animal are likely to influence the efficiency with which it is utilised. In this study, we tested the hypothesis that less efficient sheep are more responsive to exogenous administration of adrenocorticotropin hormone. This was done by firstly determining the appropriate dose (0.4, 1.6 or 6.4μg/kg LW) and peak serum cortisol response time (45min) to exogenous administration of adrenocorticotropin hormone in a pilot study (n=3 sheep). Following this, adrenocorticotropin hormone (2.0μg/kg LW) stimulated cortisol levels were measured in a larger group of sheep (n=50) of known feed efficiency (feed conversion ratio and residual feed intake values). Less efficient sheep (more positive residual feed intake values) were found to have a greater (P<0.001) increase in cortisol concentration in comparison to more efficient animals. Those sheep which had higher levels of cortisol also had a greater proportion (P<0.001) of fat tissue. These data clearly demonstrated that efficiency of energy use, when measured as residual feed intake, is significantly related to an animal's stress response. These findings have important implications for understanding the physiological mechanisms underpinning efficiency of energy use, and may be useful in successfully identifying animals which are superior in terms of feed efficiency.

The concept of residual feed intake (RFI), in determining differences among animals in converting feed into body tissue, was first raised in 1963. Feed efficiency is typically calculated as a function of liveweight gain (LWG) and feed intake (FI). Historically two versions of the same model were proposed, one where FI was adjusted for liveweight (LW) and LWG, and the other where LWG was adjusted for FI and LW. Variation in LWG or FI could then be partitioned into two parts; that which is expected and can be attributed to differences in FI or LWG; and that which is the residual portion, which is the deviation from the expected value based on regression, and therefore not accounted for by differences in FI or LWG. Based on this definition, it is the residual portion which is the measure of efficiency. Both within a livestock industry and between different livestock industries there is no set model for calculating RFI. This paper evaluated four models used to calculate RFI and one model used to calculate residual LWG (RLWG) at a standard level of nutrition. They were the main model currently in use in the Australian beef cattle industry (RFIB), the original models proposed in 1963 (RFI1963; RLWG1963); a French model which included ultrasound measures of muscle and fat depth (RFIF) and the use of the Australian feeding standards to calculate predicted intake and thus RFI (RFISCA). Using feed intake, liveweight and body composition data generated from the same group of sheep (n=52) at two ages (6mo, 13mo), the relative merits of each model were evaluated and compared to the other models, to determine the most appropriate model to calculate RFI for sheep. For all the models except that used to calculate RLWG, over half of the variation in FI could be explained by the model. The amount of variation in FI accounted for depended on the parameters included and the dataset, with less variation in FI explained by the specific models in the older animals. The RFIF model, which included measures of body composition, accounted for the greatest proportion of the variation in FI and as such suggests that the inclusion of body composition parameters is likely to more accurately reflect true biological efficiency.

Residual feed intake (RFI) is a measure of feed efficiency calculated as the difference between an animal’s actual intake and its expected intake based on its liveweight and growth rate over a specified period of time (Richardson, Herd et al. 2002). The efficiency with which an animal utilises energy during growth, is dependent on a number of physiological factors including body composition and the relative proportions of lean tissue mass (LTM) and fat tissue mass (FTM), due to differences in the energy cost of depositing and maintaining these tissues. Protein or lean tissue is continually degraded and resynthesised and thus the rate at which this occurs may contribute to the variation in energy required by an animal for maintenance and growth (Archer, Richardson et al. 1999). The objective of this work was to determine the relationship between feed conversion ratio (FCR, kg feed:kg gain) and residual feed intake (RFI) with body composition in rams at six months of age (6mo), and then again in the same rams at thirteen months of age (13mo).

Measuring differences in the efficiency of converting feed to liveweight gains of beef cattle depends on assessments of feed intake and animal growth over a specified period. Previous studies have shown that feed intake can be measured with sufficient precision after 35 days, however, to assess growth rate with acceptable precision, a feeding period of 70 days is required when the cattle are weighed fortnightly. In order to test if more frequent weighing could improve the precision of estimates of liveweight, or reduce the duration of tests, animals were tested in units where an automatic weighing system recorded the liveweight of an animal every time it entered a feeder. Eight groups of beef bulls (171 animals in total) were tested. A random coefficient regression model including a cubic spline for time was used to estimate average daily gain. Evaluation of the residual variance, slope (average daily gain), and its standard error from the models showed that through the use of automated liveweight measurement, the duration of tests could be decreased to 56 days without reducing the precision of estimates of liveweight change. Depending on the precision required, further decreases in testing time could be accommodated.

Net feed intake (NFI) is commonly used to identify animals that are more efficient at converting feed into weight gain, however, little work has evaluated the potential to use NFI in the Australian sheep industry. Net feed intake is moderately heritable (François et al. 2002) and negatively correlated with lean carcass (Knott et al. 2003). Body composition might have a regulatory role in influencing efficiency (Perry et al. 1997). We hypothesised that variation in the efficiency of energy utilisation in growing sheep, and therefore NFI, may be explained by differences in body composition.

Net feed intake (NFI) and gross feed conversion ratio (FCR) are commonly used to identify animals that are more efficient at converting feed into gain, however little work has evaluated the potential to use NFI or FCR in the sheep industry. Variation of NFI and FCR between different stages of maturity, and the influence of body composition on NFI and FCR were studied in a group of composite sire ram lambs. The results suggest that careful consideration of the stage of maturity of animals when measuring NFI and FCR is necessary when using these parameters for selection purposes. NFI and FCR were also found to be highly correlated to carcass lean tissue mass, which supports previous work undertaken in cattle.