Variation In Behavioral Responses Research Articles

Context Matters: Multiple Novelty Tests Reveal Different Aspects of Shyness-Boldness in Farmed American Mink (Neovison vison).

Animal personality research is receiving increasing interest from related fields, such as evolutionary personality psychology. By merging the conceptual understanding of personality, the contributions to both fields of research may be enhanced. In this study, we investigate animal personality based on the definition of personality traits as underlying dispositional factors, which are not directly measurable, but which predispose individuals to react through different behavioural patterns. We investigated the shyness-boldness continuum reflected in the consistency of inter-individual variation in behavioural responses towards novelty in 47 farmed American mink (Neovison vison), which were raised in identical housing conditions. Different stages of approach behaviour towards novelty, and how these related within and across contexts, were explored. Our experimental design contained four tests: two novel object tests (non-social contexts) and two novel animated stimuli tests (social contexts). Our results showed consistency in shyness measures across multiple tests, indicating the existence of personality in farmed American mink. It was found that consistency in shyness measures differs across non-social and social contexts, as well as across the various stages in the approach towards novel objects, revealing that different aspects of shyness exist in the farmed American mink. To our knowledge this is the first study to reveal aspects of the shyness-boldness continuum in the American mink. Since the mink were raised in identical housing conditions, inherited factors may have been important in shaping the consistent inter-individual variation. Body weight and sex had no effect on the personality of the mink. Altogether, our results suggest that the shyness-boldness continuum cannot be explained by a simple underlying dispositional factor, but instead encompasses a broader term of hesitating behaviour that might comprise several different personality traits.

Variability of behavioural responses to transcranial magnetic stimulation: Origins and predictors

Transcranial magnetic stimulation (TMS) may modulate the excitability of local cortical stimulation sites and distant functionally interconnected regions for minutes, hours or even days. The effects of TMS suggest that it not only acts on activity of the stimulated area, but also on its connections with remote areas. Due to these properties one of the main rationales for the application of TMS in stroke patients is to improve imbalance in interhemispheric inhibition. However, given that TMS may have excitatory or inhibitory effects the impact of stimulation is not easy to predict. In this review, we discuss the different factors that determine the magnitude and quality of physiological and behavioural responses to TMS. Whether TMS is mainly excitatory or inhibitory not only depends on the parameters of stimulation such as pulse frequency and duration, but also on baseline activity of neural tissue before stimulation, or even on cognitive factors such as attention. A major challenge for the application of TMS as therapy method is to identify predictors of positive effects in individual patients. Neuroimaging studies measuring hemodynamic or electrophysiological responses show that changes in interhemispheric competition or adaptations of functional networks in patients with focal brain lesions may predict the individual response to brain stimulation. Such techniques have the potential to select the most appropriate among different intervention methods for an individual patient.

Variation in behavioral responses of the South American sea lion to tourism disturbance: Implications for tourism management

AbstractDue to the highly predictable patterns of occupancy on land, pinnipeds are one of the main marine resources observed by tourists, which, in turn, could strongly perturb their behavior. We analyzed the behavioral responses of the South American sea lion (Otaria byronia) to the presence of tourists and its variation according to temporal (2012 vs. 2013 austral summer months), spatial (breeding vs. nonbreeding sites of the colony), and age/sex class (adult males vs. subadult males vs. females) factors, and determined the relationship between the degree of responses by sea lions and the distance of the vessel to the colony, visitation time, and tourist behavior. We recorded 1,232 boat visits during 2012 and 2013. Subadult males were the age/sex class most affected in the breeding site, followed by adult females at the nonbreeding site. More disturbing conduct by tourists, longer visitation time, and vessels closer to the colony caused greater responses by sea lions. The established minimum distance from the colony is not enforced, generating an adverse response by sea lions. We recommend the development of management plans with the local coastal communities to decrease the impact of ecotourism on the species and enhance the sustainability of this industry.

A simple rapid categorization model accounts for variations in behavioral responses across rapid scene categorization tasks

A simple rapid categorization model accounts for variations in behavioral responses across rapid scene categorization tasks

Personality predicts social dominance in male domestic fowl.

Individuals in social species commonly form dominance relationships, where dominant individuals enjoy greater access to resources compared to subordinates. A range of factors such as sex, age, body size and prior experiences has to varying degrees been observed to affect the social status an individual obtains. Recent work on animal personality (i.e. consistent variation in behavioural responses of individuals) demonstrates that personality can co-vary with social status, suggesting that also behavioural variation can play an important role in establishment of status. We investigated whether personality could predict the outcome of duels between pairs of morphologically matched male domestic fowl (Gallus gallus domesticus), a species where individuals readily form social hierarchies. We found that males that more quickly explored a novel arena, or remained vigilant for a longer period following the playback of a warning call were more likely to obtain a dominant position. These traits were uncorrelated to each other and were also uncorrelated to aggression during the initial part of the dominance-determining duel. Our results indicate that several behavioural traits independently play a role in the establishment of social status, which in turn can have implications for the reproductive success of different personality types.

Inter-individual variability of stone marten behavioral responses to a highway.

Efforts to reduce the negative impacts of roads on wildlife may be hindered if individuals within the population vary widely in their responses to roads and mitigation strategies ignore this variability. This knowledge is particularly important for medium-sized carnivores as they are vulnerable to road mortality, while also known to use available road passages (e.g., drainage culverts) for safely crossing highways. Our goal in this study was to assess whether this apparently contradictory pattern of high road-kill numbers associated with a regular use of road passages is attributable to the variation in behavioral responses toward the highway between individuals. We investigated the responses of seven radio-tracked stone martens (Martes foina) to a highway by measuring their utilization distribution, response turning angles and highway crossing patterns. We compared the observed responses to simulated movement parameterized by the observed space use and movement characteristics of each individual, but naïve to the presence of the highway. Our results suggested that martens demonstrate a diversity of responses to the highway, including attraction, indifference, or avoidance. Martens also varied in their highway crossing patterns, with some crossing repeatedly at the same location (often coincident with highway passages). We suspect that the response variability derives from the individual's familiarity of the landscape, including their awareness of highway passage locations. Because of these variable yet potentially attributable responses, we support the use of exclusionary fencing to guide transient (e.g., dispersers) individuals to existing passages to reduce the road-kill risk.

A Statistical Framework for Dealing with Endogeneity

We propose a general framework for dealing with endogeneity in models in marketing and economics. It consists of a multivariate, hierarchical, mixed discrete/continuous representation of behavioral response variables. Importantly, it includes a non-parametric approximation to unobserved sources of exogenous information. It complements the instrumental variables (IV) approach in that it may but does not need to include, observable instruments. After presenting the theoretical basis of the method, a simulation study reveals that parameters can be estimated consistently even if instruments are not observed. The proposed approach is applied in three case studies in business and economics. They include a case where a standard IV is inadequate in correcting for endogeneity bias, and two cases where IVs are not available. In the examples, the proposed framework corrects for endogeneity bias without recourse to IVs. Resulting policy actions are shown to be different from equivalent models that ignore endogeneity. We conclude that the approach has applications in marketing and economics as a framework for testing for conjectured endogeneity. The development of theoretical arguments motivating the investigation of endogeneity remains crucial, but even after such a rigorous theoretical analysis there will remain instances in which instruments are not available, cannot be found, or where empirically their quality is insufficient, in which case the proposed framework provides a useful alternative.

Temporal Dynamics of Religion as a Determinant of HIV Infection in East Zimbabwe: A Serial Cross-Sectional Analysis

BackgroundReligion is an important underlying determinant of HIV spread in sub-Saharan Africa. However, little is known about how religion influences changes in HIV prevalence and associated sexual behaviours over time.ObjectivesTo compare changes in HIV prevalence between major religious groups in eastern Zimbabwe during a period of substantial HIV risk reduction (1998–2005) and to investigate whether variations observed can be explained by differences in behaviour change.MethodsWe analysed serial cross-sectional data from two rounds of a longitudinal population survey in eastern Zimbabwe. Univariate and multivariate logistic regression models were developed to compare differences in sexual behaviour and HIV prevalence between religious groups and to investigate changes over time controlling for potential confounders.ResultsChristian churches were the most popular religious grouping. Over time, Spiritualist churches increased in popularity and, for men, Traditional religion and no religion became less and more common, respectively. At baseline (1998–2000), HIV prevalence was higher in Traditionalists and in those with no religion than in people in Christian churches (men 26.7% and 23.8% vs. 17.5%, women: 35.4% and 37.5% vs. 24.1%). These effects were explained by differences in socio-demographic characteristics (for Traditional and men with no religion) or sexual behaviour (women with no religion). Spiritualist men (but not women) had lower HIV prevalence than Christians, after adjusting for socio-demographic characteristics (14.4% vs. 17.5%, aOR = 0.8), due to safer behaviour. HIV prevalence had fallen in all religious groups at follow-up (2003–2005). Odds of infection in Christians reduced relative to those in other religious groups for both sexes, effects that were mediated largely by greater reductions in sexual-risk behaviour and, possibly, for women, by patterns of conversion between churches.ConclusionVariation in behavioural responses to HIV between the major church groupings has contributed to a change in the religious pattern of infection in eastern Zimbabwe.

Reduced Short Interval Cortical Inhibition Correlates With Atomoxetine Response in Children With Attention-Deficit Hyperactivity Disorder (ADHD)

Clinical trials in children with attention-deficit hyperactivity disorder (ADHD) show variability in behavioral responses to the selective norepinephrine reuptake inhibitor atomoxetine. The objective of this study was to determine whether transcranial magnetic stimulation-evoked short interval cortical inhibition might be a biomarker predicting, or correlating with, clinical atomoxetine response. At baseline and after 4 weeks of atomoxetine treatment in 7- to 12-year-old children with ADHD, transcranial magnetic stimulation short interval cortical inhibition was measured, blinded to clinical improvement. Primary analysis was by multivariate analysis of covariance. Baseline short interval cortical inhibition did not predict clinical responses. However, paradoxically, after 4 weeks of atomoxetine, mean short interval cortical inhibition was reduced 31.9% in responders and increased 6.1% in nonresponders (analysis of covariance t 41 = 2.88; P = .0063). Percentage reductions in short interval cortical inhibition correlated with reductions in the ADHD Rating Scale (r = 0.50; P = .0005). In children ages 7 to 12 years with ADHD treated with atomoxetine, improvements in clinical symptoms are correlated with reductions in motor cortex short interval cortical inhibition.

A pilot study to determine if a dietary mineral supplement can affect reactivity to stimuli by horses in training

Trainers have reported horses to be calmer and easier to train after receiving a calcium- and magnesium-rich mineral supplement derived from a calcified algae source. The purpose of this study was to test whether horses receiving this supplement were calmer than horses receiving a placebo. Fourteen 2-year-old Arabians in training were subjected to a ‘moving object reactivity test’ (MORT) and ‘handling reactivity test’ (HRT). The MORT involves quickly raising a bag suspended from the ceiling and scoring horses' reactions. The HRT involves placing horses into breeding stocks and scoring the horses’ nervousness. Horses were equipped with heart rate (HR) monitors and were scored by four observers blinded to treatment. Reactivity scores and HR were used to randomly striate the horses into two groups: a treated group (MIN) receiving 100 g of Aquacid/horse/day and a control group (CO) receiving a placebo. After supplementation for 60 days, horses were retested. Using PROC Mixed, changes from day 0 were examined. In the MORT, CO had an increase of 29 bpm (P=0.001), while MIN only showed a trend to increase (12 bpm; P=0.1). There was no difference between treatments (P=0.12). Reactivity scores during the MORT were not different between treatments (P=0.14) with CO horses increasing by 0.58 (1 to 5 scale) and MIN horses by 0.31. In the HRT, the peak HR of CO increased from day 0 by 17 bpm (P=0.009), but only by 11 bpm in the MIN (P=0.08). Reactivity scores for MIN horses improved by 0.45 (scale from 1 to 4) while the CO worsened by 0.04. Neither HRT measurement was significant (P=0.41 and P=0.33, respectively). Limited treatment differences suggest greater subject numbers were needed due to variability in behavioural responses despite some outcomes favouring MIN. Though inconclusive, results suggest anecdotal claims of calming effects may warrant further investigation.

Age-related variability in performance of a motor action selection task is related to differences in brain function and structure among older adults

Task performance for behaviors that engage motor cognitive processes may be particularly sensitive to age-related changes. One well-studied model of cognitive motor function involves engagement of action selection (AS) processes. In young adults, task conditions that add AS demands result in increased preparation times and greater engagement of bilateral dorsal premotor (PMd) and parietal cortices. The current study investigated the behavioral and neural response to a change in motor cognitive demands in older adults through the addition of AS to a movement task. Sixteen older adults made a joystick movement under two conditions during functional magnetic resonance imaging. In the AS condition, participants moved right or left based on an abstract rule; in the execution only (EO) condition, participants moved in the same direction on every trial. Across participants, the AS condition, as compared to the EO condition, was associated with longer reaction time and increased activation of left inferior parietal lobule. Variability in behavioral response to the AS task between participants related to differences in brain function and structure. Overall, individuals with poorer AS task performance showed greater activation in left PMd and dorsolateral prefrontal cortex and decreased structural integrity of white matter tracts that connect sensorimotor, frontal, and parietal regions—key regions for AS task performance. Additionally, two distinct patterns of functional connectivity were found. Participants with a pattern of decreased primary motor–PMd connectivity in response to the AS condition, compared to those with a pattern of increased connectivity, were older and had poorer behavioral performance. These neural changes in response to increased motor cognitive demands may be a marker for age-related changes in the motor system and have an impact on the learning of novel, complex motor skills in older adults.

Individual differences in activity levels in zebrafish (Danio rerio)

Individual differences and variation in behavioral responses have been identified in many animal species. These differences may be the result of genetic or environmental factors or the interaction between them. Analysis of individual differences in behavior may be important for many reasons. The zebrafish is a powerful model organism that is rapidly gaining popularity in behavioral brain research. However, individual differences have rarely been explored in zebrafish although significant variation in their performance has been reported. In the current study we identified individual differences in activity levels of zebrafish using a genetically heterogeneous population. Groups of zebrafish classified as high, medium, or low activity performers demonstrated consistent activity levels over a period of 7 days, and also in a subsequent open field task, suggesting stable individual differences as opposed to stochastic variation among subjects. We also uncovered a sex dependent relationship between behavioral measures. Female zebrafish in the high activity group preferred the top portion of the tank, whereas low activity females preferred the lower portion but males did not show such a relationship. The relationship between these two behaviors in females implies the potential existence of a behavioral syndrome persisting between contexts. Furthermore, females demonstrated a higher level of consistency in their behavior as compared to males, and the behavioral differences were found to be independent of both body size and weight of the tested subjects. The identification of individual differences in activity levels in zebrafish will allow the investigation of underlying genetic and/or environmental underpinnings.

The effect of breed in a hot environment on some welfare indicators in feedlot cattle

Heat stress has an important effect on the welfare of livestock and causes significant changes in biological functions. This study was carried out to investigate the behavioral differences of Brown Swiss (BS) and Holstein (H) feedlot cattle reared in a hot environment. All of the cattle were housed in a semi-open feedlot barn. The individual behavioral response variables measured were feeding, drinking, rumination, standing, resting, locomotor activity and elimination (urinating and defecating). For each animal, behavioral observations were recorded at 10 min intervals for 1 h starting at 06:00, 10:00, 13:00, 16:00, 20:00 and 23:00 h. The effect of breed, time of the day and hour of observation and the interactions of these factors were included in the model. The data were analyzed using the PROC GLM procedure in SAS. There were significant interactions between breed and time of observation for rumination (p0.05). BS cattle exhibited more frequent standing behavior at 13:00 h, whereas H cattle exhibited more frequent standing behavior at 16:00 h (p<0.01). The welfare of male H feedlot cattle was concluded to be more affected than that of male BS feedlot cattle when the ambient temperature was high (at 13:00 h).

Effect of glial cell line‐derived neurotrophic factor on behavior and key members of the brain serotonin system in mouse strains genetically predisposed to behavioral disorders

The effect of glial cell line-derived neurotrophic factor (GDNF) on behavior and on the serotonin (5-HT) system of a mouse strain predisposed to depressive-like behavior, ASC/Icg (Antidepressant Sensitive Cataleptics), in comparison with the parental "nondepressive" CBA/Lac mice was studied. Within 7 days after acute administration, GDNF (800 ng, i.c.v.) decreased cataleptic immobility but increased depressive-like behavioral traits in both investigated mouse strains and produced anxiolytic effects in ASC mice. The expression of the gene encoding the key enzyme for 5-HT biosynthesis in the brain, tryptophan hydroxylase-2 (Tph-2), and 5-HT1A receptor gene in the midbrain as well as 5-HT2A receptor gene in the frontal cortex were increased in GDNF-treated ASC mice. At the same time, GDNF decreased 5-HT1A and 5-HT2A receptor gene expression in the hippocampus of ASC mice. GDNF failed to change Tph2, 5-HT1A , or 5-HT2A receptor mRNA levels in CBA mice as well as 5-HT transporter gene expression and 5-HT1A and 5-HT2A receptor functional activity in both investigated mouse strains. The results show 1) a GDNF-induced increase in the expression of key genes of the brain 5-HT system, Tph2, 5-HT1A , and 5-HT2A receptors, and 2) significant genotype-dependent differences in the 5-HT system response to GDNF treatment. The data suggest that genetically defined cross-talk between neurotrophic factors and the brain 5-HT system underlies the variability in behavioral response to GDNF.

The amnestic syndrome: Applying the Rorschach Inkblot method for differential diagnosis

Dissociative processes were investigated in a man diagnosed with focal retrograde amnesia (FRA) following a traumatic head injury without any anterograde memory deficit. Findings were derived from the Rorschach Inkblot method, which was administered together with other performance-based tests and a self-report inventory for evaluating dissociative proneness in personality functioning. A substantial set of behavioral and test response variables indicated dissociation proneness and the activation of dissociative mechanisms. This conception was supported a few months following the evaluation when the patient reported a total spontaneous recovery of the memory deficit. The interplay between neurological and functional factors in FRA is discussed with a view for creating an integrated model.

Evaluacija interventnog programa prevladavanja osećanja kod dece na ranom osnovnoškolskom uzrastu

Ovo istraživanje ima za cilj da testira hipotezu o mogućnosti programa prevladavanja osećanja da proizvede značajan porast u navođenju konstruktivnih strategija prevladavanja averzivnih emocija. Za merenje navođenja strategija prevladavanja upotrebljen je Zadatak prevladavanja averzivnih osećanja (Saarni, 1997a). Uzorak je činilo 100 dece, prosečnog uzrasta od 7.8 godina. Polovina je prošla četvoromesečnu obuku interventnog programa prevladavanja osećanja, dok druga polovina nije bila izložena programu. Obe grupe su prošle tri merenja: pre implementacije programa, neposredno nakon implementacije programa i nakon 6 meseci od implementacije programa. Rezultati pokazuju da je kod dece koja su prošla interventni program, u odnosu na decu koja nisu bila izložena programu, došlo do značajnog povećanja u frekvenciji odgovora i širenja postojećeg verbalnog repertora novim, pozitivnim obrascima ponašanja u prevladavanju averzivnih osećanja. Najveći porast odgovora zabeležen je za emociju tuge, zatim besa, pa straha, i na kraju stida. Takođe je zabeležen i porast verbalnog navođenja konstruktivnih strategija u adaptivnom prevladavanju averzivnih osećanja tuge, straha, besa i stida, kao i značajna redukcija u navođenju nekonstruktivnih strategija. Ove promene su se održale kod dece koja su bila izložena programu i nakon 6 meseci od retestiranja. Rezultati istraživanja mogu se shvatiti kao preliminarna podrška u sprovođenju interventnih programa u pravcu širenja ideja o mogućim bihevioralnim odgovorima na različite emocionalno provokativne situacije.

Behavioral and physiological responses to subgroup size and number of people in howler monkeys inhabiting a forest fragment used for nature‐based tourism

Animals' responses to potentially threatening factors can provide important information for their conservation. Group size and human presence are potentially threatening factors to primates inhabiting small reserves used for recreation. We tested these hypotheses by evaluating behavioral and physiological responses in two groups of mantled howler monkeys (Alouatta palliata mexicana) at the "Centro Ecológico y Recreativo El Zapotal", a recreational forest reserve and zoo located in the Mexican state of Chiapas. Both groups presented fission-fusion dynamics, splitting into foraging subgroups which varied in size among, but not within days. Neither subgroup size nor number of people had an effect on fecal cortisol. Out of 16 behavioral response variables tested, the studied factors had effects on six: four were affected by subgroup size and two were affected by number of people. With increasing subgroup size, monkeys increased daily path lengths, rested less, increased foraging effort, and used more plant individuals for feeding. As the number of people increased, monkeys spent more time in lower-quality habitat, and less time engaged in social interactions. Although fecal cortisol levels were not affected by the factors studied, one of the monkey groups had almost twice the level of cortisol compared to the other group. The group with higher cortisol levels also spent significantly more time in the lower-quality habitat, compared to the other group. Our results suggest that particular behavioral adjustments might allow howler monkeys at El Zapotal to avoid physiological stress due to subgroup size and number of people. However, the fact that one of the monkey groups is showing increased cortisol levels may be interpreted as a warning sign, indicating that an adjustment threshold is being reached, at least for part of the howler monkey population in this forest fragment.

Understanding variation in behavioural responses to human-induced rapid environmental change: a conceptual overview

A key issue in animal behaviour is the need to understand variation in behavioural responses to human-induced rapid environmental change (HIREC) such as habitat loss, exotic species, pollution, human harvesting and climate change. Why do some individuals show maladaptive behaviours, while others show adaptive responses to evolutionarily novel situations? At present, we lack a unified conceptual framework for generating predictions and guiding empirical and theoretical work on this critical question. Drawing from the concept of ecological traps, I suggest that a conceptual framework for explaining this variation should include four main points: (1) behavioural responses (adaptive or not) are the result of cue–response systems, or behavioural ‘rules of thumb’; (2) limited or imprecise, unreliable information often underlies suboptimal behaviour; (3) the organism’s behavioural flexibility affects its response to novel situations; and (4) evolution (and development) in past environments has shaped cue–response systems, responses to imperfect information and degree of behavioural flexibility to be adaptive in past environments, but not necessarily in novel environments. The degree of match/mismatch between past environments and novel environments altered by HIREC is thus a key to explaining adaptive versus maladaptive behaviours. I suggest several existing frameworks that address these four points, and are thus potentially useful for explaining behavioural responses to HIREC: signal detection theory, adaptive plasticity theory, extended reaction norms and cost–benefit theory on variation in learning. I further discuss more complex aspects of reality that would be useful to add to these existing frameworks.

Adolescent Risk Taking Under Stressed and Nonstressed Conditions: Conservative, Calculating, and Impulsive Types

Adolescent risk taking may result from heightened susceptibility to environmental cues, particularly emotion and potential rewards. This study evaluated the impact of social stress on adolescent risk taking, accounting for individual differences in risk taking under nonstressed conditions. Eighty-nine older adolescents completed a computerized risk-taking and decision-making battery at baseline. At follow-up, participants were randomized to a control condition, which repeated this battery, or an experimental condition, which included a social and cognitive stressor before the battery. Baseline risk-taking data were cluster-analyzed to create groups of adolescents with similar risk-taking tendencies. The degree to which these risk-taking tendencies predicted risk taking by stress condition was assessed at follow-up. Participants in the stress condition took more risks than those in the no-stress condition. However, differences in risk taking under stress were related to baseline risk-taking tendencies. We observed three types of risk-takers: conservative, calculated, and impulsive. Impulsives were less accurate and planful under stress; calculated risk takers took fewer risks; and conservatives engaged in low risk taking regardless of stress. As a group, adolescents are more likely to take risks in "hot cognitive" than in "cold cognitive" situations. However, there is significant variability in adolescents' behavioral responses to stress related to trait-level risk-taking tendencies.

The effect of body weight on some welfare indicators in feedlot cattle in a hot environment

Heat stress has important effects on the welfare of livestock. The effects of heat stress in cattle include changes in biological functions and behaviors. The aim of this study was to investigate the behavioral differences between light and heavy feedlot cattle reared in a hot environment. Sixteen male Holstein feedlot cattle were allocated to light (353.8 ± 15.5 kg, n = 8) and heavy (737.1 ± 15.8 kg, n = 8) groups according to their live weight and were kept in a semi-open feedlot barn. The individual behavioral response variables measured were standing, lying, feeding, drinking, ruminating, locomotor activity and elimination (urinating and defecating). The effects of group, day, observation time, replicate and all interactions were included in an explanatory statistical (GLM) model. The data were analyzed using the PROC GLM procedure of SAS. Overall, the heavy cattle spent more time standing (P < 0.001), lying (P < 0.001), and eliminating (P < 0.05) compared to the light group. In contrast, the light group spent more time eating, drinking and ruminating (P < 0.001). Locomotor activity did not differ significantly between groups (P > 0.05). During the day, heavy cattle spent more time standing (at 1600 hours) and less time eating in comparison with the light cattle (P < 0.001) (at 1300 and 1600 hours). Light and heavy feedlot cattle behaved differently in a hot environment. The findings of the study indicate that the welfare of the heavy Holstein feedlot cattle was impacted negatively when the ambient temperature was high (at 1300 hours).