Nonhandled Animals Research Articles

Neonatal environmental intervention alters the vulnerability to the metabolic effects of chronic palatable diet exposure in adulthood

Previous studies have demonstrated that early environmental interventions influence the consumption of palatable food and the abdominal fat deposition in female rats chronically exposed to a highly caloric diet in adulthood. In this study, we verified the metabolic effects of chronic exposure to a highly palatable diet, and determine the response to its withdrawal in adult neonatally handled and non-handled rats. Consumption of foods (standard lab chow and chocolate), body weight gain, abdominal fat deposition, plasma triglycerides, and leptin, as well as serum butyrylcholinesterase (BuChE), and cerebral acetylcholinesterase (AChE) activities were measured during chronic chocolate exposure and after deprivation of this palatable food in female rats exposed or not to neonatal handling (10 minutes/day, 10 first days of life). Handled rats increased rebound chocolate consumption in comparison to non-handled animals after 1 week of chocolate withdrawal; these animals also decreased body weight in the first 24 hours but this effect disappeared after 7 days of withdrawal. Chocolate increased abdominal fat in non-handled females, and this effect remained after 30 days of withdrawal; no differences in plasma leptin were seen after 7 days of withdrawal. Chocolate also increased serum BuChE activity in non-handled females, this effect was still evident after 7 days of withdrawal, but it disappeared after 30 days of withdrawal. Chocolate deprivation decreased cerebral AChE activity in both handled and non-handled animals. These findings suggest that neonatal handling modulates the preference for palatable food and induces a specific metabolic response that may be more adaptive in comparison to non-handled rats.

Early handling modulates outcome of neonatal dexamethasone exposure

Synthetic glucocorticoids such as dexamethasone (DEX) are used to prevent or treat respiratory disorders in prematurely born infants. Besides the short-term benefit on lung development, numerous human and animal studies have reported adverse neurodevelopmental side effects. In contrast, maternal care is known to exert a positive influence on neurodevelopmental outcome in rodents. The aim of the current study was therefore to investigate whether neonatal handling (days 1–21), known to induce maternal care, might serve as an intervention strategy modulating the adverse effects of DEX treatment (days 1–3). For this purpose we have measured the outcome of these early-life manipulations on development as well as adult endocrine and behavioral phenotype of male rats. Maternal care was observed during the first week of life and indeed enhanced in response to handling. Eye opening was accelerated and body weight reduced in DEX-treated animals. In adulthood, we report that handling ameliorated impaired spatial learning observed in DEX treated non-handled animals in the T-maze. Additionally, handling reduced susceptibility to the impact of DEX treatment in the water maze. Although DEX treatment and handling both resulted in enhanced negative feedback of the stress-induced corticosterone response and both reduced startle reactivity, the acquisition of fear was only reduced by handling, without effect of DEX. Interestingly, handling had a beneficial effect on pre-pulse inhibition, which was diminished after DEX treatment. In conclusion, these findings indicate that handling of the neonate enhances maternal care and attenuates specific DEX-induced alterations in the adult behavioral phenotype.

Effects of a chronic exposure to a highly palatable diet and its withdrawal, in adulthood, on cerebral Na+,K+-ATPase and plasma S100B in neonatally handled rats

We have previously demonstrated that early environment influences the metabolic response, affecting abdominal fat deposition in adult female rats exposed to a long-term highly caloric diet. In the present study, our goal was to verify the effects of the chronic exposure, in adulthood, to a highly palatable diet (chocolate) on cerebral Na+,K+-ATPase activity and S100B protein concentrations, and the response to its withdrawal in neonatally handled and non-handled rats. We measured the consumption of foods (standard lab chow and chocolate), body weight gain, S100B protein concentrations, as well as cerebral Na+,K+-ATPase activity during chronic exposure and after chocolate withdrawal in adult female rats that had been exposed or not to neonatal handling (10min/day, 10 first days of life). Non-handled rats chronically exposed to chocolate exhibited increased plasma S100B levels, but there was no difference in abdominal fat S100B concentration between groups. Chronic chocolate consumption decreased Na+,K+-ATPase activity in both amygdala and hippocampus in non-handled, but not in handled rats, and this effect disappeared after chocolate withdrawal. Non-handled animals also demonstrated increased frequency of head shaking in the open field after 24h of chocolate withdrawal in comparison to handled ones. These findings suggest that neonatal handling modifies the vulnerability to metabolic and brain alterations induced by chronic exposure to a highly palatable diet in adulthood.

Handling effects on body weight and behaviour of group-housed male rabbits in a laboratory setting

In the study described in this paper we focus on the behaviour of male rabbits under modified housing conditions. We investigated whether handling has an effect on the behavioural stress response and whether this response is related to the coping strategy of the rabbits. Furthermore we studied the effect of handling from birth onwards on body weight and dominance. To assess the rabbit's coping strategy we performed a tonic immobility test, human-approach test, open-field test and a novel-object test. The results are that handling has no effect on body weight during the experimental period. Handling led to a more social and stable hierarchy among rabbits. Handled animals are less sensitive to tonic immobility, approached and made contact with the novel object and test-person's hand more often and longer, and moved around more freely in the open field than non-handled rabbits. This suggests that handled animals are proactive copers, while non-handled animals are reactive copers. However, in the second tonic immobility test handling depressed the tonic immobility response to such a level that nearly all handled animals did not react in a pro- or reactive manner at all. Altogether we provide evidence that handling pups form birth onwards, independent of nursing time, can be very effective in providing tame, less emotional and more cooperative animals.

Could Preference for Palatable Foods in Neonatally Handled Rats Alter Metabolic Patterns in Adult Life?

Previous studies indicate that, in adulthood, neonatally handled rats consume more sweet food than nonhandled rats. The aim of the present study was to assess the effects of the chronic exposure to a palatable diet (chocolate) in adult neonatally handled rats. We measured the consumption of foods (standard lab chow and chocolate), body weight gain, abdominal fat deposition, and levels of plasma lipids, glucose, insulin, and corticosterone in adult neonatally handled (10 min/d, first 10 d of life) and nonhandled rats. We found an increased intake of chocolate in handled rats, but this consumption decreased over time. Handled male animals exhibited higher body weight, higher caloric efficiency, and lower triglyceride levels. Nonhandled females that were exposed long-term to the highly caloric diet had increased abdominal fat deposition compared with handled females. Overall female rats had increased abdominal fat deposition, higher total cholesterol and glucose levels, and lower insulin in comparison with males. Interestingly, chocolate consumption diminished the weight of the adrenal glands in both handled and nonhandled animals. These findings suggest that neonatal handling induces a particular metabolic pattern that is sex specific.

Long-lasting changes in behavioural and neuroendocrine indices in the rat following neonatal maternal separation: Gender-dependent effects

Neonatal maternal separation (MS) has been used to model long-term changes in neurochemistry and behaviour associated with exposure to early-life stress. This study characterises changes in behavioural and neuroendocrine parameters following MS. On postnatal days (PND) 3–15, male and female Long–Evans rats underwent 3 h daily MS. Non-handled (NH) control offspring remained with the dams. Starting at PND 90, behaviour was assessed at weekly intervals in the elevated plus-maze, elevated T-maze, and locomotor activity boxes, and body weight monitored throughout. At the end of the study, adrenals were weighed and blood collected for analysis of plasma corticosterone and adrenocorticotropic hormone (ACTH) under basal conditions and following restraint stress. As adults, MS weighed more than NH animals. Activity on the open arms of the plus-maze was similar between MS and NH animals. In the T-maze, MS males had shorter emergence latencies than their NH counterparts. Spontaneous ambulation in a novel environment was significantly higher in MS than in NH animals, and males exhibited overall lower activity than females. Basal plasma corticosterone was lower in MS than in NH females, but no rearing condition difference was observed following restraint stress. Females had higher corticosterone and ACTH levels than males, whereas adrenal glands of MS animals weighed less than those of NH controls. The MS paradigm caused long-term gender dependent effects on behaviour and HPA axis status. The consistent gender differences confirm and expand existing results showing altered anxiety and stress reactivity in male and female rats.

Mesocortical dopamine and HPA axis regulation: Role of laterality and early environment

The infralimbic (IL) cortex is importantly involved in regulating behavioral and physiological responses to stress, including those of the hypothalamic–pituitary–adrenal (HPA) axis. The mesocortical dopamine (DA) system is an important afferent modulator of this region, is highly stress sensitive and frequently shows functional hemispheric asymmetry. Postnatal handling stimulation facilitates development of cortical asymmetry and is also associated with optimal HPA axis regulation. The present study examines the poorly understood role of the mesocortical DA system in regulating HPA axis function in adult rats which were handled (H) or nonhandled (NH) postnatally. In the first experiment, unilateral intra-IL cortex injection of the DA (D1/D2) antagonist α-flupenthixol into either hemisphere significantly exaggerated the restraint stress-induced increases in plasma adrenocorticotrophic hormone and corticosterone in NH rats. In H rats, the same effect was lateralized to the right IL cortex. In a second experiment, post mortem neurochemical analysis of DAergic measures in the IL cortex was conducted in H and NH animals following either acute or repeated (5 times) restraint stress. DAergic measures in the right IL cortex were significantly correlated with reduced stress hormone activation in both H and NH rats, especially in repeatedly restrained rats. However, while H rats showed a significant rightward shift in DA metabolism with repeated stress experience, NH rats shifted DA metabolism to the left. It is suggested that, during stress, mesocortical DA release normally acts in an adaptive, negative feedback capacity preventing excessive HPA activation and, with repeated stress, the right IL cortex is particularly important in this capacity. As well, the selective enhancement of DA metabolism in the right IL cortex of H rats may underlie, in part, their typically superior ability to adapt to stress and constrain HPA activity.

Cocaine-induced locomotor activity is increased by prior handling in adolescent but not adult female rats

Adolescence is a period of transition that is associated with increased levels of stress and a heightened propensity to initiate drug use. Neuronal development is still occurring during this transitional period, which includes the continued development of the dopamine system during the adolescent period. In the present study, the effects of pre-test handling on cocaine-induced locomotor activity were investigated among female adolescent and young adult rats upon presentation to a novel environment. On postnatal days (PND) 41–44 and 56–59 animals were handled (b.i.d.) in the colony room for 3 min. On PND 45 or PND 60, animals were removed from the colony room, weighed, and administered an acute injection of either cocaine or saline and presented to a novel environment where behavior was recorded for 30 min. Adolescent females (PND 45) that were handled prior to cocaine administration demonstrated elevated levels of cocaine-induced activity relative to their age-matched non-handled counterparts and also to their handled-adult counterparts. In contrast, among non-handled animals, young adults (PND 60) exhibited elevated drug-induced locomotion at several time points during the trial. Non-handled adolescent animals demonstrated the previously described “hyporesponsive” behavioral profile relative to their non-handled adult counterparts. The results from the present experiment indicate that adolescent animals may be more sensitive to basic laboratory manipulations such as pre-test handling, and care must be taken when utilizing adolescent animals in behavioral testing. Handling appears to be a sensitive manipulation in elucidating differences in cocaine-induced behavioral activation between ages.

Cellular mechanisms underlying an effect of “early handling” on pCREB and BDNF in the neonatal rat hippocampus

Early experiences have long-term effects on brain function and behavior. However, the precise mechanisms involved still remain elusive. In an effort to address this issue, we employed the model of “early handling”, which is known to affect the ability of the adult organism to respond to stressful stimuli, and determined its effects on hippocampal pCREB and BDNF 2, 4, and 8 h later. 8 h following “handling” on postnatal day 1, there was an increase in pCREB and BDNF positive cells in the hippocampus, a brain area which is a specific target of “handling”. On the other hand, vehicle injection resulted in decreased pCREB and BDNF in both handled and non-handled animals 2 and 4 h later. The “handling”-induced increase of pCREB and BDNF was cancelled by inhibition of NMDA, AMPA/kainate, GABA-A, 5-HT1A or 5-HT2A/C receptors, as well as L-type voltage-gated Ca 2+ channels. It thus appears that “early handling” activates these neurotransmitter receptors, leading to increased intracellular Ca 2+, phosphorylation of the transcription factor CREB, and increased BDNF expression. BDNF can then exert its morphogenetic effects and thus “imprint” the effects of “handling” on the brain.

Handling alters cocaine-induced activity in adolescent but not adult male rats

The developmental period of adolescence is one that is characterized by increased levels of stress and vulnerability to drugs. Pre-test handling is an experimental manipulation that is used to acclimate animals prior to behavioral testing and exposure to a novel environment. Therefore, the present study was conducted in order to address the issue of pre-test handling of adolescent and adult male rats on subsequent cocaine-induced locomotor activity upon presentation to a novel environment. On days one through four, postnatal day (PND) 41–44 or PND 56–59, respectively, animals were handled b.i.d. for three minutes. On the fifth day, PND 45 or PND 60, animals were administered 30 mg/kg/ip cocaine or saline and immediately placed in a novel environment where locomotor activity was measured for 30 minutes. Cocaine increased locomotor activity similarly in all non-handled animals, regardless of age. Interestingly, adolescent animals expressed a differential effect when handled prior to an acute cocaine administration. Specifically, handling increased cocaine-induced locomotor activity in adolescent but not adult animals. These findings indicate that adolescent males that have been acclimated to the handling procedure experience significantly more behavioral reactivity than do adults to a high dose of cocaine upon exposure to a novel environment.

Short-term effects of handling and permanently marking gopher tortoises (Gopherus polyphemus) on recapture rates and behavior

Limited evidence in the literature suggests that the assumption of equal catchability in mark-recapture studies of turtles may be invalid. These papers suggest that turtles may alter their behavior to avoid recapture following initial handling. If turtles are less likely to be recaptured following initial capture and handling, then population models estimating demographic characteristics and population sizes from mark-recapture data may be invalid (e.g., overestimating population size). Because conservation and management decisions are largely based on population sizes and trends, it is essential to investigate whether marking animals has any effect on behavior. We tested the effects of handling and permanently marking gopher tortoises (Gopherus polyphemus) at the Kennedy Space Center, Florida from 20-22 July 2003 to determine if short-term activity and recapture rates were affected. We used two distinct groups of tortoises: one group was handled (captured, measured, marked) and the other was not handled, but was marked with paint from a distance of 2.2 m. Although the behavior of handled and non-handled animals was distinct, we found no differences in recapture rates or time to recapture between the groups. We suggest that handled gopher tortoises are as likely to be recaptured as tortoises that have not been handled, although more subtle or long-term effects cannot be ruled out.

Effects of neonatal handling on the behavior and prolactin stress response in male and female rats at various ages and estrous cycle phases of females

Neonatal handling induces behavioral and hormonal changes, characterized by reduced fear in novel environments, and lesser elevation and faster return to basal levels of plasma corticosterone, prolactin and adrenaline, in response to stressors in adulthood. The present study aimed to analyze the effects of neonatal handling from Days 1 to 10 postnatal on prolactin response to ether stress in male and female rats at three life periods: neonatal, peripubertal and adulthood. Moreover, adult females were tested in two different phases of the estrous cycle, i.e., diestrus and estrus. In another set of experiments, the behavior of peripubertal and adult males and females in estrus and diestrus was analyzed in the elevated plus maze test. Pups were either handled for 1 min (handled group) or left undisturbed (nonhandled group) during the first 10 days after delivery. In adults, in the handled females in diestrus, stress induced a lesser increase in plasma prolactin compared with nonhandled ones, as in males. However, in estrus, handled females showed no difference in the prolactin response to stress. In the elevated plus maze, handled females in diestrus, but not in estrus, showed higher locomotor activity compared with nonhandled ones. Peripubertal male and female rats handled during the neonatal period showed no difference in behavior in the elevated plus maze compared with nonhandled animals. Early-life stimulation can induce long-lasting behavioral and stress-related hormonal changes, but they are not stable throughout life and phases of the estrous cycle.

Effect of cocaine on periadolescent rats with or without early maternal separation

Cocaine-induced behavioral sensitization and weight loss were investigated in periadolescent Wistar rats kept with their mothers or subjected to repeated maternal separation. Litters allocated to the separation procedure were placed in a temperature-controlled (33 degrees C) chamber for 3 h per day from postnatal day 6 (P6) to P20. Non-handled rats were left undisturbed until weaning. Treatments were started on P30-31 and the test was performed on P36-37. Animals received injections of saline or cocaine (10 mg/kg, sc) twice daily for 5 days. On day 6 all animals received saline. On day 7 animals were challenged with 10 mg/kg cocaine and their locomotion was evaluated in activity cages. A third group received saline throughout the 7-day period. Body weights were recorded on P30-31 and P36-37. Two-way ANOVA on body weights showed a main effect of treatment group (F(1,35) = 10.446, P = 0.003; N = 10-12). Non-handled rats treated with cocaine for 5 days gained significantly less weight, while no significant effect was observed in maternally separated rats. Two-way ANOVA revealed a main effect of drug treatment on locomotor activity (F(2,32) = 15.209, P<0.001; N = 6-8), but not on rearing condition (F(1,32)<0.001, P = 0.998). Animals pretreated with cocaine showed a clear behavioral sensitization relative to the saline group. No difference in the magnitude of sensitization was found between separated and non-handled animals. Only the effect of cocaine on weight gain was significantly affected by repeated episodes of early maternal separation during the pre-weaning period.

Gonadal hormone-induced changes in adult male and female rats exposed to early postnatal handling are not altered by prenatal morphine exposure

The purpose of the present study was to investigate the long-term effects of early postnatal handling in several gonadal hormone conditions in adult male and female rats exposed prenatally to morphine or saline. An open-field apparatus was used to test locomotor activities such as line crossing, rearing, grooming, and anxiety-like behaviors such as visiting squares alongside the walls of the open field and boli dropping. Postnatal handling increased locomotor activities in gonadally intact males and in all groups of hormone-manipulated females, but did not change them in gonadectomized (GNX) males. Additionally, there was a decrease in anxiety-like behavior in ovariectomized (OVX) females after estradiol benzoate (EB) or EB and progesterone (P) replacement due to handling. Handling did not affect anxiety-like behaviors in OVX females or in GNX or gonadally intact males. Prenatal morphine exposure did not alter any open-field measures in handled or nonhandled animals when compared to saline controls. Thus, the present study demonstrates that early postnatal handling induces long-lasting changes in locomotor and anxiety-like behaviors of adult male and female rats regardless of their prenatal exposure to morphine. These changes are gonadal hormone specific.

Effects of prenatal ethanol exposure and postnatal handling on conditioned taste aversion

Studies have shown that animals prenatally exposed to ethanol (E) exhibit deficits in conditioned taste aversion as well as displaying hypothalamic–pituitary–adrenal (HPA) hyperresponsiveness during exposure to stressors. In contrast, postnatal handling has been shown to attenuate both emotional and HPA reactivity under certain conditions. The present study tested the hypothesis that handling could attenuate adverse effects of prenatal ethanol exposure on consummatory behavior and HPA activity in a conditioned taste aversion task. We found that both prenatal ethanol exposure and handling independently increased saccharin consumption over 5 days of pretoxicosis exposure, suggesting that neophobia decreased at a faster rate in these animals. When conditioned aversion was assessed in handled animals under nondeprived conditions, E animals showed increased consumption compared to controls. Furthermore, across prenatal groups, lower corticosterone (CORT) levels were found in handled compared to nonhandled animals during reexposure under food-deprived conditions, emphasizing the importance of assessing both behavior and HPA function when examining an animal's response to a task and indicating that handling may not be effective at attenuating some deficits in E animals.

Effects of neonatal handling on sympathoadrenal activity and body composition in adult male rats.

Neonatal handling permanently alters the hypothalamic-pituitary-adrenal (HPA) response to stress. Because the sympathetic nervous system (SNS) and adrenal medulla also participate in stress responses, the impact of daily handling between birth and weaning on SNS and adrenal medullary function was examined in adult rats using techniques of [(3)H]norepinephrine ([(3)H]NE) turnover and urinary catecholamine excretion. Handled animals exhibited a 23% reduction in [(3)H]NE turnover in heart and a 53% decrease in spleen. [(3)H]NE turnover in brown adipose tissue, stomach, and kidney did not differ between handled and nonhandled animals. In contrast, urinary epinephrine (Epi) excretion was significantly greater in handled rats in response to a 3-day fast than in nonhandled animals. Although body weight, weight gain in response to dietary enrichment with sucrose or lard, or body fat content did not differ in handled and nonhandled animals, handled rats displayed heavier abdominal fat depots than nonhandled animals, implying a difference in body fat distribution. Neonatal handling thus leads to decreased sympathetic activity within specific subdivisions of the SNS and, by contrast, to increased adrenal medullary responsiveness.

Postnatal Handling Does Not Attenuate Hypothalamic‐Pituitary‐Adrenal Hyperresponsiveness After Prenatal Ethanol Exposure

Prenatal ethanol exposure results in hypothalamic-pituitary-adrenal (HPA) hyperresponsiveness to stress in the adult animal. In contrast, an early environmental manipulation, termed "postnatal handling," has been shown to result in decreased and/or less prolonged HPA activity in response to moderate stressors throughout the lifespan of the animal. The effects of both prenatal ethanol exposure and postnatal handling on HPA activity may be mediated by altered feedback regulation of the HPA axis. The present study tested the hypothesis that postnatal handling could attenuate the impact of prenatal ethanol exposure on hormonal responses to stressors. Male and female Sprague Dawley rats from prenatal ethanol (E), pair-fed (PF), and ad libitum-fed control (C) groups were either handled (H) or nonhandled (NH) during the preweaning period and were tested at 4 to 5 months of age. Animals were subjected to a 60 min restraint stress, 3 hr after intraperitoneal injection with either saline (SAL) or a synthetic glucocorticoid, dexamethasone-21-phosphate (DEX), in order to examine HPA responsiveness after DEX blockade of endogenous HPA activity. Blood samples were collected via jugular cannulae immediately before restraint (0 min), during restraint (10, 30, and 60 min), and 30 min after the termination of restraint (90 min). For both males and females, DEX administration significantly reduced plasma adrenocorticotropic hormone (ACTH) and corticosterone (CORT) concentrations compared with SAL administration. H animals showed greater suppression of HPA activity (i.e., lower ACTH and/or CORT levels) than NH animals regardless of prenatal group. In addition, E females from both the H and NH treatments showed elevated ACTH and CORT after both SAL and DEX administration, whereas H and NH E males showed elevations in ACTH and CORT only after SAL, compared with their PF and C counterparts. These data extend results from previous studies that demonstrated HPA hyperresponsiveness in E animals. The finding that E females but not males exhibit elevated ACTH and CORT after DEX administration suggests that prenatal ethanol exposure results in sex-specific alterations of HPA feedback. Consistent with previous data, handling in itself reduced the HPA response to restraint stress. However, handling did not attenuate either HPA hyperresponsiveness or feedback deficits in E animals.

Schedule-Induced Polydipsia: Gender-Specific Effects and Consequences of Prenatal Cocaine and Postnatal Handling

The impact of gestational cocaine in conjunction with postnatal handling on schedule-induced polydipsia (SIP) was examined. Rat offspring were derived from Sprague–Dawley dams injected subcutaneously with 40 mg/kg/3 cc cocaine hydrochloride (C40) on gestational days 8–20, dams injected with vehicle and pair fed 4 (PF4) days to mimic the acute anorexic effects of cocaine administration, and nontreated (NT) control dams. In adulthood, offspring were food deprived and given 13 daily 30-min SIP sessions, with water intake recorded during the scheduled (fixed time 60 s—FT60) food delivery. For 4 days thereafter, animals received saline, 5 or 10 mg/kg of cocaine in counterbalanced order prior to SIP testing. Acquisition and maintenance of SIP, but not cocaine-induced suppression of SIP performance, were observed to be dependent upon prenatal treatment, handling, and gender. Females acquired SIP faster and exhibited notably higher levels of polydipsia than males. Early handling increased levels of established SIP in NT offspring, while enhancing SIP acquisition in both PF4 and C40 offspring. In nonhandled animals, NT offspring exhibited less SIP than PF4 and C40 offspring, differences that were attenuated by early handling. These effects are discussed in relation to previously reported neurohormonal characteristics of these gender and treatment variables.

The effect of early handling is dependent upon the state of the rabbit (Oryctolagus cuniculus) pups around nursing.

We investigated the behavior toward humans in 4-week-old pups and adult rabbits handled daily at different times around the nursing visits during their 1st week of life. The timing of handling significantly influenced its efficiency in altering the subsequent behavior of rabbits. Animals handled around nursing readily approached a human hand when tested at weaning. Other pups, handled either 6, 12, or 18 hr after nursing, avoided the human hand. Our results show that there is a narrow sensitive period for successful stimulation, because only those rabbits that were handled within the interval starting 15 min before and ending 30 min after nursing became tame. The effect of early handling proved to be long-lasting because nonhandled rabbits tested as adults were afraid of humans and showed behavioral elements of avoidance, while the handled ones behaved fearlessly in the open field. The effect of handling proved to be specific toward humans because both handled and nonhandled animals showed avoidance toward a stuffed fox.

Effect of gentle handling on the reactivity of zebu crossed calves to humans

The effects of gentle handling of zebu crossed beef calves by humans were studied. Forty Nelore × European male and female calves, born in spring and reared under free-range conditions, were randomly divided into two groups: treatment ( n = 20) and control ( n = 20). The treatment animals were individually exposed at 1–2 months of age to one daily session of 90 s of gentle handling in the crush for 10 days, during 3 weeks. A response-to-humans test was conducted in the pound 3 days after the handling sessions. Animals were individually introduced into the pound and their reactions to two stationary experimenters were videorecorded and quantified. Non-handled calves moved more ( P < 0.01) and looked less ( P < 0.01) at the experimenters than handled ones. More non-handled animals showed aggressive behaviour towards humans ( P < 0.05). None of the handled calves attempted to escape, while 30% ( n = 6) of the non-handled calves did ( P < 0.05), and, in fact, escaped by jumping over the wall or gates of the pound. Although production traits of zebu crossbred cattle are well recognized, most farmers in the south of Brazil complain of the difficulty of handling these animals due to their ‘wild temperament’. Gentler handling methods could improve the ease of handling of these animals, diminishing losses due to injury of animals, as well as labour costs.