Lack of adaptation to repeated emotional stress evoked by isolation of sheep from the flock

Influence of Excitability Rate on Physiological Responses to Stress in Goats

This study was conducted to determine if excitability score (ES) in goats can influence their physiological responses when subjected to stress. Thirty-six intact male Spanish goats (8-mo-old) were individually weighed and scored for excitability: 1 for calm (13 goats), 2 for moderately excitable (11 goats), and 3 for highly excitable (12 goats). To impose stress, goats were assigned to one of three treatments (TRT) for 90 min: (i) isolation in an open pen with metal grill panels, (ii) isolation in a pen with side panels covered using tarp sheets, and (iii) no isolation (control). Blood samples were collected at 0, 30, 60, and 90 min of isolation and physiological data were analyzed using MIXED procedures in SAS. The data from the two isolation treatments were pooled and compared with that of the control group. Plasma cortisol and non-esterified fatty acid concentrations were the lowest in goats with ES 1 (p < 0.05). Neutrophil−lymphocyte ratios were also the lowest in goats with a calm temperament (p < 0.01). Application of full quadratic model using response surface methodology (PROC RSREG) in SAS revealed that the influence of ES on physiological stress responses over time was not the same between the TRT groups. The results indicate that physiological stress responses are greater in goats with an excitable temperament compared to goats with a calm temperament.

Social isolation of goats: significance of visual contact with conspecifics on behavioral and physiological responses

Social isolation can increase distress in goats, particularly when they cannot maintain visual contact with conspecifics. This experiment was conducted to determine the behavioral and physiological responses in goats during isolation with or without visual contact with conspecifics. Male Spanish goats (uncastrated, 8 mo old, average weight 29.4 ± 0.59 kg) were randomly assigned to a control (CO) group with no isolation or to one of four isolation treatment (TRT) pens (1.5 × 1.5 m) with: 1) open grill panels but with no visual contact with conspecifics (IO), 2) covered grill to prevent visual contact (IC), 3) open grill with visual contact (IV), or 4) covered grill with a 30 × 30 cm window to allow visual contact (IW), for 90 min of social isolation (n = 12 goats per TRT). Blood samples were collected at 0, 30, 60, and 90 min (Time) from isolated and control goats. The experiment was repeated 1 wk later using the same animals, with each goat being subjected to the same isolation TRT the second time to study the effect of prior exposure to isolation. Friedman's two-way analysis of variance by Ranks test in SAS showed that the median frequency of vocalization (rank score) in goats was high in the IO group, low in the IV and IW groups, and intermediate in the IC group (P < 0.01). The vocalization rank score was also higher (P < 0.01) during the first 30 min of isolation in goats. The median frequency of visual contact was higher in the IW group than in the IV group (P < 0.01). The frequency of climbing behavior was high in the IC and IO groups, low in the IV group, and intermediate in the IW group (P < 0.01). Repeated measures analysis using general linear models procedures in SAS revealed that plasma cortisol and glucose concentrations tended (P < 0.1) to be the highest in the IO group than in CO, IC, IV, and IW groups. Cortisol levels were also higher (Time; P < 0.05) at 0 and 90 min compared with 30 and 60 min. Norepinephrine concentrations decreased (P < 0.05) with Time, and plasma nonesterified fatty acid (NEFA) levels were affected by TRT × Time interaction (P < 0.01). Overall, epinephrine, norepinephrine, glucose, and NEFA concentrations were lower (P < 0.01) and cortisol concentrations and lymphocyte counts were higher (P < 0.01) when goats were exposed to isolation the second time. The results showed that goats with no visual contact with conspecifics during social isolation had greater physiological stress responses and spent more time vocalizing or trying to escape the pen, which may indicate distress.

Interpreting Stress Responses during Routine Toxicity Studies

Stress often occurs during toxicity studies. The perception of sensory stimuli as stressful primarily results in catecholamine release and activation of the hypothalamic–pituitary–adrenal (HPA) axis to increase serum glucocorticoid concentrations. Downstream effects of these neuroendocrine signals may include decreased total body weights or body weight gain; food consumption and activity; altered organ weights (e.g., thymus, spleen, adrenal); lymphocyte depletion in thymus and spleen; altered circulating leukocyte counts (e.g., increased neutrophils with decreased lymphocytes and eosinophils); and altered reproductive functions. Typically, only some of these findings occur in a given study. Stress responses should be interpreted as secondary (indirect) rather than primary (direct) test article–related findings. Determining whether effects are the result of stress requires a weight-of-evidence approach. The evaluation and interpretation of routinely collected data (standard in-life, clinical pathology, and anatomic pathology endpoints) are appropriate and generally sufficient to assess whether or not changes are secondary to stress. The impact of possible stress-induced effects on data interpretation can partially be mitigated by toxicity study designs that use appropriate control groups (e.g., cohorts treated with vehicle and subjected to the same procedures as those dosed with test article), housing that minimizes isolation and offers environmental enrichment, and experimental procedures that minimize stress and sampling and analytical bias.

This article is a comprehensive overview of the biological aspects of the stress response, beginning with a Summary (Section 1) and an Introduction (Section 2) that describes the historical and conventional methods used to characterize acute and chronic stress responses. These sections are followed by reviews of the primary systems and parameters that regulate and/or are influenced by stress, with an emphasis on parameters evaluated in toxicity studies: In-life Procedures (Section 3), Nervous System (Section 4), Endocrine System (Section 5), Reproductive System (Section 6), Clinical Pathology (Section 7), and Immune System (Section 8). The paper concludes (Section 9) with a brief discussion on Minimizing Stress-Related Effects (9.1.), and a final section explaining why Parameters routinely measured are appropriate for assessing the role of stress in toxicology studies (9.2.).

Multiple exposures to familiar conspecific withdrawal is a novel robust stress paradigm in ewes

Paradigms used so far to study the effects of social isolation in sheep confound the effects of social isolation with those of other stressors (e.g. new environment) and showed contradictory effects after multiple social isolations. We propose here to characterize and examine the repeatable effects of social isolation induced by the familiar conspecific withdrawal (FCW). This latter test consists of socially isolating the ewe by the removal of group mates from the room test for 3 h. Behavioral and endocrine responses of adult ovariectomized-estradiol implanted ewes were compared 90 min before and 90 min after FCW, which was applied three times every fourteen days. We observed that each FCW induced significant increases in plasma cortisol level, in the number of vocalizations, foot pawing, circling attempts and a significant decrease in time spent lying down. An increase in plasma cortisol levels and decrease in duration of maintenance behaviors were significantly lower after the third FCW than after the first one. These differences could be explained by higher plasma cortisol levels and lower duration of maintenance behaviors before the third FCW than before the first FCW suggesting an anticipation of the social isolation period. These data indicate that social isolation is sufficient to induce distress with stable stressful responses after multiple exposures to familiar conspecific withdrawal.

Xylazine, Ketamine and their Combination for Lumbar Epidural Analgesia in Water Buffalo Calves (Bubalus bubalis)

The study was conducted to evaluate the effects of xylazine individually (0.05 mg/kg), ketamine individually (2.5 mg/kg), and a combination of xylazine and ketamine (0.05 mg/kg and 2.5 mg/kg) after lumbar epidural administration in water buffalo calves. Fifteen non-descript, male water buffalo calves of 6-8 months of age weighing between 55 and 75 kg were randomly placed in three groups (groups A, B and C). The agents were administered at the first lumbar epidural space. Clinico-physiological parameters, such as analgesia, ataxia, sedation, salivation, heart rate, respiratory rate and rectal temperature were studied. Other haematological and biochemical parameters monitored were haemoglobin, packed cell volume, total leukocyte count, plasma glucose, cortisol, protein albumin, globulin, blood urea nitrogen (BUN), creatinine, alanineamino transferase (ALT), sodium, potassium and chloride. The onset of analgesia (mean +/- SEM) was faster in group C (3.2 +/- 0.20 min) compared with that of group B (4.6 +/- 0.22 min) and group A (34.0 +/- 1.86 min). Analgesia of the thorax, flank, inguinal region, hind limbs, perineum and tail was complete in group C, but mild to moderate in groups A and B. Ataxia was severe in group C and mild in groups A and B. Mild to deep sedation was produced by groups A and C animals. Group B animals failed to produce sedation. Longer duration and greater depth of analgesia was produced in animals of group C. Heart rate, respiratory rate and rectal temperature decreased in groups A and C. The haematological parameters decreased in all the groups. The biochemical parameters like glucose, cortisol, BUN, creatinine, and ALT increased in all the animals. However, total proteins and albumin decreased in the three groups. The plasma electrolytes sodium, potassium and chloride did not show any significant change. The results of this study indicated a possible synergistic analgesic interaction between epidurally administered xylazine and ketamine, without causing any marked systemic effects in water buffalo calves.

Simulated preslaughter holding and isolation effects on stress responses and live weight shrinkage in meat goats

The objective of this experiment was to determine the effects of preslaughter isolation and feed withdrawal duration on physiological responses and shrinkage in goats. A total of 84 Spanish does (36 mo of age, average weight 35 kg) were individually weighed and scored for excitability before two replicate (day) trials. The does were feed-deprived (FD) or fed (F) in holding pens (treatment, TRT) for either 0, 7, 14, or 21 h (TIME). At the end of the holding periods, FD and F does were blood-sampled (n = 6 does/treatment/time/replicate) and weighed again to assess physiological responses and shrinkage, respectively. Individual does from each pen were blood-sampled again after imposing one of three handling post-treatments: a 15-min isolation with no visual contact with other does (I); a 15-min isolation with visual contact (IV); or no isolation (C, control). Plasma cortisol concentrations were higher at 0 h than at other holding time periods (P < 0.01). Plasma triiodothyronine, thyroxine, and leptin concentrations, and differential leukocyte counts were not influenced by any of the factors. The rate of decline in glucose concentrations over TIME was greater in FD than in F group (TRT x TIME, P < 0.05). The overall plasma creatine kinase activity peaked at 7 h before reaching a lower level at 14- and 21-h holding (P < 0.05). Plasma urea nitrogen concentrations were higher at 0- and 21-h than at 7- and 14-h holding (P < 0.01). Plasma nonesterified FA concentrations in the FD group remained at an elevated level during holding, but in the F group the levels decreased at 7 h and remained at that level (TRT x TIME, P < 0.01). Excitability scores did not have any effect on the variables measured. Shrinkage increased with longer holding time, but more prominently in the FD group (TRT x TIME, P < 0.01). Plasma cortisol concentrations were greater in I and IV groups than in the C group (P < 0.01). The novelty of environment during preslaughter holding, and social isolation may be more potent stressors than feed deprivation in goats, although shrinkage may increase with increasing feed-withdrawal times.

Experimental inoculations with Ostertagia ostertagi or exposure to artificial illumination alter peripheral cortisol in dairy calves (Bos taurus)

A series of experiments were conducted on dairy calves (Bos taurus) to assess, by way of circulating cortisol, the impact of a parasitic infection as a systemic stressor. The first study was designed to assess the effects of chronic stress on dairy calves resulting from a large bolus inoculation of the nematode parasite, Ostertagia ostertagi. Peripheral cortisol concentrations and adrenal cortical competency to adrenocorticotropic hormone (ACTH) challenge were utilized as indicators of chronic stress for 5 weeks. Calves were cleared of nematodes by anthelminthic treatment after the third week of infection. Calves were challenged with ACTH on weeks 0 and 2, and blood samples were obtained at a 12 x 10-min bleeding schedule. Cortisol concentrations were significantly higher (P < 0.05) in the infected calves than in the uninfected calves. The maximal response level to the ACTH challenge was also higher while the calves were infected. Two additional experiments were conducted to investigate the effects of experimental procedures that became evident during Experiment 1. Firstly, calves that had previously been fitted with jugular cannulae were sampled from 3 hr predawn until 5 hr after dawn under red- or white-light incandescent illumination. Calves under red lights had lower initial cortisol concentrations but increased to the concentrations in calves under white lights, indicating a compounding effect of lighting with the procedures of blood-sample acquisition. Secondly, 12 calves were inoculated with 10,000, 100,000, or 200,000 third-stage, infective larvae of O. ostertagi. Blood samples were obtained similarly to the regimen in Experiment 1. Cortisol concentrations were elevated only in the 200,000-dose group during week 3, correlating with the period immediately after emergence of the young adult parasites from the gastric glands. Continuous emergence of these parasites might induce chronic hyperadrenocorticism and the concomitant negative consequences on metabolic and immunological processes.

Cortisol as an indicator of severity of parasitic infections of Haemonchus contortus in lambs (Ovis aries)

Two experiments were conducted with lambs to examine the effects of experimental infections of Haemonchus contortus on circulating cortisol levels. In both experiments, naive lambs were divided into three groups based on inoculum doses of 0 (control), 2000 (low dose) and 20,000 (high dose) infective larvae. In experiment 1, the lambs were sampled once daily from day 1 post-inoculation (p.i.) until day 39 p.i. Lambs from the high-dose group had significantly higher sustained levels of cortisol throughout the course of the infection than either the low-dose group or control lambs. In experiment 2, blood was sampled at 30-min intervals for 4 hr on day 21 p.i. The high-dose group also had highest cortisol levels. The consequences of chronic stress and the resultant elevated cortisol concentrations potentially could compromise animal health and animal well-being.

Individual Variation in Response to Stressors in Farm Animals: Implications for Experimenters

Physiological and behavioural responses to stressors may affect experimental results. Since individual animals differ in their pattern of response to stressors, it is suggested that stress during experiments has the potential for increasing variability in responses to experimental treatments. Evidence supporting this is given from experiments carried out on farm animals. The main factors accounting for individual differences in response to stressors such as handling are habituation, early experiences and genetic background. Several ways of reducing stress during experiments are suggested and the need for skilful and humane handling is emphasized. It is concluded that reducing stress during experiments will have welfare benefits and may reduce the number of animals that need to be used.

Pentobarbitone inhibits the stress response to transport in male goats

Pentobarbitone (20 mg/kg i.v.) blocked plasma cortisol release when administered either before a 20 min journey or during a 2 h journey. This confirms that pentobarbitone can block stimulated, as well as resting, cortisol secretion. In general, blood glucose concentrations were not increased above 90 mg/100 ml until at least 30 min after the start of transport; however, this increase was also blocked by pentobarbitone administered 30 min into the 2 h journey. Significant increases in respiratory and heart rates occurred within 15 min of the start of transport; pentobarbitone caused an immediate decrease in these parameters. In conclusion, pentobarbitone was shown to reverse many metabolic changes induced by transport.