Simulations of Future Trends in Welfare-Centric Egg Production Systems: Impacts on Productivity and Prices.

The implementation of more animal welfare-centric livestock production systems holds considerable potential for achieving sustainable production in Japan. However, such systems generally reduce productivity per unit area, impose financial burdens on farmers that adversely affect their physical and mental health, and require increased consumer awareness. In particular, declines in productivity per unit area substantially affect the farming economy, giving rise to concerns about the sufficient egg production for the population, which consequently exacerbates Japan's food security concerns. In this study, our goal was to predict temporal trends in the Japanese transition to welfare-centric facilities by analyzing desired egg consumption. We formulated five scenarios, ending in 2050, to assess the future impact of changing the proportions of types of egg production on total production, numbers of hens, total farm area, production costs, and retail prices. Multiple issues were identified in our analysis. First, Japanese production uses conventional caging, which provides high efficiency, maximum output, and decreased prices. Our simulations suggest that ensuring optimal production is likely to present challenges as animal welfare is addressed. They also suggest that the poultry industry or the Japanese government will likely need to plan changes in production methods will likely be necessary to prevent egg surpluses and/or shortages. Additional issues were identified, including price increases, numbers of hens, total farm area, and production costs. This study offers valuable insights for policymakers in their decision-making processes to help optimize production methods while considering food security, animal welfare, and farmers' welfare.

Comparison of behavioral and physiological changes in postpartum healthy and inflammatory diseased cows.

During parturition, cows often experience intense pain and stress, which increases the risk of inflammatory diseases. This study aimed to compare the postpartum health status between healthy cows and those diagnoses with inflammatory diseases by examining behavioral and heart rate (HR) variability (HRV) changes, to provide information before the onset of disease. Eight Holstein cows were used in this study. HR, parameters of HRV (low-frequency power: LF; high-frequency power: HF; LF/HF ratio, and total power) and time budget of individual maintenance behaviors (standing, recumbency, feeding, rumination while standing and lying, and sleep) were continuously recorded from 0 to 168 h postpartum. Milk and blood samples were collected daily. Cows were categorized as diseases based on the positive result of California mastitis test and/or serum haptoglobin concentration that exceeded 50 µg/ml after all blood samples have been collected. Compared to healthy individuals (n = 3), diseased cows (n = 5) exhibited higher HR, LF/HF, and lower total power (p < 0.05), suggesting the dominance of the sympathetic nervous system in cows with inflammatory diseases. Additionally, diseased cows showed an increased standing time budget and reduced recumbency (p < 0.05), which may be a behavioral strategy in response to discomfort from inflammation.

Heart rate variability and behavioral alterations during prepartum period in dairy cows as predictors of calving: a preliminary study.

OBJECTIVE: Parturition is crucial for dams, their calves, and cow managers. The prediction of calving time, which assists cow managers to decide on the relocation of cows to maternity pens and necessity of human supervision, is a pivotal aspect of livestock farming. However, existing methods of predicting calving time in dairy cows based on hormonal changes and clinical symptoms are time-consuming and yield unreliable predictions. Accordingly, we investigated whether heart rate variability (HRV) which is a non-invasive assessment of autonomic nervous system (ANS) activity and behavior during the prepartum period would be useful for predicting calving time in dairy cows. METHODS: Eight pregnant cows were surveilled under electrocardiogram and video recordings for HRV and behavioral analyses, respectively. HRV parameters in time and frequency domains were evaluated. A 24-h time budget was calculated for each of six types of behavior (standing and lying with or without rumination, sleeping, and eating). RESULTS: Heart rate on calving day is considerably higher than those recorded on the days preceding calving. Low frequency power declined, whereas high frequency power escalated on the calving day compared to the period between 24 and 48 h before calving. The time budget for ruminating while lying decreased and that while standing increased markedly on the calving day compared to those allocated on the preceding days; nonetheless, the total time budget for ruminating did not differ during the prepartum period. CONCLUSION: We elucidated the ANS activity and behavioral profiles during prepartum period. Our results confirm that HRV parameters and behavior are useful for predicting calving time, and interestingly indicate that the time budget for ruminating while standing (or lying) may serve as a valuable predictor of calving. Collectively, our findings lay the foundation for future investigations to determine other potential predictors and formulate an algorithm for predicting calving time.

Behavior and heart rate variability after intranasal administration of oxytocin in Holstein steers.

Oxytocin (OXT) is a neuropeptide that regulates memory, emotion, stress response, and behavior in the brain. In our previous study with cattle, we demonstrated the anti-stress effect of intracerebroventricularly administered OXT on the central nervous system. However, it is important to investigate the effects of this peptide after intranasal administration, as it offers convenience and non-invasiveness for practical use. Therefore, this study investigated the effects of intranasal OXT on the behavior and autonomic nervous system of Holstein steers. The experiment followed a within-subjects design, including a total of six steers. Each steer received intranasal administration of either 1 mL of saline (SAL), 100 µg OXT (OXT100), or 200 µg OXT (OXT200). However, due to some issues, the sample size for the OXT200 group was reduced to five. After these treatments, we conducted electrocardiography recordings to analyze heart rate variability (HRV) and also made behavioral observations for 90 min. OXT200 tended to increase the time spent ruminating while lying down (Steel's multiple comparison test; P=0.053). In contrast, OXT treatment did not affect HRV indices. In conclusion, the current OXT dosage did not significantly affects behavior or the autonomic nervous system. However, the observed tendency to increase rumination may suggest a central effect of OXT.

Heart rate variability in dairy cows with postpartum fever during night phase.

Autonomic nervous function evaluated by heart rate variability (HRV) and blood characteristics were compared between Holstein Friesian cows that developed postpartum fever (PF; n = 5) and clinically healthy (CH; n = 6) puerperal cows in this case-control study. A cow was defined as having PF when its rectal temperature rose to ≥39.5°C between 1 and 3 days postpartum. We recorded electrocardiograms during this period using a Holter-type electrocardiograph and applied power spectral analysis of HRV. Comparisons between the groups were analyzed by t test or Mann-Whitney U test, and the relationship between rectal temperature and each parameter was analyzed using multiple regression analysis. Heart rate was higher in PF cows than in CH cows (Mean ± SE, 103.3 ± 2.7 vs. 91.5 ± 1.7 bpm). This result suggested that PF cows had a relatively dominant sympathetic nervous function. Total (44,472 ± 2,301 vs. 55,373 ± 1,997 ms) and low frequency power (24.5 ± 3.8 vs. 39.9 ± 5.3 ms) were lower in PF cows than in CH cows. These findings were possibly caused by a reduction in autonomic nervous function. The total white blood cell count (54.3 ± 5.1 vs. 84.5 ± 6.4 ×102/µL) and the serum magnesium (2.1 ± 0.1 vs. 2.4 ± 0.1 mg/dL) and iron (81.5 ± 8.0 vs. 134.4 ± 9.1 µg/dL) concentrations were lower and the serum amyloid A concentration (277 ± 33 vs. 149 ± 21 µg/mL) was higher in PF cows than in CH cows. These results imply that more inflammation was present in PF cows than in CH cows. Multiple regression analysis showed that both of low frequency power and concentration of serum iron were associated with rectal temperature. We found differences in changes in hematologic results, biochemical findings, and HRV patterns between PF cows and CH cows.

Effects of intravenous tryptophan infusion on thermoregulation in steers exposed to acute heat stress.

This study was conducted to investigate the effect of tryptophan (TRP) supply on the thermoregulatory responses via brain serotonin (5-HT) in cattle. In period 1, 12 Holstein steers were kept under a constant room temperature (22°C) and were administered the intravenous (i.v.) infusion of saline or TRP (38.5 mg/kg/2 h). Changes in rectal temperature (RT), 5-HT concentration in the cerebrospinal fluid (CSF), and other factors involved in thermoregulation were measured. In period 2, the steers received the same treatments as in period 1; however, the room temperature was elevated from 22°C to 33°C during i.v. infusion and maintained at 33°C for 3 h. 5-HT concentration in CSF increased following TRP infusion in both periods, and RT significantly decreased following TRP infusion only in period 2. The effect of TRP on respiration rate and plasma prolactin and total triiodothyronine concentrations was not significant. These results suggest that increase in TRP supply can attenuate increase in RT in response to acute heat stress through the increase in brain 5-HT, followed by presumable increase in evaporative heat loss from the skin surface in cattle. It is possible that the increase in peripheral blood TRP metabolites could also participate in the hypothermic effect of TRP.

The effects of l-DOPA and sulpiride on growth hormone secretion at different injection times in Holstein steers.

The effects of l-DOPA, a precursor of dopamine (DA), and sulpiride, a D2 -type DA receptor blocker, on growth hormone (GH) and prolactin (PRL) secretion were investigated in steers. Eight Holstein steers (212.8 ± 7.8 kg body weight) were used. Lighting conditions were 12:12 L:D (lights on: 06.00-18.00 hours). Blood samplings were performed during the daytime (11.00-15.00 hours) and nighttime (23.00-03.00 hours). Intravenous injections of drugs or saline were performed at 12.00 hour for the daytime and 00.00 hour for the nighttime, respectively. Plasma GH and PRL concentrations were determined by radioimmunoassay. l-DOPA did not alter the GH secretion when it was injected at 12.00 hour (spontaneous GH level at its peak). On the other hand, l-DOPA increased GH secretion at 00.00 hour (GH level at its trough). Injection of sulpiride suppressed GH secretion at 12.00 hour but did not affect GH levels at 00.00 hour. l-DOPA inhibited and sulpiride stimulated PRL release during both periods. These results suggest that dopaminergic neurons have stimulatory action on GH secretion and inhibitory action on PRL secretion in cattle. In addition, injection time should be considered to evaluate the exact effects on GH secretion due to its ultradian rhythm of GH secretion in cattle.

Involvement of circadian clock in crowing of red jungle fowls (Gallus gallus).

The rhythmic locomotor behavior of flies and mice provides a phenotype for the identification of clock genes, and the underlying molecular mechanism is well studied. However, interestingly, when examining locomotor rhythm in the wild, several key laboratory-based assumptions on circadian behavior are not supported in natural conditions. The rooster crowing 'cock-a-doodle-doo' is a symbol of the break of dawn in many countries. Previously, we used domestic inbred roosters and showed that the timing of roosters' crowing is regulated by the circadian clock under laboratory conditions. However, it is still unknown whether the regulation of crowing by circadian clock is observed under natural conditions. Therefore, here we used red jungle fowls and first confirmed that similar crowing rhythms with domesticated chickens are observed in red jungle fowls under the laboratory conditions. Red jungle fowls show predawn crowing before light onset under 12:12 light : dim light conditions and the free-running rhythm of crowing under total dim light conditions. We next examined the crowing rhythms under semi-wild conditions. Although the crowing of red jungle fowls changed seasonally under semi-wild conditions, predawn crowing was observed before sunrise in all seasons. This evidence suggests that seasonally changed crowing of red jungle fowls is under the control of a circadian clock.

Intravenous tryptophan administration attenuates cortisol secretion induced by intracerebroventricular injection of noradrenaline.

This study was conducted to investigate the possibility of suppression of stress-induced cortisol (CORT) secretion by tryptophan (TRP) administration and to better understand its regulatory mechanisms by using a noradrenaline (NA) injection into the third ventricle (3V) as a stress model in cattle. A total of 25 Holstein steers with a cannula in the 3V were used. First, the increase in CORT secretion was observed following a NA injection into the 3V in a dose-dependent manner, verifying the appropriateness of this treatment as a stress model of CORT secretion (Experiment 1). The effect of prior-administration of TRP into peripheral blood with a dose that has been demonstrated to increase brain 5-hydroxytryptamine levels on the elevation of plasma CORT induced by NA or corticotropin-releasing hormone (CRH) was then examined (Experiment 2). The prior administration of TRP suppressed NA-induced, but not CRH-induced, CORT elevation. These results suggest that an increase in TRP absorption into peripheral blood could suppress the stress-induced CORT secretion in cattle via the attenuation of the stimulatory effect of NA on the hypothalamic CRH release.

Relationships between postnatal plasma oxytocin concentrations and social behaviors in cattle.

We examined the associations between natural individual variations in basal oxytocin (OXT) in postnatal cattle and social behavioral traits. At 1, 2 and 6 weeks of age, the basal OXT exhibited individual variability in 20 Holstein heifer calves. Cluster analysis of mean OXT for these time periods obtained two subgroups: high OXT (HOXT; n = 9) and low OXT (LOXT; n = 11). Social behaviors were observed for 2 days at week 6 after introduction into a four-peer group, and at 10-14 months of age (10 months) immediately and 1 week, 1 month and 5 months after introduction into 11-15 heifers. At week 6, the main effect of the OXT groups was not significant for all social behaviors. At 10 months, there tended to be interactions between the OXT groups and time periods with respect to the frequency of escape behaviors. LOXT heifers exhibited more escape behaviors than HOXT heifers on the first day of the second sociality tests. At 10 months, HOXT heifers exhibited both attacking and affiliative behavior for peers more than LOXT heifers during 5 months after the second social introduction. This suggests that postnatal OXT concentrations may have long-lasting effects on individual differences among social behavioral traits in cattle.

Relationships of neonatal plasma oxytocin with the behavioral characteristics of cattle introduced into a novel environment.

To examine the influence of postnatal oxytocin (OXT) on behavioral development, we examined individual variations in basal OXT and suckling-induced changes in OXT, and their relationship with emotional traits during development. Blood OXT were measured in 20 Holstein heifer calves at 1 (wk1), 2 (wk2), and 6 weeks of age (wk6). The relationships of OXT variables with principal component scores in the open-field tests at wk2 and 2 months and the number of flinch, step and kick responses during first artificial insemination and machine milking were analyzed. The basal OXT showed individual variability and significantly correlated (wk1 vs. wk2: r = 0.753, P < 0.001; wk1 vs. wk6: r = 0.499, P < 0.05; wk2 vs. wk6: r = 0.476, P < 0.05). The personality traits reflecting a response in the form of escape from novel environments in the open-field test at wk2 were inversely correlated with basal OXT at wk1 (rs = -0.640, P < 0.01) and wk2 (rs = -0.447, P < 0.05). However, none of the behavioral variables after 2 months correlated with OXT. These findings suggest that, postnatal OXT might be related to behavioral characteristics in novel environments only during the early stages of life.

Effects of intracerebroventricularly administered carbetocin on social behavior in Holstein steers.

To shed light on the role of central oxytocin (OXT) in regulating social behavior in cattle, the impact of intracerebroventricularly administered OXT agonist, carbetocin (CBT), on the social behavior of a group of familiar steers was investigated. In the first experiment, we determined the dose response of intracerebroventricularly administered CBT (0.5, 5 or 50 nmol) on plasma cortisol level and behavior using 7 steers aged from 6 to 10 months. Five of the steers were assigned to the second experiment. CBT (50 or 200 nmol/200 µl) in artificial cerebrospinal fluid (aCSF) or aCSF (200 µl) was injected into the third ventricle. Immediately after the injection, the animal and two peers were taken outside to the adjacent paddock. Thirty minutes later, maintenance and social behaviors of the animal were observed for 2 hr. CBT had no effect either on the basal cortisol level or on the maintenance and the abnormal behavior in steers with their movement restricted by a stanchion stall in the first experiment. However, in the same steers with no movement restrictions in the second experiment, CBT facilitated lying, probably because of its sedative effect via OXT receptor activation, which disturbed some aspects of social behavior. These results suggest that central OXT receptor activation might not affect social behavior itself among "familiar members", because the stimulation of the central OXT system by intracerebroventricular administration of CBT did not facilitate social behavior between familiar steers.

L-DOPA attenuates prolactin secretion in response to isolation stress in Holstein steers.

To clarify endocrine responses to psychological stressors in cattle, the effects of isolation from familiar peers on plasma prolactin (PRL) and cortisol (CORT) concentrations, and the effect of 3,4-dihydroxy-L-phenylalanine (L-DOPA), a precursor of dopamine (DA), on stress-induced PRL secretion were determined in Holstein steers. First, the potency of peripheral L-DOPA administration on attenuation of central DA levels was confirmed. Cerebrospinal fluid (CSF) collected from a chronic cannula in the third ventricle and plasma were sampled 1 h before and 3 h after intravenous injection of L-DOPA (100 mg/head). DA concentrations in CSF increased just after L-DOPA injection with subsequent decrease in PRL secretion. Injection of L-DOPA increased CORT secretion. Second, one experimental steer was isolated in its stall by removing its peers for 2 h with or without- pre-injection of L-DOPA. The concentration of PRL was elevated by isolation treatment, whereas the effect of isolation on CORT concentration could not be detected. The increase in PRL concentration after isolation was abolished by pre-injection of L-DOPA. These results suggest that PRL responds to isolation and that DA neurons in the central nervous system may regulate stress-induced PRL secretion in steers.

Effects of exposure to plant-derived odorants on behavior and the concentration of stress-related hormones in steers isolated under a novel environment.

This study was conducted to investigate physiological and behavioral effects of the exposure to plant-derived odorants in Holstein steers (8 month of age) under the acute stress of social isolation in a novel environment. Each steer was tethered in a new room alone and exposed to one of three odorants: a mixture of equal amounts of trans-2-hexenal and cis-3-hexenol (green odor, GO; n = 5), essential oil of grapefruits (EOG; n = 5) and solvent (SOL; n = 6). Behaviors were recorded and blood samples were taken at intervals of 10-15 min for 6 h. Compared with SOL, exposure to GO or EOG decreased the frequency of vocalization (P < 0.05), shortened the latency period before the onset of rumination (P < 0.05) and increased the duration of rumination (P < 0.05). Plasma cortisol concentrations in steers exposed to plant-derived odorants (GO and EOG) during 90-130 min from commencement of sampling were significantly lower (P < 0.05) compared with SOL. These results suggest that appeasing effects of plant-derived odorants on behavioral and physiological stress responses previously reported in laboratory rodents could be also be expected in steers.

Central administration of neurokinin B activates kisspeptin/NKB neurons in the arcuate nucleus and stimulates luteinizing hormone secretion in ewes during the non-breeding season.

Human genetic studies have suggested that kisspeptin and neurokinin B (NKB) play pivotal roles in the control of gonadotropin-releasing hormone (GnRH) secretion. However, the role of NKB in this context is less clear compared with that of kisspeptin. In the present study, we investigated the ratio of colocalization of kisspeptin and NKB in neurons in the arcuate nucleus (ARC), the effects of intracerebroventricular infusion of NKB on luteinizing hormone (LH) secretion and whether the treatment activates ARC kisspeptin/NKB neurons in seasonally anestrous ewes. Double-labeling immunohistochemistry revealed that the majority of kisspeptin neurons coexpressed NKB in the ARC. Infusion of NKB for 2 h into the lateral ventricle elicited a discharge of LH, which resulted in significant increases in LH concentrations between 20 and 50 min after the start of infusion compared with a saline-infused control. Animals were sacrificed immediately after the end of infusion, and Fos expression in ARC kisspeptin neurons was immunohistochemically examined. The NKB treatment activated kisspeptin neurons throughout the ARC, and approximately 70% of kisspeptin neurons expressed Fos immunoreactivity at the caudal portion of the nucleus. The present study demonstrated that a central infusion of NKB elicited a discharge of LH, which was associated with the activation of a large population of ARC kisspeptin/NKB neurons in seasonally anestrous ewes. The results suggest that NKB plays a stimulatory role in the control of pulsatile GnRH secretion and that the population of ARC kisspeptin/NKB neurons is one of sites of the NKB action in sheep.

The effect of lighting conditions on the rhythmicity of growth hormone secretion in Holstein steers.

Growth hormone (GH) secretion regularity and the effects of lighting condition and GH-releasing hormone (GHRH) on GH release were determined in steers. First, steers were kept under 12:12 L : D conditions (light: 06.00-18.00 hours). The animals were then subjected to a 1-h advancement in lighting on/off conditions (05.00 and 17.00 hours, respectively). Blood was sampled for 24 h at 1-h interval on the seventh day of each condition. Second, GHRH was injected intravenously (IV) at 12.00 and 00.00 hours under 12:12 L : D and blood was sampled at 15-min interval for 4-h (1 h before and 3 h after the injection). Plasma GH concentrations were measured by a radioimmunoassay. Periodicity of GH secretory profile was calculated by power spectrum analysis using the maximum entropy method. Plasma GH concentrations showed a characteristic pattern consisting of four distinct peaks. Mean periodicity of GH secretory profile was 5.7 h, and it was not altered by any change in lighting conditions. IV injection of GHRH increased GH secretion during the day and night. The increase in GH secretory volume after GHRH injection during the night was equal to that during the day. The present results suggest that GH secreted from the anterior pituitary have regularity in steers.

Effect of oxytocin, prolactin-releasing peptide, or corticotropin-releasing hormone on feeding behavior in steers.

As a preliminary step to elucidate the involvement of central neurotransmitters in the dip in voluntary feed intake during the perinatal period in cows, we investigated the effect of intracerebroventricular (ICV) administration of oxytocin, prolactin-releasing peptide (PrRP), or corticotropin-releasing hormone (CRH), the central functions of all of which undergo drastic changes during the perinatal period, on feed intake in steers. Thirty minutes before the onset of feeding, the treatment solution was injected into the third ventricle through an implanted cannula, and feeding-related behaviors were observed for 1 h after the onset of feeding. Neither ICV oxytocin (5 and 50 µg) nor PrRP (2 and 20 nmol) reduced feed intake (n=6). Twenty nanomoles of bovine CRH noticeably inhibited feeding behavior compared with vehicle treatment (n=5, p<0.05). Fifty micrograms of oxytocin reduced latency to the first water access after feeding onset (p<0.1), which may be because of the stimulation of arginine vasopressin V1b receptor by the high dose of oxytocin. We conclude that CRH inhibits feeding behavior by its central action in this species, although this could also be an indirect effect due to the increased expression of abnormal behaviors caused by CRH. Central administration of neither oxytocin nor PrRP reduced feed intake in steers. Although the effects of sex steroids need to be examined, it appears that increased activity of oxytocin, and possibly PrRP, during the perinatal period does not contribute to the dip in voluntary feed intake in this species. On the other hand, it makes sense that suppressed central CRH activity during the perinatal period should act in the direction of maintaining or even increasing food intake to aid a steady supply of energy to the fetus or offspring. We thus speculate that CRH is not a prime candidate involved in the dip in voluntary feed intake during the perinatal period in cows.

Effect of intracerebroventricular injections of prolactin-releasing peptide on prolactin release and stress-related responses in steers.

Some evidence suggests that there might be a species difference in the effect of intracerebroventricularly administered (ICV) prolactin-releasing peptide (PrRP) between rodents and sheep. We compared the levels of cortisol (CORT) and prolactin (PRL), rectal temperature (RT) and behavioral responses to ICV bovine PrRP (bPrRP) in steers. ICV bPrRP (0.2, 2 and 20 nmol/200 µL) tended to evoke a dose-related increase in CORT concentrations and 0.2 nmol of bPrRP induced transient increase in PRL concentrations. A significant time-treatment interaction was observed for the percent change of CORT (P<0.05) and PRL (P<0.05) from pre-injection value. The time-treatment interaction for changes in RT was not significant (P=0.50). There tended to be a difference among the four treatments in terms of maximum change in RT from the pre-injection value between 0 and 90 min (P<0.1). Stress-related behavioral signs were not observed in the present experiment. These findings indicate that ICV bPrRP increased CORT and PRL levels, suggesting that central PrRP might participate in controlling the hypothalamo-pituitary-adrenal axis and PRL release in cattle, unlike sheep. In contrast, central PrRP is unlikely to be involved in controlling the behavior of this species because ICV bPrRP did not induce marked changes in their behavior.

A possible role of central serotonin in L-tryptophan-induced GH secretion in cattle.

To clarify the role of serotonin (5-HT) in the regulatory mechanism of L-tryptophan (TRP)--induced growth hormone (GH) secretion in cattle, changes in 5-HT concentrations in the cerebrospinal fluid (CSF) in the third ventricle (3V) and GH in plasma before and after the peripheral infusion of TRP were determined simultaneously. The direct effect of TRP on GH release from the dispersed anterior pituitary cells was also assessed. A chronic cannula was placed in 3V by stereotaxic surgery, then CSF and blood were withdrawn under physiological conditions. TRP (38.5 mg/kg BW) was infused through an intravenous catheter from 12.00 to 14.00 hours and CSF and blood sampling were performed from 11.00 to 18.00 hours at 1-h intervals. The concentration of 5-HT in CSF was determined by high-performance liquid chromatography with electrochemical detection. GH, melatonin (MEL), and cortisol (CORT) concentrations were measured by radio-immunoassay and enzyme-immunoassay. Concentrations of 5-HT were increased by TRP infusion. The TRP infusion significantly increased GH release. On the other hand, TRP did not stimulate GH release from the bovine pituitary cells. MEL and CORT concentrations were not altered by TRP infusion. These results suggest that TRP induced GH release via the activation of serotonergic neurons in cattle.

Relationships of stress responses with plasma oxytocin and prolactin in heifer calves.

Oxytocin and prolactin are potential candidates for the regulation of behavioral and physiological stress responses in the brain. To investigate the neurobiological basis of individual differences in stress responses in cattle, we examined the association of behavioral and hypothalamo-pituitary-adrenal axis reactivity to acute stressors and basal and stimulated levels of oxytocin and prolactin. Twenty Holstein heifer calves aged 2 weeks were subjected to a 10 min open-field test (OFT) followed by presentation of a feeding bucket for 15 min in the OF. If the calf contacted the bucket, a blast of air was applied to its muzzle (surprise test). Jugular blood samples collected before and after both tests were analyzed for oxytocin, prolactin, and cortisol. Relationships of basal and percent change in oxytocin or prolactin with behavioral responses in each test and percent change in cortisol were analyzed using principal components analysis and Spearman rank correlations. Plasma cortisol and prolactin concentrations were significantly elevated by the tests (p<0.005), but plasma oxytocin concentration did not significantly change (p>0.1). Four principal components explained 56.1% of the total variation: curiosity, general activity, fearfulness, and dependence on humans. Curiosity was inversely correlated with basal oxytocin level (rS=-0.683, p<0.05). General activity was positively correlated with prolactin reactivity (rS=0.448, p<0.05) and inversely with oxytocin reactivity to the novel environment (rS=-0.717, p<0.05). Fearfulness tended to correlate positively with basal oxytocin level (rS=0.583, p<0.1). Dependence on humans correlated with none of the hormonal parameters. The relationships of basal oxytocin level with curiosity and fearfulness for novel environments are of particular interest for future study.