Single-dose meloxicam treatment improves standing ability of low-vitality dairy calves.

A promising strategy to improve newborn calf survival could be the administration of nonsteroidal antiinflammatory drugs (NSAID) especially in cases of low vitality calves born from difficult calvings. The objective of this clinical trial was to determine the effect of a single-dose meloxicam treatment [target dosage = 0.5 mg/kg ad usum veterinarium (A.U.V.) injection] on parameters of lying behavior of Holstein-Friesian dairy calves (n = 180) born to eutocic (n = 98) compared with dystocic dams (n = 82). Animal-based measures included newborn calf vitality (low, 1-6 scores; normal, 7-12 scores, scored immediately after birth), calf sex and birth weight, parity of the dam, and early maternal behavior (the time spent licking the calf). Parameters of the complex lying behavior were recorded during the first 48 h after delivery and included (1) the time spent standing, (2) lying down frequency, (3) the longest standing bout, (4) the average duration of standing bouts, (5) the first successful standing, and (6) the first attempt to stand. None of the parameters related to lying behavior were influenced by the parity of the dam, calf sex, or birth weight and maternal grooming behavior. The latency and the first attempt to stand were not influenced by the NSAID treatment; however, the time spent standing, the longest standing bout, and the average duration of standing indicated increased standing ability of meloxicam-treated calves with low vitality, but not in normal-vitality calves. The latency to stand and first attempt to stand were both increased by dystocia. Based on the present findings, sensory measurement of parameters of lying behavior during the immediate neonatal period might be useful to evaluate the efficiency of NSAID protocols. A single-dose meloxicam treatment showed considerable promise for improving standing ability of low-vitality calves.

Cardiac vagal tone, plasma cortisol, and dehydroepiandrosterone response to an ACTH challenge in lame and nonlame dairy cows.

We studied the adrenocortical and vagal tone responses to a single ACTH challenge in lame (n = 9) vs nonlame (n = 9) dairy cows. Cows were paired according to parity, days in milk, and milk yield. Plasma cortisol and dehydroepiandrosterone concentrations and cardiac vagal tone response (high-frequency component of heart rate variability) were compared after intravenous ACTH administration. Baseline, minimum or maximum, amplitude of the response and area under the response curve were compared. No difference was detected between groups in the cortisol response. Dehydroepiandrosterone was irresponsive to ACTH treatment, and concentrations did not differ between lame and nonlame cows. Vagal tone decreased in response to the ACTH treatment. High frequency component of heart rate variability was lower in the lame group at all sampling times. Lameness was associated with delayed return to baseline. We concluded that the adrenal response capacity is not influenced by lameness, which supports the concept of lameness being a chronic intermittent rather than a chronically persistent stressor. Dehydroepiandrosterone concentrations were not proven to be useful indicators of hypothalamus-pituitary axis dysfunction in cattle. A decreased vagal contribution to heart rate variability-possibly coupled with increased sympathetic modulation-was observed in lame cows, which suggests that lameness affects the mechanisms underlying the action of ACTH on cardiovascular activity.

Short communication: Upper critical temperature-humidity index for dairy calves based on physiological stress variables.

In this study, upper critical values of the temperature-humidity index (THI) were determined in Holstein bull calves (n = 16) based on noninvasive physiological variables. Meteorological and animal-based data were recorded for a 4-d period following a 24-h habituation. The estimated upper critical THI values based on the assessment of respiratory rate, rectal temperature, ear temperature, heart rate, and salivary cortisol concentrations were 82.4, 88.1, 83.0, 78.3, and 88.8, respectively. We inferred that welfare of young calves may be compromised above a THI of 78 and that calves experience significant heat stress above a THI of 88. Based on the present findings, upper critical THI should be considered to minimize the duration of impaired welfare during summer heat stress episodes.

Short communication: Heart rate variability, step, and rumination behavior of dairy cows milked in a rotary milking system.

Step behavior, heart rate (HR), the high-frequency (HF) component of heart rate variability (HRV), the ratio of the low-frequency (LF) and HF components (LF/HF ratio) as well as rumination behavior during milking were investigated in dairy cows milked in a high-capacity rotary milking system (n = 49) to study animals' stress responses to the milking process. Cardiac parameters were analyzed for undisturbed standing (baseline) and for the stages of the morning, afternoon, and evening milking processes (i.e., driving animals from the barn to the pre-milking holding pen, pre-milking holding pen, preparation, milking, and waiting after milking in the milking stall). During driving, HR was greater than during all other stages. After driving, a gradual decrease in HR was observed. The HF decreased during driving, indicating a decrease in vagal tone compared with baseline. When animals were in the holding pen, vagal tone decreased, whereas sympathetic tone increased with lower values than recorded for baseline and driving. During preparation, HF values were still lower than those recorded for baseline. The recovery of the autonomic activity was observed following preparation as indicated by increased HF and decreased LF/HF ratio during milking and waiting stages. During milking, 53.1% of the animals ruminated. The frequency of steps was greater during preparation (3.7 ± 1.8 steps/min) than during milking (0.7 ± 0.4 steps/min) and waiting after milking (1.6 ± 1.0 steps/min). Our results suggest that being in the holding pen is stressful for cows; however, vagal predominance from the onset of milking, the low frequency of steps, and the high prevalence of rumination during milking suggest a possible welfare benefit of the investigated rotary milking system.

Effect of artificial shade on saliva cortisol concentrations of heat-stressed dairy calves.

Responses to heat stress have not been evaluated in dairy cattle by noninvasive techniques such as analysis of saliva cortisol concentrations. The aim of the present study was the assessment of saliva cortisol levels in Holstein bull calves with (n = 8) or without supplemental shade (n = 8) in response to acute heat stress. Measurements were carried out during a 5-d period [temperature, average/max (°C); day 1 (control, all calves shaded): 22.9/29.4, day 2 (heat stress day): 28.3/38.8, day 3: 26.2/33.5, day 4: 23.7/28.7, and day 5: 21.2/24.7]. The level of thermal stress was characterized with a temperature-humidity index (THI). Saliva cortisol levels did not differ between groups during the control day. On the heat stress day, saliva cortisol levels increased from 8:00 to 12:00 by 51% and 342% in shaded and nonshaded calves, respectively, and nonshaded calves showed higher cortisol concentrations at 12:00, 16:00, and 24:00. Saliva cortisol levels peaked at 12:00 on day 3 in both groups. On days 4 and 5, saliva cortisol did not show significant daytime elevations in either group; however, group differences remained significant until 20:00 on day 4. Based on our results, measurement of saliva cortisol concentrations is a promising approach to detect acute heat stress in dairy calves, which could be reduced by artificial shading.

Fetal metacarpal/metatarsal bone thickness as possible predictor of dystocia in Holstein cows.

Dystocia and perinatal calf mortality cause significant economic losses in the dairy cattle industry. Despite advanced ultrasound examination procedures, there is no reliable method to estimate the birth weight of calves in order to predict, prepartum, the risk of dystocia. The aim of this study was to predict calf birth weight and dystocia based on transrectal ultrasonographic (TRUS) examinations in late-term Holstein heifers and cows. Therefore, TRUS examination was performed on 128 animals that were between 265 and 282 d of gestation to measure the bone thickness of the fetal metacarpus (MC) or metatarsus (MT). Fetal TRUS measurements were successful in 104 cases. Excluding twin deliveries, 97 fetal MC/MT bone thicknesses were measured and the mean (±SD) MC/MT thickness was 2.54 ± 0.37 cm. A novel index, the metacarpal/metatarsal index [MCTI = maternal body weight (kg)/fetal MC or MT thickness (cm)], was also calculated to study its association with calving ease. The average MCTI was 257.3 kg/cm in the studied population. A lower MCTI was associated with the risk of dystocia with an odds ratio of 2.074 that was not significantly different from 1 (95% confidence interval: 0.002-11.104). Fetal presentation, fetal age, fetal sex, body condition score of the dam, age of dam, and intercoxal and interischiadic distances were not related to dystocia. A fair phenotypic correlation (0.226) was found between MC/MT thickness and calf birth weight. The genetic correlation between MC/MT thickness and calf birth weight was 0.235. Our results indicate that late-term measurement of the fetal MC/MT bone thickness by means of TRUS examination augmented with the MCTI may have clinical significance in the prediction of dystocia in Holstein cattle. Because the odds ratio for dystocia based on MCTI determination was not significant, the applied technique should be improved based on further studies on prepartum TRUS examinations combined with dam pelvic measurements.

Association between human and animal thermal comfort indices and physiological heat stress indicators in dairy calves.

Warm summer episodes have a significant effect on the overall health and well-being of young cattle; however, it is not known which temperature measure should be used for estimating heat stress in dairy calves. In this study, generalized linear mixed-effects models were used to estimate the relationships between thermal comfort indices and animal-based heat stress indicators in sixteen Holstein bull calves that were housed in individual calf hutches. Data were collected under continental weather characteristics over a 5-day period: day 1 (lower-temperature day), days 2 and 3 (heat stress days), and a 2-day post-stress period. Relative humidity, ambient temperature, the heat index, the humidex and five different temperature-humidity indices (THI) were used as thermal indices. Physiological variables monitored included respiratory rate, rectal temperature, ear skin temperature and heart rate. The heat index and the humidex measuring human thermal comfort were more closely associated with physiological measures than were the ambient temperature or the THIs (in case of heat index: R2 = 0.87 for respiratory rate, R2 = 0.63 for rectal temperature, R2 = 0.70 for ear skin temperature, and R2 = 0.78 for heart rate, respectively; in case of humidex: R2 = 0.85 for respiratory rate, R2 = 0.60 for rectal temperature, R2 = 0.68 for ear skin temperature, and R2 = 0.75 for heart rate, respectively). Based on our results, parameters of human outdoor comfort seem better to estimate heat stress in dairy calves in a continental region than those of THIs or ambient temperature.

Seasonal and maternal effects on acid-base, l-lactate, electrolyte, and hematological status of 205 dairy calves born to eutocic dams.

In this study, we used linear mixed models to determine the effects of season, time of sampling relative to birth (factors), duration of the delivery process, duration of maternal grooming, calf body weight (BW) at birth, and time of day (covariates) on values of venous blood gas, acid-base and electrolyte parameters, and l-lactate concentrations in dairy calves born to eutocic dams in summer (SUM, n = 101) and winter (WIN, n = 104). Neonatal vitality was assessed at 0, 1, and 24 h after delivery in a linear scoring system using muscle tone, erection of the head, muscle reflexes, heart rate, and sucking drive as criteria. Simultaneously with vitality scoring, venous blood samples were collected by jugular venipuncture. Blood was tested for pH, partial pressure of CO2 (pCO2; mmHg) and oxygen (pO2; mmHg), l-lactate (mmol/L), hemoglobin (Hb; g/L), ionized calcium (Ca2+; mmol/L), sodium (Na+; mmol/L), potassium (K+; mmol/L) and chloride (Cl-; mmol/L). Bicarbonate (HCO3-; mmol/L), base excess (BE; mmol/L), total carbon dioxide (TCO2; mmol/L), and anion gap (mmol/L) were calculated. Electrolyte parameters were affected by none of the factors or covariates. Time of day at birth did not affect any of the parameters of interest. Vitality score tended to increase over time and it showed higher values in WIN calves than in SUM calves. Concentrations of HCO3-, BE, and l-lactate indicated a higher degree of metabolic acidosis in SUM calves; however, pH was not affected by season. Concentrations of Hb were higher in SUM calves than in WIN calves; however, covariates did not affect Hb concentrations. Blood pH, concentrations of pO2, HCO3-, and BE decreased, whereas l-lactate concentrations and values of pCO2, TCO2, and anion gap increased with longer duration of delivery. A shift in acid-base balance was also linked to BW of the calf at birth, with lower values of blood pH, HCO3-, and BE in calves with higher BW compared with those with lower BW at birth, whereas TCO2 and l-lactate concentrations increased with higher calf BW at birth. Values of pO2 increased and pCO2 decreased with longer duration of maternal grooming. Blood pH, HCO3-, and BE increased, whereas l-lactate concentrations and anion gap decreased with longer duration of licking the calf. Our results indicate that prolonged delivery can impair acid-base status and can cause slight lactic acidosis, even in calves born from spontaneous or eutocic calvings, and that high BW at birth predisposes calves to acidosis. The positive effect of maternal grooming on neonatal acid-base status should be considered in parturition management. Season, duration of the delivery process, calf BW at birth, and duration of maternal grooming are recommended for consideration in future studies on blood gas and acid-base parameters in dairy calves in the immediate neonatal period.

Rumination time and reticuloruminal temperature as possible predictors of dystocia in dairy cows.

The objectives of this study were to explore changes of rumination time and reticuloruminal pH and temperature of dairy cows and heifers (means ± standard deviation; age = 5.8 ± 1.9; parity = 2.7 ± 1.4; body condition score = 3.2 ± 0.2) with eutocic (EUT, n = 10) and dystocic calving (DYS, n = 8). The recording period lasted from 3 d before calving until 7 d in milk. For the comparison of rumination time and reticuloruminal characteristics between groups, time to return to baseline (the time interval required to return to baseline from the delivery of the calf) and area under the curve (AUC; both for prepartum and postpartum periods) were calculated for each parameter. Rumination time decreased from baseline 28 h before calving both for EUT and DYS cows; after 20 h before calving, it decreased to 32.4 ± 2.3 and 13.2 ± 2.0 min/4 h between 8 and 4 h before delivery in EUT and DYS cows, respectively, and then it decreased below 10 and 5 min during the last 4 h before calving. Until 12 h after delivery, rumination time reached 42.6 ± 2.7 and 51.0 ± 3.1 min/4 h in DYS and EUT dams, respectively; however, AUC and time to return to baseline suggested lower rumination activity in DYS cows than in EUT dams for the 168-h postpartum observational period. Reticuloruminal pH decreased from baseline 56 h before calving both for EUT and DYS cows, but did not differ between groups before delivery. Reticuloruminal pH showed a decreasing tendency and clear diurnal variation after calving for both EUT and DYS cows, with slightly higher AUC values in DYS cows. In DYS cows, reticuloruminal temperature decreased from baseline 32 h before calving by 0.23 ± 0.02°C, whereas in EUT cows such a decrease was found only 20 h before delivery (0.48 ± 0.05°C). The AUC of reticuloruminal temperature calculated for the prepartum period was greater in EUT cows than in DYS cows. During the first 4 h after calving, reticuloruminal temperature decreased from 39.68 ± 0.09 to 38.96 ± 0.10°C and from 39.80 ± 0.06 to 38.81 ± 0.08°C in EUT and DYS cows, respectively, and reached baseline levels after 35.4 ± 3.4 and 37.8 ± 4.2 h after calving in EUT and DYS cows, respectively. Based on our results, continuous monitoring of changes in rumination time and reticuloruminal temperature seems to be promising in the early detection of cows with a higher risk of dystocia. Depressed rumination activity of DYS cows after calving highlights the importance of the postpartum monitoring of cows experiencing difficulties at calving. The effect of dystocia on postpartum reticuloruminal pH was not pronounced.

Effect of calving process on the outcomes of delivery and postpartum health of dairy cows with unassisted and assisted calvings.

Welfare aspects of obstetrical assistance were studied in multiparous Holstein-Friesian cows (n=176) with (1) unassisted calving in an individual pen (UCIP; n=42), (2) unassisted calving in a group pen (UCG; n=48), (3) assisted calving with appropriately timed obstetrical assistance (ACAP; n=50), and (4) assisted calving with inappropriately timed (premature) obstetrical assistance (ACIN; n=36). Duration of the stages of calving, the prevalence and the degree of dystocia, stillbirth ratio, newborn calf vitality, and the occurrence of postpartum health problems (i.e., retained placenta and vulvovaginal laceration) were recorded. The time from amniotic sac and hooves appearance to birth and the total duration of calving (from the onset of calving restlessness to delivery) were shorter for UCG cows than for any other groups. The overall incidence of dystocia was 31.3% in the calvings studied. The prevalence of dystocia was below 10% in cases of unassisted calvings. The proportion of severe dystocia was higher in ACIN cows than in ACAP cows (47.2 vs. 12.0%, respectively). The prevalence of stillbirths was the highest in ACIN calvings (22.2%), followed by ACAP, UCI, and UCG cows (8.0, 4.8, and 0.0%, respectively). The ACIN calves had lower vitality scores than calves born from ACAP, UCG, and UCIP dams immediately after delivery and 24h after birth. Although ACAP calves had lower vitality scores than UCG and UCIP calves at birth, a delayed recovery of vitality was mirrored by satisfactory vitality scores 24h after birth. Retained placenta and vulvovaginal laceration occurred more often with assisted dams (i.e., ACAP and ACIN animals) compared with UCIP cows with the highest prevalence in ACIN cows. In UCG cows, no injuries occurred in the vulva or vagina, and we noted only 4 cases of retained placenta (8.3%), proportions lower than in cows with unassisted calving in the maternity pen. Our results suggest that calving in a group might have benefits over calving in an individual pen in terms of calving ease, duration of the delivery process, and postpartum health of the dam vitality of her offspring. Premature obstetrical assistance leads to a high prevalence of dystocia, impairs postpartum health of the dam, and poses a potential risk to calf survival.

Hypothalamic-pituitary-adrenal and cardiac autonomic responses to transrectal examination differ with behavioral reactivity in dairy cows.

Behavior, hypothalamic-pituitary-adrenal axis, and cardiac autonomic nervous system (ANS) activity were evaluated in response to transrectal examination in nonlactating Holstein-Friesian cows with different behavioral reactivity. According to behavioral reactions shown to the procedure of fixing the heart rate (HR) monitors, the 20 cows with the highest and the 20 cows with the lowest behavioral reactivity were involved in the study (high responder, n=20; and low responder, n=20, respectively). Activity of the ANS was assessed by HR and HR variability parameters. Blood and saliva were collected at 5 min before (baseline) and 0, 5 10, 15, 20, 30, 40, 60, and 120 min after the examination to determine cortisol concentrations. The examination lasted for 5 min. Cardiac parameters included HR, the root mean square of successive differences between the consecutive interbeat intervals, the high frequency (HF) component of heart rate variability, and the ratio between the low frequency (LF) and HF parameter (LF/HF). Following the examination, peak plasma and saliva cortisol levels and the amplitude of the plasma and saliva cortisol response were higher in high responder cows than in low responders. Areas under the plasma and saliva cortisol response curves were greater in high responder cows. Plasma and salivary cortisol levels correlated significantly at baseline (r=0.91), right after examination (r=0.98), and at peak levels (r=0.96). Area under the HR response curve was higher in low responder cows; however, maximum HR and the amplitude of the HR response showed no differences between groups. Minimum values of both parameters calculated for the examination were higher in high responders. Following the examination, response parameters of root mean square of successive differences and HF did not differ between groups. The maximum and the amplitude of LF/HF response and area under the LF/HF response curve were lower in low responder cows, suggesting a lower sympathetic activation of the ANS. Although changes in behaviors indicated that the procedure was painful for the animals, no differences were observed either in vocalization or in attendant behavior between groups during the examination. Our results demonstrate that behaviorally more reactive animals exhibit increased plasma and salivary cortisol concentrations and higher cardiac autonomic responsiveness to transrectal examination than less reactive cows. Salivary cortisol may substitute for plasma cortisol when assessing response of cattle to stress.

Step behaviour and autonomic nervous system activity in multiparous dairy cows during milking in a herringbone milking system.

Behavioural and cardiac responses of multiparous dairy cows (n=24) during milking in a 2×4 stall herringbone milking system were evaluated in this study. Heart rate (HR), parasympathetic tone index (high frequency component, HF) of heart rate variability and sympathovagal balance indicator LF/HF ratio (the ratio of the low frequency (LF) and the HF component) were analysed. Measurement periods were established as follows: (1) standing calm (baseline), (2) udder preparation, (3) milking, (4) waiting after milking in the milking stall and (5) in the night (2 h after milking). Step behaviour was recorded and calculated per minute for the three phases of the milking process (udder preparation, milking and waiting after milking). HR was higher during udder preparation and milking compared with baseline (P=0.03, 0.027, respectively). HF was significantly lower than baseline levels during waiting in the milking stall after milking (P=0.009), however, during udder preparation, milking and 2 h after milking did not differ from baseline (P>0.05, in either case). LF/HF during the three phases of the milking process differed neither from baseline levels nor from each other. Steps occurred more often during waiting after milking than during udder preparation (P=0.042) or during milking (23; P=0.017). Our results suggest that the milking procedure itself was not stressful for these animals. After milking (following the removal of the last teat cup and before leaving the milking stall), both decreased parasympathetic tone (lower HF) and increased stepping rate indicated a sensitive period for animals during this phase.

Heart rate and heart rate variability in multiparous dairy cows with unassisted calvings in the periparturient period.

Behavioural changes before calving can be monitored on farms; however, predicting the onset of calving is sometimes difficult based only on clinical signs. Heart rate (HR) and heart rate variability (HRV) as non-invasive measures of autonomic nervous system (ANS) activity were investigated in Holstein-Friesian cows (N=20) with unassisted calvings in the periparturient period to predict the onset of calving and assess the stress associated with calving. R-R-intervals were analysed in 5-min time windows during the following three main periods of measurement: 1) between 0 and 96 h before the onset of calving restlessness (prepartum period); 2) during four stages of calving: (I) early first stage; between the onset of calving restlessness and the first abdominal contractions; (II) late first stage (between the first abdominal contractions and the appearance of the amniotic sac); (III) early second stage (between the appearance of the amniotic sac and the appearance of the foetal hooves); (IV) late second stage (between the appearance of the foetal hooves and delivery of the calf), and 3) over 48 h following calving (postpartum period). Data collected between 72 and 96 h before calving restlessness was used as baseline. Besides HR, Poincaré measures [standard deviation 1 (SD1) and 2 (SD2) and SD2/SD1 ratio], the root mean square of successive differences (RMSSD) in R-R intervals, the high-frequency (HF) component of HRV and the ratio between the low-frequency (LF) and the HF components (LF/HF ratio) were calculated. Heart rate increased only following the onset of the behavioural signs, peaked before delivery of the calf, then decreased immediately after calving. Parasympathetic indices of HRV (RMSSD, HFnorm and SD1) decreased, whereas sympathovagal indices (LF/HF ratio and SD2/SD1 ratio) increased significantly from baseline between 12 and 24 before the onset of calving restlessness. The same pattern was observed between 0 and 1h before calving restlessness. Following the onset of behavioural signs, parasympathetic activity increased gradually with a parallel shift in sympathovagal balance towards parasympathetic tone, which was possibly a consequence of oxytocin release, which induces an increase in vagus nerve activity. Parasympathetic activity decreased rapidly between 0 and 0.5h following calving and was lower than measured during all other stages of the study, while sympathetic activity peaked during this stage and was higher than measured during any other stages. Between 0 and 4h after calving vagal tone was lower than baseline, whereas sympathovagal balance was higher, reflecting a prolonged physiological challenge caused by calving. Vagal activity decreased, whereas sympathovagal balance shifted towards sympathetic tone with increased live body weight of the calf during the late second stage of calving, suggesting higher levels of stress associated with the higher body weight of calves. All HRV indices, measured either at the late second stage of calving and between 12 and 24h after calving, were affected by the duration of calving. Our results indicate that ANS activity measured by HRV indices is a more immediate indicator of the onset of calving than behaviour or HR, as it changed earlier than when restlessness or elevation in HR could be observed. However, because of the possible effects of other physiological mechanisms (e.g. oxytocin release) on ANS activity it seems to be difficult to measure stress associated with calving by means of HRV between the onset of calving restlessness and delivery. Further research is needed to enable more precise interpretation of the prepartum changes in HR and HRV in dairy cattle.

Cardiac responses to palpation per rectum in lactating and nonlactating dairy cows.

Interest in the monitoring of heart rate variability (HRV) has increased recently, as it gives more detailed and immediate information about the level of stress than traditional behavioral or hypothalamus-pituitary-adrenal measures. In this study, we evaluated heart rate (HR) and parasympathetic HRV parameters to monitor cardiac stress responses to palpation per rectum (PPR) in lactating (LACT; n = 11) and nonlactating (NLACT; n = 12) dairy cows. Heart rate and HRV were recorded from 40 min before PPR until 120 min after it was completed. Heart rate, the root mean square of successive differences (RMSSD), and the high-frequency component (HF) of HRV were analyzed by examining 5-min time windows. To compare cardiac responses to PPR between groups, changes in HR and HRV parameters were calculated as area under the curve (AUC) for LACT and NLACT cows. An immediate increase in HR was detected during PPR in both LACT (+21.4 ± 2.4 beats/min) and NLACT cows (+20.6 ± 2.3 beats/min); however, no differences were found between groups on the basis of parameters of AUC. The increase in HR in both groups along with a parallel decrease in RMSSD (LACT cows: -5.2 ± 0.4 ms; NLACT cows: -5.1 ± 0.4 ms) and HF [LACT cows: -10.1 ± 0.8 nu (where nu = normalized units); NLACT cows: -16.9 ± 1.2 nu] during PPR indicate an increase in the sympathetic, and a decrease in the parasympathetic tone of the autonomic nervous system. The increase in RMSSD (LACT cows: +7.3 ± 0.7 ms; NL cows: +17.8 ± 2.2 ms) and in HF (LACT cows: +24.3 ± 2.6 nu; NLACT cows: +32.7 ± 3.5 nu) immediately after PPR indicated a rapid increase in parasympathetic activity, which decreased under the baseline values 10 min following PPR. The amplitude and the maximum RMSSD and HF values were greater in NLACT cows than in LACT animals, suggesting a higher short-term cardiac responsiveness of NLACT cows. However, the magnitude and the duration of the stress response were greater in LACT cows, as indicated by the analysis of AUC parameters (area under the HRV response curve and time to return to baseline). Cow response to the PPR was more prominent in parasympathetic HRV measures than in HR. Based on our results, the effect of PPR on the cows' cardiac stress responses may have an impact on animal welfare on dairy farms, and investigating the effect of lactation on the cardiac stress reactions could prove useful in modeling bovine stress sensitivity. Further research is needed to find out whether the differences due to lactation are physiological or management related.