Levente Kovács

Welfare implication of measuring heart rate and heart rate variability in dairy cattle: literature review and conclusions for future research

Heart rate (HR) measurements have been used to determine stress in livestock species since the beginning of the 1970s. However, according to the latest studies in veterinary and behaviour-physiological sciences, heart rate variability (HRV) proved to be more precise for studying the activity of the autonomic nervous system. In dairy cattle, HR and HRV indices have been used to detect stress caused by routine management practices, pain or milking. This review provides the significance of HR and HRV measurements in dairy cattle by summarising current knowledge and research results in this area. First, the biological background and the interrelation of the autonomic regulation of cardiovascular function, stress, HR and HRV are discussed. Equipment and methodological approaches developed to measure interbeat intervals and estimate HRV in dairy cattle are described. The methods of HRV analysis in time, frequency and non-linear domains are also explained in detail emphasising their physiological background. Finally, the most important scientific results and potential possibilities for future research are presented.

Heart Rate Variability as an Indicator of Chronic Stress Caused by Lameness in Dairy Cows

Most experimental studies on animal stress physiology have focused on acute stress, while chronic stress, which is also encountered in intensive dairy cattle farming–e.g. in case of lameness–, has received little attention. We investigated heart rate (HR) and heart rate variability (HRV) as indicators of the autonomic nervous system activity and fecal glucocorticoid concentrations as the indicator of the hypothalamic–pituitary–adrenal axis activity in lame (with locomotion scores 4 and 5; n = 51) and non-lame (with locomotion scores 1 and 2; n = 52) Holstein-Friesian cows. Data recorded during the periods of undisturbed lying–representing baseline cardiac activity–were involved in the analysis. Besides linear analysis methods of the cardiac inter-beat interval (time-domain geometric, frequency domain and Poincaré analyses) non-linear HRV parameters were also evaluated. With the exception of standard deviation 1 (SD1), all HRV indices were affected by lameness. Heart rate was lower in lame cows than in non-lame ones. Vagal tone parameters were higher in lame cows than in non-lame animals, while indices of the sympathovagal balance reflected on a decreased sympathetic activity in lame cows. All geometric and non-linear HRV measures were lower in lame cows compared to non-lame ones suggesting that chronic stress influenced linear and non-linear characteristics of cardiac function. Lameness had no effect on fecal glucocorticoid concentrations. Our results demonstrate that HRV analysis is a reliable method in the assessment of chronic stress, however, it requires further studies to fully understand the elevated parasympathetic and decreased sympathetic tone in lame animals.

Short communication: Changes in heart rate variability of dairy cows during conventional milking with nonvoluntary exit

Heart rate variability (HRV), as a physiological measure of animal welfare, was investigated in 36 cows milked in a parallel milking parlor with nonvoluntary exit. Heart rate variability parameters measured during the morning resting (baseline period) were compared with those measured during different stages of the entire milking process. No differences were found in HRV parameters between the baseline period, preparation, and main milking. A considerable reduction in vagal activity was detected during the movement of the cows to the milking parlor (driving) and while cows were in the holding area. The parasympathetic measures of HRV decreased whereas the sympatho-vagal balance increased compared with baseline. The same pattern was observed regarding the stage between removing the teat cups and leaving the milking parlor (waiting). No differences in any sympathetic measures were observed between the baseline period and any of the milking stages. These findings indicate that the milking process itself (preparation and main milking) is not stressful for cows. Decreased parasympathetic activity during driving might be the result of the physical activity of the cows, whereas waiting in the holding area and in the milking stall after milking caused stress for animals.

Heart Rate and Heart Rate Variability in Dairy Cows with Different Temperament and Behavioural Reactivity to Humans.

From the 1990s, extensive research was started on the physiological aspects of individual traits in animals. Previous research has established two extreme (proactive and reactive) coping styles in several animal species, but the means of reactivity with the autonomic nervous system (ANS) activity has not yet been investigated in cattle. The aim of this study was the characterization of cardiac autonomic activity under different conditions in cows with different individual characteristics. For this purpose, we investigated heart rate and ANS-related heart rate variability (HRV) parameters of dairy cows (N = 282) on smaller- and larger-scale farms grouped by (1) temperament and (2) behavioural reactivity to humans (BRH). Animals with high BRH scores were defined as impulsive, while animals with low BRH scores were defined as reserved. Cardiac parameters were calculated for undisturbed lying (baseline) and for milking bouts, the latter with the presence of an unfamiliar person (stressful situation). Sympathetic tone was higher, while vagal activity was lower in temperamental cows than in calm animals during rest both on smaller- and larger-scale farms. During milking, HRV parameters were indicative of a higher sympathetic and a lower vagal activity of temperamental cows as compared to calm ones in farms of both sizes. Basal heart rate did not differ between BRH groups either on smaller- or larger-scale farms. Differences between basal ANS activity of impulsive and reserved cows reflected a higher resting vagal and lower sympathetic activity of reserved animals compared to impulsive ones both on smaller- and larger-scale farms. There was no difference either in heart rate or in HRV parameters between groups during milking neither in smaller- nor in larger-scale farms. These two groupings allowed to draw possible parallels between personality and cardiac autonomic activity during both rest and milking in dairy cows. Heart rate and HRV seem to be useful for characterisation of physiological differences related to temperament and BRH.

Associations between Heart Rate Variability Parameters and Housing- and Individual-Related Variables in Dairy Cows Using Canonical Correspondence Analysis.

We investigated the associations between heart rate variability (HRV) parameters and some housing- and individual-related variables using the canonical correspondence analysis (CCOA) method in lactating Holstein-Friesian dairy cows. We collected a total of 5200 5-min interbeat interval (IBI) samples from 260 animals on five commercial dairy farms [smaller-scale farms with 70 (Farm 1, n = 50) and 80 cows per farm (Farm 2, n = 40), and larger-scale farms with 850 (Farm 3, n = 66), 1900 (Farm 4, n = 60) and 1200 (Farm 5, n = 45) cows. Dependent variables included HRV parameters, which reflect the activity of the autonomic nervous system: heart rate (HR), the root mean square of successive differences (RMSSD) in IBIs, the standard deviation 1 (SD1), the high frequency (HF) component of HRV and the ratio between the low frequency (LF) and the HF parameter (LF/HF). Explanatory variables were group size, space allowance, milking frequency, parity, daily milk yield, body condition score, locomotion score, farm, season and physical activity (lying, lying and rumination, standing, standing and rumination and feeding). Physical activity involved in standing, feeding and in rumination was associated with HRV parameters, indicating a decreasing sympathetic and an increasing vagal tone in the following order: feeding, standing, standing and rumination, lying and rumination, lying. Objects representing summer positioned close to HR and LF and far from SD1, RMSSD and HF indicate a higher sympathetic and a lower vagal activity. Objects representing autumn, spring and winter associated with increasing vagal activity, in this order. Time-domain measures of HRV were associated with most of the housing- and individual-related explanatory variables. Higher HR and lower RMSSD and SD1 were associated with higher group size, milking frequency, parity and milk yield, and low space allowance. Higher parity and milk yield were associated with higher sympathetic activity as well (higher LF/HF), while individuals with lower locomotion scores (lower degree of lameness) were characterized with a higher sympathetic and a lower vagal tone (higher HR and LF/HF and lower RMSSD and SD1). Our findings indicate that the CCOA method is useful in demonstrating associations between HRV and selected explanatory variables. We consider physical activity, space allowance, group size, milking frequency, parity, daily milk yield, locomotion score and season to be the most important variables in further HRV studies on dairy cows.

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.

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

ABSTRACT 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.