Timing of obstetrical assistance affects peripartal cardiac autonomic function and early maternal behavior of dairy cows.

Peripartal autonomic nervous system function and early maternal behavior were investigated in 79 multiparous Holstein-Friesian cows. Animals were allocated into four groups based on the technology of calving management: 1) unassisted calving in a group pen (UCG; N=19), 2) unassisted calving in an individual pen (UCI; N=21), 3) assisted calving with appropriately timed obstetrical assistance (ACA; N=20), and 4) assisted calving with premature obstetrical assistance (ACP; N=19). Heart rate, the high frequency (HF) component of heart rate variability (HRV) as a measure of vagal activity and the ratio between the low frequency (LF) and HF components (LF/HF ratio) as a parameter of sympathetic nervous system activity were calculated. Heart rate and HRV parameters were presented as areas under the curves (AUC) for the following periods: 1) prepartum period (between 96h before the onset of calving restlessness and the onset of restlessness), 2) parturition (between the onset calving restlessness and delivery), and 3) postpartum period (during a 48-h period after delivery). Pain-related behaviors were recorded during parturition (i.e., the occurrence of vocalization and stretching the neck towards the abdomen) and during a 2-h observation period after calving (i.e., the occurrence of vocalization, stretching the neck towards the abdomen and the duration of standing with an arched back). Early maternal behavior was observed during the first 2h following calving as follows: 1) latency and duration of sniffing calf's head/body, and 2) latency and duration of licking calf's head/body. No difference was found across groups in autonomic function before the onset of calving restlessness. Area under the heart rate curve was higher in ACP cows during parturition (39.6±2.5beats/min×h) compared to UCG, UCI and ACA animals (AUC=13.1±0.9beats/min×h, AUC=22.3±1.4beats/min×h and AUC=25.0±2.1beats/min×h, respectively). Area under the heart rate curve did not differ across the UCG, UCI and ACA groups during the postpartum period (AUC=65.2±16.7beats/min×h, AUC=58.0±14.2beats/min×h and AUC=62.9±12.1beats/min×h, respectively) but it was higher in ACP cows compared to the former groups (AUC=269.1±36.3beats/min×h). During parturition, area under the HF curve reflected a lower vagal tone (AUC=-30.5±1.6n.u.×h) in cows with premature obstetrical assistance than in animals that calved individually without farmer assistance (AUC=2.7±0.4n.u.×h) or with appropriately timed assistance (AUC=3.2±1.2n.u.×h). During parturition, LF/HF ratio showed greater sympathetic activity in ACP cows than in animals from any other group. Area under the HF curve was similar across UCG, UCI and ACA cows (AUC=-232.1±42.0n.u.×h, AUC=-163.4±35.6n.u.×h and AUC=-331.4±56.2n.u.×h, respectively) during the postpartum period and was the lowest in ACP cows (AUC=-1025.6±44.2n.u.×h) reflecting a long-term stress load in the latter group. During parturition, both vocalization and stretching the neck towards the abdomen occurred more often in UCG cows than in cows from any other groups, and the incidence of both behaviors was statistically higher in ACP cows than in UCI and ACA animals. There were no significant differences across groups in these behaviors during the 2-h postpartum observation. UCG cows had a shorter latency and a longer duration of maternal grooming during the first 2h following delivery compared to any other groups. UCI and ACA dams spent more time with licking the calf within the 2-h period after calving and had a shorter latency to sniff and lick the offspring compared to cows that received premature assistance. Group calving is less stressful for cows than calving in an individual pen either with or without obstetrical assistance. Calving in a group or with appropriately timed farmer assistance supports the expression of early maternal behavior and lead to a rapid postpartum recovery of the autonomic nervous system. Premature obstetrical assistance means stress for cows during parturition, leads to a prolonged postpartum recovery of the autonomic nervous system and inhibits the expression of early maternal behavior.