Duration of parturition and frequency of abdominal contractions in primiparous, 2-year-old Angus heifers and the relevance of body dimensions of calves to dystocia

The predominant cause of dystocia in 2-year-old heifers is feto-maternal disproportion, and consequently, birthweight of the calf explains much variation in dystocia. This experiment was carried out to identify other factors in addition to birthweight that contribute to the probability of dystocia. Seventy-three primiparous, 2-year-old Angus heifers were observed continuously during the calving period and record was made of the time at which various events occurred during parturition. Frequency of abdominal contractions was lower 30 min after onset of parturition than at 60-180 min after onset of parturition (P < 0.05). The longest stage of parturition was the time from the first abdominal contraction until the appearance of amnion, while the time from the appearance of the head until delivery of the calf was the shortest stage. Frequency of abdominal contractions was negatively correlated with duration of parturition. Duration of parturition was less than 135 min for 75% of the non-assisted heifers. Body dimensions of calves did not explain any additional variation in dystocia beyond that explained by birthweight and sex of calf and postpartum liveweight of the heifer. Calves that had an assisted birth took longer to attempt to stand, to stand and to suckle after birth than non-assisted calves. Within the non-assisted calves, there was no impact of duration of parturition on these behaviours of the newborn calf. In conclusion, body dimensions of the calf did not contribute to the probability of dystocia, but more frequent abdominal contractions contributed to a shorter duration of parturition. Behaviour of newborn calves was adversely affected by dystocia. © CSIRO 2008.