A total of 59 farrowings were studied in either a conventional, narrow farrowing crate (0.43 m wide) or a much wider alternative design with sides spaced 1.2 m apart at the sow’s standing height but narrowing near the floor to limit the sow’s lying area. Using video recording, we monitored each “birth interval” (i.e. the period between two successive births) and noted the interval’s length, the sow’s posture and postural changes during the interval, and whether the interval ended with a live-born or stillborn piglet. The wide and conventional crates did not differ significantly in median interval between piglets (15.9 versus 16.0 min, respectively), incidence of stillbirth (5.8 versus 7.0%), in any measures of posture or postural change, or in piglet survival and weight gain to 3 days of age. Sows were most active during the first two birth intervals; as farrowing continued they made progressively fewer postural changes and spent more time lying. Sows differed greatly in the frequency of postural changes and the time they spent in different postures; however, these measures were largely unrelated to stillbirths, except that stillbirths were rare if the sow sat during much of the interval (P < 0.001). Birth intervals were longer, on average, before a stillbirth (median of 34 min) than before a live birth (13 min; P < 0.001). The greater incidence of stillbirths late in the farrowing was associated with a greater proportion of long birth intervals late in the farrowing, and greater likelihood of stillbirth even for shorter and medium intervals. Stillbirths were more common in longer farrowings (P = 0.01), evidently because these tended to involve larger litter sizes and more long birth intervals of over 60 min. However, the proportion stillborn in a litter was not correlated with median birth interval. The results of this and related studies suggest that greater freedom of movement in the farrowing environment does not consistently produce shorter duration of farrowing or a lower incidence of stillbirth.
Fraser, D., Phillips, P. A., & Thompson, B. K. (1997). Farrowing behaviour and stillbirth in two environments: an evaluation of the restraint-stillbirth hypothesis. Applied Animal Behaviour Science, 55(1-2), 51-66.