Piglets from 51 litters were weighed weekly over a 5-wk lactation in an experiment that studied the effects of farrowing crate design and other factors on variation in piglet weight. Of two farrowing crates used, one had low horizontal bars that tended to impede access to the upper row of teats, while the other had angled vertical bars which permitted freer access. Fourteen-day weights were more uniform in the vertical-bar crates than in the horizontal-bar crates (P < 0.025), but the difference waned by day 35 (P > 0.05). There were no significant differences in mean body weight owing to crate type (P < 0.05) for any of the weekly measurements but, by day 14, there was a significant linear trend (P < 0.05) at decreasing main body weight with increasing litter size. The interaction between crate type and litter size was significant at the later ages (P < 0.01 at day 35) because the linear trend was more pronounced for horizontal-bar crates than for vertical. Litters differed greatly in the uniformity of their body weights. Much of the variation became established in the first and, to a lesser extent, the second week after birth. In those weeks, weight gains were highly variable and were not closely related to weight at the beginning of the week. Thereafter, the established differences tended to be perpetuated to 35 d, because weight gains were largely proportional to body weight. Within-litter competition appeared to influence weight gain considerably.
Thompson, B. K., & Fraser, D. (1986). Variation in piglet weights: development of within-litter variation over a 5-week lactation and effect of farrowing crate design. Canadian Journal of Animal Science, 66(2), 361-372.