The smaller pigs of a litter, if they are able to compete successfully for milk after birth, may be able to catch up in their growth by the time of weaning. Below a birth weight of about 1 kg, however, runt piglets are doomed to produce carcasses with less muscle and extra fat. Splayleg Piglets Sows sometimes sit on their unwary offspring and kill them, and any degree of locomotor impairment in baby pigs increases this risk. Splayleg is a condition in which the hindlimbs and sometimes the forelimbs of a newborn pig temporarily are unable to support the body. If affected pigs are nursed through the period of high risk just after farrowing, they may compensate by enhanced synthesis of muscle proteins and then may grow normally.
Slippery floors make the splayleg problem worse.
Affected pigs may be helped with a loose coupling between the hindlimbs to prevent the limbs splaying outwards. In poultry, embryology is different to that in mammals because the developing embryo is flattened into a disk on top of the yolk. Cleavage occurs as the zygote is passing along the oviduct before the egg is laid. The cytoplasm is concentrated in the blastodisc at the opposite pole to the yolk mass. The roles of cells from various regions of the epiblast and hypoblast in the developing embryo may be determined experimentally by marking the cells with nontoxic dyes.