Preweaning piglet mortality in relation to placental efficiency

The relationship between placental efficiency (PLEFF, i.e., the ratio of birth weight [BWB] to placental weight [PLW]) and neonatal pig vitality as measured by the probability of preweaning death of live born piglets was examined for 1,036 live born piglets of 118 litters. The data were first analyzed to establish whether the relationships between PLEFF, PLW, and BWB were affected by parity (first vs. higher). Furthermore, the data collected were used to establish whether PLEFF is a better predictor of the risk of neonatal pig mortality before weaning than BWB and PLW. The relationships of BWB to PLW and PLEFF to PLW differed (P <0.01 and P <0.05, respectively) between piglets from gilts and sows. This difference appeared to be due mainly to an additional population of piglets with very large placentas in sows that were not present in gilts. Despite being significant, the courses of the relationships were essentially similar for piglets in gilts and in sows. For the curvilinear relationship of BWB to PLW, up to a certain threshold value, an increase of PLW resulted in an increase in BWB, and thereafter BWB did not change. A consequence of this is that PLEFF at relatively high PLW does not give the same information as PLEFF at relatively low PLW. For the second-order relationship of PLEFF to BWB, PLEFF increased with an increase in BWB, until BWB = 1,657 g, and decreased thereafter. The PLEFF decreased linearly with PLW. A change in PLW had a much larger impact on the value of PLEFF than a change in BWB. Although BWB and PLW were negatively associated with the chance of dying before weaning (P <0.001 and P <0.01, respectively), only PLEFF tended to be negatively associated with the chance of dying only before weaning (P = 0.08). Its underlying trait, BWB, played a greater role on the effect of PLEFF on the chance of preweaning death than PLW. In conclusion, PLEFF in swine is a complicated trait that should be treated with care. It is merely a mathematical derivative of BWB and PLW, whereby the extent to which BWB depends on PLW depends on the value of PLW. Placental functioning and fetal growth capacity, however, also have their effects on the value of BWB. It is concluded that, of the three traits (BWB, PLW, and PLEFF), the best predictor for the chance of preweaning mortality, which also happens to be easiest to measure, remains BWB