The relationship between placental and piglet birth weights and growth traits

Our laboratory recently reported that the ratio of a piglet's weight to that of its placenta (RATIO) varies approximately three-fold within a litter, due predominantly to variation in placental size which is known to be a limiting factor in litter size. It was further determined that selection of boars and gilts with a higher than average RATIO for breeding resulted in an increased litter size and reduced placental weights. The objective of this experiment was to examine the effects of RATIO on economically important production traits (piglet survival to weaning, 21-day weights, days to 105 kg, backfat depth and loin muscle area at 105 kg) in a purebred breeding stock herd of Finnish Yorkshire and Landrace pigs. Sows were monitored throughout farrowing and each piglet was matched to its placenta. Each piglet and its placenta were individually weighed and a RATIO determined Placental weight but not piglet birth weight exhibited a strong (P < 0.001) negative correlation with RATIO (r = -0.73). Up to three-fold differences in RATIO were observed within a single litter. These differences were much greater than the variation noted between litters and litter mean RATIO was not significantly associated with litter size. The distribution of individual piglet RATIOS across the entire group of pigs ranged from 2.8 to 11.4 suggesting a marked difference in placental efficiencies. No significant association was seen between RATIO and 21-day weight, days to 105 kg, backfat depth or loin muscle area. Thus, an above average ratio of a piglet's weight to that of its placenta is indicative of a smaller move efficient placenta and appears to have Mo subsequent detrimental effects on growth efficiency.