Neonatal Deaths
Significant neonatal mortality was noted in MCAD−/− pups. Although equal numbers of pups were born from MCAD+/+ and MCAD−/− mice, only 41% of MCAD−/− mice survived to weaning as compared to 98% of MCAD+/+ mice (Table 1). The mechanism of neonatal loss remains undetermined. The MCAD−/− pups are abandoned more frequently than MCAD+/+ pups for unknown reasons. They are likely more prone to hypothermia than MCAD+/+. Because of the difficulty of distinguishing the MCAD−/− mutants from the MCAD+/− heterozygous pups by molecular analysis due to the insertion mutation, we could only compare MCAD+/+ × MCAD+/+ matings with MCAD−/− × MCAD−/− matings. Thus, we were unable to evaluate the pedigrees from heterozygous matings.