129 Evaluating effects of myostatin loss-of-function mutation on piglets for potential causes of early mortality

Abstract

Abstract Pigs with an engineered myostatin loss-of-function mutation in exon 3 (-1T) experience perinatal mortality of unknown cause. From 36 litters resulting from matings of sows and boars both heterozygous for the mutation, 240 total piglets were born but only 14% (5/35) of piglets with myostatin loss-of-function mutation survived or were viable beyond postnatal d 3. Thus, the objective was to evaluate the effects of this myostatin loss-of-function mutation on piglet organ and muscle development and blood parameters to determine potential causes of this excess mortality. Blood was collected for complete blood count and then piglets (n = 50) were euthanized at postnatal d 3. Piglets were dissected and longissimus muscle, semitendinosus muscle, heart, liver, lungs, kidneys, pancreas, spleen, stomach, small intestine, large intestine, testicles or female reproductive tract, and tongue were weighed. Front girth, back girth, and snout to rump were measured. Loin samples were used to genotype piglets into one of three groups: wild type (WT; unmutated myostatin, n = 13), heterozygous (HET, n = 21) and myostatin mutant (MKO, n = 10). Data were analyzed as a two-way ANOVA using the MIXED procedure of SAS to determine the effect of sex, genotype, and their interaction. Body weight (P = 0.67) and front girth (P = 0.13) were not different between genotypes, but back girth was reduced (P = 0.04) in MKO by 2.3 cm compared with WT and by 2.1 cm compared with HET piglets. MKO piglets had lighter (P ≤ 0.03) hearts, livers, kidneys, pancreases, spleens, stomachs, and small intestine compared with HET and WT piglets, on both an absolute basis and as a percentage of body weight. In general, compared with other other genotypes, MKO organs were 5 to 19% lighter. Surprisingly, muscle weights, both longissimus and semitendinosus muscles, were not different (P ≥ 0.15) between genotypes, either on an absolute basis or as a percentage of body weight. White blood cell count was not different; however, neutrophil count was increased in MKO compared with other genotypes. These data suggest that underdeveloped or undersized organs in MKO piglets may compromise their survivability. Additionally, increased neutrophil counts may be indicative of a stress response in MKO piglets.