Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 12/7/2005
Publication Date: 3/20/2006
Citation: Freetly, H.C., Mcdonagh, M.B., Ferrell, C.L. 2006. Fetal growth of lambs paternally heterozygous for the callipyge mutation [abstract]. Journal of Animal Science. 84(Suppl. 2):59.
Technical Abstract: A mutation on chromosome 18 results in some of the skeletal muscles becoming enlarged in sheep. The phenotypic expression of this mutation has been termed callipyge. We hypothesized that phenotypic differences in muscle weight begins during fetal development. Mature ewes were mated to rams that were homozygous for the mutation or did not have the mutation. Ewes with heterozygous twin fetuses (n = 19) and ewes with normal twin fetuses (n = 20) were serially slaughtered from 58 through 141 days of gestation and fetal and placental tissues were dissected and weighed. Fetal tissue weights on time were fit with a logistic function and placental tissues were fit with quadratic functions. Genotype-specific equations fit the weight data better than a pooled equation for the adductor, gastrocnemius, semitendinosus, semimembranosus, plantaris, and longissimus muscles (P < 0.05) and genotype-specific equations tended to fit better than a pooled equation for the gluteus medius (P < 0.10) and quadriceps (P < 0.11). Genotype-specific equations did not fit better for femur, tibia, and humerus length (P > 0.23); however, they did fit better for femur, tibia, and humerus weight (P < 0.05). Genotype-specific equations fit total fetal weight better than a pooled equation. Differences between the genotypes were the result of heavier tissue weights in the last trimester of callipyge fetuses. Caruncular weight and cotyledonary weight increased during mid gestation and decreased during late gestation. Caruncular weight of ewes with callipyge fetuses was lower than that of ewes with normal fetuses. Expression of the callipyge phenotype begins in utero. Deviation in muscle weight between genotypes begins to occur in the last trimester which coincides with the expected onset of muscle hypertrophy. These data suggest that mechanisms associated with expression of the callipyge phenotype occur during muscle hypertrophy.