Effects of mid-gestational L-citrulline supplementation to twin-bearing ewes on umbilical blood flow, placental development, and lamb production traits
The interaction between the embryo and fetus with the maternal environment can have both short- and long-term consequences on health and development after birth. In some cases, these changes may be detrimental to the individual, but in other cases these developmental changes may be beneficial and manipulated to produce desired effects. Our interest is to use this concept of fetal programming to improve skeletal muscle development and meat production in ruminants. To achieve this, we targeted the period of gestation when fetal muscle fiber formation occurs. Primary muscle fibers form during embryonic development, and it is this small number of primary muscle fibers that will serve as templates for secondary fiber formation that occurs in the fetus during mid-gestation. Supplementing amino acids that influence blood flow within the reproductive tract is one potential way to provide fetuses with added nutrients during gestation, and this supplementation strategy may be especially useful when the maternal diet is compromised. L-citrulline was chosen for this work because of its long half-life in maternal circulation. This work utilized twin-bearing ewes with a moderate dietary energy restriction to assess the effects of mid-gestational L-citrulline supplementation on umbilical blood flow, placental function, neonatal lamb size, and lamb performance. We hypothesize that i.v. administration of L-citrulline will increase uterine and placental blood flow in gestating ewes and this will improve fetal growth, development, and overall postnatal performance. Blood flow parameters were not influenced by treatment (P>0.05). Circulating levels of progesterone and pregnancy-specific protein B (PSPB) were used as indicators of placental function and were unaffected by treatment administration (P>0.05). A treatment by time interaction was detected in both analyses, but no differences between treatments were detected within any time points. There was no effect of treatment on lamb weights or survival to weaning (P>0.05). Lamb sex effects are absent with the exception that body weights were greater in ewe lambs (P>0.05). There was no effect of treatment on any carcass traits or visceral organ weights assessed, though there was an effect of sex on dressing percentage and pancreas weight with wethers having a greater dressing percentage and heavier pancreases per kg body weight than that of ewes (P<0.05). In summary, contrary to our hypothesis L-citrulline supplementation to pregnant ewes under a minor to moderate metabolic challenge had no impact on blood flow and provided no programming benefit to the lambs.