L. A. Lekatz

Maternal selenium supplementation and timing of nutrient restriction in pregnant sheep: Effects on maternal endocrine status and placental characteristics

To determine the effects of maternal Se intake and plane of nutrition during midgestation, late gestation, or both on hormone and metabolite concentrations in the dam and on placental characteristics, pregnant ewe lambs (n = 64) were assigned to 1 of 8 treatments arranged in a 2 x 2 x 2 factorial array: Se level [initiated at breeding; adequate (3.05 microg/kg of BW) or high (70.4 microg/kg of BW)] and nutritional level [100% (control) or 60% (restricted) of NRC recommendations] fed at different times of gestation [d 50 to 90 (midgestation) or d 91 to 130 (late gestation)]. The control ewes had a greater (P = 0.01) percentage change in BW from d 50 than restricted ewes during both mid- and late gestation. Although blood urea N was not affected by either Se or nutritional level, restricted ewes had greater (P = 0.01) concentrations of circulating Se on d 66, 78, 106, 120, and 130 of gestation compared with control ewes. Both Se and timing of the nutritional level affected circulating progesterone; however, only nutritional level affected thyroxine and triiodothyronine concentrations in the dam. Nutrient restriction during late gestation decreased (P <or= 0.01) fetal BW and fetal fluid weight compared with the control ewes (3.75 vs. 4.13 +/- 0.10 kg and 1.61 vs. 2.11 +/- 0.11 kg). Although neither Se nor nutritional level affected (P >or= 0.1) placental, caruncular, or cotyledonary weights, cotyledonary cellular proliferation was decreased (P < 0.05) in ewes receiving a high concentration of Se compared with those receiving adequate Se. In addition, either Se or nutritional level affected vascular endothelial growth factor (VEGFA), VEGFA-receptor 1, VEGFA-receptor 2, and NO synthase mRNA abundance in the cotyledonary tissue. In the caruncular tissue, either Se or nutritional level affected VEGFA-receptor 1, placental growth factor, and NO synthase mRNA abundance. Selenium supplementation and the duration or timing of nutrient restriction appear to influence the endocrine and metabolic status of the ewe, which may influence nutrient transport and placental function.

Cotyledonary responses to maternal selenium and dietary restriction may influence alterations in fetal weight and fetal liver glycogen in sheep

To examine the effects of maternal supranutritional selenium (Se) and nutrient restriction during mid and late gestation on placental characteristics and fetal liver glycogen, ewes received either adequate Se (ASe) or high Se (HSe) prior to breeding. On d 64 of gestation, ASe and HSe ewes remained at 100% of requirements (controls; CON) or were restricted (RES; 60% of requirements). On d 135 of gestation, fetal weight (P< or =0.08) was greatest in both HSe and CON ewes. Placentome number, mass, and caruncular and cotyledonary weight were not different (P> or =0.17) among treatments. Fetal mass:placental mass ratio was less (P=0.06) in RES compared to CON ewes. Compared to ASe, HSe exhibited increased (P< or =0.08) cellular proliferation and DNA concentration and decreased (P=0.07) cellular size in cotyledonary tissue. Nutritional restriction decreased (P< or =0.08) cotyledonary protein concentration and cellular size. VEGF receptor 1 (Flt) mRNA in cotyledonary tissue was greater in HSe compared with ASe ewes (P=0.06) and in RES compared with CON ewes (P=0.08). There was no effect of diet on caruncular growth variables (P> or =0.13) or on placental vascularity (P> or =0.11). Progesterone was greater (P< or =0.08) in ASe-RES ewes compared to all groups at d 90 and ASe-CON and HSe-CON at d 104. Although fetal glucose and cortisol concentrations were not affected by diet, fetal liver glycogen was greater (P=0.04) in ASe-RES compared to ASe-CON and HSe-RES ewes with HSe-CON being intermediate. Both Se and nutritional plane may impact placental function and fetal growth, as fetal weight and liver glycogen are altered despite similar placental vascularity measurements.

Supplementing metabolizable protein to ewes during late gestation: I. Effects on ewe performance and offspring performance from birth to weaning.

We hypothesized that a maternal diet greater in MP during the last third of gestation would yield improved offspring growth due to enhanced placental or mammary gland function. Our objective was to determine how MP intake during late gestation affected ewe and offspring performance from birth to weaning in ewes fed diets similar in total energy. In yr 1, maternal dietary treatments were applied at d 100 of gestation, were similar in total energy, and contained 60% of MP requirements (60MP1), 80% of MP requirements (80MP1), and 100% of the MP requirements (100MP1) on a DM basis during late gestation. In yr 2, maternal dietary treatments were similar in total energy and contained 60% of MP requirements (60MP2), 100% of the MP requirements (100MP2), and 140% of MP requirements (140MP2) on a DM basis during late gestation. In yr 1, there was no effect (P ≥ 0.30) of maternal MP restriction on gestation length, lamb birth weight, or milk production of the dam. At lambing, ewe BW (P = 0.02) and BCS (P = 0.01) increased linearly as MP in the diet increased. While there were no differences in lamb BW at birth, lamb weaning BW (P = 0.08) and ADG from birth to weaning (P = 0.10) tended to increase linearly as maternal MP intake increased. In yr 2, maternal BW increased with increased dietary MP. However, there were no significant effects (P ≥ 0.45) of maternal dietary treatment on maternal BCS or lamb birth weight. Moreover, lamb weaning weight and ADG were not influenced by maternal MP levels. These results suggest that ewes maintain and gain BW and BCS when consuming diets similar in total energy with increased MP during late gestation, but the increased MP had minimal effects on lamb performance through weaning.

Maternal selenium supplementation and timing of nutrient restriction in pregnant sheep: Impacts on nutrient availability to the fetus

To determine the effects of maternal Se intake and plane of nutrition during mid or late gestation or both on AA concentrations and metabolite concentrations in the dam and fetus, pregnant ewe lambs (n = 64) were assigned to 1 of 8 treatments arranged in a 2 × 2 × 2 factorial array: Se level [initiated at breeding; adequate (ASe; 3.05 μg/kg of BW) or high (HSe; 70.4 μg/kg of BW)] and nutritional level [100% (control; CON) or 60% (restricted; RES) of NRC recommendations] fed at different times of gestation [d 50 to 90 (mid) or d 91 to 132 (late)]. A blood sample was obtained from each ewe and fetus on d 132 of gestation and used to measure circulating concentrations of glucose, NEFA, blood urea N, and AA. The late RES ewes and their fetuses had less (P ≤ 0.03) circulating glucose compared with late CON ewes and fetuses at d 132; however, no effect (P ≥ 0.14) of diet on the fetal:maternal glucose concentration ratio was observed. Late RES ewes had a smaller (P = 0.01) fetal:maternal NEFA ratio compared with late CON ewes. Ewes fed ASe had a greater (P = 0.01) fetal:maternal blood urea N ratio compared with HSe ewes. Fetal:maternal ratios of total circulating AA, total essential AA, and total nonessential AA were each affected (P ≤ 0.03) by the combination of Se treatment and late gestation nutritional level.

Maternal metabolizable protein restriction during late gestation on uterine and umbilical blood flows and maternal and fetal amino acid concentrations near term in sheep

To examine the effects of maternal metabolizable protein (MP) restriction during late gestation on uterine and umbilical blood flows, conceptus size, and amino acid concentrations in the uterine and umbilical vessels, 11 ewes with singleton pregnancies were assigned to one of three isocaloric diets formulated to provide 60% of MP (MP60), 80% of MP (MP80), or 100% of MP (MP100) requirements from days 100 to 130 of gestation. On day 130 of gestation, intraoperative uterine and umbilical blood flows were obtained as well as serum samples from the uterine artery, uterine vein, umbilical artery, and umbilical vein. Ewes on the MP60 diet had lighter (P=0.04) and smaller (P≤0.05) fetuses, but increased (P=0.02) uterine blood flow relative to fetal weight compared with MP100 ewes, with MP80 being intermediate. Umbilical blood flow was similar (P=0.70) across treatments. Glutamine, glycine, isoleucine, leucine, ornithine, serine, and valine concentrations were impacted (P≤0.02) by maternal treatment. While uterine flux of total serum nitrites was greater (P=0.03) in MP60 and MP80 ewes compared with MP100 ewes, fetal flux did not differ. Decreased maternal protein intake resulted in less (P<0.01) maternal cytochrome P450 1A enzyme activity. There were minimal impacts of maternal diet on steroid concentrations. Maternal dietary protein may alter fetal growth by impacting placental vasculature function and nutrient absorptive capabilities.

Thyroid Hormones and Cortisol Concentrations in Offspring are Influenced by Maternal Supranutritional Selenium and Nutritional Plane in Sheep

To determine the effects of maternal supranutritional selenium (Se) supplementation and maternal nutritional plane on offspring growth potential, ewes were randomly assigned to 1 of 6 treatments in a 2 × 3 factorial arrangement [dietary Se (adequate Se; 9.5 μg/kg body weight vs. high Se; 81.8 μg/kg body weight initiated at breeding) and plane of nutrition [60%, 100%, or 140% of requirements; initiated on day 50 of gestation]]. Lambs were immediately removed from dams at birth and reared. Cortisol concentrations at birth were similar, but by 24 h, a relationship (P = 0.02) between maternal Se supplementation and nutritional plane on cortisol concentrations was observed in lambs. A sex of offspring × day of age interaction (P = 0.01) and a maternal Se supplementation × nutritional plane × day of age interaction (P = 0.04) was observed for thyroxine concentrations. Differences in growth may be influenced by thyroid hormone production early in neonatal life.