Effects of nutrient restriction and subsequent realimentation in pregnant beef cows: Maternal endocrine profile, umbilical hemodynamics, and mammary gland development and hemodynamics.

Our hypothesis was that maternal nutrient restriction would negatively impact the endocrine and metabolic status of the pregnant cow, therefore influencing the mammary gland in preparation for lactation. We further hypothesized that earlier timing of realimentation could prevent negative impacts of nutrient restriction. The objectives were to investigate the influence of nutrient restriction and realimentation during early to late gestation on endocrine profile, umbilical hemodynamics, and mammary gland development and hemodynamics in pregnant beef cows. In Experiment 1, on d 30 of pregnancy cows (initial BW = 667.5 ± 13.4 kg, BCS = 6.2 ± 0.1) were randomly assigned to one of 3 treatments: 1) 100% NRC requirements from d 30 to 254 of gestation (CCC; n = 6); 2) 60% NRC from d 30 to 85, thereafter being re-alimented to 100% NRC to d 254 (RCC; n = 5); 3) or receive 60% NRC from d 30 to 140, thereafter being re-alimented to 100% NRC to d 254 (RRC; n = 6). Cows were returned to a common outdoor facility for calving thereafter and were fed ad libitum. In Experiment 2, on d 30 of pregnancy, cows (initial BW = 620.5 ± 11.3 kg, BCS = 5.1 ± 0.1) were randomly assigned to dietary treatments including: control (CON; 100% NRC; n = 18) and nutrient restriction (RES; 60% NRC; n = 30). On d 85 of pregnancy, cows were either slaughtered (CON, n = 6 and RES, n = 6), remained on control (CC; n = 12) and restricted (RR; n = 12) treatments, or were realimented to control (RC; n = 11). On d 140 of pregnancy, cows were either slaughtered (CC, n = 6; RR, n = 6; RC, n = 5), remained on control (CCC, n = 6; RCC, n = 5), or were realimented to control (RRC, n = 6). On d 254 of pregnancy, all remaining cows were slaughtered (CCC, n = 6; RCC, n = 5; RRC, n = 6). Mammary hemodynamics and endocrine profile were measured. Serum urea nitrogen, NEFA, as well as fetal parameters were measured in Experiment 1; whereas in Experiment 2, mammary gland development was recorded. In Experiment 1, RRC cows had lower dry matter intake (P = 0.001) and consequently lower BW change (P = 0.06). However, maternal nutrition did not alter mammary hemodynamics, hormonal patterns, and fetal characteristics (P > 0.11). In Experiment 2, CCC cows had increased (P = 0.02) mammary gland blood flow ipsilateral to the gravid horn as well as greater (P = 0.02) mammary gland fat on d 254. Nevertheless, plane of nutrition did not alter hormonal concentrations nor mammary gland characteristics (P > 0.15). These data indicate that nutrient restriction did not alter mammary hemodynamics nor endocrine profile throughout gestation.

Effects of maternal nutrient restriction followed by realimentation during early and mid-gestation in beef cows. II. Placental development, umbilical blood flow, and uterine blood flow responses to diet alterations.

The objectives were to examine the effects of maternal nutrient restriction followed by realimentation during early to mid-gestation on placental development and uterine and umbilical hemodynamics in the beef cow. On day 30 of pregnancy, multiparous, non-lactating beef cows (620.5 ±â€¯11.3 kg) were assigned to 1 of 2 dietary treatments: control (C; 100% National Research Council [NRC] recommendations; n = 18) and restricted (R; 60% NRC; n = 30). On day 85, cows were slaughtered (C, n = 6; R, n = 6), remained on control (CC; n = 12) and restricted (RR; n = 12), or were realimented to control (RC; n = 11). On day 140, cows were slaughtered (CC, n = 6; RR, n = 6; RC, n = 5), remained on control (CCC, n = 6; RCC, n = 5), or were realimented to control (RRC, n = 6). On day 254, all remaining cows were slaughtered. Heart rate and umbilical and uterine hemodynamics [blood flow, resistance index (RI), and pulsatility index (PI)] were determined via Doppler ultrasonography. As expected umbilical blood flow increased and fetal heart rate decreased as gestation advanced. Umbilical PI in RRC cows was less (P = 0.01) compared to RCC and CCC. During late gestation, RCC cows had greater (P = 0.02) ipsilateral and total uterine blood flow vs. CCC and RRC. There was an increase in the number and weight of placentomes from R cows (P ≤ 0.02) compared to C cows (i.e. day 85). There were more placentomes (P = 0.03) in RR vs. CC and RC cows, but placentome weight was not affected (P = 0.18) by maternal dietary treatment at day 140. Maternal nutrient restriction during early to mid-gestation increased the weight (by day 85) and number (day 85 and 140) of placentomes, and did not reduce fetal weight compared to control cows. A longer realimentation period may enhance uterine blood flow and individual placentome size during later gestation, which may compensate for reduced nutrients experienced early in gestation.

Uteroplacental secretion of progesterone and estradiol-17ß in an ovine model of intrauterine growth restriction.

Using a mid to late gestation model of intrauterine growth restriction, uteroplacental secretion of progesterone and estradiol-17ß were examined. From day 50 to 130 of gestation, 31 ewe lambs were allocated to receive 100% (ADQ) or 60% (RES) of nutrient requirements. At day 130, umbilical and uterine artery blood flows were determined and blood samples were collected from maternal saphenous artery, gravid uterine vein, umbilical vein, and umbilical artery. Uteroplacental secretion of progesterone was increased in RES compared to ADQ fed dams. There was a net secretion and net metabolism of estradiol-17ß in RES, and ADQ fed dams, respectively. In relation to steroid synthesis, cotyledonary abundance of steroidogenic acute regulatory protein was greater in RES compared with ADQ fed dams, while abundance of aromatase was not different between dietary treatments. Caruncular aldo-keto reductase 1C abundance was less in RES compared to ADQ fed dams. The increase in progesterone secretion, therefore, is due in part to an increase in synthesis and a decrease in placental catabolism. Caruncular cytochrome P450 3A, which catalyzes the conversion of estrogens to catechol-estrogens, was in lesser abundance in RES compared to ADQ fed dams. Opposite responses in estradiol-17ß uteroplacental secretion compared with metabolism may be mediated through placental estrogen metabolism via cytochrome P450 enzymes.

Effects of realimentation after nutrient restriction during mid- to late gestation on pancreatic digestive enzymes, serum insulin and glucose levels, and insulin-containing cell cluster morphology.

This study examined effects of stage of gestation and nutrient restriction with subsequent realimentation on maternal and foetal bovine pancreatic function. Dietary treatments were assigned on day 30 of pregnancy and included: control (CON; 100% requirements; n = 18) and restricted (R; 60% requirements; n = 30). On day 85, cows were slaughtered (CON, n = 6; R, n = 6), remained on control (CC; n = 12) and restricted (RR; n = 12), or realimented to control (RC; n = 11). On day 140, cows were slaughtered (CC, n = 6; RR, n = 6; RC, n = 5), remained on control (CCC, n = 6; RCC, n = 5) or realimented to control (RRC, n = 6). On day 254, the remaining cows were slaughtered and serum samples were collected from the maternal jugular vein and umbilical cord to determine insulin and glucose concentrations. Pancreases from cows and foetuses were removed, weighed, and subsampled for enzyme and histological analysis. As gestation progressed, maternal pancreatic α-amylase activity decreased and serum insulin concentrations increased (p ≤ 0.03). Foetal pancreatic trypsin activity increased (p < 0.001) with advancing gestation. Foetal pancreases subjected to realimentation (CCC vs. RCC and RRC) had increased protein and α-amylase activity at day 254 (p ≤ 0.02), while trypsin (U/g protein; p = 0.02) demonstrated the opposite effect. No treatment effects were observed for maternal or foetal pancreatic insulin-containing cell clusters. Foetal serum insulin and glucose levels were reduced with advancing gestation (p ≤ 0.03). The largest maternal insulin-containing cell cluster was not influenced by advancing gestation, while foetal clusters grew throughout (p = 0.01). These effects indicate that maternal digestive enzymes are influenced by nutrient restriction and there is a potential for programming of increased foetal digestive enzyme production resulting from previous maternal nutrient restriction.

Supplementation of distiller's grains during late gestation in beef cows consuming low-quality forage decreases uterine, but not mammary, blood flow.

Positive effects have been observed in offspring from beef cows supplemented with corn dried distillers grain with solubles (DDGS) during late gestation. The hypothesis of this study was that late gestational DDGS supplementation to beef cows would increase blood flow (BF) to the gravid uterus and mammary gland thus impacting birthweight and post-natal growth of the offspring. Experiment 1 investigated mammary gland BF in multiparous cows during late pregnancy. Beef cows were fed a control (CON1) diet of low-quality hay (n = 5) or a supplement diet (SUP1) of low-quality hay with DDGS [1.7 g/kg of body weight (BW); n = 6]. In Experiment 2, multiparous late pregnant beef cows were fed either a control (CON2) diet of a low-quality hay (n = 4) or a supplement diet (SUP2) of low-quality hay with DDGS (1.7 g/kg of BW; n = 5). Uterine and mammary gland BF were recorded every 21 days during late gestation. In Experiment 1, there were no effects of diet or day on mammary gland hemodynamics. In Experiment 2, total and ipsilateral uterine BF was less (p ≤ 0.04) in SUP2 vs. CON2 cows and similar BF to contralateral horns. Mammary gland BF was unaltered by maternal supplementation. Even when measured in two different years in two different environments, mammary gland BF remained unaltered to DDGS supplementation. Investigations on the mechanism that may impact uterine BF during late gestation remain to be known.

Nutrient restriction and realimentation in beef cows during early and mid-gestation and maternal and fetal hepatic and small intestinal in vitro oxygen consumption.

Objectives were to determine the effects of advancing gestation, maternal nutrient restriction during early and mid-gestation, and realimentation on fetal liver and jejunal mass and energy use in both dams and fetuses. On day 30 of pregnancy, multiparous, non-lactating beef cows (initial BW=621±11.3 kg and body condition score=5.1±0.1) were assigned to one of the two dietary treatments: control (CON; 100% requirements; n=18) and restricted (R; 60% requirements; n=28). On day 85, cows were slaughtered (CON, n=6; R, n=6), and remaining cows continued on control (CC; n=12) and restricted (RR; n=12) diets, or were realimented to the control diet (RC; n=11). On day 140, cows were slaughtered (CC, n=6; RR, n=6; RC, n=5), remaining cows continued on the control diet (CCC, n=6; RCC, n=5), or were realimented to the control diet (RRC, n=6). On day 254, all remaining cows were slaughtered. Maternal liver O2 consumption linearly increased (P⩽0.04) and jejunal weight (g/kg) linearly decreased (P=0.04) as gestation advanced in CON groups. Fetal BW, and hepatic and small intestinal absolute mass, protein content and O2 consumption linearly increased (P⩽0.04) as pregnancy advanced in CON groups. However, mass and O2 consumption relative to BW linearly decreased (P⩽0.001) in the fetal liver in CON groups. When analyzing the effects of dietary treatment, at day 85, fetal jejunal O2 consumption (mol/min per kg BW) was lower (P=0.02) in the R group when compared with the CON group. At day 140, maternal hepatic weight (g) was lower (P=0.02) in RC and RR cows when compared with CC, and fetal jejunual O2 consumption (mmol/min per mg tissue and mmol/min per g protein) was greater (P⩽0.02) in RC when compared with RR. At day 254, maternal hepatic O2 consumption (absolute and relative to BW) was lower (P⩽0.04) in the RCC cows when compared with RRC. Fetal hepatic weight was lower (P=0.05) in the CCC group when compared with RCC and RRC. The changes in response to nutrient restriction and realimentation in both the dam and fetus may indicate an adaptation to a lower amount of available nutrients by altering tissue mass and metabolism.

Influence of nutrient restriction and melatonin supplementation of pregnant ewes on maternal and fetal pancreatic digestive enzymes and insulin-containing clusters.

Primiparous ewes (n=32) were assigned to dietary treatments in a 2×2 factorial arrangement to determine effects of nutrient restriction and melatonin supplementation on maternal and fetal pancreatic weight, digestive enzyme activity, concentration of insulin-containing clusters and plasma insulin concentrations. Treatments consisted of nutrient intake with 60% (RES) or 100% (ADQ) of requirements and melatonin supplementation at 0 (CON) or 5 mg/day (MEL). Treatments began on day 50 of gestation and continued until day 130. On day 130, blood was collected under general anesthesia from the uterine artery, uterine vein, umbilical artery and umbilical vein for plasma insulin analysis. Ewes were then euthanized and the pancreas removed from the ewe and fetus, trimmed of mesentery and fat, weighed and snap-frozen until enzyme analysis. In addition, samples of pancreatic tissue were fixed in 10% formalin solution for histological examination including quantitative characterization of size and distribution of insulin-containing cell clusters. Nutrient restriction decreased (P⩽0.001) maternal pancreatic mass (g) and α-amylase activity (U/g, kU/pancreas, U/kg BW). Ewes supplemented with melatonin had increased pancreatic mass (P=0.03) and α-amylase content (kU/pancreas and U/kg BW). Melatonin supplementation decreased (P=0.002) maternal pancreatic insulin-positive tissue area (relative to section of tissue), and size of the largest insulin-containing cell cluster (P=0.04). Nutrient restriction decreased pancreatic insulin-positive tissue area (P=0.03) and percent of large (32 001 to 512 000 µm2) and giant (⩾512 001 µm2) insulin-containing cell clusters (P=0.04) in the fetus. Insulin concentrations in plasma from the uterine vein, umbilical artery and umbilical vein were greater (P⩽0.01) in animals receiving 100% requirements. When comparing ewes to fetuses, ewes had a greater percentage of medium insulin-containing cell clusters (2001 to 32 000 µm2) while fetuses had more (P<0.001) pancreatic insulin-positive area (relative to section of tissue) and a greater percent of small, large and giant insulin-containing cell clusters (P⩽0.02). Larger insulin-containing clusters were observed in fetuses (P<0.001) compared with ewes. In summary, the maternal pancreas responded to nutrient restriction by decreasing pancreatic weight and activity of digestive enzymes while melatonin supplementation increased α-amylase content. Nutrient restriction decreased the number of pancreatic insulin-containing clusters in fetuses while melatonin supplementation did not influence insulin concentration. This indicated using melatonin as a therapeutic agent to mitigate reduced pancreatic function in the fetus due to maternal nutrient restriction may not be beneficial.

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.

The consequence of level of nutrition on heifer ovarian and mammary development.

Replacing cows in the herd is second only to nutrition as the single greatest input cost in cow/calf beef production. The increased availability of cereal grains for feeding livestock has allowed replacement heifers to enter the production system at younger ages. Many heifer development programs feed to ensure heifers reach puberty before the time that they are mated to calve at 2 yr of age. Nutrition level during development has been associated with altered milk production and stayability. We hypothesized that heifers exposed to a lower nutrition level during the peripubertal period would have less methylation of the DNA in the mammary gland and ovarian cortex. We also hypothesized that the ovarian reserve would decrease in heifers fed for rapid growth compared to heifers fed for slow growth during puberty. At 257±1 d of age, heifers in the Stair-Step treatment (n=6) received 157 kcal ME/BW kg0.75 for 84 d and heifers in the Conventional treatment (n=6) were offered 228 kcal ME/BW kg0.75. At d 84, heifers were fed for an additional 83 d. Stair-Step heifers were offered 277 kcal ME/BW kg0.75, and heifers on the Conventional treatment received 228 kcal ME/BW kg0.75. Mammary weights (P=0.43), capillary area density (P=0.74), and capillary surface density (P=0.18) did not differ between treatments and neither did alveolar number (P=0.55) and alveolar density (P=0.49). Reproductive tract weights (P=0.69) and ovarian weight (P=0.68) and ovarian size (P>0.75) did not differ between treatments. In histological sections, Stair-Step heifers had more primordial follicles than Conventional heifers (P=0.02), but primary (P=0.59) and secondary (P=0.15) follicles did not differ. Global methylation of parenchymal tissue (P=0.82), mammary fat pad (P=0.45), and ovarian cortex (P=0.14) did not differ between treatments. Anterior pituitary weight did not differ between treatments (P=0.16). Our hypothesis that modifying peripubertal nutrition modifies global methylation of the mammary and ovary is not supported; however, our hypothesis that it modifies the ovarian reserve is supported.

Effects of nutrient restriction and melatonin supplementation on maternal and foetal hepatic and small intestinal energy utilization.

To determine how nutrient restriction and melatonin supplementation influence ewe and foetal hepatic and small intestinal energy use, 32 primiparous ewes on d 50 of gestation were fed 60% (RES) or 100% (ADQ) of NRC recommendations with 0 (CON) or 5 mg/d (MEL) of dietary melatonin. On d 130 of gestation, small intestine and liver were weighed and collected. Data were analysed as a completely randomized design with a 2 × 2 factorial arrangement of treatments. Liver weight (g/kg EBW) decreased (p = 0.02) in RES ewes. Jejunum weight (g/kg BW) increased (interaction p = 0.04) in ADQ-MEL ewes compared with all other treatments. Total in vitro O2 consumption (mol/min/tissue) and total citrate synthase activity (mol/min/tissue and mol/min/kg EBW) in liver decreased (p ≤ 0.03) in RES ewes. Oxygen consumption (mol/min/kg EBW) increased (interaction p = 0.02) in jejunum of ADQ-CON versus RES-MEL and ADQ-CON. Citrate synthase activity (mol/min/kg of EBW) increased (interaction p = 0.03) in jejunum of ADQ-MEL compared with RES-MEL and ADQ-CON. Foetal liver weight (g/kg BW) decreased (p = 0.02) in RES versus ADQ. Foetal small intestine weight (g/kg BW) decreased (interaction p = 0.05) in RES-MEL versus ADQ-MEL. Total O2 consumption (mol/min/tissue) and total citrate synthase activity (mol/min/kg of BW) in foetal liver decreased (p ≤ 0.05) in RES versus ADQ. Foetal small intestinal O2 consumption (mol/min/kg of BW) was greater (interaction p = 0.03) in RES-CON and ADQ-MEL than RES-MEL and ADQ-CON. Maternal nutrient restriction had a greater effect than melatonin supplementation on liver and jejunum mass and energy utilization in dams and foetuses. Because intestinal mass and energy utilization were more responsive to melatonin supplementation in ewes fed adequate nutrition compared with restricted ewes, melatonin may have limited use as a therapeutic supplement to help overcome potential negative effects of nutrient restriction.

Hepatic steroid metabolizing enzyme activity during early, mid, and late bovine pregnancy.

The objective was to examine hepatic steroid inactivating enzymes throughout gestation and determine the effect of early to mid-gestation maternal nutrient restriction followed by realimentation on the activity of these enzymes. On day 30 of gestation, cows were assigned to dietary treatments: control (CON; 100% National Research Council; n = 18) and restricted (RES; 60% National Research Council; n = 30). On day 85, cows were slaughtered (CON, n = 6 and RES, n = 6), remained on control (CC, n = 12) and restricted (RR, n = 12), or were realimented to control (RC, n = 11). On day 140, cows were slaughtered (CC, n = 6; RR, n = 6; RC, n = 5), remained on control (CCC, n = 6; RCC, n = 5), or were realimented to control (RRC, n = 6). On day 254, all remaining cows were slaughtered. Jugular blood samples were collected before the slaughter for steroid analysis. At slaughter, maternal liver samples were collected for hepatic enzyme activity analysis. Activity of cytochrome P450 3A decreased (P = 0.05) from mid- to late-gestation. Peroxisome proliferator-activated receptor alpha DNA binding activity was increased (P < 0.01) on day 140 and 254 of gestation vs day 85. Concentrations of estradiol-17ß (E2) increased (P < 0.01) as gestation proceeded, whereas progesterone concentrations (P4) tended to increase (P = 0.06) from mid- to late-gestation. Activity of cytochrome P450 1A and 2C were decreased (P < 0.05) in nutrient restricted cows vs control, whereas concentrations of E2 were increased (P < 0.05) in nutrient restricted cows vs control. A longer period of nutrient realimentation from mid- to late-gestation increased (P < 0.05) aldo-keto reductase 1C activity and decreased (P < 0.05) P4 concentrations compared with the shorter period of nutrient realimentation. In addition, significant negative correlations were observed for cytochrome P450 3A activity vs E2 (r(2) = -0.30; P < 0.05) and aldo-keto reductase 1C activity vs P4 (r(2) = -0.29; P < 0.05). The present study implicates hepatic steroid inactivation in the partial modulation of peripheral concentrations of E2 and P4 during gestation.

Effects of maternal nutrient restriction followed by realimentation during midgestation on uterine blood flow in beef cows.

The objective was to examine the effect of maternal nutrient restriction followed by realimentation during midgestation on uterine blood flow (BF). On Day 30 of pregnancy, lactating, multiparous Simmental beef cows were assigned randomly to treatments: control (CON; 100% National Research Council; n = 6) and nutrient restriction (RES; 60% of CON; n = 4) from Day 30 to 140 (period 1), and thereafter, realimented to CON until Day 198 of gestation (period 2). Uterine BF, pulsatility index (PI), and resistance index (RI) were obtained from both the ipsilateral and contralateral uterine arteries via Doppler ultrasonography. Generalized least square analysis was performed. Ipsilateral uterine BF in both groups increased quadratically (P < 0.01) during period 1 and linearly (P < 0.01) during period 2. There was a treatment (P = 0.05) effect during period 2; where RES cows had greater ipsilateral BF versus CON. Ipsilateral uterine PI and RI decreased linearly (P ≤ 0.01) during period 1 across treatments. Contralateral uterine BF in CON cows tended (P < 0.09) to be greater versus RES in both periods. Contralateral PI in both groups increased linearly (P ≤ 0.01) during period 1. Contralateral uterine RI was increased (P ≤ 0.05) in RES cows versus CON in both periods. There was no interaction or treatment effect (P ≥ 0.24) for total BF during either period. Nutrient restriction does not alter total uterine BF, but it may increase vascular resistance. However, up on realimentation, local conceptus-derived vasoactive factors appear to influence ipsilateral uterine BF.

Effects of maternal nutrient restriction followed by realimentation during early and midgestation on beef cows. I. Maternal performance and organ weights at different stages of gestation.

The objectives were to evaluate the effects of nutrient restriction during early to midgestation followed by realimentation on maternal performance and organ mass in pregnant beef cows. On d 30 of pregnancy, multiparous, nonlactating cows (initial BW = 620.5 ± 11.3 kg and BCS = 5.1 ± 0.1) were assigned to 1 of 3 dietary treatments: control (CON; 100% NRC; n = 18) and restricted (RES; 60% NRC; n = 30). On d 85, cows were slaughtered (CON, n = 6; R, n = 6), remained on control (CC; n = 12) and restricted (RR; n = 12), or were realimented to control (RC; n = 11). On d 140, cows were slaughtered (CC, n = 6; RR, n = 6; RC, n = 5), remained on control (CCC, n = 6; RCC, n = 5), or were realimented to control (RRC, n = 6). On d 254, all remaining cows were slaughtered. Cows were weighed before slaughter and all maternal organs were dissected and weighed. The diet consisted of grass hay to meet 100 or 60% NEm recommendations for fetal growth and to meet or exceed recommendations for other nutrients. At d 85 slaughters, BW and empty BW (EBW) were not affected (P ≥ 0.84) by maternal nutrition. However back fat was decreased (P = 0.05) in RES vs. CON cows. Large intestine and abomasum mass were increased (P ≤ 0.05) in RES cows vs. CON. At d 140, BW was decreased (P = 0.05) and EBW tended to be decreased (P = 0.10) in RRC cows vs. CCC and RCC being intermediate. Liver mass was decreased (P = 0.02) in RR vs. CC with RC being intermediate. Ruminal mass was decreased (P = 0.003) in RR vs. CC and RC cows. At d 254, BW and EBW were similar (P ≥ 0.78) across treatments. We observed partial changes in maternal weight and organ masses due to different lengths of maternal nutrient restriction followed by realimentation. It appears that the dam undergoes some adaptations during an early to midgestation nutrient restriction and becomes more efficient in the utilization of nutrients after being realimented and as gestation advances.

Dietary selenium and nutritional plane alter specific aspects of maternal endocrine status during pregnancy and lactation.

Objectives were to examine effects of selenium (Se) supply and maternal nutritional plane during gestation on placental size at term and maternal endocrine profiles throughout gestation and early lactation. Ewe lambs (n = 84) were allocated to treatments that included Se supply of adequate Se (ASe; 11.5 µg/kg BW) or high Se (HSe; 77 µg/kg BW) initiated at breeding and nutritional plane of 60% (RES), 100% (CON), or 140% (EXC) of requirements beginning on day 40 of gestation. At parturition, lambs were removed from their dams, and ewes were transitioned to a common diet that met requirements of lactation. Blood samples were taken from a subset of ewes (n = 42) throughout gestation, during parturition, and throughout lactation to determine hormone concentrations. Cotyledon number was reduced (P = 0.03) in RES and EXC ewes compared with CON ewes. Placental delivery time tended (P = 0.08) to be shorter in HSe ewes than in ASe ewes, whereas placental delivery time was longer (P = 0.02) in RES ewes than in CON and EXC ewes. During gestation, maternal progesterone, estradiol-17ß, and GH were increased (P < 0.05) in RES ewes and decreased (P < 0.05) in EXC ewes compared with CON ewes. In contrast, maternal cortisol, IGF-I, prolactin, triiodothyronine, and thyroxine were decreased in RES ewes and increased in EXC ewes compared with CON ewes during gestation. Selenium supply did not alter maternal hormone profiles during gestation. During parturition and lactation, maternal hormone concentrations were influenced by both Se and maternal nutritional plane. During the parturient process, HSe ewes tended to have greater (P = 0.06) concentrations of estradiol-17ß than ASe ewes. Three hours after parturition a surge of GH was observed in ASe-RES ewes that was muted in HSe-RES ewes and not apparent in other ewes. Growth hormone area under the curve during the parturient process was increased (P < 0.05) in ASe-RES vs HSe-RES ewes. Ewes that were overfed during gestation had reduced (P < 0.05) estradiol-17ß but greater IGF-I, triiodothyronine, and thyroxine (P < 0.05) compared with RES ewes. Even though ewes were transitioned to a common diet after parturition, endocrine status continued to be affected into lactation. Moreover, it appears that gestational diet may partially affect lactational performance through altered endocrine status.

Realimentation of nutrient restricted pregnant beef cows supports compensatory fetal muscle growth.

Drought and other weather-related disasters impact the amount and quality of grains and forages available to beef cattle. The impact of nutrient restriction at specific gestational timeframes on fetal skeletal muscle growth was examined. Crossbred beef cows were fed to NRC recommendations (CCC) or restricted to 60% of said levels for the first 85 or 140 d of pregnancy followed by realimentation to recommended protein and energy levels (RCC and RRC, respectively). Fetal infraspinatus (INF) morphometrics and gene expression analyses were performed at d 85, 140, and 254 of gestation. Results demonstrate that fetal primary myofibers are larger (P < 0.05) after 85 d of maternal caloric restriction by comparison to controls. Realimentation of pregnant dams at d 85 causes an increase (P < 0.05) in RCC INF cross-sectional area (CSA) by comparison to RRC at d 140 but the fibers remain smaller (P < 0.05) than CCC muscle cells. Returning nutrient load to recommended levels at d 140 of pregnancy increases RRC CSA equivalent to CCC fibers at d 254 (343.4 ± 5.2 and 345.2 ± 5.3 µm(2), respectively). Fetal RRC and CCC muscle fibers are smaller (P < 0.05) than RCC fibers at d 254 suggesting the later experienced compensatory growth. Numbers of Paired box 7 (Pax7) immunopositive cells were fewer (P < 0.05) in the nutrient restricted fetuses at d 85 suggesting a loss of muscle progenitor cells. Moreover, mRNA content for the collagen crosslinking enzymes, lysyl oxidase and bone morphogenetic protein 1, were greater (P < 0.05) in the d 85 nutrient restricted fetal INF than CCC suggesting increased connective tissue cell numbers and/or activity. Because myogenesis is acutely regulated by the IGF, mRNA content of these growth factors and their receptors was examined. Fetal IGF1 mRNA content was lower in the d 85 nutrient restriction fetuses (P < 0.05) by comparison to CCC. Levels of INF IGF2 mRNA were greater (P < 0.05) in d 85 NR fetuses than CCC. Continued nutrient restriction through d 140 resulted in a reduction (P < 0.05) in IGF2 expression by comparison to CCC. No treatment effect on IGF1R or IGF2R mRNA content was noted. In summary, NR for 85 d causes an increase in primary INF fiber size that may be a result of increased IGF2 transcription and Pax7-immunopositive cell fusion. Realimentation of NR beef cows supports compensatory growth of the fetal musculature such that normal muscle fiber size and muscle progenitor numbers are achieved before birth.

Dietary melatonin supplementation alters uteroplacental amino acid flux during intrauterine growth restriction in ewes.

Dietary melatonin supplementation during mid- to late-gestation increased umbilical artery blood flow and caused disproportionate fetal growth. This melatonin-induced increase in umbilical artery blood flow may alter nutrient availability to the fetus, which may lead to alterations in fetal size. The objectives of the current experiment were to determine amino acid (AA) and glucose concentrations as well as AA and glucose flux across the uteroplacenta using a mid- to late-gestation model of intrauterine growth restriction supplemented with dietary melatonin as a 2 × 2 factorial design. At day 50 of gestation, 32 ewes were supplemented with 5 mg of melatonin (MEL) or no melatonin (CON) and were allocated to receive 100% (adequate; ADQ) or 60% (restricted; RES) of nutrient requirements. On day 130 of gestation, uterine and umbilical blood flows were determined via Doppler ultrasonography during a non-survival surgery. Blood samples were collected under general anesthesia from the maternal saphenous artery, gravid uterine vein, umbilical artery, and umbilical vein for AA analysis and glucose. Total α-AA concentrations in maternal artery and gravid uterine vein were decreased (P < 0.05) in RES v. ADQ fed ewes. Maternal arterial - venous difference in total α-AA was increased (P ⩽ 0.01) in RES v. ADQ fed ewes, while total uterine α-AA flux was not different (P > 0.40) across all treatment groups. Fetal venous - arterial difference in total α-AA as well as uteroplacental flux of total α-AA were decreased (P < 0.05) in CON-RES v. CON-ADQ, and similar (P > 0.20) in MEL-RES v. CON-ADQ. Maternal concentrations and uterine flux of branched-chain AA (BCAA) were not different across all treatment groups; however, fetal uptake of BCAA was decreased (P < 0.05) in CON-RES v. CON-ADQ, and similar (P > 0.20) in MEL-RES v. CON-ADQ. Uterine uptake of glucose was not different (P ⩾ 0.08) across all treatment groups, while uteroplacental uptake of glucose was increased (P ⩽ 0.05) in RES v. ADQ ewes. In conclusion, maternal nutrient restriction increased maternal arterial - venous difference in total α-AA, while total uterine α-AA flux was unaffected by maternal nutrient restriction. Melatonin supplementation did not impact maternal serum concentrations or uterine flux of glucose or AA; however, melatonin did improve fetal BCAA uptake during maternal nutrient restriction.

Serum hormone profiles, pregnancy rates, and offspring performance of Rambouillet ewes treated with recombinant bovine somatotropin before breeding.

An experiment was conducted to examine effects of bovine ST (bST) on serum hormone concentrations, pregnancy rates, and offspring performance. Before initiation of a fall breeding period, 75 Rambouillet ewes (68.8 ± 1.5 kg) received an intravaginal insert containing 0.3 g of progesterone (P4) to synchronize onset of estrus. After 12 d, inserts were removed (d 0), and ewes (stratified by BW and age) received either 0 (control, n = 37) or 250 (n = 38) mg of recombinant bST (Posilac, Monsanto, St. Louis, MO, subcutaneously). Ewes were joined with fertile rams 24 h after insert removal. Blood samples were collected from 12 ewes in each treatment group daily from d 0 to 20 after insert removal. Serum IGF-I concentrations were 315 and 437 (± 58) ng/mL in control and bST-treated ewes 2 d after receiving bST (P = 0.02) and remained increased (P < 0.03) in bST-treated ewes throughout the 13-d period (P < 0.05). Serum prolactin (P > 0.10) and estradiol (P = 0.65) were similar between treatments. Serum triiodothyronine (T3) and thyroxine (T4) concentrations were similar (P > 0.20) between treatments from d 0 through 8. Controls had greater (P < 0.04) serum T3 and T4 concentrations than treated ewes did until d 18. Serum P4 was similar (P > 0.10) in control and bST-treated ewes from d 0 through 3 but was increased (P < 0.05) from d 4 to 8 in control ewes. Serum P4 was again similar (P > 0.10) between treatments from d 9 to 20. Serum insulin concentrations were 0.44 and 1.74 (± 0.19) ng/mL in control and bST-treated ewes, respectively, 1 d after receiving bST (P < 0.001) and remained increased (P < 0.03) in bST-treated ewes through d 9 (P < 0.03). Serum glucose was increased (P = 0.003) from d 0 to 10 in bST-treated ewes compared with controls. Thirty-three of 37 (89%) control ewes were pregnant, whereas 27 of 38 (71%) bST-treated ewes were pregnant (P = 0.05). As a percentage of ewes lambing, 61% and 39% of control ewes produced single and twin lambs, respectively, compared with 41% and 59% of bST-treated ewes (P = 0.12). Lamb 60-d adjusted weaning weights were 23.0 and 21.2 (± 0.65) kg for offspring produced by control and bST-treated dams, respectively (P = 0.04). In conclusion, serum IGF-I, insulin, and glucose were greater whereas serum T3, T4, and P4 were less in bST-treated ewes than in controls. Pregnancy rates and offspring adjusted weaning weights were decreased by bST treatment immediately before breeding.