Maternal nutrient restriction in late pregnancy programs postnatal metabolism and pituitary development in beef heifers.

Maternal undernutrition during pregnancy followed by ad libitum access to nutrients during postnatal life induces postnatal metabolic disruptions in multiple species. Therefore, an experiment was conducted to evaluate postnatal growth, metabolism, and development of beef heifers exposed to late gestation maternal nutrient restriction. Pregnancies were generated via transfer of in vitro embryos produced using X-bearing sperm from a single Angus sire. Pregnant dams were randomly assigned to receive either 100% (control; n = 9) or 70% (restricted; n = 9) of their total energy requirements from gestational day 158 to parturition. From post-natal day (PND) 301 until slaughter (PND485), heifers were individually fed ad libitum in a Calan gate facility. Calves from restricted dams were lighter than controls at birth (P<0.05) through PND70 (P<0.05) with no difference in body weight from PND105 through PND485 (P>0.10). To assess pancreatic function, glucose tolerance tests were performed on PND315 and PND482 and a diet effect was seen with glucose area under the curve being greater (P<0.05) in calves born to restricted dams compared to controls. At slaughter, total internal fat was greater (P<0.05) in heifers born to restricted dams, while whole pituitary weight was lighter (P<0.05). Heifers from restricted dams had fewer growth hormone-positive cells (somatotrophs) compared to controls (P<0.05). Results demonstrate an impaired ability to clear peripheral glucose in heifers born to restricted dams leading to increased deposition of internal fat. A reduction in the number of somatotrophs may contribute to the adipogenic phenotype of heifers born to restricted dams due to growth hormone's known anabolic roles in growth, lipolysis, and pancreatic islet function.

Effects of monensin inclusion and level of intake in limit-feeding strategies for beef cows.

A study was conducted to evaluate the effects of intake management and ionophore inclusion on diet utilization under managed intake conditions in beef cattle. Two experiments utilized common diets fed at 120% (H) or 80% (L) of maintenance with either 0 or 200 mg/d monensin in a factorial arrangement. Forty cows were fed for 56 d (Exp. 1) to evaluate effects on diet utilization and energy retention; diets were fed to 16 ruminally cannulated steers (Exp. 2) to determine effects on digestion, energy value, and ruminal fermentation. Cows fed H had greater body weight (BW) gain (P < 0.01) and retained energy (RE; P < 0.01), although estimated heat production was also greater (P < 0.01). Monensin had limited effects on overall BW gain (P = 0.97). Monensin had no effect on RE (P = 0.94) or calculated heat energy (HE; P = 0.53) despite effects on diet utilization observed in steers. In steers, L increased (P < 0.01) digestion of dry matter, organic matter, acid detergent fiber, and gross energy (GE) and reduced (P < 0.01) passage rate; monensin did not affect digestion (P > 0.15) but did reduce passage rate (P < 0.03). Monensin lowered (P < 0.01) acetate:propionate ratio and increased (P < 0.05) ruminal pH. Monensin did not alter feed required for maintenance; however, limit-feeding reduced apparent daily maintenance requirement to 62.85 kcal/kg BW0.75, a 26% reduction from model-predicted values.

Technical note: Relationship between placentome location and gene expression in bovine pregnancy.

A novel, non-terminal surgical procedure to remove a single placentome from the pregnant ewe for gene expression and histological analyses was recently developed in our laboratory. This technique allows for evaluation of nutritional insults on placental development at more than one stage of gestation using a single animal. Early attempts to develop a similar technique in cattle were met with complications due to inaccessibility of the gravid uterine horn because of its location and mass. One alternative is to collect a placentome from the contralateral uterine horn; however, the question remains as to whether gene expression varies among placentomes based on location relative to the fetus. Pregnant heifers were maintained on forage during early gestation and later moved into pens with a Calan gate system (American Calan, Northwood, NH). On gestational day (GD) 158, five heifers were assigned to receive a hay-based diet formulated to meet 100% of NRC requirements, and five heifers were fed 70% of NRC requirements until necropsy on GD244. At necropsy, a single representative placentome was selected for analysis from the antimesometrial side: (1) of the gravid uterine horn central to the amnion, (2) over the allantois immediately adjacent to the amnion, (3) in the tip of the gravid uterine horn, and (4) in the tip of the contralateral uterine horn. Mean placentome weight was greater (P < 0.05) for locations central to the amnion and allantois compared to locations within the tips of the ipsilateral and contralateral horns, respectively. Gene expression for angiogenic factors (FGF2, ODC1, VEGFA, and FLT1), nutrient transporters (SLC7A1 and SLC2A1), and factors associated with hormone action (ESR1, IGF1, IGFBP3, CSH1, and PAG1) were unaffected (P > 0.05) by dietary treatment or location of the placentome. Results indicate that location of the placentome in relation to the fetus does not impact gene expression, enhancing the efficacy of nonterminal methodologies for sampling gene expression in placentomes.

Limit feeding as a strategy to increase energy efficiency in intensified cow-calf production systems.

Two experiments were conducted to measure efficiency of energy use in limit-fed cows. In Exp. 1, 32 pregnant, crossbred cows were used to examine the effects of dietary energy concentration and intake level on energy utilization and digestion. In a 2 × 2 factorial treatment arrangement, cows received diets formulated at either 1.54 Mcal NEm/kg high energy (H) or 1.08 Mcal NEm/kg low energy (L); amounts of each diet were fed at amounts to achieve either 80% (80) or 120% (120) of maintenance energy requirements. Fecal grab samples were collected on days 14, 28, 42, and 56 for determination of energy digestion and metabolizable energy (ME) intake. Acid detergent insoluble ash and bomb calorimetry were used to estimate fecal energy production. Cow body weight and 12th rib fat thickness were used to estimate body energy, using 8 different methods, at the beginning and end of a 56-d feeding period. Energy retention (RE) was calculated as the difference in body energy on days 0 and 56. Heat energy (HE) was calculated as the difference in ME intake and RE. Energy digestion increased (P = 0.04) with intake restriction. Cows consuming H tended to have greater (P = 0.08) empty body weight (EBW) gain than cows consuming L, but no difference was observed (P = 0.12) between cows fed 120 compared with cows fed 80. Estimates of HE were greater for L than H (P < 0.01) and greater for 120 than 80 (P < 0.01), such that estimated fasting heat production of H (57.2 kcal/kg EBW0.75) was lower than that of L (73.3 kcal/kg EBW0.75). In Exp. 2, 16 ruminally cannulated, crossbred steers were used to examine the effects of dietary energy concentration and intake level on energy digestion. Treatment arrangement and laboratory methods were replicated from Exp. 1. Following a 14-d adaptation period, fecal samples were collected, such that samples were represented in 2-h intervals post-feeding across 24 h. Diet × intake interactions were observed for nutrient digestibility. Energy digestibility was greater in steers fed H than in steers fed L (P < 0.01); however, digestibility of each nutrient increased by approximately 10% in steers fed H80 vs. those fed H120 (P ≤ 0.03); nutrient digestibility was similar among levels of intake in steers fed L (P = 0.54). These results suggest that intake restriction may increase diet utilization and that the magnitude of change may be related to diet energy density.