Reproductive Tract Score: A Tool for Evaluating Beef Heifer Reproductive Potential

This publication explains the RTS methodology and suggests how it can be implemented in a cow-calf operation. Written by Mario Binelli, Thiago Martins, Cecilia C. Rocha, Felipe A. C. C. Silva, João Bittar, Philipe Moriel, Angela M. Gonella-Diaza, Lauren Butler, and Cindy Sanders, and published by the UF/IFAS Department of Animal Sciences, October 2021.

218 Effects of feeding a vitamin and mineral supplement and (or) an energy supplement on concentrations of amino acids in beef heifer serum and fetal fluids at d 83 of gestation

Objectives were to evaluate effects of feeding vitamin and mineral (VTM) and (or) energy (NRG) supplements on concentrations of amino acids (AA) in heifer serum and allantoic (ALF) and amniotic (AMF) fluids at d 83 of gestation. Thirty-five crossbred Angus heifers (body weight = 359.5 ± 7.1 kg) were randomly assigned to one of four treatments (n = 8 or 9/group) in a 2 × 2 factorial arrangement with main effects of vitamin and mineral (NoVTM or VTM) and energy (NoNRG or NRG) supplements. Heifers were fed a basal total mixed ration once daily with VTM and NRG treatments top-dressed. The VTM treatment (113 g•heifer-1•d-1) was initiated 71 to 148 d before artificial insemination (AI). The NRG treatment was initiated at AI targeting gains of 0.28 kg/d for NoNRG and 0.79 kg/d for NRG. Serum, ALF, and AMF were collected at d 83 ± 0.27 of gestation and analyzed for concentrations of AA. In serum, a VTM × NRG interaction (P = 0.02) was observed for Glu, with greater concentrations for VTM-NoNRG than VTM-NRG. Concentrations of serum Cys, Met, and Trp were greater (P ≤ 0.03) for NRG than No-NRG. In ALF, concentrations of Glu were affected by a VTM × NRG interaction, where VTM-NRG was greater (P < 0.01) than all others. In ALF, VTM increased (P ≤ 0.05) concentrations of His, Asp, and 12 of the 14 neutral AA, whereas NRG increased (P ≤ 0.05) Arg, Cys, and Asp. In AMF, AA concentrations were not affected (P ≥ 0.10) by VTM, NRG, or their interaction. In conclusion, an increase in neutral AA concentration in ALF from beef heifers was observed at d 83 of gestation with VTM supplementation, suggesting effects on the mechanisms of AA uptake and balance between the maternal circulation and fetal fluid compartments.

PSVIII-37 Late-Breaking Abstract: Effects of feeding a vitamin and mineral supplement and (or) an energy supplement on the abundance of SLC7A5 transporter in beef heifer placentomes at d 83 of gestation

Objectives were to evaluate effects of vitamin and mineral (VTM) and (or) energy (NRG) supplements on the abundance of the neutral amino acid (AA) transporter SLC7A5 in heifer placentomes at d 83 of gestation. Thirty-five crossbred Angus heifers (Body weight = 359.5 ± 7.1 kg) were randomly assigned to one of four treatments (n = 8 or 9/group) in a 2 × 2 factorial arrangement with main effects of vitamin and mineral (NoVTM or VTM) and energy (NoNRG or NRG) supplements. The VTM treatment was initiated 71 to 148 d before artificial insemination (AI). The NRG treatment was initiated at AI. Heifers were ovariohysterectomized at d 83 of gestation. Placentome cross sections (5 μm) were mounted onto glass slides, deparaffinized, and stained for SLC7A5. Fluorescent images of tissue areas including fetal membranes, caruncles (CAR), endometrial epithelium (EP), superficial glands (SG), deep glands (DG), and myometrium were obtained and analyzed for relative intensity of fluorescence within the areas of interest as an indicator of transporter abundance. The abundance of SLC7A5 was influenced by a VTM × NRG interaction (P = 0.05) in DG, with NoVTM-NRG being greater than heifers receiving VTM. Abundance of SLC7A5 was not influenced by NRG (P > 0.12) in any structures evaluated. In EP and SG abundance of SLC7A5 was less (P ≤ 0.05) in VTM than NoVTM heifers and tended to be less in CAR (P = 0.07). Our previous work revealed no differences in maternal serum AA concentrations, but VTM heifers had greater AA concentrations in allantoic fluid than NoVTM. We hypothesize that transporter efficiency may be reduced in NoVTM heifers, with greater transporter abundance being a mechanism of compensation to supply AA to the fetus. Together, these data help to further elucidate mechanisms of AA uptake and balance between the maternal and fetal compartments.

404 Beef heifer development: Managing nutrition to optimize fertility

Beef cattle longevity can be tied to reproductive performance. Developing heifers that will thrive in their environment, under specific management systems, is crucial for today’s producers. Management decisions influencing heifer fertility are numerous; however, the most commonly discussed and studied revolves around nutrition. The objectives of this presentation are to review our understanding of the influence of nutrition on beef heifer fertility and identify potential mechanisms which may improve heifer fertility and beef producer profitability. Also, we will identify management decisions that may impact body weight gain or efficiency of weight gain, thus impacting fertility. Management strategies delaying heifer growth patterns pre- or post-weaning have been reported to alter heifer reproductive performance. Additionally, developing heifers on native range compared to in the dry lot or confinement settings may alter growth rates/patterns, thus affecting the heifer’s ability to become pregnant, or maintain that pregnancy. Supplementing heifers with specific nutrient profiles has also been reported to improve pregnancy rates compared with non-supplemented or control animals. Previously, it was believed heifers are born with a finite number of follicles within their ovaries, and the depletion of the ovarian reserve occurs at a constant rate. Recent research has challenged this, reporting heifers developed on a stair-step growth program had an increased number of primordial follicles compared to constant gain developed heifers. Additionally, development system (native range vs. dry lot) appears to impact ovarian function. Continued research increasing our understanding of mechanisms involved in improving heifer fertility are warranted. These efforts will aid in identifying management strategies that will optimize animal reproductive performance.

PSI-2 Effects of extended release eprinomectin on heifer performance while grazed on endophyte-infected tall fescue or housed in drylot

Objectives were to evaluate the effects of LongRange, an extended-release eprinomectin, on beef heifer performance while grazed on endophyte-infected tall fescue or housed in drylot. Fall-born, Angus × Simmental heifers (n = 153) were utilized in a split-plot design. Heifers were stratified by BW and assigned to 6 groups. Groups were randomly assigned to 1 of 2 environmental treatments: grazed endophyte-infected tall fescue (Pasture) or housed in drylot and fed alfalfa hay. Within environmental treatment groups, heifers were randomly assigned to LongRange (LR) or control (Saline). Prior to experiment initiation, heifers were treated with oral fenbendazole (SafeGuard) to minimize parasite load. Data were analyzed using the MIXED procedure of SAS. At d 0, 56, and 112, heifer BW, ADG, BCS, hair coat score (HCS), and fecal egg counts (FEC) were collected. Treatments did not affect (P ≥ 0.17) BW on d 0 and 56. On d 112, drylot heifers tended (P = 0.08) to be heavier than pasture heifers and LR increased (P = 0.01) BW. There was an interaction (P = 0.02) for ADG; LR increased ADG to a greater magnitude in pasture than drylot heifers. On d 0, 56, and 112, there was no interaction or LongRange effect (P ≥ 0.11) on BCS; however, pasture heifers had greater (P = 0.05) d 112 BCS than drylot heifers. On d 56, there was an interaction (P = 0.01) on HCS; LR decreased HCS in pasture heifers, but did not affect HCS in drylot heifers. Although treatment did not effect (P ≤ 0.33) FEC at d 0, there was an interaction (P = 0.01) observed on d 56. LongRange decreased FEC in pasture heifers but not in drylot. In conclusion, LongRange increased heifer growth performance with a greater difference for heifers grazing tall fescue, compared with heifers in drylot.