Pregnancy risk in beef and dairy cows after supplementing semen with transforming growth factor beta-1 at the time of artificial insemination.

Our objective was to determine if the addition of a concentrated human recombinant transforming growth factor beta-1 (TGF) to bovine semen at the time of AI would result in increased risk of pregnancy in beef and dairy cows. Suckled beef cows (n = 1,132) in 11 herds across 2 states and lactating dairy cows (n = 2,208) in one organic-certified herd were enrolled. Beef cows received fixed-time AI (FTAI) following a 7 d CO-Synch + controlled internal drug release estrous synchronization protocol. Dairy cows were inseminated following observation of natural estrus expression. Cows received either no treatment as a control (CON) or 10 ng of TGF in 10 µl added through the cut-end of a thawed straw of semen immediately prior to AI. At the time of FTAI of beef cows, the mean ± SD age was 5.0 ± 2.4 yr, BCS was 5.3 ± 0.7, and days postpartum was 78.2 ± 15.5 d. The overall pregnancy risk in beef cows was 55.2% to AI and 90.5% season-long. Pregnancy risk in beef cows was not affected (P = 0.27) by addition of TGF (53.1% vs. 58.1%). Further, there was no difference (P = 0.88) for season-long pregnancy risk in beef cows that received TGF (91.2% vs. 91.5%). At the time of insemination of dairy cows, the mean ± SD lactation was 3.0 ± 1.3 lactations, BCS was 2.9 ± 0.3, days in milk was 115.6 ± 56.6 d, and cows had received 2.4 ± 1.5 inseminations per cow. The overall pregnancy risk to AI in dairy cows was 23.1%. Pregnancy risk to AI for dairy cows was not affected (P = 0.32) by addition of TGF (22.0% vs. 23.8%). In conclusion, pregnancy risk to AI was not affected by addition of TGF to thawed semen immediately prior to AI in beef or dairy cows.

Evaluation of biological and economic efficiency of the All Heifer, No Cow beef production system using a system dynamics model based on 6 yr of demonstration herd data.

Alternative management strategies with no cows and all heifers may improve biological and economic efficiency of beef production. The All Heifer, No Cow (AHNC) beef production system involves insemination of nulliparous heifers with female sex-selected semen (FSS) to produce primarily female calves that are early weaned at 3 mo of age. Dams are finished on a high concentrate diet and harvested before 30 mo of age. The objectives of this research were to: 1) build a dynamic model of an AHNC beef production system to quantify system biological and economic efficiency; 2) compare effects of utilizing FSS vs. conventional semen on biological and economic efficiency; 3) evaluate what-if scenarios to determine the effects on biological and economic efficiency of changing variables ±5%, 10%, 15%, and 20% from initial observed values; and 4) evaluate the effects on biological and economic efficiency of changing variables ±10% from initial observed values. A model was built over a 21-yr horizon using Stella Architect. Biological parameter values in the model were based on the 6 yr of data collected from the management of an AHNC demonstration herd. In the model animal, total digestible nutrients (TDN) intake, hot carcass weight (HCW), and age at harvest were randomized. Feed, animal, and carcass prices included in the model were based on 10 yr of historical U.S. price data. Key response variables were biological and economic efficiency (mean ± SD). Biological efficiency was defined as the ratio of output (kilograms of HCW produced) to input (lifetime kilograms of feed TDN consumed), and economic efficiency was measured using a benefit-cost ratio (BCR) and unit variable cost (UVC). Over 40 simulation runs, the predicted mean biological efficiency was 0.0714 ± 0.0008. Economic efficiency was 0.95 ± 0.02 and US $445.41 ± 0.06 for BCR and UVC, respectively. Biological and economic efficiency was improved in the conventional semen scenario; biological efficiency was 0.0738 ± 0.0008, and BCR and UVC were 0.99 ± 0.04 and US $407.24 ± 0.006, respectively. Under this parameterization and market conditions, the AHNC beef production system failed to achieve profitability under any scenario that was evaluated. However, this review did not account for the potential increased genetic benefit from a decreased generation interval and the reduction in feed energy in comparison to a conventional cow/calf system.

Evaluation of performance and carcass traits for a five-cohort All Heifer, No Cow beef production system demonstration herd.

The All Heifer, No Cow (AHNC) beef production system is an alternative to conventional cow/calf production that involves insemination of nulliparous heifers with sexed semen to produce female calves that are early weaned at 3 mo of age. Dams are finished on a high-concentrate diet and harvested before reaching 30 mo of age. Objectives of this research were to document reproductive, feedyard, calf, and carcass performance of an AHNC herd; evaluate effects of carcass maturity on carcass quality; and determine if performance of initial cohorts (i.e., cohorts 1 and 2) differed from sustaining cohorts (i.e., cohorts 3-5). A total of 272 heifers were enrolled in the AHNC system via five annual cohorts. The system was initiated with 51 yearling, Angus-based heifers, and a replicate set (n = 56) was started 12 mo after. Heifers in cohorts 3 (n = 53), 4 (n = 56), and 5 (n = 56) were primarily offspring of prior cohorts (i.e., cohort 3 heifers born to cohort 1 females), but some were purchased to maintain inventory. Angus replacement heifers were purchased in cohorts 3 (n = 26), 4 (n = 26), and 5 (n = 28). Mean (±standard deviation) pregnancy rate at 30 d after fixed-time artificial insemination (AI) with sexed semen was 50.8% ± 9.4%, and 140-d pregnancy rate was 93.0% ± 1.5%. With AHNC, 61.0% ± 6.5% of females replaced themselves with a heifer. During finishing, average daily gain (ADG) was 1.9 ± 0.4 kg • d-1 and dry matter intake (DMI) was 14.9 ± 1.9 kg • d-1. Hot carcass weight (HCW) was 367 ± 35 kg. The USDA grading system classified 20.5% of all carcasses (n = 220) as C maturity (A00 = 100, B00 = 200, etc.), 62.4% ± 29.1% of carcasses as USDA Choice. USDA yield grade (YG) was 2.6 ± 0.7. Based on cohorts 1 and 2, there were no differences (P = 0.96) in Warner-Bratzler shear force values between A and B maturity vs. C maturity carcasses. Across all cohorts, there were no differences in USDA YG, marbling score (MA), and lean maturity between A and B maturity vs. C maturity carcasses; there were differences in age (P < 0.001), bone maturity (P < 0.001), and overall maturity (P <0.001). A comparison of initial vs. sustaining cohorts showed that initial cohorts had lower (P < 0.001) DMI, heavier (P < 0.001) HCW, and more advanced (P < 0.05) bone maturity. However, there were no differences for 30- and 140-d pregnancy rates, ADG, USDA YG, and MA between initial and sustaining cohorts. The AHNC beef production system can effectively produce female calves and quality carcasses for harvest.

Postmortem regulation of glycolysis by 6-phosphofructokinase in bovine M. Sternocephalicus pars mandibularis.

This experiment addressed the hypothesis that 6-phosphofructokinase (6-PFK) regulates glycolysis in postmortem in M. sternocephalicus pars mandibularis. In two separate experiments, muscle samples were excised from randomly-selected steers that would typically be found on a commercial slaughter floor. In the first experiment, two samples were obtained from each of 6 steers immediately post-exsanguination; one sample was immersed immediately in liquid nitrogen and the other was stored at 4°C for 4 d, to compare 6-PFK enzyme activity and glycolytic intermediate concentrations between fresh and d 4 postmortem samples. The greatest activity of 6-PFK was measured in fresh muscle extracts at pH 7.4, whereas little activity was detectable at pH 7.0. 6-PFK activity measured at pH 7.4 in d 4 samples also was barely detectable. Hill coefficient values for 6-PFK in fresh samples measured at pH 7.4 or 7.0, and d 4 samples measured at pH 7.4 were 2.9, 0.8, and 0.7, respectively, indicating loss of cooperativity with both lowered pH during assay and with time postmortem. Glycogen concentrations decreased 45% from d 0 to d 4, to 39.6µmol glycogen/g muscle. Muscle concentrations of free glucose increased (P<0.001) from 0.84µmol/g at d 0 to 6.54µmol/g at d 4. Fructose-6-phosphate and glucose-6-phosphate increased (P<0.001) from d 0 to d 4 (2.8-fold and 4.7-fold, respectively). Lactate began accumulating immediately (3.33µmol/g) and was elevated to 45.9µmol/g by d 4. In the second experiment, conversion of [U-(14)C]glucose to lactate, glycogen, and CO(2) was measured in vitro at pH 7.4 and 7.0 in fresh M. sternocephalicus pars mandibularis strips from four steers. Total [U-(14)C]glucose was less in muscle strips incubated at pH 7.0 than in those incubated at pH 7.4 (55.5 vs. 123nmol glucose utilized per 100mg muscle per h; P=0.04), due primarily to a reduction in glucose conversion to lactate. The conversion of glucose to glycogen or CO(2) in vitro was unaffected by media pH. These results suggest that the postmortem decline in pH in M. sternocephalicus pars mandibularis ultimately inactivates 6-PFK; this occurs prior to the depletion of glycogen reserves.