109 Effect of ruminal infusion with propylene glycol on the in vitro embryo production of Holstein (Bos taurus) prepubertal heifers and pregnancy rate of the embryo transfer

Abstract

The aim of this study was to evaluate the effect of ruminal infusion with propylene glycol (PG) on the in vitro embryo production (IVEP) of Holstein (Bos taurus) prepubertal heifers (7 to 8 months). For this study, 16 prepubertal heifers were distributed into two groups: Propylene Glycol Group (PGG; n = 8) and Control Group (CG; n = 7). Additionally, 8 pubertal heifers were used for the positive control group (PUB). All animals (n = 23) underwent an ovum pickup (OPU) for follicular ablation on Day 0, followed by an FSH protocol treatment (160 mg performed in 4 injections twice a day in decreasing doses, designated as D2PM, D3AM, D3PM, and D4AM). Animals from PGG received a ruminal infusion with 250 mL of PG twice a day on Days 0, 1, 2, 3, and 4, using a drench. Animals from CG and PUB did not receive any additional treatment. On Day 5 all animals underwent another OPU, and oocytes were used for the IVEP (Sexing Technologies commercial laboratory). The produced embryos were transferred fresh to Holstein heifer recipients. Additionally, blood sampling was performed on D4PM (M1) and on the day of OPU (D5AM, M2) for insulin-like growth factor (IGF-1, via radioimmunoassay) and glucose (hexokinase) analysis. Data were analysed using the GLIMMIX procedure of SAS. No difference was observed between groups for number of recovered oocytes (CG: 14.28 ± 1.9; PGG: 14.87 ± 3.9; PUB: 10.50 ± 2.2; P = 0.24), number of viable oocytes (CG: 10.71 ± 2.5; PGG: 10.75 ± 2.7; PUB: 9.50 ± 2.0; P = 0.80), cleaved oocytes (CG: 7.71 ± 1.5; PGG: 9.50 ± 2.1; PUB: 6.25 ± 1.4; P = 0.14), cleavage rate (CG: 54.2% (7.7 out of 14.2); PGG: 64.1% (9.5 of 14.8); PUB: 59.0% (6.2 of 10.5); P = 0.35) and number of blastocysts (CG: 1.71 ± 0.5; PGG: 2.00 ± 0.6; PUB: 3.12 ± 1.0; P = 0.71). Pubertal heifers had higher blastocyst rates compared with prepubertal heifers, regardless of PG treatment (CG: 11.9% (1.7 of 14.2); PGG: 13.5% (2 of 14.8); PUB: 29.5% (3.1 of 10.5); P = 0.01). No difference was observed between groups for 30-day (CG: 41.7% (5 of 12); PGG: 46.7% (7 of 15); PUB: 42.9% (6 of 14); P = 0.96) or 60-day pregnancy rates (CG: 41.7% (5 of 12); PGG: 33.3% (5 of 15); PUB: 42.9% (6 of 14); P = 0.86). In addition, no difference was observed for pregnancy loss between 30 and 60 days (CG: 0.0% (0 of 12); PGG: 13.3% (2 of 15); PUB: 0.0% (0 of 14); P = 0.99). Regarding metabolic blood analysis, no difference was observed for IGF-1 (ng mL⁻¹) between groups (P = 0.38), moment of sample collection (P = 0.06), and interaction of group × moment (P = 0.87; CG/M1: 263.36 ± 15.2; CG/M2: 297.71 ± 18.7; PGG/M1: 304.25 ± 26.9; PGG/M2: 332.61 ± 31.6; PUB/M1: 309.16 ± 19.9; PUB/M2: 311.07 ± 18.8). Glucose (mg dL⁻¹) was higher (P = 0.0001) for pubertal heifers (91.63 ± 1.4) compared with the other groups (CG: 102.25 ± 1.1; PGG: 107.71 ± 3.5); however, no difference was observed for moment of sample collection (P = 0.35) or interaction of group × moment (P = 0.36). These data show that treatment with PG was not efficient to improve the IVEP of prepubertal Holstein heifers, embryos from prepubertal heifers treated with PG did not have increased pregnancy rate, and treatment did not increase IGF-1 or glucose blood levels.