231 EFFECTS OF DIETARY PROPYLENE GLYCOL ON FOLLICULAR FLUID AND OVUM PICK UP IN VITRO EMBRYO PRODUCTION IN GROWTH-RESTRICTED HEIFERS WITH TWO PROFILES OF ANTI-MÜLLERIAN HORMONE

Abstract

Fertility and embryo quality can be improved in cattle by using diets that induce a programmed modulation of circulating insulin concentrations. The aim of this study was to test whether the daily oral administration of propylene glycol (PG) could modify metabolite and hormone plasma and follicular fluid concentrations and improve in vitro embryo production in superovulated growth-restricted heifers (600 g day^–1). Sixteen Holstein heifers were grouped according to their pre-experimental anti-Müllerian hormone (AMH) plasma concentrations: low (L = 1–80 pg mL^–1; n = 7) or high (H: >150 pg mL^–1; n = 9). Heifers received a single daily drench from Day 1 to Day 9 of an oestrous cycle [first cycle, 400 mL of water (control) and second cycle, 400 mL of PG]. Serial jugular blood samples were collected on Day 7 of each cycle to monitor plasma insulin, glucose, and β-hydroxybutyrate (BHB) concentrations in relation to the drench. Blood samples were also collected to measure insulin-like growth factor-1 (IGF1) and progesterone (P4) concentrations on Days 0, 2, 5, 7, and 9 of the oestrous cycle. Follicular fluid was collected on Day 9 to measure insulin and IGF1 concentrations. Ovarian ultrasonography was performed on Days 2 and 5 to count follicles between 2 and 8 mm in diameter and estimate their size. After ovum pickup (OPU) performed following superovulation on Day 5 of the oestrous cycle, oocytes were matured and fertilized in vitro, then embryos were cultured for 7 days. Propylene glycol increased plasma concentrations of insulin and glucose and reduced BHB in both groups of heifers compared with control. It also increased IGF1 concentrations on Days 5 and 7 in AMH L heifers and on Days 2, 5, and 7 in AMH H heifers, and reduced P4 concentrations on Days 5 and 9 of the oestrous cycle in all heifers. In follicular fluid, there was no difference in insulin concentrations between groups, but PG increased IGF1 concentrations in all heifers. In ovaries, PG increased the number of small follicles (2–3 mm) and total follicles on Day 2 of the cycle in all heifers, and medium follicles (4–8 mm) and total follicles on Day 5 in AMH H heifers. Propylene glycol improved the in vitro embryo development rate (total number of embryos/number of fertilized oocytes) in all heifers (AMH L: control, 37.9% v. PG, 50.0%; P < 0.05; AMH H: control, 36.4% v. PG, 48.3%; P < 0.05). In AMH H, the number of grade 1 blastocysts was increased by PG (control, 5.2 ± 1.0 v. PG, 8.9 ± 1.0; P < 0.01), whereas there was no difference between treatments in AMH L heifers (control, 1.9 ± 1.1 v. PG, 3.2 ± 1.1; P > 0.05). These results indicate that short-term oral PG supplementation affects the concentrations of metabolites and metabolic hormones in blood and IGF1 concentrations in follicular fluid. PG administration is effective in improving in vitro embryo production more markedly in heifers with high AMH compared with low AMH endocrine levels.