This study aimed to investigate the hormonal and metabolic status of heifers subjected to short-term variation of energy intake and associated growth rate;; oocytes were collected by ovum pick-up (OPU) for in vitro embryo production. Experimental scheme, diets and OPU protocol have been described previously (Freret et al., 2003 Theriogenology, 59, 445 abst). Briefly, oocytes from 16 Prim′Holstein heifers (14±1 months old, 340±25kg) were collected by OPU every two weeks after superovulation treatment (total dose of 250μg FSH (Stimufol®, Merial, France) divided into 5 i.m. injections 12 hours apart, at decreasing doses). They received individually for 6 weeks (Period 1=OPU 1 to 4) a diet aimed at a 1000g day−1 body weight gain (BWG). Heifers were then allocated to 2 groups (overfeeding or dietary restriction), for 8 weeks after OPU 4 (Period 2=OPU 5 to 8). COCs were collected 12h after the last FSH injection for IVF and IVC. Blood sample analyses were performed once a week to determine glucose, insulin, IGF1, non esterified fatty acids (NEFA), β-hydroxybutyrate (βOH) and urea concentrations, and at the time of follicular puncture for estradiol assay. Effects of period, group of growth rate and their interaction where analyzed using the mixed procedure of SAS (female effect as random) and least-squares means were subsequently compared with Scheffe’s test. Three groups of growth rate were determined according to results observed during period 2 (Table 1). A period effect was observed for glucose, insuline and estradiol (P<0.05). But Scheffe’s test showed a significant variation between periods only in the ‘600gday−1’ group, with more estradiol and less glucose in period 2 which was associated with more blastocysts and grade 1 embryos (Freret et al., 2003 Theriogenology, 59, 445 abst), and in the ‘1400g day−1’ group with more insulin in period 2 (associated with more follicles <8mm 2 days before FSH treatment). In period 2, βOH concentration was significantly higher in the ‘1400gday−1’ group when compared to the others (Table 1). For urea, NEFA and IGF1 concentrations, no difference between groups or periods was observed. These results illustrate the role of glucose and insulin as mediators of nutritional effects on reproduction in growing animals. These results suggest that nutritional requirements aimed at optimizing follicular growth and embryonic development may be different.
Table 1
Chronic low BPS exposure through diet impairs in vitro embryo production parameters according to metabolic status in the ewe
