Feed restriction as a biostimulant of the production of oocyte, their quality and GDF-9 gene expression in rabbit oocytes

The use of short-term feed restriction (R) without or with subsequent refeeding (F) as biostimulant of rabbit fertility was examined in this study. A total of 40 mature, non-pregnant, non-lactating New Zealand white female rabbits were allocated to five treatments. The rabbits were individually caged and fed a complete pelleted diet (16.7% CP; 13.1 CF; 2490 kcal DE/kg). Rabbits on the control (C) treatment received 150 g/d of the diet. Two groups of 8 rabbits received 70% of the control daily feed intake (105 g/d; moderate restriction; M) and the other two groups received 50% of the control feed intake (75 g/d; severe restriction; S) for 21 d. At the end of this period, one group each of M and S fed rabbits were slaughtered for oocyte recovery. Rabbits in the remaining three groups (C, MF and SF) were retained for a further 8 d before slaughter and fed the control level of the diet during this period. The effects on body weight, oocyte number and quality, GDF-9 gene expression in oocytes, and changes in serum levels of leptin and IGF-1 were recorded. Initial mean body weights were not significantly different ranging from 2.50 ± 0.33 kg (S) to 2.58 ± 0.24 kg (C). After 3 wk on treatment the C rabbits were significantly heavier (2.65 ± 0.32 kg; P < 0.05) than rabbits on the M (2.26 ± 0.33 kg) or S (2.10 ± 0.33 kg) treatments. Following 8 d of refeeding, the remaining group of S treated rabbits (SF) were still significantly lighter (2.40 ± 0.21 kg; P < 0.05) than C (2.71 ± 0.31 kg) with MF rabbits having an intermediate weight (2.50 ± 0.20 kg). The number of mature grade A oocytes recovered per ovary was significantly lower for control (3.3 ± 0.35) than the refed treatments (MF 4.0 ± 0.30; SF 4.5 ± 0.39; P < 0.05). Semi-quantitative PCR analysis of GDF-9 expression showed that control mature grade A oocytes had significantly lower levels of expression (1.27 ± 0.20; P < 0.05) than those of refed rabbits (MF 1.60 ± 0.10; SF 1.39 ± 0.01). Leptin and IGF-1 values for refed rabbits were significantly higher (P < 0.05) than at the end of feed restriction and the start point. It was concluded that this biostimulant method has the potential to improve the fertility of rabbits.