Effect of short-term nutritional supplementation on oocyte quality in superovulated goats

Energy-dense diets in small ruminants have significant effects on the reproductive physiology, including the ovarian function and fertility. Thus, the use of nutritional strategies for a short period (short nutritional flushing) can be used to stimulate folliculogenesis, through the use of dietary supplements with activity in the ovary, such as glycerin or linseed, increasing the levels of glucose and fatty acids in the plasma and consequently the number of follicles and viable oocytes. Therefore, the aim of this study was to evaluate the effect of short nutritional flushing on the viability and oocyte quality in goats superovulated and fed with different nutritional sources. Thirty adult mixed breed goats, with homogenous body condition score (3.0 ± 0.2; Mean ± SD), body mass index (7.2 ± 0.8) and age (28.2 ± 3.4 months), were grouped in three (n = 10) shaded collective boxes and fed with a total mixed ration (TMR) based on chopped elephant grass (Pennisetum purpureum spp.) and concentrate (10% Crude Protein and 67% Total Digestible Nutrients). Feed mixtures were provided to satisfy the requirement for breeding of adult non-dairy goats (NRC, 2007), during 15 days, from estrus synchronization to oocyte recovery. Seven days prior to oocyte recovery, the three groups of animals (n=10 each) were fed on a daily basis with: (a) TMR diet (Control Group, CG); (b) 200 mL/goat of crude glycerin (80% glycerin) and water in a 9:1 ratio (Glycerin Group, GG), with each dose of crude glycerin equivalent to 1.03 Mcal of metabolizable energy; and (c) ground flaxseed (Linum usitatissimum L.) on a 30% Dry Matter basis (Linseed Group, LG). The TMR feed mixture in the CG and LG groups were prepared in a water solution. Estrus synchronization was initiated by the insertion of an intravaginal progesterone (CIDR®) insert on Day 0 (D0), 12 days prior to slaughter. On Day 6 (D6) the intravaginal insert was removed and 0.075 mg PGF2a (Prolise®) and 150 IU eCG (Folligon®) were given i.m. After 36 h (Day 7), a 0.125-mg GnRH (Gestran®) dose was given i.m. For superovulation, a total of 200 mg pFSH (Folltropin®) was applied i.m. at 12 h intervals (5 applications of 40 mg/mL) from Day 9 (D9) thorugh Day 11 (D11) (Menchaca et al., 2007). Ovaries were collected upon slaughter on Day 12 (D12), 6 h after the last FSH injection, and transported to the laboratory in saline solution at 25°C. Then, cumulus-oocyte complexes (COCs) were recovered by follicular aspiration, classified morphologically according to the characteristics of cumulus investment and cytoplasm as non-viable (degenerate) and viable (grade I, oocytes with multilayered compact cumulus oophorus and an homogeneous cytoplasm; grade II, compacted COCs with at least 3 layers of cells and homogeneous or heterogeneous cytoplasm; grade III, COCs partially denuded and/or with cytoplasm having few pyknotic areas). Data were analyzed by the Chi-square test (P<0.05). The LG group had significantly higher rates of oocyte viability (88.9%, 152/171) when compared with the GG (80.1%, 137/171) and GC (78.4%, 149/190) groups. Furthermore, proportion of grade I COCs did not differ between treatment groups (LG: 7.9%, 12/152; GG: 5.1%, 7/137; GC: 10.7%, 16/149). However, the LG group had significantly lower and higher percentages of grade II (44.7; 68/152) and grade III (47.4%; 72/152) COCs, respectively, compared with the CG group (56.4 %; 84/149), grade III (CG: 32.9%; 49/149)], being not different from the GG group for grade II (52.6%; 72/137) or grade III (42.3; 58/137) COCs. The short nutritional flushing using polyunsaturated fatty acids (linseed) appear to stimulate folliculogenesis and oocyte development. Thus, nutritional strategies using this feed stuff may safeguard oocyte viability, increasing reproductive efficiency in superovulated female goats. Further studies are needed to confirm the effects of nutritional additives, which may interfere with the rate of maturation and subsequent embryonic development.