title: The effects of season and moderate nutritional restriction on ovarian function and oocyte nuclear maturation in cycling gilts.
abstract: The fertility of female pigs is impaired during summer and in response to restriction of feed intake, resulting in reduced productivity of the breeding herd. This study determined the effect of season and moderate nutritional restriction on ovarian function and oocyte developmental competence of cycling gilts. Eighty prepubescent gilts were used across two seasons-summer (S: January to March) and winter (W: June to August)-and received either a high (2.5× maintenance) or a moderately restricted (1.5× maintenance) feeding level for the first 19 days of their second estrous cycle. On Day 19, ovaries were collected post-slaughter. Diameters of all surface follicles over 1 mm were measured. All follicles ≥4 mm were aspirated and cumulus-oocyte complexes underwent in vitro maturation for ∼44 hours to assess oocyte developmental competence on the basis of metaphase II (MII) attainment. Moderate dietary nutrition reduced daily liveweight gain but did not affect the ovarian follicle population or oocyte developmental competence. The number of large follicles (≥6 mm) was lower during summer (S: 10.7 ± 1.74 vs. W: 15.5 ± 1.15, P < 0.05), as was the proportion of oocytes at the germinal vesicle stage of meiosis (S: 0.06 ± 0.02 vs. W: 0.08 ± 0.02, P < 0.05). However, the proportion of oocytes attaining MII was similar in summer and winter (S: 0.72 ± 0.04 and W: 0.69 ± 0.06, P > 0.05). Intrafollicular concentrations of luteinizing hormone were higher in summer (S: 43.05 ± 6.44 vs. W: 12.05 ± 5.12 ng/mL, P < 0.001), whereas estradiol was lower (S: 1.27 ± 0.36 vs. W: 27.52 ± 5.59 ng/mL, P < 0.001). In conclusion, our data demonstrated that in summer, follicle growth beyond 6 mm is impaired during the periovulatory period, without affecting oocyte meiotic competence. Importantly, these data also demonstrated that ovarian follicle growth and the capacity of oocytes to reach MII in vitro appear unaffected by moderate nutritional restriction during the preceding estrous cycle.
authors.affiliation: School of Animal and Veterinary Sciences, University of Adelaide, Roseworthy, South Australia. Electronic address: alyce-maree.swinbourne@adelaide.edu.au.
authors.forename: A M
authors.initials: AM
authors.lastname: Swinbourne
authors.affiliation: South Australia Research and Development Institute, Turretfield Research Centre, Holland House, Rosedale, South Australia.
authors.forename: J M
authors.initials: JM
authors.lastname: Kelly
authors.affiliation: School of Animal and Veterinary Sciences, University of Adelaide, Roseworthy, South Australia.
authors.forename: K L
authors.initials: KL
authors.lastname: Kind
authors.affiliation: School of Paediatrics and Reproductive Health, University of Adelaide, South Australia.
authors.forename: D J
authors.initials: DJ
authors.lastname: Kennaway
authors.affiliation: School of Animal and Veterinary Sciences, University of Adelaide, Roseworthy, South Australia.
authors.forename: W H E J
authors.initials: WH
authors.lastname: van Wettere
mesh_terms: D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D004032:Diet; D030762:Estrous Cycle / Q000502:physiology; D005260:Female; D015571:Follicular Fluid / Q000378:metabolism; D009865:Oocytes / Q000254:growth & development*; D010053:Ovary / Q000502:physiology*; D012621:Seasons; D013552:Swine / Q000502:physiology*
keywords: Diet; Follicle size; In vitro maturation; Oocyte development; Pig