Gestational nutrition 1: alterations to gestational nutrition can increase indicators of fertility in sheep

in Reproduction
Correspondence should be addressed to P Smith; Email: peter.smith@agresearch.co.nz
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The aim of this study was to examine the relationships between gestational nutrition, fetal ovarian development and offspring fertility in female sheep and to highlight the potential mechanisms underlying these relationships. Adult sheep (n = 79) were fed either a maintenance or 0.6 of maintenance plane of nutrition for the first 55 days of gestation and thereafter fed ad libitum. Fetuses were collected for analysis at days 55 and 75 of gestation. Female offspring were monitored from birth until 19 months of age. Effects of restricted nutrition were observed on maternal plasma concentrations of progesterone, creatinine, albumin and Ca2+ at day 55 and creatinine at day 75. Concentrations of metabolic factors and steroid hormones in day 75 fetal plasma were not affected by the restricted maternal plane of nutrition. At day 55 of gestation, fetal ovarian germ cell development was not affected by maternal plane of nutrition. At day 75 of gestation ovaries from fetuses whose dams were exposed to restricted nutrition contained more germ cells but had lower germ cell proliferation rates than controls. For female offspring at 8 months of age, the dams gestational plane of nutrition did not affect the onset of puberty, ovulation rate (OR) and antral follicle counts (AFC). At 19 months of age, ewes from dams exposed to the restricted plane of gestational nutrition had higher OR, AFC and progesterone concentrations while concentrations of FSH were lower. In conclusion, while effects on fertility per se are yet to be determined, a reduced maternal plane of gestational nutrition can improve indicators of fertility in female offspring.

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  • Table 1. Breakdown of daily intake for maintenance diet and restricted diet (in parenthesis). Daily intake values for fibre, protein, fat and ME are based on dry matter intake. Daily intake for the restricted diet consisted of 0.6 x maintenance values

 

    Society for Reproduction and Fertility

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    Effect of altered nutrition on maternal weights early – mid gestation. Results are presented as means and standard errors following nutrition restriction from day 0–55 of gestation and ad libitum nutrition thereafter. Effects of day of pregnancy (P < 0.01), and nutritional group (P < 0.01) on body weight were noted, with a group × day interaction (P < 0.05), (RMANCOVA). Significant differences between groups were evident from day 10 of gestation (10 days after introduction of dietary restriction) until the last recorded weight at day 90 (35 days after introduction of ad libitum diet for all animals).

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    Differing morphologies associated with germ cell atresia. (A and B) Day 75 H&E maintenance and restricted respectively. (C) Day 75 TUNEL maintenance. (D) MAPLC3B Day 75 restricted. Scale bars = 20 µm. (A and B) Black arrows illustrate germ cells with condensed nuclei and eosinophilic cytoplasm typical of apoptosis. White arrow illustrates germ cell with fragmented nuclei and pale cytoplasm. Red arrows illustrate germ cells with the presence of large cytoplasmic vacuoles. (C) Black arrow illustrates the absence of TUNEL staining in germ cell with condensed and fragmented nuclei. Blue arrows indicate pregranulosa cells. Dashed line indicates an example of the boundary between an ovigerous cord (below line) and stromal tissue (above line). (D) Black arrow illustrates the absence of MAPLC3B staining in germ cell with condensed and fragmented nuclei. Blue arrows indicate pregranulosa cells.

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    Immunohistochemical staining of fetal ovaries. (A, B, C and D) Ki-67, (E, F and G) Tunel and (I, J, K, L and M) MAPLC3B. Scale bars = 100 µm for (A, B, C, D, E, F, G, H, I, J, K and L) and 50 µm for (M). (A) Negative control. (B) Day 55 = maintenance ovary relative density positive cells = 0.84. (C) Day 75 maintenance ovary, relative density = 1.12. (D) Day 75 restricted ovary, relative density positive cells = 0.35. No difference in the density of positive staining cells was observed between day 55 and day 75 maintenance animals. At day 75, the density of positive staining cells maintenance animals is significantly higher when compared with restricted ovaries (P < 0.01). (E) Negative control slide. (F) Positive control slide. (G) Day 55 restricted ovary relative density of positive cells = 1.72. (H) Day 75 maintenance ovary relative density of positive cells = 2.08. No group or age differences were observed in the density of positive staining cells. (I) Negative control slide. (J) Day 55 maintenance ovary, relative area of positive staining = 0.0043. (L) Day 75 restricted ovary, relative area of positive staining = 0.0010. (M) Day 55 maintenance ovary illustrating positive MAPLC3B staining in germ cells within ovigerous cords. No group differences were observed in the cortical area of positive staining. The cortical area of positive staining is less at day 75 compared with day 55, with staining being increasingly confined to the outer regions of the cortex. The intensity of staining was significantly higher in maintenance ovaries compared with restricted ovaries at day 75 (P < 0.05, comparative images not shown).

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    Daily progesterone concentrations in female offspring throughout the estrous cycle. Data are presented as means and SE for 17 animals from 13 maintenance dams (solid line) and 13 animals from 12 restricted dams (dashed line). *Indicates significant group difference P > 0.05, Bonferrroni multiple ranges tests.

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    Daily FSH concentration in female offspring throughout the estrous cycle. Data are presented as means and s.e. for 12 animals from maintenance dams (solid line) and 12 animals from restricted dams (dashed line). GLM indicated no overall nutritional group effect but, a day of the cycle effect (P < 0.01) and a day of the cycle × nutritional group interaction (P < 0.01). *Indicates significant group difference P > 0.05, Bonferrroni multiple ranges tests.

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