The effect of undernutrition on the establishment of pregnancy in the ewe

Effect of undernutrition on the uterine environment during maternal recognition of pregnancy in sheep

The effects of pregnancy and undernutrition on endometrial gene expression were investigated in ewes fed all or half their maintenance requirements and killed on Day 14 of pregnancy or of the oestrous cycle. The endometrial expression of progesterone, oestrogen, oxytocin and interferon receptors (PR, ERα, OXTR and IFNAR, respectively), cyclo-oxygenase (COX)-2, proliferating cell nuclear antigen (PCNA), insulin-like growth factors (IGF)-I and -II, and IGF-1 receptor (IGF-1R) was studied by immunohistochemistry or real-time reverse transcription–polymerase chain reaction. The luminal epithelium of cyclic control ewes was devoid of PR staining and had relatively high levels of ERα, OXTR, COX-2 and IFNAR2. The presence of a conceptus decreased the in vitro uterine secretion of prostaglandin (PG) F2α and the expression of IFNAR2 in most cell types, and increased the gene expression of IGF-I and IGF-II. Undernutrition tended to increase ERα protein and gene, but decreased in vitro uterine secretion of PGE2 and the gene expression of IFNAR2 in cyclic ewes. There was no effect of undernutrition on pregnancy rates or the number of conceptuses recovered. Consistent with this, undernutrition of pregnant ewes did not have any effect on uterine gene expression. Moreover, in cases where changes were observed in cyclic ewes, these changes were negated when a conceptus was present.

Undernutrition reduces the oviductal mRNA expression of progesterone and oestrogen receptors in sheep

The effect of undernutrition on the oviductal mRNA expression of oestrogen and progesterone receptors (ERalpha and PR) determined by a solution hybridisation assay in sheep was investigated. Adult ewes were fed either 1.5 (C) or 0.5 (L) times their maintenance requirements and were slaughtered on day 5 or 14 of a synchronised oestrous cycle (day 0=oestrus). In the oviduct ipsilateral to the corpus luteum, Group L presented lesser concentrations of ERalpha mRNA than Group C on day 5 (P<0.05), and lesser PR mRNA concentrations on both days (P<0.05). No effect of undernutrition was observed in the contralateral oviduct, and there was no difference in transcripts concentrations between days 5 and 14. The lesser sensitivity of the oviduct to ovarian steroids found in undernourished ewes could compromise the embryo environment and partly explain the retarded development reported in embryos collected from nutritionally restricted ewes.

Effects of body condition and protein supplementation on LH secretion and luteal function in sheep

In ruminants, nutrition is one of the exogenous inputs affecting reproductive function at different levels of the hypothalamic-hypophyseal-gonadal axis. However, the exact mechanisms or even the identification of the signalling metabolic compounds by which nutrition affects reproductive function still need further clarification. The role of static body condition (BC) and its interaction with a short-term protein supplementation (PL), on secretion of metabolic hormones [growth hormone (GH), insulin and insulin-like growth factor-1 (IGF-1)], as well as on secretion of LH and progesterone (P4) was evaluated in sheep. Twenty-four Rambouillet ewes divided into two groups, with lower (LBC) and higher body condition (HBC), were randomly assigned within BC to one of two PL levels: low (LPL, 24% of crude protein; 14 g/animal/day), and high (HPL, 44% of crude protein; 30 g/animal/day). The secretion of GH, insulin, IGF-1 and LH was evaluated on day 10 of the oestrous cycle; appearance and timing of oestrous behaviour were previously detected using rams. Progesterone secretion was evaluated on day 13 of the same cycle. No differences were found (p > 0.05) between PL groups on serum GH concentrations during the sampling period (overall mean of 4.0 +/- 0.3 ng/ml), but a trend for lower values in HBC sheep was found (3.6 +/- 0.4 vs 4.4 +/- 0.4 ng/ml, p = 0.06). A BC effect was observed (p < 0.05) on serum IGF-1 level, with higher values in HBC sheep (p < 0.05). Neither BC nor PL affected (p > 0.05) secretion of LH and the number of corpora lutea, nor serum P4 and insulin concentrations. Results indicate a predominance of the static component of nutrition on sheep metabolic hormone responses, GH and IGF-1, with no effect of short-term PL on secretion of pituitary and ovarian hormones as well as luteal number and activity.