Abstract. Protein restriction in early bovine gestation affects post-natal reproduction and production traits in progeny. This experiment evaluated the effects of dietary protein restriction during the peri-conception period and first trimester in yearling heifers on conceptus growth and development; this period of dietary intervention being earlier than any previous bovine fetal programming studies. Three-hundred and sixty primiparous 12-month-old Santa Gertrudis heifers were individually fed high [14% crude protein (CP)] or low (7% CP) diets for 60 days before conception. At 23 days postconception (dpc), each high (HPERI) or low (LPERI) group was again split into high (HPOST) or low (LPOST) protein groups yielding four treatment groups in a 2 · 2 factorial design. From the end of the first trimester of gestation (98dpc), the pregnant heifers were individually fed a 12% CP diet until parturition. Forty-six fetuses were excised at 98dpc. Sixty-four heifers went on to calve. Conceptus development was assessed via transrectal ultrasound from 36dpc, fetal necropsy at 98dpc and live calf measures at term. At 36dpc, HPERI diet increased fetal crown-rump length (CRL) (P < 0.05) and at the 60dpc scan, biparietal diameter (BPD) tended to be increased by HPOST diet (P < 0.1) though the greater effect upon BPD was still the HPERI diet (P < 0.05). At 60dpc, BPD in the male fetus was affected by the peri-conception diet (P < 0.05), while in females, BPD was not different among nutritional groups. These ultrasound measures of fetal growth were validated by measures of the excised fetus at 98dpc. Fetal weight was heavier (P < 0.01) in those whose mothers were fed the HPOST diet than their LPOST counterparts. Males fetuses were heavier than female fetuses (P < 0.001). Fetal CRL was increased by HPERI diet (P < 0.05) and tended to be increased by HPOST diet (P < 0.1). Fetal BPD tended to be increased by HPERI diet (P < 0.1). In males, BPD tended to be increased in those fetuses whose mothers were fed HPERI (P < 0.1). For females, maternal nutrition during PERI or POST did not affect BPD at 98dpc (P > 0.1). At term, no dietary effect on birthweight was observed (P > 0.1) and males were not heavier than females (P > 0.1). These results suggest that maternal protein intake during the peri-conception (-60 to 23dpc) and first trimester (24-98dpc) may influence early conceptus growth and development in the bovine. The long-term effects on offspring metabolism and post-natal development of this dietary intervention are yet to be determined.

During ovarian development stroma from the mesonephros penetrates and expands into the ovarian primordium and thus appears to be involved, at least physically, in the formation of ovigerous cords, follicles and surface epithelium. Cortical stromal development during gestation in bovine fetal ovaries (n=27) was characterised by immunohistochemistry and by mRNA analyses. Stroma was identified by immunostaining of stromal matrix collagen type I and proliferating cells were identified by Ki67 expression. The cortical and medullar volume expanded across gestation, with the rate of cortical expansion slowing over time. During gestation, the proportion of stroma in the cortex and total volume in the cortex significantly increased (P&lt;0.05). The proliferation index and numerical density of proliferating cells in the stroma significantly decreased (P&lt;0.05), whereas the numerical density of cells in the stroma did not change (P&gt;0.05). The expression levels of 12 genes out of 18 examined, including osteoglycin (OGN) and lumican (LUM), were significantly increased later in development (P&lt;0.05) and the expression of many genes was positively correlated with other genes and with gestational age. Thus, the rate of cortical stromal expansion peaked in early gestation due to cell proliferation, whilst late in development expression of extracellular matrix genes increased.

Abstract. Nutritional perturbation during gestation alters male reproductive development in rodents and sheep. In cattle both the developmental trajectory of the feto-placental unit and its response to dietary perturbations is dissimilar to that of these species. This study examined the effects of dietary protein perturbation during the peri-conception and first trimester periods upon reproductive development in bulls. Nulliparous heifers (n ¼ 360) were individually fed a high-or low-protein diet (HPeri and LPeri) from 60 days before conception. From 24 until 98 days post conception, half of each treatment group changed to the alternative post-conception high-or low-protein diet (HPost and LPost) yielding four treatment groups in a 2 Â 2 factorial design. A subset of male fetuses (n ¼ 25) was excised at 98 days post conception and fetal testis development was assessed. Reproductive development of singleton male progeny (n ¼ 40) was assessed until slaughter at 598 days of age, when adult testicular cytology was evaluated. Low peri-conception diet delayed reproductive development: sperm quality was lowered during pubertal development with a concomitant delay in reaching puberty. These effects were subsequent to lower FSH concentrations at 330 and 438 days of age. In the fetus, the low periconception diet increased the proportion of seminiferous tubules and decreased blood vessel area in the testis, whereas low first trimester diet increased blood vessel number in the adult testis. We conclude that maternal dietary protein perturbation during conception and early gestation may alter male testis development and delay puberty in bulls.

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