43 Effect of early life nutrition on endometrial gland development and endometrial gene expression in heifers

Abstract

In cattle, uterine gland development (adenogenesis) occurs postnatally, beginning immediately after birth, and is normally complete by approximately 2 months of age. Normal development of uterine glands is essential for subsequent fertility. Early life plane of nutrition can impact age at puberty, but the impact of early postnatal nutrition on adenogenesis is unclear. The aim of this study was to examine the effect of enhanced nutrition during the first 21 weeks of life on heifer reproductive organ growth, endometrial gland development, and endometrial gene expression. To this end, Angus × Holstein-Friesian heifer calves with a mean (± s.d.) age and body weight of 19 (± 5) days and 51.2 (± 7.8) kg, respectively, were assigned to either a high (HIGH; n = 16; targeted average daily gain, ADG, 1.2 kg/d) or a moderate plane of nutrition (MOD; n = 16; targeted ADG 0.5 kg/d). Calves were slaughtered at five months of age, and their reproductive tracts were collected and dissected for analysis. To assess endometrial gland number, a cross-section of the midpoint of one horn (n = 8 per group) was fixed in 10% neutral buffered formalin, embedded, and processed for histology. Slides were stained with haematoxylin-eosin. Five pictures were randomly taken on each slide using a stereomicroscope at 40× magnification and the number of glands was counted using ImageJ (https://imagej.nih.gov/ij/) software. In addition, endometrial tissue samples were collected and snap frozen for subsequent quantitative RT-PCR analysis. At the time of slaughter, calves on the HIGH and MOD diets presented a body weight of 189.6 and 110.2 kg, respectively (P < 0.001), indicating an ADG of 1.18 kg/d for the HIGH group and 0.50 kg/d for the MOD group (P < 0.001). Calves in the HIGH group had a greater (P < 0.001) total reproductive tract (mean ± s.d.; 114.01 ± 35.56 g v. 52.67 ± 14.29 g), isolated cervix (33.17 ± 9.35 g v. 16.14 ± 5.27 g), uterus (59.35 ± 25.78 g v. 27.46 ± 10.61 g), and ovarian (14.80 ± 11.38 g v. 5.40 ± 1.94 g) tissue weights compared with those in the MOD group. This difference was also present when organ weight was expressed on a per unit of body weight basis (P < 0.05). However, no differences were found in the number of endometrial glands between groups (HIGH: 453.50 ± 94.18 v. MOD: 482.38 ± 124.69). In accordance with this result, transcript abundance of six paracrine mediators of gland development (ESR1, IGF1, IGFBP1, WNT5A, WNT7A, and FGF10) was not affected by diet. In conclusion, enhanced early-life plane of nutrition increased the size of the reproductive tract in heifer calves but did not affect endometrial gland development. Future studies will compare the global endometrial transcriptome between groups to explore other putative effects of diet on uterine development.

Research was supported by EU, Horizon 2020 Marie Sklodowska-Curie, REPBIOTECH 675526, Science Foundation Ireland 13/IA/1983, and São Paulo Research Foundation (FAPESP) 2017/21415-5.