Nutritional supplementation in high and low AFC heifers

Within our cattle herds, there are animals with high and low numbers of antral follicles on their ovaries. In animals with low numbers of antral follicles, general fertility is reduced and this is associated with low of concentrations of the ovarian hormone progesterone in blood. The reduced progesterone concentration might influence quality of the oocytes and/or the uterine environment. It has been recently shown that an immunomodulatory nutritional supplement (OmniGen-AF) can increase circulating progesterone concentration. The question arises, if this supplementation can compensate negative effects of low follicle numbers on fertility and if this is achieved via improved oocyte developmental competence, changes in the uterine environment or singularly the effect of increased progesterone concentrations. We hypothesize that feeding the nutritional supplement to heifers with low numbers of antral follicles before breeding will increase circulating progesterone concentrations and improve conceptus development. As follicles grow in the bovine ovary for approximately 100 days, the oocytes are potentially influenced by nutritional supplementation. The second objective is, therefore, to determine the effect of the supplement on oocyte quality, by examining in-vitro formation rate of early embryos. In heifers, bodyweight, number of antral follicles, ovarian size and uterine horn diameter will be determined. Consecutively heifers will be divided into groups with high and low numbers of follicles by splitting at the 50% point. Half of the heifers with high and half of the heifers with low follicle numbers will be randomly assigned to receive the nutritional supplement. Following a second examination, heifers with highest and lowest number of follicles in each group will be selected for synchronization and artificial insemination. Sixteen days later the reproductive tract will be collected. Blood samples will be collected to determine progesterone concentrations. Length of the conceptus will be measured and analyses for transcript abundance will be performed. The oocytes will be fertilized in-vitro and embryonic development will be monitored. In these embryos transcript abundance in markers of early embryonic development will be determined. The project will answer the question if alterations in reproductive efficiency in heifers with low antral follicles is caused by changes in oocyte quality, alteration of uterine environment or decreased progesterone concentration or a combination of these factors. In addition, a better understanding of the effects of nutritional supplements will provide management methods for cow-calf producers to improve fertility in animals with low numbers of antral follicles and on herd level.

Heifers with high and low antral follicle counts - A nutrition-based strategy for reproductive success Context: Within our cattle herds, there are animals with high and low numbers of antral follicles on their ovaries. Low numbers of antral follicles are linked to phenotypic characteristics associated to reduced reproductive performance, such as low progesterone concentration, increased concentration of gonadotrophins and impaired uterine milk composition. Aims: This project aimed to further characterize differences in the reproductive physiology of heifers with low and high AFC and to evaluate if nutritional supplementation might be a suitable management tool to improve reproductive performance. A yeast based immunomodulatory nutritional supplement has previously shown to increase endogenous progesterone concentration in cattle. We, therefore, hypothesized, that feeding this supplement during the 60 days prior to breeding will increase circulating progesterone concentration in heifers with low numbers of antral follicles and reproductive outcome. Results: Findings obtained during this project revealed that the greater concentration of circulating progesterone in heifers with high AFC does not result in improved developmental growth of embryos in early pregnancy or improved embryo-maternal signaling. Nevertheless, we found differences in the timing of oxytocin receptor upregulation in the uterus. Upregulation of those receptors occurs only in non-pregnant animals and is the prerequisite to induce the dissolution of the corpus luteum. This process is called luteolysis and leads to the return to normal estrous cyclicity. Results obtained from transcriptomic analysis of corpus luteum tissue also show transcription patterns clearly associated to early luteolysis in heifers with low antral follicle count. This earlier onset of luteolysis in heifers with low AFC might result in a shorter window of recognition of pregnancy by the dam and, therefore, contribute to reduced reproductive performance compared to heifers with greater AFC. Feeding the nutritional supplement did not alter the antral follicle count itself and does consequently not affect signaling of follicular recruitment. Further developmental competence of collected oocytes is not positively affected. The results indicate that the nutritional supplementation indeed increases circulating concentrations of progesterone. Conclusions and Perspectives: Nutritional supplementation might thus be a promising management tool to improve reproductive performance, especially in heifers with reduced numbers of antral follicle counts. In addition, increase of endogenous progesterone in low AFC heifers by nutritional supplementation will be a valuable and harmless scientific tool to further investigate the mechanistic differences in reproductive physiology among heifers with differing antral follicle counts. Further collaboration with the host institution is envisaged to further elucidate those differences in reproductive physiology.