Maternal dietary environment modulates programming responses in avian offspring during embryonic and post-hatch development

Abstract

It is well recognised the maternal environment elicits strong programming effects during embryonic development and that these effects are regulated via epigenetic mechanisms. Furthermore, the degree to which these effects are expressed in offspring is further determined by the “predictive adaptive response” (PAR), whereby the combined effect of the maternal and offspring diet dictates if developmental programming phenotypes are expressed or ameliorated during adult life. Due to the various dietary insults imposed on broiler breeder hens, developmental programming and the PAR effect may have strong application in the broiler industry but currently is poorly acknowledged. This thesis presents an overarching hypothesis that the breeder dietary environment elicits epigenetic programming effects, signalled to the developing embryo via mediators present in the yolk. It is hypothesised developmental programming events in ovo will have significant long effects on offspring health and performance, dependant on both maternal and offspring environmental conditions. Findings identify broiler breeder dietary environment causes strong programming effects in offspring, identifiable at various stages of development and in a sex-dependent manner. Differences in hen body weight significantly altered offspring organ weight as early as embryonic day 14 (ED14). Somewhat surprisingly, adult (D42) offspring organ weight (duodenum, jejunum, illium, pancreas and breast muscle) was significantly influenced by maternal body weight, irrespective of any early dietary insults imposed on the chick. It is proposed the observed changes in embryonic and adult organ weight are likely attributed to changes histological and morphology changes in response in ovo yolk profile exposure and warrants further investigation. A PAR effect was also apparent across various dietary conditions. Changing the predominating grain source between generations, irrespective of the grain source, significantly altered progeny body weight and response to immune challenge from 7 days post-hatch to 42 days. Similarly, differences in feed allocation across generations also influenced progeny bodyweight and jejunum weight, specifically in male offspring. These results indicate a PAR effect, hence transgenerational dietary management is an important consideration in poultry production. Manipulation of the maternal diet altered various biologically active compounds within yolk including hormones, nutrients and miRNA. Altering hen bodyweight and ‘stress’ response in broiler breeders significantly altered yolk corticosterone concentration, while naturally occurring differences in yolk glucose, insulin, testosterone and thyroxine concentration were found between broiler and layer breeds. Maternal grain source was associated with changes in expression levels of yolk microRNAs. Encouragingly, the miRNAs detected are associated with hen reproductive performance and embryonic development, indicating manipulation of microRNA via the maternal diet may attribute to programming effects in ovo. These results highlight the exciting opportunity of epigenetic modulators within the yolk in characterising programming events attributing to embryonic development in avians. In summary, the current findings provide strong evidence the broiler breeder hen diet provides a mechanism to alter embryonic development and induce long-term effects and the concept of PAR has significant consequences for progeny health and performance. Future investigations should target the in ovo environment and potential epigenetic mechanisms for improved health and performance.