Maternal nutritional programming in the sheep : effects on post-natal growth, mammogenesis and lactation in adult-ewe offspring : a thesis submitted for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, Aotearoa New Zealand

Abstract

Developmental programming is the concept that environmental factors, particularly during foetal life, can alter development, metabolism and physiology of an organism and this can have consequences later in life. There is growing interest in developmental programming in livestock species, particularly effects of maternal pregnancy nutrition, which is easy to manipulate. Recent research, using a sheep model, has shown that milk production in ewe offspring may be susceptible to maternal nutritional programming, such that over nutrition (ad libitum) of the pregnant dam, compared with maintenance nutrition, may impair their first lactation performance and result in the weaning of lighter lambs. The present study however revealed that maternal nutritional programming effects on lactation performance in ewe offspring did not persist over their productive lifetime. In a new study, the critical programming period was narrowed down to early gestation, coinciding with early mammogenesis in the foetus. In this study only twin-­‐born ewes were examined due to their economic significance in commercial sheep production and due to their increased susceptibility to nutritional insult in-­‐utero. It was revealed that, in addition to over nutrition (ad libitum), under-­‐nutrition (sub-­‐maintenance) of the dam during early pregnancy also impaired first lactation performance of twin-­‐born ewe offspring when compared with maintenance. Transcriptomics analysis using RNA-­‐seq identified that nutritional programming affects late pregnancy mammogenesis, rather than secretory cell function during lactation, in ewe offspring during their first parity. Ewes born to ad libitum-­‐fed dams, in particular, appeared to have impaired regulation of cell cycle while ewes born to sub-­‐maintenance-­‐fed dams had reduced expression of genes associated with the extracellular matrix, both of which may influence cell proliferation. As a consequence, both ewes born to ad libitum and sub-­‐maintenance-­‐fed dams may have had fewer mammary secretory cells, resulting in reduced lactation performance. The findings of this thesis indicate that differences in first-­‐lactation performance of ewe offspring, as a result of maternal nutritional programming, may be mediated by impaired proliferation of secretory epithelial cells. These findings contribute to our knowledge of the mechanisms of developmental programming of the mammary gland and presents a platform for future investigations which may ultimately lead to the ability to manage and manipulate lactation performance.