Nutritional programming in replacement dairy heifers: Future-proofing herd performance, health and behaviour

Background and justification:
Dairy calf lifetime performance is heavily influenced by early life health, nutrition and environment. If these factors are sub optimal they will have detrimental impacts on the ability of the animal to achieve its genetic potential, therefore compromising productivity, health and welfare (e.g. Heinrichs et al., 2011). In dairy calves, the plane and composition of ingested nutrients during early life has been associated with future lactation performance (e.g. Soberon et al., 2012; 2013). Variations in the intake of nutritive and non-nutritive components from colostrum, milk or milk replacers may be associated with changes in calf metabolism and persist during the productive lifespan.
Additionally, nutrients provided in early life can impact on the gut microbiota (e.g. Dill-McFarland et al., 2018). For example, in monogastric species the diet and microbiota within the digestive tract have a strong influence on immunity and health (Maslowski and Mackay, 2011), with the development of several immune cells occurring in the intestines at contact with digestive tract bacteria. However, in ruminants these mechanisms need to be characterized before they can be utilised to manipulate the microbiota to favour bovine health and immunity (Plaizier et al., 2018; Skelly et al., 2019). Furthermore, an increasing body of evidence has highlighted the pivotal role of the gut microbiota in the development of key physiological functions in vertebrates, this not only including growth and metabolism, but also on brain development and behaviour (Kraimi et al., 2019). Furthermore, dairy cattle which display less reactive behaviours have improved milk quality and production parameters (Cziszter et al., 2016). As such, a better understanding of the links between the microbiota-gut-brain axis could have implications for animal production, health and welfare. These aspects could be improved through nutrition and management practices which take into account the role of gut microbiota (Kraimi et al., 2019).

Hypothesis:
This study will examine metabotypes from animals fed different dietary treatments in early life and their long-term stability and association with production profiles in adult life. It will test the hypothesis that different early life nutrient and non-nutrient intakes from the diet will result in different gut microbiota and metabotypes that affect the energy metabolism, phenotype (these including feed efficiency and milk production and quality) and behaviour of the animal.

Objectives:
Identify biomarkers for altered plasma metabolic pathways (metabotype) that may correspond to the intake of nutrients fed to pre-weaned calves.
Study the effect of dietary nutrients and non- nutrients on the microbiome that stablishes in the gastrointestinal tract of pre- and post-weaned calves, and their long term stability to adulthood.
Analyse the longitudinal stability of metabotypes identified in early life through to adulthood, to look for correlations between metabotypes and animal phenotype (including DMI, feed efficiency, BW and milk production and quality which have a direct impact on system resilience and sustainability).
Identify associations between the gut microbiota, metabotype and temperament in early calfhood and examine if these traits persist to adulthood.
Identify biomarkers for improved immune system function as a means of reducing ill-health and animal losses.

Results from this project will extend our understanding of the effects of early life nutrition and help to develop nutritional strategies in calves for metabolic programing of future lactating cows. This will enable the development of strategies for targeted selection of traits which will contribute to an environmentally sustainable, high welfare and productive dairy system. Improving the production quality of milk products will also have a positive impact on human nutrition.