# Early Life Nutrition and Its Effects on the Developing Heifer: Immune and Metabolic Responses to Immune Challenges

## TL;DR

This study explores how early nutrition affects the immune and metabolic responses of dairy heifers to immune challenges later in life.

## Contribution

The study provides insights into the long-term immune benefits of increased preweaning nutrition in dairy heifers.

## Key findings

- Higher preweaning milk feeding improved immune competence in calves, with higher monocyte and eosinophil counts.
- Differences in eosinophil counts from preweaning persisted until 13 months of age.
- Metabolic responses to immune challenges reflected current nutritional status rather than preweaning effects.

## Abstract

Combinations of pre- and postweaning nutritional strategies were used to determine the effect early life nutrition has on the future resilience of dairy replacement heifers. Positive influences of increased milk feeding on calf immune responses and metabolic characteristics were observed in the preweaning phase. However, while somewhat apparent, the longer-term advantages of increased preweaning nutrition on immunity need to be confirmed. These results may lead to new early-life management strategies that reduce the high incidence of young replacement stock losses, improving the welfare, economic and environmental impacts of the Australian dairy industry.

This experiment aimed to assess the effects of both preweaning nutrition and postweaning growth rate on the resilience of dairy heifers from birth to 20 months of age. Immune competence and metabolic characteristics were assessed via repeated vaccine immune challenges throughout early life. Heifers were subject to either a high or low preweaning nutritional treatment (high: 8 L vs. low: 4 L of milk per day). Calves in these treatment groups were then equally divided into either a high or low postweaning growth rate treatment until 20 months of age. Nutritional intake, growth and metabolic data can be found in a companion paper, while the current paper outlines the responses to the three immune challenges. In the preweaning phase, heifers on a high milk volume had superior immune competence, demonstrated by higher monocyte and eosinophil counts. All other immune biomarkers were not different between treatments. By 8 months of age, the differences in monocytes were lost; however, the differences in preweaning eosinophil counts remained at 8 months and through to 13 months of age. At 13 months of age, there were also three-way interaction effects of preweaning nutrition, postweaning growth rate and vaccination for white blood cell count and neutrophil count; however, the trends in these responses appear random and do not align towards any clear advantages of pre- or postweaning nutrition. Metabolic responses to the immune challenges do not suggest any form of carryover effect from the preweaning phase and seemed to reflect the nutritional input at the time.