# Association of Acute-Phase Proteins and IgG with Bovine Respiratory Disease, Seroconversion to Respiratory Infections and Farm-Level Factors in Rearing Calves

## TL;DR

This study explores how blood proteins in calves can predict respiratory disease risk and how housing conditions affect their health.

## Contribution

The study identifies acute-phase proteins and IgG as potential biomarkers for respiratory disease in calves and links housing conditions to immune responses.

## Key findings

- Calves with respiratory disease and those in pens with more sick animals had higher levels of acute-phase proteins.
- Calves in larger pens had lower levels of certain acute-phase proteins, suggesting better health outcomes.
- Lower IgG levels at arrival were linked to a higher risk of illness in early rearing.

## Abstract

Bovine respiratory disease is a common and costly health issue in young calves, negatively affecting both growth and welfare. This study investigated whether acute-phase proteins (APPs) in blood could serve as biomarkers to guide management strategies aimed at improving health and welfare in calf-rearing systems. We conducted a trial involving 476 calves in Finland over a 50-day period at rearing farms, where the blood of calves was sampled and their health was monitored. We found that calves with signs of respiratory disease, as well as those housed in pens with a higher number of sick animals, had higher levels of APPs in their blood. Interestingly, calves housed in larger pens had lower levels of certain APPs, suggesting that management practices can influence the risk of inflammation-related illness. Additionally, calves with lower levels of immunoglobulin G (IgG) upon arrival at the rearing farms were more likely to become ill early in the rearing period, indicating a protective effect of higher serum IgG at arrival. Our results suggest that early immune monitoring using APPs and IgG may support calf health and welfare, enabling farmers and veterinarians to implement targeted housing and veterinary interventions.

This study investigated the associations between acute-phase proteins (APPs) such as serum amyloid A (SAA), haptoglobin (Hp), and albumin (Alb) as well as immunoglobulin G (IgG) with bovine respiratory disease (BRD), seroconversion to respiratory infections and farm-level factors in rearing calves. Datasets were obtained from a randomised trial of 476 calves in Finland that compared morbidity in large- versus small-group housing. Calves were assessed for clinical BRD, and their blood was sampled three times during the first 50 rearing days to measure APPs and IgG concentrations and virus-specific antibodies against Mycoplasma bovis (M. bovis), bovine respiratory syncytial virus (BRSV), bovine parainfluenza virus 3 (BPIV3), and bovine coronavirus (BCV). Linear mixed-effects regression models showed higher serum SAA and Hp concentrations in calves with clinical BRD. BRSV seroconversion was associated with increased serum SAA and lower Alb while M. bovis seroconversion with increased serum Hp. Calves in larger groups had lower serum Hp, SAA and Alb, and pens with higher BRD cases were associated with increased serum SAA and lower Alb. IgG concentration was associated with BRSV seroconversion. These results suggest that early immune monitoring using APPs and IgG could help guide targeted management strategies to improve calf health and welfare.