# Herd-Level Prevalence of High Fat-to-Protein Ratio and Associated Factors During Early Lactation in Irish Spring-Calving Dairy Herds

## TL;DR

This study analyzed milk data from over 11,000 Irish dairy herds to understand the prevalence of high fat-to-protein ratios, a sign of energy imbalance, and its risk factors during early lactation.

## Contribution

The study identifies seasonal and herd-level factors influencing high fat-to-protein ratios in Irish dairy herds during early lactation.

## Key findings

- The median herd-level prevalence of high FPR (>1.4) was 14.57% in the first 30 days in milk.
- February and March showed the highest prevalence, linked to housing, feeding, and calving.
- Higher-yielding herds had lower odds of high FPR, indicating reduced risk of energy imbalance.

## Abstract

This study used national milk data from over 11,051 Irish spring-calving dairy herds from 2014 to 2023 to assess herd-level prevalence of high fat-to-protein ratio (FPR) (>1.4), as a proxy measure for negative energy balance (NEB), and associated factors. NEB during early lactation increases the risk of metabolic disease, reduces fertility performance, and limits profitability in dairy systems. Median herd-level prevalence of high FPR (>1.4) <30 DIM had a 10-year mean of 14.57% (annual median ranged from 10.81 to 20%), decreasing to 8.10% (annual median ranged from 6.09 to 12.90%) from ≥30 to <60 DIM, with annual variation noted. Results highlighted seasonal and herd-level factors influencing herd-level prevalence of high FPR. The months of February and March, coinciding with housing, feeding of conserved forage, peak calving, and early grazing periods, were associated with the highest prevalence. Genetic traits and 305-day milk yield were linked to herd-level prevalence of high FPR. Higher-yielding herds were associated with reduced odds of increased herd-level prevalence of high FPR, i.e., reduced risk of NEB at herd level. These findings identify important factors associated with herd-level prevalence of high FPR during early lactation, which can help inform future preventative strategies aimed at improving herd health, productivity, and sustainability in Irish dairy herds.

High fat-to-protein ratio (FPR) has been used as a proxy measure for negative energy balance (NEB) in dairy herds. This study describes herd-level prevalence of high FPR during early lactation in Irish spring-calving dairy herds and associated risk factors. A retrospective observational study was conducted using 10 years (2014–2023) of national milk recording data from 11,051 unique herds. Median herd-level prevalence of high FPR (>1.4) <30 days in milk (DIM) had a 10-year mean of 14.57% (annual median ranged from 10.81 to 20%), decreasing to 8.10% (annual median ranged from 6.09 to 12.90%) from ≥30 to <60 DIM, with annual variation noted. Multivariable binomial mixed-effects regression models identified factors associated with an increased herd-level prevalence of high FPR including, in the <30 DIM model, months of February and March; genetic predicted transmitting ability (PTA) for Fat kg and an increase in herd percentage of primiparous cows by 10%. In the ≥30 to <60 DIM model, the month of February, a 10% increase in herd percentage of primiparous cows, a 10% increase in herd percentage of parity 4+ cows, and genetic PTA for Fat kg, were associated with increased herd-level prevalence of high FPR. In both models, higher-yielding herds were associated with reduced odds of increased herd-level prevalence of high FPR. These findings suggest that the greatest risk period for high herd-level prevalence of FPR in this system occurs during the spring housing period and shortly after turnout to grass. Higher-yielding herds appeared to have lower risk of NEB and genetic selection for milk Fat kg had an influence on herd-level prevalence of high FPR.