# Genetic parameters of milk β-hydroxybutyrate as an indicator of metabolic diseases in Spanish dairy cows

## TL;DR

The study explores how milk β-hydroxybutyrate can be used to genetically select dairy cows less prone to ketosis, a common metabolic disease.

## Contribution

The study identifies optimal genetic evaluation methods for using milk β-hydroxybutyrate as an indicator of subclinical ketosis resistance in dairy cows.

## Key findings

- Milk β-hydroxybutyrate has low heritability but high genetic correlations across lactations.
- Using two test-day records within the first 68 days in milk from the first three lactations is sufficient for reliable genetic evaluations.
- Genetic selection for subclinical ketosis resistance is feasible using milk β-hydroxybutyrate data.

## Abstract

Summary: Ketosis is one of the most prevalent metabolic disorders in dairy herds and typically occurs during early lactation due to a negative energy balance, the subsequent mobilization of adipose tissue reserves, and the accumulation of ketone bodies. Milk β-hydroxybutyrate (mBHB) concentration is used as an indicator of subclinical ketosis, as it can be routinely recorded in the milk recording system. This study estimated the genetic parameters of mBHB across 5 lactations, compared sire rankings, and evaluated the minimum test-day records for implementing efficient routine genetic evaluations. The 5 mBHB traits showed low heritability but high genetic correlations. The estimated breeding value reliabilities and rank correlations among sires suggest that using 2 test-day records within the first 68 days in milk from the first 3 lactations is preferable for incorporating mBHB as an indicator trait of subclinical ketosis resistance in the Spanish Holstein breeding program. Cow image by OpenClipart-Vectors from Pixabay; close-up image by Wolfgang Ehrecke from Pixabay.

Summary: Ketosis is one of the most prevalent metabolic disorders in dairy herds and typically occurs during early lactation due to a negative energy balance, the subsequent mobilization of adipose tissue reserves, and the accumulation of ketone bodies. Milk β-hydroxybutyrate (mBHB) concentration is used as an indicator of subclinical ketosis, as it can be routinely recorded in the milk recording system. This study estimated the genetic parameters of mBHB across 5 lactations, compared sire rankings, and evaluated the minimum test-day records for implementing efficient routine genetic evaluations. The 5 mBHB traits showed low heritability but high genetic correlations. The estimated breeding value reliabilities and rank correlations among sires suggest that using 2 test-day records within the first 68 days in milk from the first 3 lactations is preferable for incorporating mBHB as an indicator trait of subclinical ketosis resistance in the Spanish Holstein breeding program. Cow image by OpenClipart-Vectors from Pixabay; close-up image by Wolfgang Ehrecke from Pixabay.

•Ketosis is the most prevalent metabolic disease in dairy herds.•Milk β-hydroxybutyrate showed genetic variability as a subclinical ketosis indicator.•Genetic selection to reduce ketosis is possible with data from the first 3 lactations.

Ketosis is the most prevalent metabolic disease in dairy herds.

Milk β-hydroxybutyrate showed genetic variability as a subclinical ketosis indicator.

Genetic selection to reduce ketosis is possible with data from the first 3 lactations.

Ketosis is the most prevalent metabolic disorder in dairy herds, and reducing its incidence is a key objective in most dairy cattle breeding programs. Whereas clinical ketosis is rarely recorded, milk β-hydroxybutyrate (mBHB) concentration is routinely available through milk recording systems and can serve as a reliable indicator of subclinical ketosis. The objective of this study was to evaluate mBHB as a metabolic disease trait for inclusion in the Spanish Holstein breeding program, aiming to identify animals less susceptible to ketosis by exploring alternative trait definitions for future genetic evaluations. Five mBHB traits were studied, one for each of the first 5 lactations. Two datasets were compared to assess the benefit of using either all available test-day records or only the first test-day available within the initial 68 DIM, which reduced the data volume to 49% of total records. The statistical model included fixed effects of lactation-age at calving, month of calving, and DIM as a linear covariate. Random effects included herd-year of calving, the additive genetic effect, and the permanent environmental effect of repeated measures (test-day records) within lactation. Heritability estimates for mBHB traits ranged from 0.04 to 0.12, with consistent results across both datasets. Genetic correlations among lactations were high (0.67–0.98), 2 test-day records yielded better predictions, mean EBV reliabilities for sires ranged from 12% to 42%, and moderate rank correlations (0.12–0.52) among sires were observed. These findings suggest that using 2 test-day records and data from the first 3 lactations may be sufficient for incorporating mBHB as an indicator trait of subclinical ketosis in the Spanish Holstein breeding program.