Estimating the nonlinear association of online somatic cell count, lactate dehydrogenase, and electrical conductivity with milk yield

John Bonestroo,Mariska Van Der Voort,Nils Fall,Ulf Emanuelson,Ilka Christine Klaas,Henk Hogeveen

doi:10.3168/jds.2021-21351

Abstract

Reduction of milk yield is one of the principal components in the cost of mastitis. However, past research into the association between milk yield and mastitis indicators is limited. Past research has not been based on online or in-line daily measurements and has not fully explored nonlinearity and the thresholds at which milk yield starts to decrease. In dairy herds with automated milking systems equipped with sensors, mastitis indicators of individual cows are measured on an intraday frequency, which provides unprecedented avenues to explore such effects in detail. The aim of this observational study was primarily to investigate the nonlinear associations of lactate dehydrogenase (LDH), electrical conductivity (EC), and somatic cell count (SCC) with milk yield at various stages of lactation, parity, and mastitis chronicity status (i.e., whether the cow had SCC ≥200,000 SCC/mL for the last 28 d). We also investigated thresholds at which mastitis indicators (LDH, EC, and SCC) started to be negatively associated with milk yield. We used data from 21 automated milking system herds measuring EC and online SCC. Of these herds, 7 of the 21 additionally measured online LDH. We operationalized milk yield as milk synthesis rate in kilograms per hour. Applying a generalized additive model, we estimated the milk synthesis rate as a function of the 3 mastitis indicators for 3 different subgroups based on parity, stage of lactation, and mastitis chronicity. Partial dependence plots of the mastitis indicators were used to evaluate the milk synthesis rate to study if the milk synthesis rate was associated with mastitis indicators at a specific level. Results showed that milk synthesis rate decreased with increasing SCC, LDH, and EC, but in a nonlinear fashion. The thresholds at which milk synthesis rate started to decrease were 2.5 LnSCC (12,000 SCC/mL) to 3.75 LnSCC (43,000 SCC/mL), 0 to 1 LnLDH (1-2.7 U/L), and 5.0 to 6.0 mS/cm for EC. Additionally, another substantial decrease of milk synthesis rate was observed at thresholds of 5.625 LnSCC (277,000 SCC/mL) and 3 LnLDH (20 LDH U/L) but not for EC. Having chronic mastitis decreased milk synthesis rate in all models. The identified nonlinearities between mastitis indicators and milk synthesis rate should be incorporated in statistical models for more accurate estimations of milk loss due to mastitis.

Highlights

Mastitis is one of the most important diseases on commercial dairy farms, and the costliest consequence of it is loss of milk production (Hogeveen et al, 2019), both in subclinical (72% of the subclinical mastitis cost) as well as in clinical mastitis cases (48% of the clinical mastitis cost; Aghamohammadi et al, 2018)
It can be seen from the results that LnLDH was negatively associated with milk synthesis rate after the threshold for all parity, stage of lactation, and chronicity subgroups
The threshold of milk synthesis rate decrease was within the range of 5.0 to 6.0 mS/cm mean electrical conductivity (EC) for all subgroups

Summary

Introduction

Mastitis is one of the most important diseases on commercial dairy farms, and the costliest consequence of it is loss of milk production (Hogeveen et al, 2019), both in subclinical (72% of the subclinical mastitis cost) as well as in clinical mastitis cases (48% of the clinical mastitis cost; Aghamohammadi et al, 2018). To support farmer decision-making regarding udder health, insight into the milk production losses due to mastitis is important. The higher the mastitis indicator, the more severe the inflammation is in the udder, resulting in a larger milk yield loss (Hortet et al, 1999; Hagnestam-Nielsen et al, 2009). Somatic cell count is the most widely studied mastitis indicator for estimating losses of milk yield. Measuring SCC in DHI tests or in an experimental setting showed that milk yield is negatively associated with increasing SCC with greater losses at higher SCC (Jones et Bonestroo et al.: MASTITIS INDICATORS AND MILK YIELD al., 1984; Hortet et al, 1999; Hagnestam-Nielsen et al, 2009). A significantly reduced milk yield due to subclinical chronic mastitis was found by Hadrich et al (2018)

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