Indicating resilience or reflecting disease? Relating milk fluctuations and mastitis in dairy cows

Dairy cows are exposed to pathogens, management transitions and other challenges throughout the lactation cycle. Resilience is the capacity to be minimally affected by such disturbances. Ultimate resilience would be absence of disease and easy transitions, whereas lack of resilience can result in an increase in incidence or severity of disease. Fluctuations in milk yield throughout lactation have been used as indicator of resilience and were associated with breeding values for disease. However, it is unclear whether fluctuations in milk yield indicate resilience in the absence of disease, or whether these fluctuations reflect the reduction in milk yield upon disease. In this study, we related fluctuations in milk yield in early lactation to the occurrence of mastitis later in lactation. The dataset included daily milk yield of 414 cows, of which 249 had no mastitis in the 305 days lactation (NO); 29 had mastitis in the first 30 days in milk (EARLY); and 136 had mastitis later in lactation (LATE). Individual lactation curves were fit using quantile regression. Fluctuations were defined as deviations of realised daily milk yields from the fitted lactation curve; and fluctuations in early lactation were summarised as natural logarithm of the variance between 10 and 30 days in milk (lnVAR). A linear model was used to assess the difference in lnVAR between cows with no, early and late mastitis. Milk yield level was included as a covariate, as it was strongly correlated with lnVAR. Early mastitis was associated with a higher lnVAR in early lactation, i.e. greater fluctuations in milk yield, than no or late mastitis (lnVAR of 2.9, 2.0 and 2.1 for EARLY, NO and LATE, respectively). No difference was detected in lnVAR in early lactation between cows that remained healthy versus cows with mastitis later in lactation. However, mastitis was preceded by a drop in milk yield 2 days in advance. In this study, fluctuations in milk yield reflected disease, but did not indicate resilience in healthy cows.

Bibliographic Details

Main Authors:	Kok, A., Tsousis, G., Niozas, G., Kaske, M., van Knegsel, A.T.M.
Format:	Article in monograph or in proceedings biblioteca
Language:	English
Published:	Wageningen Academic Publishers
Subjects:	Life Science,
Online Access:	https://research.wur.nl/en/publications/indicating-resilience-or-reflecting-disease-relating-milk-fluctua
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