Submitted to: Journal of Dairy Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/10/2007
Publication Date: 9/1/2007
Citation: Appuhamy, J., Cassell, B.G., Dechow, C.D., Cole, J.B. 2007. Phenotypic Relationships of Common Health Disorders in Dairy Cows to Lactation Persistency Estimated from Daily Milk Weights. Journal of Dairy Science. 90(9):4424-4434. Interpretive Summary: The objective of this study was to investigate the phenotypic relationships between lactation persistency and common health disorders in dairy cows. Daily milk weights and treatment incidence records from research farms under close veterinary support were used. Lactation persistency was calculated to be phenotypically uncorrelated with 305 d yield. Disease traits for mastitis, metritis, displaced abomasum, milk fever, ketosis and lameness were developed. We examined the effect of persistency on likelihood of disease occurrence as well as the effects of the diseases on persistency. Results revealed that increasing persistency can reduce likelihood of mastitis specifically in late stages of current lactation. Conversely, except lameness, all the other diseases tend to significantly affect persistency, particularly in multiparous cows.
Technical Abstract: The objective of this study was to investigate the phenotypic relationship between common health disorders in dairy cows and lactation persistency, uncorrelated with 305 d yield. The relationships with peak yield and days in milk (DIM) at peak were also studied. Daily milk weights and treatment incidence records of 991 Holstein lactations from experimental dairy herds at Virginia Tech and Pennsylvania State University were used. Persistency was calculated as a function of daily yield deviations from standard lactations curves, separately developed for first (FL) and later lactations (LL), and deviations of DIM around reference dates: 128 for FL and 125 for LL. DIM at peak and peak yield were computed for each lactation using Wood’s function. The disease traits studied were mastitis only during first 100 days (MAST1), only after 100 DIM (MAST2), both before and after 100 DIM (MAST12) and at any stage of lactation (MAST1/2), and Metritis (MET), displaced abomasums (DA), lameness (LAME), and metabolic diseases (METAB). Each disease was defined as a binary trait distinguishing between lactations with at least one incidence (1) and lactations with no incidences (0). Effect of diseases on persistency, DIM at peak and peak yield were investigated separately for FL and LL for all disease traits except MAST12, which was investigated across parities. The effect of persistency on probability of the diseases in same lactation and in next lactation was examined using odds ratios from a logistic regression model. MET and DA had significantly positive effects on persistency in both FL and LL. The positive effects of METB and MAST1 on persistency were significant in LL. The effects of MAST2, in both FL and LL, and MAST12, across parities, were significant but negative. Overall, cows affected by mastitis tended to have less persistent lactations. Majority of the diseases tended to significantly affect DIM at peak in LL. In LL, MET, METAB, and DA tended to significantly delay DIM at peak while MAST2 was associated with significantly early DIM at peak in LL. Increasing persistency tended to reduce likelihood of MAST2 and MAST1/2 in current lactations of primiparous cows. None of the diseases studied was significantly affected by persistency of previous lactation.