A.D.R.N. APPUHAMY1, B.G. CASSELL1, and J.B. COLE2
1Department of Dairy Science,
Virginia Polytechnic Institute and State University, Blacksburg, VA24061
2 Animal Improvement Programs Laboratory, Agricultural Research
Service, USDA, Beltsville, MD 20705-2350
2008 J. Dairy Sci. (?)
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The objective of this study was to investigate phenotypic and genetic relationships of common health disorders in dairy cows to milk (PMY) and fat (PFY) yield persistencies. Health and production data from 398 commercial dairy herds were used. Disease traits were developed in binary form for individual lactations considering mastitis only during the first 100 DIM (MAST1), only after 100 DIM (MAST2) and at any stage of lactation (MAST), and reproductive disorders (REPRO), metabolic disorders (METAB) and lameness (LAME). PMY and PFY were defined to be uncorrelated with 305 d yield. Impact of the diseases on PMY and PFY were investigated separately in first (FL) and later (LL) lactations. Phenotypic associations of PMY and PFY with likelihood of diseases in current and next lactation were examined using odds ratios from a logistic regression model. A linear-threshold sire-maternal grandsire models were used to estimate genetic correlations of displaced abomasums (DA), ketosis (KET), metritis (MET), MAST, MAST1, and MAST2 with PMY and PFY across parities. Metabolic diseases and REPRO had significant, positive relationships with PMY and PFY in both FL and LL. MAST1 tended to associate with significantly greater PMY and PFY in LL. MAST2 was related to significantly lower PMY and PFY in both FL and LL while cows affected by MAST tended to have significantly less persistent lactations. Incidence of MAST and MAST2 tended to decrease for increasing PMY and PFY in present and previous lactation. Heritability of disease incidences were 0.03, 0.01, 0.10, 0.02 to 0.05, 0.02, and 0.04 to 0.10 respectively for DA, KET, MAST, MAST1, MAST2, and MET. Displaced abomasum, KET, MAST, MAST1, and MET had unfavorable genetic correlations of 0.35, 0.46, 0.17, 0.02 and 0.27 with PMY and 0.16, 0.21, 0.07, 0.06, and 0.12 with PFY. Favorable genetic correlations of -0.24 and -0.04 were found for MAST2 with PMY and PFY respectively. Results suggest that diseases in early lactation increase persistency of milk and fat. Selection for greater lactation persistency must consider these antagonistic relationships.
(Key words: persistency, diseases, genetic relationships)