Our objective was to estimate the effect of Mycobacterium paratuberculosis infection on milk, fat,
and protein yield deviations, pregnancy rate, lactation somatic cell score, and projected total months
in milk (productive life). A serum ELISA and fecal culture for M. paratuberculosis were performed
on 4375 Holsteins in 232 DHIA herds throughout the US. Primarily first through third lactation cows
(99% of total) were assayed for infection. Trait information (except productive life) was obtained for
the lactation concurrent with disease tests. Productive life was total months in milk through a cow’s
life, which was projected if a cow was still milking. For most analyses, case definition for M.
paratuberculosis infection was defined as either an ELISA S/P ratio 0.25 or a positive fecal culture
for M. paratuberculosis or both. To determine if diagnostic test affected estimates, case definition was
redefined to include only cows with ELISA S/P ratios 0.25 or only fecal culture-positive cows.
Linear models were used to estimate effect of M. paratuberculosis infection on traits. M. paratuberculosis-infected
cows (7.89% of cows) produced 303.9 kg less milk/lactation, 11.46 kg less fat lactation, and 9.49 kg less protein/lactation (P 0.003). Infected cows had higher pregnancy rates
(1.39%) (P = 0.0385) and lower productive life (2.85 months) (P 0.0001). M. paratuberculosis
infection did not affect somatic cell score. Effect of infection on milk and protein yields was larger in
first lactation M. paratuberculosis-positive cows relative to cows that tested positive in later
lactations. Fecal culture-positive cows had consistently larger effects on all traits than ELISApositive
cows. M. paratuberculosisinfection, and not just clinical Johne’s disease, decreases milk, fat,
and protein yields, thus increasing the estimated cost of paratuberculosis to the US dairy industry.
Our objective was to estimate the effect of Mycobacterium paratuberculosis infection on milk, fat,and protein yield deviations, pregnancy rate, lactation somatic cell score, and projected total monthsin milk (productive life). A serum ELISA and fecal culture for M. paratuberculosis were performedon 4375 Holsteins in 232 DHIA herds throughout the US. Primarily first through third lactation cows(99% of total) were assayed for infection. Trait information (except productive life) was obtained forthe lactation concurrent with disease tests. Productive life was total months in milk through a cow’slife, which was projected if a cow was still milking. For most analyses, case definition for M.paratuberculosis infection was defined as either an ELISA S/P ratio 0.25 or a positive fecal culturefor M. paratuberculosis or both. To determine if diagnostic test affected estimates, case definition wasredefined to include only cows with ELISA S/P ratios 0.25 or only fecal culture-positive cows.Linear models were used to estimate effect of M. paratuberculosis infection on traits. M. paratuberculosis-infectedcows (7.89% of cows) produced 303.9 kg less milk/lactation, 11.46 kg less fat lactation, and 9.49 kg less protein/lactation (P 0.003). Infected cows had higher pregnancy rates(1.39%) (P = 0.0385) and lower productive life (2.85 months) (P 0.0001). M. paratuberculosisinfection did not affect somatic cell score. Effect of infection on milk and protein yields was larger infirst lactation M. paratuberculosis-positive cows relative to cows that tested positive in later
lactations. Fecal culture-positive cows had consistently larger effects on all traits than ELISApositive
cows. M. paratuberculosisinfection, and not just clinical Johne’s disease, decreases milk, fat,
and protein yields, thus increasing the estimated cost of paratuberculosis to the US dairy industry.
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