Calf milk pasteurization
In the ongoing quest for improved biosecurity and maximum dairy herd health, it stands to reason that pasteurizing calf milk would be a worthwhile and beneficial management practice. Yet in reality, conservative industry estimates indicate that far fewer than half of all dairies currently perform any type of heat treatment on waste milk fed to calves. Is calf milk pasteurization effective? Does it address current disease and biosecurity concerns on the average dairy? And if so, what role can dairy practitioners play in promoting its adoption?
Survival of Mycobacterium paratuberculosis and preservation of immunoglobulin G in bovine colostrum under experimental conditions simulating pasteurization.
OBJECTIVE
To determine whether Mycobacterium paratuberculosis could survive in colostrum after pasteurization. Additionally, this study investigated the effect pasteurization had on IgG concentration in colostrum.


ANIMALS
Colostrum samples were collected from cattle (beef and dairy) owned by the state of Ohio.


PROCEDURE
Colostrum was divided into aliquots and inoculated with variable concentrations of M paratuberculosis (ATCC No. 19698: 10(4), 10(3), and 10(2) colony-forming units/ml). Half the samples at each concentration were subjected to pasteurization temperatures (63 C) for 30 minutes and the remainder were kept at approximately 20 to 23 C. All samples were incubated (Herrold's egg yolk medium with and without mycobactin J) and observed for growth during the next 16 weeks. Additionally, the IgG concentration of colostrum was determined by radioimmunoassay before and after pasteurization. Samples that coagulated at pasteurization temperatures were mechanically resuspended before measurement of IgG concentration.


RESULTS
Growth of M paratuberculosis was retarded but not eliminated by pasteurization. Growth was observed in all unpasteurized samples incubated on Herrold's egg yolk medium with mycobactin J but in only 2 of 18 pasteurized samples similarly cultured. Growth from pasteurized samples appeared 5 to 9 weeks after growth was observed from nonpasteurized samples. Mean colostral IgG concentration was 44.4 g/L in nonpasteurized samples and 37.2 g/L in pasteurized samples, a decrease of 12.3%. High-quality colostrum (> 48 g of IgG/L) had a significantly greater loss of IgG concentration than did colostrum of lesser quality (P = 0.002).


CONCLUSIONS
Pasteurization lessened, but did not eliminate, growth of M paratuberculosis from experimentally inoculated colostrum samples. Pasteurization resulted in a significant decrease in colostral IgG concentration but not to an unmanageable level that would preclude the colostrum's use for passive transfer of immunity.


CLINICAL RELEVANCE
Colostrum is macrophage rich and may serve as a source of M paratuberculosis infection to calves. Pasteurization of colostrum may lessen the risk of infection, but will not totally eliminate M paratuberculosis.
Milkborne outbreak of Mycoplasma mycoides subspecies mycoides infection in a commercial goat dairy.
A commercial goat dairy comprised of about 300 lactating does suddenly began to have a problem with polyarthritis in the kids and clinical mastitis in the does. The problem began 3 to 4 weeks following the introduction of 27 lactating does from a herd with a history of mastitis caused by Mycoplasma mycoides subsp mycoides (Mmm). Over 2 kidding seasons (about 12 months), approximately 170 kids and 70 does died or were euthanatized. Affected kids were 2 to 8 weeks old, had multiple warm swollen joints, body temperature of 40.8 to 41.5 C, marked weight loss, and pneumonia. All were lame and some experienced so much discomfort that they were unable to get up. The predominant necropsy finding was severe fibrinopurulent polyarthritis, but fibrinous pleuritis, fibrinous pericarditis, interstitial pneumonia, and bronchopneumonia also were found in some kids. Culturing of affected joints and of bulk tank milk yielded large numbers of Mmm. The outbreak was terminated by feeding heat-treated colostrum (56 C for 1 hr) and pasteurized milk to kids. Milk from the does was cultured repeatedly; by this procedure, the does shedding Mmm in the milk were identified and culled.