TY - JOUR
T1 - Genetic correlations between pathogen-specific mastitis and somatic cell count in Danish Holsteins
AU - Sørensen, Lars Peter
AU - Mark, Thomas
AU - Madsen, P.
AU - Lund, M.S.
PY - 2009
Y1 - 2009
N2 - The aim of this study was to estimate genetic correlations (r(a)) between 2 lactation average somatic cell count (LASCC) traits and 6 different mastitis traits in 226,482 first-parity Danish Holstein cows that calved between 1998 and 2008. The LASCC traits were defined from 5 to either 170 d (LASCC_170) or 300 d (LASCC_300) after calving, and the mastitis traits were unspecific mastitis (all mastitis treatments, both clinical and subclinical, regardless of the causative pathogen) and mastitis caused by either Streptococcus dysgalactiae, Escherichia coli, coagulase-negative staphylococci (CNS), Staphylococcus aureus, or Streptococcus uberis. Variance components were estimated using bivariate threshold-Gaussian models via Gibbs sampling. The posterior means of r(a) between LASCC_170 and the mastitis traits were greatest for unspecific mastitis (r(a) = 0.71), followed by CNS, Strep. dysgalactiae, Strep. uberis, and E. coli (r(a) = 0.54 to 0.69) and were lowest for Staph. aureus mastitis (r(a) = 0.44). The genetic correlation between LASCC_300 and the mastitis traits were generally smaller (r(a) = 0.47 to 0.69). Caution should be taken when interpreting the results, however, because some posterior density intervals for r(a) were large (between 0.14 and 0.47 units). Phenotypically, Staph. aureus is known to be associated with high SCC and especially with subclinical mastitis through chronic infections, so the low r(a) between Staph. aureus mastitis and LASCC, compared with r(a) for the other pathogens, was not expected. Subclinical cases are usually submitted to dry cow therapy (not included in the present study), not treated at all, or wrongly recorded as clinical cases. Thus, the incidence of Staph. aureus mastitis is likely too low, and the genetic correlation between Staph. aureus mastitis and LASCC may therefore be underestimated in the present study. The results for the remaining pathogens were as expected, smallest for E. coli and larger but similar for Strep. dysgalactiae, Strep. uberis, and CNS. Selection for lower LASCC is expected to decrease the incidence of pathogen-specific mastitis, especially for Strep. uberis, Strep. dysgalactiae, and CNS and, to a lesser extent, for Staph. aureus and E. coli. Data recording should preferably be improved, and economic weights for the pathogen-specific mastitis traits should be estimated before implementing an udder health index that includes pathogen-specific mastitis traits.
AB - The aim of this study was to estimate genetic correlations (r(a)) between 2 lactation average somatic cell count (LASCC) traits and 6 different mastitis traits in 226,482 first-parity Danish Holstein cows that calved between 1998 and 2008. The LASCC traits were defined from 5 to either 170 d (LASCC_170) or 300 d (LASCC_300) after calving, and the mastitis traits were unspecific mastitis (all mastitis treatments, both clinical and subclinical, regardless of the causative pathogen) and mastitis caused by either Streptococcus dysgalactiae, Escherichia coli, coagulase-negative staphylococci (CNS), Staphylococcus aureus, or Streptococcus uberis. Variance components were estimated using bivariate threshold-Gaussian models via Gibbs sampling. The posterior means of r(a) between LASCC_170 and the mastitis traits were greatest for unspecific mastitis (r(a) = 0.71), followed by CNS, Strep. dysgalactiae, Strep. uberis, and E. coli (r(a) = 0.54 to 0.69) and were lowest for Staph. aureus mastitis (r(a) = 0.44). The genetic correlation between LASCC_300 and the mastitis traits were generally smaller (r(a) = 0.47 to 0.69). Caution should be taken when interpreting the results, however, because some posterior density intervals for r(a) were large (between 0.14 and 0.47 units). Phenotypically, Staph. aureus is known to be associated with high SCC and especially with subclinical mastitis through chronic infections, so the low r(a) between Staph. aureus mastitis and LASCC, compared with r(a) for the other pathogens, was not expected. Subclinical cases are usually submitted to dry cow therapy (not included in the present study), not treated at all, or wrongly recorded as clinical cases. Thus, the incidence of Staph. aureus mastitis is likely too low, and the genetic correlation between Staph. aureus mastitis and LASCC may therefore be underestimated in the present study. The results for the remaining pathogens were as expected, smallest for E. coli and larger but similar for Strep. dysgalactiae, Strep. uberis, and CNS. Selection for lower LASCC is expected to decrease the incidence of pathogen-specific mastitis, especially for Strep. uberis, Strep. dysgalactiae, and CNS and, to a lesser extent, for Staph. aureus and E. coli. Data recording should preferably be improved, and economic weights for the pathogen-specific mastitis traits should be estimated before implementing an udder health index that includes pathogen-specific mastitis traits.
U2 - 10.3168/jds.2008-1870
DO - 10.3168/jds.2008-1870
M3 - Journal article
C2 - 19528624
SN - 0022-0302
VL - 92
SP - 3457
EP - 3471
JO - Journal of Dairy Science
JF - Journal of Dairy Science
IS - 7
ER -