REDUCED CONCEPTION RATES IN DAIRY-CATTLE ASSOCIATED WITH SEROLOGICAL EVIDENCE OF LEPTOSPIRA-INTERROGANS SEROVAR HARDJO INFECTION

Fertility data from 673 cows in five dairy herds with a moderate to hi gh seroprevalence of microscopic agglutination titres (MAT) Of greater than or equal to 1:10 against Leptospira interrogans serovar hardjo w ere collated to assess the relationship between pregnancy rates and an tibody titres to serovar hardjo. A significant proportion of failures of conception (10 to 13 per cent, P<0.001) were associated with MATS o f 1:10 to 1:100; the overall pregnancy rate of the seronegative cows w as 28.5 per cent higher (P<0.001) than that of the cows with MATS Of g reater than or equal to 1:100. First service pregnancy rates showed a similar trend but the differences were significant (P<0.05) only in co ws with antibody titres greater than or equal to 1:30. An assessment o f other possible risk factors for reduced pregnancy rates, such as lac tation number and calving to first service interval, had no effect on the statistical results of the study or its conclusions.