LEPTOSPIRA INTERROGANS SEROVAR HARDJO VACCINATION OF PREGNANT BEEF COWS AND SUBSEQUENT GROWTH RATE OF PROGENY

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Abstract
SUMMARY Five experiments with Leptospira interrogans serovar hardjo vaccine were carried out over a 6‐year period in pregnant Brahman‐cross and Sahiwal‐cross cows in the dry tropics of northern Queensland. The numbers ranged from 127 breeders aged 2 to 5 years in 1972 to 344 breeders aged 2 to 9 years in 1977. Half of the cows were vaccinated twice in midpregnancy except for 1977, when they were vaccinated once. In 1975–1977 inclusive, half of the heifers were given an additional dose of vaccine at commencement of mating.Vaccination caused a significant (P<0.01) reduction of prenatal loss but not of perinatal or postnatal losses. Growth rates of calves from vaccinated and unvaccinated dams were similar.