Reduced ovulatory and oestrous activity in zebu heifers following Trypanosoma vivax infection.

This paper describes a study on the oestrous and ovarian activity and responses to prostaglandin F2 alpha (PGF2 alpha) administration and artificial insemination in zebu heifers. Four cycling heifers were artificially infected with 5 x 10(6) Trypanosoma vivax organisms. Two heifers served as controls. Two injections of PGF2 alpha were given 11 days apart, commencing at the peak of parasitaemia in the infected animals, followed by artificial insemination 72 and 96 h after the second administration of PGF2 alpha. Sera were analysed for progesterone by radioimmunoassay, while ovarian activity and oestrus were determined by rectal palpation and visual observation, respectively. All the infected heifers developed the clinical disease. All control and infected heifers had progesterone profiles consistent with luteolysis and the occurrence of oestrus following the second administration of PGF2 alpha. Progesterone levels did not return to normal luteal values in infected animals, however, whilst they did so in control animals. No control or infected heifers became pregnant. The findings suggest that PGF2 alpha will induce a non-fertile oestrus in zebu heifers acutely infected with T. vivax. Re-ovulation is also inhibited within 22 days in a majority of infected animals.