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

This paper describes a study on the oestrous and ovarian activity and respo nses to prostaglandin F-2 alpha (PGF(2 alpha)) administration and artificia l 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 PGF(2 al pha) were given 11 days apart, commencing at the peak of parasitaemia in th e infected animals, followed by artificial insemination 72 and 96 h after t he second administration of PGF(2 alpha). Sera were analysed for progestero ne 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 ha d progesterone pro les consistent with luteolysis and the occurrence of oes trus following the second administration of PGF(2 alpha). Progesterone leve ls did not return to normal luteal values in infected animals, however, whi lst they did so in control animals. No control or infected heifers became p regnant. The findings suggest that PGF(2 alpha) will induce a non-fertile oestrus in zebu heifers acutely infected with T. vivax. Re-ovulation is also inhibite d within 22 days in a majority of infected animals.