ONSET AND DURATION OF ESTRUS RELATED TO THE TIME OF OVULATION AND FERTILITY IN A HERD OF NGUNI CATTLE IN SOUTH MOZAMBIQUE

In a Nguni-herd of 40 cows managed under extensive range conditions on an experimental farm in Southern Mozambique oestrus duration and ovul ation time was studied by intensive oestrus observation and transrecta l sonography of the ovaries. In 30 oestrus cycles an average durantion of standing oestrus of 25.4 h, an average interval between end of oes trus and ovulation of 12h was detected. The mean interval between AI a nd ovulation was of 23.7h for single inseminated cows and of 11.3 h fo r cows inseminated twice. The four month-pregnancy rate was 62.6%. The data indicate that the Nguni-cattle show an oestrus behaviour that is more similar to that of European cattle than to that of Zebu cattle. To obtain reliable fertility results after AI it is recommended to per form a first insemination 12h after detection of standing oestrus and repeat this insemination if the cow still presents oestrus symptoms th e next day.