Accuracy of the diagnosis of functional corpora lutea through rectal palpations, seasonal variations of oestrous cycle length, and progesterone values in Fulani zebu

Mean oestrous cycle length was 23.1±5.4 days, longer cycles were observed in the wet (23.9±6.2) than in the dry season (22.4±4.7) (P>0,05). The rate of oestrous cycle detected by using vasectomized bull with a ratio of 2 bulls per 30 females was 95%. In both seasons, plasma progesterone (P4) levels were below 1 ng/ml from the day of oestrus (Day 0) till day 3 after oestrus, subsequently, values gradually increased till day 9 when they stabilised to a plateau level until day 16. Concentration of P4 than sharply decreased to reach levels similar to those of oestrus by day 21 and 23 for dry and wet season respectively. No significant difference (P>0.05) was observed in P4 values for the two periods. The overall accuracy of rectal palpation in assessing the presence/absence of a functional CL was 69.7%. The highest rate of correct diagnosis (80.9%) was obtained from day 3 to day 21 (di-oestrus), whereas from day 1 to 2 (meta-oestrus), and from day 21 to 22 (pro-oestrus) accuracy was 29.7 and 34.7% respectively, and the day of oestrus was 44.4%. When uterus tone was superimposed to the diagnosis of the CL, assuming that a tonic uterus indicate an animal either in pro-oestrus, oestrus, or in meta-oestrus phase it was estimated that probability correct diagnosis could increase to 85.2% and 81.9% for pro-oestrous meta-oestrous phase while the overall rate would have been 82.3%.