Aim The aim of this study was to investigate the effects of two growth-promoting implants (zeranol and oestradiol-17 beta) on performance and feed digestibility of finishing White Fulani cattle in the feedlot. This was with a view to determining an alternative means of enhancing cattle performance without grazing the animals. Methods A 60-day feedlot trial was conducted using 27 stocker White Fulani bulls that were allotted randomly to three treatment groups (i.e. non-implanted, oestradiol-implanted and zeranol-implanted) in a completely randomised experimental design. Cattle were offered a compounded feedlot ration consisting of 14% crude protein ad libitum. The bulls were weighed initially and fortnightly thereafter for the duration of the study. Coefficients of dry matter and nutrients digestibility were determined using lignin as an internal marker. Data were analysed using the general linear model procedure of ANOVA and mean values were compared using Fisher's least significant difference (l.s.d.(0.05)). Key results The average final liveweight, total weight gain, average daily gain (ADG) and average daily feed intake (ADFI) of implanted feedlot cattle were higher (P < 0.05) than for non-implanted cattle; and higher in oestradiol-implanted cattle compared with zeranol-implanted ones. The ADG was 29.16 and 20.48% higher, and the ADFI was 35.06 and 18.18% higher for oestradiol-implanted and zeranol-implanted feedlot cattle, respectively than for non-implanted cattle. Irrespective of the treatment, feed conversion ratio of experimental bulls remained below the range (4.5-7.5) established for feedlot beef cattle; an indication of better efficiency of feed utilisation by White Fulani cattle. The apparent digestibility of dry matter (59.76-64.31%) of the feedlot ration was in the order: non-implanted = oestradiol-implanted > zeranol-implanted while the apparent digestibility of crude protein (73.91-77.99%) was in the order: non-implanted > oestradiol-implanted = zeranol-implanted. Conclusions and implications The results of this study show that the use of an oestradiol implant in finishing zero-grazed White Fulani cattle was beneficial for improving growth performance. Both implanted and non-implanted cattle showed good coefficients of nutrient digestibility, indicating that the mode of action of the growth implants in enhancing performance characteristics does not depend on indices of digestibility.
