Abstract
This study determined the effect of different immunocastration vaccine administration intervals on growth, carcass traits and testis development of ram lambs. The trial consisted of four treatment groups of 10 Dohne Merino rams per group. The trial was initiated when the rams were 5.5 months of age, with the control treatment being represented by intact (R) ram lambs. The treatments consisted of two (IC2), three (IC3) and four (IC4) week intervals between the primary and secondary vaccine administration and the total duration of the trial was 9 weeks. Slaughter age was fixed at 4 weeks post second vaccination for all treatment groups. Live body weight, scrotal circumference and temperature as well as injection reaction score and temperature were recorded weekly. At slaughter, the carcass and individual offal items were weighed, and shoulder circumference, neck circumference and subcutaneous backfat thickness measured 24h post-mortem. Vaccination interval was found to influence the average daily gain (ADG) between first and second vaccination; with this difference not observed when ADG was considered for the overall trial period. Vaccination schedule did not influence slaughter weight, carcass weight, subcutaneous backfat thickness, and linear carcass measurements. It was found that vaccination schedule had an effect on the percentage contribution of the gastrointestinal tract to total carcass weight, indicating a possible effect on gut fill. Differences in scrotal circumference between the immunocastrated groups and R were evident from week 4. From week 5, the scrotal circumferences of rams from the IC3 and IC2 treatment groups were smaller when compared to the control group, and remained smaller until the end of the trial. The immunocastration protocols followed in the study thus were successful in inhibiting testis growth and potentially function, without impacting negatively on the overall growth performance and slaughter performance of the ram lambs.
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