Veterinary session

The aim of this was study to examine the effects of different nitrogen sources (i.e.: micellar casein, urea, and defatted soybean meal) on growth performance of four selected insect species such as Jamaican field cricket ([JFC] Gryllus assimilis), house cricket ([HC] Acheta domesticus), yellow mealworm ([YM] Tenebrio molitor) and superworm ([SW] Zophobas morio).

Six isonitrogenous feeds composed of 3.52% nitrogen (22% crude protein) with 4 replicates/group were designed: Group 1 = 100% micellar casein, Group 2 = 75% micellar casein, 25% urea; Group 3 = 50-50% micellar casein and urea, Group 4 = 25% micellar casein, 75% urea, Group 5 = 100% urea, Group 6 = 100% defatted soybean meal). Beside the nitrogen sources corn starch was added as a carbohydrate source and feeds were provided ad libitum. In case of cricket species nymphs were either housed individually (n=4/group) or in groups (n=15/group). Larvae of YM (n=20/group) and SW (n=15/group) were group housed. The survival rate, body weight and feed consumption were measured weekly. Data were evaluated on week 4, 5, 14 in crickets, JM and SW, respectively.

The final mean individual body weight of crickets was the lowest in Group 5 and highest in Group 6. In general group housed crickets had better weight gain than individually housed crickets. Survival rate of individually housed crickets was 100% on week 4. Survival rates of group housed crickets were low (<30%) in both cricket species without significant difference between the groups.

In the larvae, the highest mean individual body weight was recorded in Group 1 (YM) and Group 6 (SW), while it was the lowest in Group 5 (YM, SW). The survival rate of YM was the highest in Group 3 (77.5%) and the lowest in Group 6 (18.8%). The survival rate of SW decreased with the increased urea inclusion level. It was the highest in Group 1 (75%) and the lowest in Group 6 (33.3%). The feed conversion ratio of YM and SW increased stepwise with the urea inclusion level. The feed conversion ratio was the best in Group 6 followed by Group 1, and it was the worst in Group 5.

The selected insect species are able utilise urea. However, the urea as an only nitrogen source resulted in low final body weight. In HC, JFC and YM urea can replace 25% of micellar casein without having negative effect on the growth performance and survival rate in comparison to 100% micellar casein group. In SW 25% urea inclusion level did not have effect on the final body weight but significantly decreased the survival rate in comparison to 100% micellar casein group.