ABSTRACT

Background and Aim: Sustainable livestock production requires feeding strategies that reduce competition between human food and animal feed while improving the utilization of locally available biomass. Although non-conventional feed resources have been incorporated into ruminant diets as supplements, their exclusive use in complete diets remains poorly investigated, particularly under tropical island conditions. This study evaluated the effects of densified complete feed blocks (DCFB) formulated exclusively from non-conventional tropical feed resources on growth performance, nutrient utilization, digestibility, and nitrogen balance in Blackbelly ewe lambs, and compared performance with a conventional tropical grass-based feeding system.

Materials and Methods: Fifty Blackbelly ewe lambs (approximately 4 months old; initial body weight: 20.6 ± 1.56 kg) were randomly allocated to five dietary treatments (n = 10/group) with groups balanced according to initial body weight. Four diets consisted of DCFB formulated with sorghum straw combined with either molasses or sorghum grain and Leucaena leucocephala foliage or whole cottonseed, while the control diet comprised tropical grass hay supplemented with commercial concentrate. The growth trial included a 3-week adaptation period followed by a 4-week measurement period. Subsequently, six lambs per DCFB treatment were randomly selected for a digestibility and nitrogen balance study. Feed intake, average daily gain (ADG), feed conversion ratio, nutrient digestibility, nitrogen balance, and predicted growth based on digestible protein and energy intake were determined using standard analytical and statistical procedures.

Results: Dry matter (DM) intake ranged from 948.5 to 1,158.1 g/day. Diet 2 produced the greatest feed intake (p < 0.01), whereas Diets 1 and 3 achieved ADG (92.3 and 99.7 g/day, respectively) comparable to the control diet (92.7 g/day). Diets containing sorghum grain (Diets 2 and 4) resulted in significantly lower ADG (62.7 and 49.7 g/day, respectively) and poorer feed conversion efficiency (p < 0.01). DM and organic matter digestibility were similar among diets; however, crude protein digestibility was significantly reduced in sorghum grain-based diets (p < 0.001), whereas nitrogen retention was greatest in Diet 1 and lowest in Diet 4 (p < 0.01). Growth responses were more closely associated with digestible protein intake than with predicted energy supply, highlighting the importance of protein availability and nutrient synchronization.

Conclusion: DCFB formulated exclusively from non-conventional tropical feed resources successfully sustained growth performance comparable to that obtained with conventional high-quality tropical forage when appropriate combinations of rapidly fermentable carbohydrate and protein sources were used. Molasses-based formulations containing L. leucocephala or whole cottonseed demonstrated superior nutritional utilization, growth performance, and nitrogen retention compared with sorghum grain-based formulations. These findings demonstrate the potential of DCFB technology to enhance feed self-sufficiency, improve the valorization of agricultural and agro-industrial by-products, and support environmentally sustainable ruminant production in tropical island production systems.

Keywords: agro-industrial by-products, Blackbelly sheep, circular livestock systems, densified complete feed blocks, feed digestibility, nitrogen balance, non-conventional feed resources, tropical ruminant production.