Supplementation with Calliandra calothyrsus improves nitrogen retention in cattle fed low-protein diets

Ruminant productivity in the tropical Africa has remained low despite decades of research on animal nutrition and introduction of new breeds of animals mainly because oflow-quality feeds available, especially during the dry season that is inefficiently utilised. This results in prolonged time for animals to mature and increased nutrient excretion to the environment.We conducted a study using yearling steers (n = 12, live weight (LW) = 161.8± 10.89 kg) in a 3 · 3 Latin square to evaluate the effect of protein supplementation and supplementation frequency on intake, digestibility, nitrogen (N) retention and microbial N supply in cattle consuming low-protein diets. The steers were maintained on ad libitum wheat straw (DM = 877± 5 g/kg, crude protein (CP) = 20.0 ± 1.1 g/kg), with supplemental protein supplied as air-dried Calliandra calothyrsus leaves (DM = 897 ± 3 g/kg, CP = 257.5 ± 4.1 g/kg on a DM basis). Samples of basal diet, supplement, refusals, faecal matter and urine were collected and analysed per treatment. Supplementation increased intakes by the steers (P < 0.001), with no difference between the two supplementation frequencies (P > 0.404). Steers lost bodyweight (P < 0.05) on all treatments, but less so when supplemented. Nitrogen losses was reduced (P < 0.001) with supplementation (–33.3% vs 15.7%, s.e.m. 0.06). The increased N balance in animals receiving supplemented diets indicated that N retention actually improves with increased protein supplementation in animals fed low-protein diets, implying that improving protein supply to animals fed submaintenance diets will not only ameliorate production losses, but will actually decrease non-enteric greenhouse gas production and environmental N losses per animal product unit obtained.