High feed costs arising from the use of expensive imported protein sources limits intensive broiler production by smallholder farmers in developing countries. This necessitates the search for cheaper locally available alternative protein-rich feedstuffs. However, these are invariably laden with anti-nutritional factors (ANFs), investigation of strategies to counter the deleterious effects of which is of necessity. The aim of this study was to investigate marula (Sclerocarya birrea A. Rich. subsp. caffra) seed cake (MSC) as an alternative dietary protein source for broiler chickens at finisher phase and whether its deleterious effects on productive performance and carcass characteristics could be ameliorated through supplementation with DL-methionine or phytase. Two hundred and seventy 28-day-old Cobb 500 broilers weighing 1.60 kg were fed 18 treatment diets containing MSC (0, 200 and 300 g/kg) and DL-methionine [0.14% (Control), 0.28% (Low) and 0.56% (High)] or phytase [0% (Control), 0.01% (1000 FTU/kg; Low) and 0.02% (2000 FTU/kg; High)] for 16 days. Each treatment diet consisted of 3 replicates in experiments 1 and 2, with 5 birds per replicate. The birds in both experiments 1 and 2 (135 birds in each) were fed in a 3 x 3 factorial design, and ran concurrently. Dietary MSC decreased body weight gain (BWG; P < 0.01), feed conversion efficiency (FCE; P < 0.05), slaughter weight (P < 0.01) and weights of the heart (P < 0.05), neck (P < 0.05) and feet (P < 0.01) in DL-methionine supplemented broilers. Also, MSC decreased BWG (P < 0.01), feed intake (FI; P = 0.05) and slaughter weight (P < 0.001) in phytase supplemented birds. There was no ameliorative effect (P > 0.05) of DL-methionine or phytase nor were there any significant MSC x DL-methionine and MSC x phytase interactions on all performance parameters and carcass characteristics. Only a phytase-induced decrease in gizzard weight at 0 g/kg level of MSC in contrast to an increase in this parameter at both 200 and 300 g/kg levels was observed, resulting in a significant MSC x phytase interaction (P < 0.05) for this parameter. MSC increased weights of the gizzard (P < 0.001) and intestine (P = 0.001) in DL-methionine supplemented broilers and weights of the gizzard (P < 0.001), neck (P < 0.01) and feet (P < 0.01) in phytase supplemented birds. In conclusion, MSC deleteriously affected broiler productive performance and carcass characteristics which could not be ameliorated through DL-methionine or phytase supplementation.
Keywords: Marula (Sclerocarya birrea caffra) seed cake, anti-nutritional factors, DL-methionine, phytase, broilers, feed intake, productive performance, carcass characteristics