Towards the optimization of brown seaweed (Ecklonia maxima) for indigenous chickens using oyster mushrooms.

Abstract

Ecklonia maxima is a type of brown seaweed, commonly known as sea bamboo or Osbeck, which is found in aquatic ecosystems. Sea bamboo meal (SBM) could be used in chicken diets as a natural source of nutrients and phytochemicals such as polyphenols and terpenoids. However, its high fibre and secondary metabolites such as lectins, trypsin and alpha-amylase inhibitors, alginate, and phlorotannins content restricts the amount that can be incorporated into Boschveld cockerels' diets. Thus, this thesis aimed to enhance the feed value of SBM in the diets of Boschveld cockerels using oyster mushroom (Pleurotus ostreatus) spawn (OMS). A total of 225, four-week-old Boschveld cockerels (316.4 ± 23.01 g live-weight) were randomly assigned to 25 pens (experimental units), with 9 birds per pen replicated five times per dietary treatment (SBM: 0, 20, 40, 60 and 80) in a completely randomised design (CRD). The objective was to determine the effect of including varying levels of dietary SBM in a diet of Boschveld cockerels on growth performance, apparent retention (AR) of feed components, physiological (blood and viscera morphometry) responses, carcass characteristics, and meat quality . Five dietary treatments were formulated as follows: a standard grower diet containing 0 (SBM0), 20 (SBM20), 40 (SBM40), 60 (SBM60), and 80 g/kg (SBM80). The cockerel's initial body weights were measured at 5 weeks of age, and then subsequently weighed weekly to calculate average weekly body weight gain (BWG). Feed intake was measured daily and used to determine average weekly feed intake (FI). The gain-to-feed ratio (G:F) was calculated using the weekly BWG and FI data measured during the 11-week feeding trial. At 15 weeks and 6 days of age, blood collected from wing vein of two randomly selected birds per pen was used to determine the haematology and clinical biochemistry. At 11 weeks of age, two cockerels per pen were randomly selected for measurements of AR, while the remaining birds were slaughtered, visceral morphometry and meat quality were determined. The results showed neither linear nor quadratic effects (P >0.05) for overall BWG, G:F, AR of dry matter, organic matter, crude protein, neutral detergent fibre and acid detergent fibre, haematology and clinical biochemistry and meat quality in Boschveld cockerels as SBM levels increased. However, linear increases were recorded for overall FI [R2 = 0.397; P = 0.021], relative ceca weight [R2= 0.417; P = 0.013], duodenum length [R2 = 0.537; P = 0.04] and small intestine length [R2 = 0.305; P = 0.04]. Birds reared on the SBM0 diet had higher blood calcium levels (2.675 mmol/L) than those reared on diet SBM60 (1.834 mmol/L). In conclusion, dietary inclusion of SBM in Boschveld cockerels' diets increased overall FI, masses and lengths of proventriculus, caeca, duodenum, ileum and small intestines but did not have an effect on growth metrices, blood profiles, AR of proximate components, carcass characteristics, meat quality and stability attributes. From the previous experiments, the optimum inclusion level of dietary SBM could not be generated, thus, the inclusion level of 150 g SBM /kg diet was evaluated further in the next experiment. To counteract the anticipated negative effects of fibre, the SBM was inoculated with different levels of OMS. This experiment evaluated the proximate composition of SBM spent mushroon substrate and its potential impact when included in a diet of Boschveld cockerels using growth performance, physiological responses, and meat quality. A total of 324, four-week-old Boschveld cockerels (310.8 ± 13.98 g live-weight) were used. The cockerels were randomly assigned to 36 pens (experimental units), with 9 birds per pen to give six replicates per dietary treatment in a CRD. Six experimental diets were formulated as follows: a standard grower diet (CON); and CON containing 150 g/kg of SBM after inoculating with 0 (SMS0), 20 (SMS20), 30 (SMS30), 40 (SMS40) and 50% OMS/kg SBM (SMS50). Body weight gain increased linearly (P <0.05) in weeks 8, 11, 14 and 15 in response to SMS inclusion in the diet. Furthermore, the inclusion of SMS in the diet induced linear increases for final body weight [R2 = 0.197; P = 0.017] and breast weight [R2 = 0.197; P = 0.020]. However, a linear decline was noted for relative caecal weight [R2 = 0.176; P = 0.035]. Quadratic responses (P<0.05) were also recorded for white cell counts, platelets, lymphocytes, heterophils, monocytes, relative spleen weight, and large intestine lengths. Birds reared on SMS40 diet had a longer (P <0.05) caeca (21.12 cm) than those reared on CON and the other SMS treatment groups. For breast meat stability, there were significant dietary effects on meat pH on day 3,where all the SMS treatments promoted the least (P <0.05) pH values than CON. In conclusion, growth performance, slaughter and breast weights were improved by feeding Boschveld cockerels with a diet containing SBM-spent oyster mushroom substrate. Furthermore, the inclusion of SBM spent oyster mushroom substrates altered haematological parameters andrelative caeca weights without affecting the cockerel's overall health, serum biocheemistry and meat quality. The results of this study showed that the use of oyster mushroom spawn is an effective strategy to improve the feed value of sea bamboo meal for use in the diets of Boschveld cockerels.