Improving the feed value of seaweed for broiler chickens using feed enzymes

Abstract

The study aimed to enhance the feed value of green seaweed (Ulva sp.) meal using exogenous feed enzymes in the diets of Cobb 500 broiler chickens. Chapter One provides the background, problem statement, justification, aims and objectives of the study. Chapter Two gives an overview of broiler chicken production as well as the nutritional profile and importance of seaweed in chicken feeds. It also provides an outline of the use of various exogenous feed enzymes in chicken diets and summarises the gaps and discordance that exist in literature. In Chapter Three, a preliminary feeding trial was conducted using 300, two-week-old male chicks (159.3 ± 11.76 g live-weight) that were bought from Montshego Chicken Farm (25o03'49” S, 26o15'64” E) in Zeerust (North West, South Africa). The objective was to determine the maximum tolerance level of dietary seaweed meal (SWM) in broilers. To this end, this experiment investigated the effect of incremental levels of dietary SWM on growth performance, blood parameters, internal organ sizes, and carcass and meat quality characteristics in Cobb 500 broiler chickens. Five dietary treatments were formulated by including 0, 20, 25, 30, and 35 g of SWM /kg of standard grower and finisher diets. The chicks were randomly allocated to 30 pens (experimental unit), which were replicated six times per dietary treatment. Neither linear nor quadratic trends (P >0.05) were observed for overall feed intake (FI), overall body weight gain, and carcass and meat quality attributes of Cobb 500 broiler chickens as SWM levels increased. However, overall gain-to-feed ratio [G:F, R2 = 0.192, P = 0.018] and spleen weights [R2 = 0.182; P = 0.020] linearly declined as dietary SWM levels increased. No linear or quadratic responses (P >0.05) were observed for serum biochemical and haematological parameters except for lymphocytes [R2 = 0.123, P = 0.042]. For meat shelf life, quadratic trends (P >0.05) were observed for pH on days 4, 5 and 6 of storage. Meat lightness (L*) linearly increased on days 1, 2, 3 and 7 of storage, whereas meat redness (a*) quadratically responded to dietary SWM levels only on day 3 of storage. In x conclusion, the optimum level of dietary SWM inclusion could not be determined based on the growth performance data. However, the linear decline in G:F suggests a need to pre-treat the SWM with exogenous feed enzymes to improve its protein and fibre digestibility. The purpose of Chapter Four was to assess the effect of dietary treatments pre-treated with fibrolytic multi-enzymes on growth performance, haemato-biochemistry, internal organs, and carcass and meat quality characteristics of Cobb 500 broiler chickens. The aim was to use fibrolytic enzymes to break down the fibre components of SWM and subsequently improve its utilisation by broilers. Three hundred and thirty (330), two-week-old male chicks (318.9 ± 16.12 g live-weight) were used in this study and randomly allocated in 30 pens (experimental units), with 11 birds per pen replicated six times. Five dietary treatments were developed as follows: a commercial grower or finisher diet containing 35 g SWM /kg (the maximum inclusion level investigated in Chapter 3) pre-treated with fibrolytic enzymes (Viscozyme® -L) at the rate of 0 (SW35), 2.0 (V20), 5.0 (V50), 7.5 (V75) and 12.0 (V120) g enzymes/kg SWM. No linear or quadratic trends (P >0.05) for overall FI, growth performance, blood parameters, and visceral organ weights in response to pre-treatment levels of fibrolytic enzyme were observed. However, linear increases for hot carcass weight [R2 = 0.176, P = 0.033] and cold carcass weight [R2 = 0.164, P = 0.040] were observed, as enzyme levels increased. Seaweed meal pre-treatment with fibrolytic enzyme levels did not influence (P >0.05) overall FI, physiological responses, carcass traits, visceral organs and meat quality parameters except for breast meat lightness (L*i). The control treatment SW35 promoted the highest L*i value (66.33) than diets V75 and V120, which did not differ (P > 0.05). The optimum level of the fibrolytic multi-enzyme pre-treatment of SWM could not be determined using growth performance, blood parameters, internal organs, and carcass and meat quality attributes of the Cobb 500 broiler chickens. Seaweed meal pre-treatment with fibrolytic enzymes alone was an ineffective strategy to increase its utilisation in broiler chickens. It was, therefore, hypothesised that poor protein digestibility, and not the xi incalcitrant fibre fraction, could be the reason seaweed utilisation is poor in broilers. To test this hypothesis, a combination of the fibrolytic multi-enzymes and a proteolytic monoenzyme was evaluated as a strategy to enhance the feed value of SWM for broiler chickens in Chapter Five. Synergistic effects of fibrolytic multi-enzymes and protease monoenzyme were investigated using growth performance, physiological responses, and meat quality attributes of Cobb 500 broiler chickens. Dietary treatments were formulated as follows: a standard chicken diet with 35 g SWM/kg diet (SW35); SW35 pre-treated with 12 g/kg fibrolytic enzymes (V120); V120 pre-treated with protease monoenzyme at 5 (VP50), 10 (VP100) and 15 (VP150) g protease enzyme/kg SWM. A total of 300, two-week-old chicks (239.3 ± 8.57 g live-weight) were randomly allocated to 30 pens (experimental units) with 10 birds per pen, replicated six times per dietary treatment. At six weeks of age, chickens fed with the SW35 treatment had the highest (P <0.05) feed intake (1144.5 g/bird) when compared to chickens fed with the VP50, V120 and VP150 diets. Neither quadratic nor linear trends (P >0.05) were found in relation to protease pre-treatment levels for growth performance and carcass attributes. Gizzard weight increased linearly (P <0.05), whereas calcium, symmetric dimethylarginine, meat pH24, and hue angle24 responded quadratically (P <0.05) to protease pre-treatment levels. Chickens reared on the SW35 treatment had the lowest phosphorus levels (3.37 mmol/L) as compared to the other diets. In conclusion, indicators of physiological and meat quality were not improved by seaweed pre-treated with a combination of fibrolytic and proteolytic enzymes in Cobb 500 broiler chickens. The use of fibrolytic and proteolytic exogenous feed enzymes is an ineffective strategy to improve the feed value of green seaweed meal in broiler chicken diets.