Effects of Dietary Exogenous Hydrophilic Emulsifier Supplementation on Growth Performance and Carcass Traits in Broilers

All experimental procedures involving animals were performed in accordance with the Animal Experimental Guidelines of the Seoul National University Institutional Animal Care and Use Committee. A total of 200 one day-old broiler (Ross 308), with an average body weight of 44.0 g were used for 5-week feeding trial at Seoul National University experimental farm. Broilers were allotted to each treatment in 5 replicates with 10 chicks per pen in a randomized complete block design. The birds were fed the experimental diets for 5 weeks (Phase 1: 0 to 3 weeks, Phase 2: 3 to 5 weeks). The experimental diets were formulated to meet or exceed the nutritional requirement of Korean Feeding Standard (KFS) for poultry (2007). However, experimental diet for 5 weeks intentionally contained less than 75 kcal of ME/kg compared to the dietary energy suggested by KFS for poultry (2007). Different levels of exogenous hydrophilic emulsifier were supplemented in the diets at 0, 0.025, 0.050, or 0.075% (Tables 1 and 2). Exogenous hydrophilic emulsifier was powder type of sodium stearoyl-2-lactylate (SOLMAX^®50). The product was provided by Kimin Inc. (Seoul, Republic of Korea).

All broilers were housed in a rice hull floored, equipped with a feeder and an automatic waterer and allowed ad libitum access to feed and water during the whole experimental period. The ambient temperature was maintained at 35°C for 2 days, 31°C in the first week and then temperature was gradually decreased by 2°C per week to 22°C at the end of the experiment.

Body weight (BW) and feed intake were recorded at the end of phase 1 and phase 2 to calculate the BW, body weight gain (BWG), average daily feed intake (ADFI) and feed conversion ratio (FCR).

A total of 20 5-week-old broilers were slaughtered for the anatomy trial. Five broilers were selected from each treatment at the end of the experiment. After slaughtering, liver, left breast muscle, left leg muscle samples were collected and weighed. Abdominal fat, considered to be that surrounding the gizzard and intestines, was carefully dissected and weighted. The relative weights of organs and muscle to live BW were calculated.

The experimental data were analyzed using the General Linear Model (GLM) procedure of SAS software (ver. 9.1; SAS Institute, 2004, Cary, NC, USA). Data on growth performance, a pen was considered as an experimental unit, while individual bird was the experimental unit for carcass data. Linear and quadratic effects for equally spaced treatments were assessed by measurement of orthogonal polynomial contrast. Statistical significance was set at P<0.05 and tendencies at 0.05≤P≤0.10.

The effects of different levels of dietary exogenous hydrophilic emulsifier on growth performance in broiler are presented in Table 3. During the Phase 1 (0 to 3 weeks), BW and BWG were decreased linearly (P<0.05) as dietary emulsifier level increased. However, the BW, BWG, and FCR for Phase 2 (3 to 5 weeks) were linearly improved (P<0.05) as dietary emulsifier level increased. For the overall period (0 to 5 weeks), BWG, and FCR were linearly improved (P<0.05) in proportion to dietary emulsifier level, while ADFI showed a tendency of quadratic response (P=0.09) by dietary emulsifier level.

The observed result of improved growth performance of broilers fed the diets with emulsifier supplementation for the overall period was consistent with the previous findings. Smulikowa et al. (1999) reported that there are significant positive effects of 1% crude rapeseed lecithin in 7 days old chickens. Zobac et al. (1998) also observed that a substantial increase of BW in 21 days old broilers was observed when lecithin was added to diets. Guerreiro (2011) reported that there was no effect of dietary emulsifier on the growth performance of 7-day-old broilers. Dietary emulsifier in broiler diet did not improve the performance of 7-day-old broilers due to their low lipase activity during this period (Jeason et al., 1992; Nir et al., 1993). Lipase activity is improved at 7-day-old broiler but it is less than matured chicken. Azman et al. (2004) found that added soybean oil or beef tallow in broiler diet with lecithin did not make any difference in performance during starter period (0 to 14 days). Marzooqi et al. (1999) demonstrated that inefficient digestion and absorption of fat have occured in young chickens due to a low level of endogenous lipase production. Also a low rate of bile salt synthesis in young chicks is considered a potential confounding factor (Jackson et al., 1971). In chickens the activity and net duodenal secretion of lipase increases as the chick ages (Noy et al., 1995). Nir et al. (1993) observed that fat absorption increases with bird age, as young broilers have a physiological limitation to absorb that nutrient. Those physiological limitations of the digestive system of poultry may be overcome using endogenous and/or exogenous strategies to maximize feed digestion and absorption. Thus, dietary exogenous hydrophilic emulsifier could improve the growth performance of broilers during phase 2 (3 to 5 weeks). The experimental diets were formulated to meet or exceed the nutritional requirement of Korean Feeding Standard (KFS) for poultry (2007). However, experimental diet intentionally contained less than 75 kcal of ME/kg compared to the dietary energy suggested by KFS for poultry (2007) to show the benefit through the addition of dietary exogenous hydrophilic emulsifier, metabolizable energy (ME) in KFS for poultry (2007) was 3,100 and 3,150 kcal of ME/kg for phase 1 (0-3 week) and phase 2 (3-5 week), respectively. And metabolizable energy (ME) in experimental diet was 3,025 and 3,075 kcal of ME/kg for phase 1 (0 to 3 weeks) and phase 2 (3 to 5 weeks), respectively. Waewaree (2016) demonstrated that low energy diet with lysophospholipid could minimize detrimental effects by increasing in bird BW during grower period. Hyun(2014) observed that low energy diet with lysophospholipid could improve growth performance without growth retardation in broiler.

The effects of different levels of dietary exogenous hydrophilic emulsifier on carcass traits in broiler are presented in Table 4. As the dietary emulsifier level increased, a linear and quadratic increases in relative weight of abdominal fat were observed (P<0.01). However, there were no significant differences in relative weights of liver, breast and leg muscles. Guerreiro (2011) did not observe any difference in carcass traits of broiler when dietary emulsifier was supplemented. In addition, Cho et al. (2012) demonstrated that dietary emulsifier did not affect the relative weight of liver, breast meat, abdominal fat and gizzard in broilers. In contrast, Kassim and Suwanpradit (1996) reported that low energy diet in broiler chickens from 21 to 42 days of age significantly reduced the abdominal fat percentage and total body fat deposition. Rabie and Szilagyi (1998) also showed that the abdominal fat deposition was reduced significantly in low energy diet in broilers from 18 to 53 days of age. Regarding these results, deposition of abdominal fat was decreased by low dietary energy intake. The current study found that the dietary emulsifier level increased, a linear response was observed in relative weight of abdominal fat. It is possible that dietary emulsifier could partly be attributed to the improved absorption of dietary saturated fat from tallow (Vila and Esteve-Garcia, 1996). Fouad and El-Senousey (2014) observed that increasing dietary energy level to improve feed conversion leads to the increased deposition of fat. Sanz (1999) reported that abdominal fat weight was significantly affected by the dietary fat source. Moreover, inclusion of saturated fats in broiler diets produced higher fat accumulation both intramuscular fat and abdominal fat than unsaturated fat (Sanz, 1999). Vila and Esteve-Garcia (1996) suggested that abdominal fat deposition increased with increasing fat inclusion level in birds fed tallow. Current study showed abdominal fat level was between 0.93 and 1.9 g/100g BW, and it was lower range compared to Waewaree (2016) and Hyun (2014). Waewaree (2016) reported that 5 week-old broiler had 1.13-1.21 g/100g BW of abdominal fat, and Hyun (2014) observed that 5 week-old broiler had 1.72-2.18 g/100g BW of abdominal fat.