Effect of taurine on lipid metabolism of broilers

Abstract

To evaluate the effect of taurine supplements on broiler lipid metabolism, two hundred and forty 1-day-old Avian broilers were randomly divided into five groups, each group with three replicates for 21 days. The groups were fed basal diets with 0 (control group), 0.05%, 0.10%, 0.15% and 0.20% taurine, respectively. The results showed that dietary taurine of 0.15% increased apparent metabolisable energy and crude fat digestibility (P<0.05), enhanced the activity of lipase in pancreas and small intestine (P<0.05); compared to the control group, 0.15% taurine significantly decreased the content of serum total cholesterol (TC), triglycerides (TG), free fatty acids (FFA), glucose (GLU) and liver TG, FFA (P<0.05), increased the content of serum high density lipoprotein cholesterol (HDL-C) (P<0.05). A total of 0.20% taurine remarkably decreased the content of serum TC, low density lipoprotein cholesterol (LDL-C), GLU and liver LDL-C, FFA (P<0.05), increased the content of serum HDL-C, serum lipoprotein lipase and liver hepatic lipase activity (P < 0.05). Considering the physiological and biochemical indexes above, adding 0.15% taurine was optimal.

Keywords:

• taurine
• broiler
• lipid metabolism
• activity of lipase
• serum
• liver

Introduction

Taurine (2-amino ethane sulfonic acid) is a free acid amino that is found in high concentrations in most types of animal tissues (Huxtable 1992). Numerous experiments using various animal models including rats, guinea pigs, rabbits and cats provided extensive proof of the hypolipidemic and antiatherogenic effects of taurine, the addition of taurine to the diet had clearly an effect on preventing the serum and liver cholesterol and triglycerides (TG) from pathological increasing, and reduced atherosclerotic lipid accumulation (Matsushima et al. 2003; Militante and Lombardini 2004). Mostly the broiler feeding with high-energy and high-protein diets lead to fat accumulation, then affect feed conversion and the meat quality of broilers. Previous studies on poultry involved in the role of taurine in lipid metabolism was minimal. The present study was an attempt to evaluate the effect of taurine supplement on broiler lipid metabolism and the possible supplemented dose.

Materials and methods

Animals and experimental diets

Two hundred and forty 1-day-old Avian broilers were divided randomly into five groups, each group with three replicates of 12 broilers for a 21-day trial. The groups were fed basal diets with 0 (control group), 0.05%, 0.10%, 0.15% and 0.20% taurine, respectively. The basal diets were formulated based on the recommendation for broilers (NRC 1994), and the composition and nutrient levels of experimental diet are shown in Table 1. The chicks were fed experimental diets and water ad libitum, vaccinated according to the normal immunisation procedures.

Table 1. Composition and nutrient levels of basal diets (air-dry basis)%.

Composition	0–3 Weeks	Nutrient levels	0–3 Weeks
Corn	58.00	ME (MJ/kg)	12.8
Soybean meal	28.20	CP	21.13
Wheat bran	5.00	Ca	1.00
Fish meal	3.50	Total P	0.71
Soybean oil	2.00	Available P	0.45
Dicalcium phosphate	1.00	Lys	1.10
Shell meal	1.30	Met + Cys	0.88
Salt	0.30
DL-Met	0.20
Premix^a	0.50
Total	100.00
^aThe premix provided following for a kilogram of diet: Cu 10 mg, Fe 75 mg, Zn 50 mg, Mn 110 mg, Se 0.2 mg, I 0.4 mg, VA 2250 IU, VD3 250 IU, VE 15.75 mg, VK3 1.50 mg, VB1 2.5 mg, VB2 7.5 mg, VB6 5 mg, VB12 0.025 mg, Biotin 0.10 mg, Pantothenate 15 mg, Nicotinic acid 50 mg, Folic acid 1.25 mg, Choline 1300 mg.

Metabolism trial

The metabolism trial using total faeces collection method was conducted with two broilers from each replicate to determine the apparent metabolisable energy (AME), dry matter (DM) and crude fat digestibility during 18–21 days. Samples of faeces, urine and feed were dried at 65°C for 48 h, grounded to pass a 1 mm screen with a mill. Samples were analyzed for DM and crude fat with the method of AOAC (1995). AME was calculated between the gross energy intake and subtract the energy excreted in excreta, energy determination with automatic calorimeter (WZR-1A, Changsha Bente Instrument Co., Ltd., China).

Sample collection

At the age of 21 days, two broilers from each replicate were selected randomly and blooded from their wing veins. Serum was separated by centrifugation on 3000 r/min for 10 min and stored at −20 °C. The chicks were killed by neck cutting, and their livers, pancreas and chyme in small intestine were removed, homogenated with normal saline (W/V = 1/4) for 60 s, freezed centrifugation on 5000 r/min for 10 min, the supernatant was stored at −20 °C.

Measurements

The serum and liver lipid biochemical indexes including total cholesterol (TC), TG, free fatty acids (FFA), high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), glucose (GLU), the activity of lipoprotein lipase (LPL) and hepatic lipase (HL) were determined according to the procedure of commercial kits provided by Nanjing Jiancheng Bioengineering Institute (China).

Lipase (triacylglycerol lipase, EC 3.1.1.3.) activity was assayed using the method described by Tietz and Fiereck (1966). One hundred lipase activity unit (Sigma-Tietz units) was equal to the 1 ml of 0.05 M NaOH required to neutralise the fatty acid liberated during 15 min of incubation with 4 ml of intestinal supernatant at 38 °C pH 7.5. Olive oil was used as the substrate in this assay.

Statistical analysis

Experimental data were analyzed by one-way ANOVA using SPSS 11.5 statistical program. The LSD was applied to compare the means of all treatments. Results were expressed as means±standard deviation.

Results

The effect of taurine on AME and crude fat digestibility of broilers are shown in Table 2. Dietary of 0.10%, 0.15% and 0.20% taurine increased the AME of broilers (P<0.05). Addition of 0.15% taurine increased crude fat digestibility (P<0.05).

Table 2. Effect of taurine on AME and crude fat digestibility of broilers.

Items	I	II	III	IV	V
DM (%)	66.21±1.41	66.64±1.03	68.31±1.06	68.27±0.79	66.84±0.18
AME (MJ/kg)	12.28±0.05^b	12.50±0.12^ab	12.72±0.15^a	12.81±0.06^a	12.66±0.12^a
Crude fat (%)	67.99±0.99^b	70.46±0.80^ab	72.42±1.32^ab	74.08±3.85^a	69.51±0.39^ab
Note: In the same row, values with same letter or no letter means no significant difference (P>0.05), with different letters mean significant difference (P<0.05). AME, apparent metabolisable energy.

The effect of taurine on the lipase activity of broilers are shown in Table 3. Addition of 0.15% taurine increased the activity of lipase in pancreas and small intestine (P<0.05). Taurine (0.20%) increased the activity of lipase in pancreas (P<0.05).

Table 3. Effect of taurine on the lipase activity of broilers (U).

Items	I	II	III	IV	V
Pancreas	671.29±44.20^b	688.38±28.36^b	754.38±25.87^bc	855.00±47.62^a	803.00±19.94^ac
Small intestine	56.86±6.75^b	60.63±4.06^b	67.14±5.22^ab	84.38±8.53^a	76.25±7.66^ab
Note: In the same row, values with same letter or no letter means no significant difference (P>0.05), with different letters mean significant difference (P<0.05).

The serum lipid concentrations in control and experimental animals are shown in Table 4. Taurine (0.10%) decreased the content of serum LDL-C, FFA (P < 0.05), increased the content of serum HDL-C, serum LPL activity (P<0.05). Taurine (0.15%) decreased the content of serum TC, TG, FFA, GLU (P<0.05), increased the content of serum HDL-C (P<0.05). Taurine (0.20%) decreased the content of serum TC, LDL-C, GLU (P<0.05), increased the content of serum HDL-C, serum LPL activity (P < 0.05).

Table 4. Effect of taurine on the serum lipid biochemical index of broilers.

Items	I	II	III	IV	V
TC (mmol/L)	2.69±0.15^a	2.51±0.19^ab	2.59±0.04^ac	2.01±0.03^b	2.16±0.32^bc
TG (mmol/L)	0.36±0.05^a	0.35±0.04^a	0.29±0.04^ab	0.22±0.02^b	0.31±0.04^ab
HDL-C (mmol/L)	1.58±0.21^b	1.75±0.16^bc	1.99±0.09^ac	2.12±0.15^ac	2.31±0.13^a
LDL-C (mmol/L)	4.15±0.44^a	3.21±0.24^b	2.80±0.24^b	3.13±0.20^b	3.18±0.21^b
FFA (µmol/L)	3268.42±677.68^a	2671.05±548.66^ab	1899.30±344.52^b	1475.79±112.26^b	2185.26±338.07^ab
GLU (mmol/L)	9.49±0.87^a	6.71±0.40^b	8.52±0.80^ab	6.99±0.58^b	7.02±0.56^b
LPL (U/ml)	3.01±0.92^b	4.88±0.82^ab	5.16±0.35^a	3.75±0.85^ab	5.16±0.28^a
Note: In the same row, values with same letter or no letter means no significant difference (P>0.05), with different letters mean significant difference (P<0.05).

The liver lipid concentrations in control and experimental animals are shown in Table 5. Taurine (0.10%) decreased the content of liver FFA, GLU (P<0.05), increased liver HL activity (P<0.05). Taurine (0.15%) decreased the content of liver TG, FFA (P<0.05). Taurine (0.20%) decreased the content of liver LDL-C, FFA (P<0.05), increased liver HL activity (P<0.05). Adding taurine seemed to reduce the content of liver TC, and tended to elevate HDL-C content, but the changes were not significant.

Table 5. Effect of taurine on the liver lipid biochemical index of broilers.

Items	I	II	III	IV	V
TC (mmol/L)	0.53±0.05	0.40±0.03	0.50±0.04	0.49±0.07	0.53±0.02
TG (mmol/L)	4.38±0.33^a	3.93±0.38^ab	3.85±0.28^ab	3.41±0.32^b	3.96±0.15^ab
HDL-C (mmol/L)	0.077±0.007	0.088±0.011	0.083±0.010	0.087±0.011	0.082±0.011
LDL-C (mmol/L)	0.078±0.010^a	0.068±0.006^ab	0.062±0.005^ab	0.073±0.006^ab	0.056±0.007^b
FFA (µmol/L)	3130.44±151.16^a	2475.36±180.20^ab	1844.20±179.76^b	2202.90±351.22^ab	1648.67±451.55^b
GLU (mmol/L)	4.07±0.46^a	3.90±0.43^ab	3.04±0.17^b	4.00±0.24^a	3.67±0.18^ab
HL (U/ml)	3.00±0.90^b	5.03±0.71^ab	5.16±0.35^a	4.00±0.89^ab	5.16±0.28^a
Note: In the same row, values with same letter or no letter means no significant difference (P>0.05), with different letters mean significant difference (P<0.05).

Discussion

Adding taurine could increase the AME and crude fat digestibility of 18–21-day broiler, the effect was similar to some studies reported that taurine promoted the growth performance and improved feed conversion (Tufft and Jensen 1992; Lee et al. 2004). The lipase activity of poultry pancreas was very low at born, and elevated along with growth (Nir et al. 1993), the insufficiency of lipase activity was a factor that restrict fat digestion and utilisation. The results of our experiment showed that taurine could enhance the activity of lipase in pancreas and small intestine, with adding 0.15% taurine significantly (P<0.05). Taurine conjugated with bile could promote fat emulsification and enhance lipase activity, then increased the digestibility of neutral fat, TC, fat-soluble vitamins and other fat-soluble substance, which improved feed conversion and promoted growth performance.

Our study showed dietary taurine could decrease the content of TC, TG, LDL-C, while increase the content of HDL-C in serum and liver of broilers. Bile-conjugated taurine promoted fat lipolysis and fatty acid formation, then significantly improved lipid metabolism. The hypolipidemic effect of taurine were associated with elevated cholesterol 7α-hydroxylase activity (the rate-limiting enzyme in the catabolism of cholesterol into bile acids), diminished ACAT (Acyl CoA: cholesterol acyltransferase) activity, up-regulation of LDL receptors in liver, and related acceleration of LDL turnover (Nakamura-Yamanaka et al. 1987; Murakami et al. 2002). LPL and HL were two key enzymes of lipoprotein metabolism. Anitha Nandhini et al. (2002), reported that the reduced TG in plasma and liver of rats were associated with the enhanced TG cleaning in peripheral tissues and the increased LPL activity. By increasing serum LPL activity and liver HL activity, taurine could enhance plasma TG hydrolysis and HDL maturation, then reduce the content of TG and TC.

The reduced of FFA, GLU content was related to taurine involved in insulin regulation. Insulin can regulate FFA metabolism, a defect in the ability of insulin to regulate the FFA metabolism could cause the increase of FFA levels. FFA was an important substrate for hepatic triglyceride synthesis, and a diminished insulin suppression of plasma FFA could lead to higher plasma triglyceride concentrations. It was found that taurine could combine with insulin receptor, then promote the uptake and use of GLU in muscle cells, enhance glycolysis and reduce the content of GLU and FFA in plasma. However, Latour et al. (2001), reported that there were no differences in circulating lipids of broiler breeders affected by diet, so the mechanism of taurine affects lipid metabolism of broilers need further study.

The study clearly showed that diets supplemented with taurine increased AME and crude fat digestibility of broilers, and this effect was partly from taurine enhanced the lipase activity in pancreas and small intestine. Taurine supplements decreased the content of TC, TG, LDL-C, FFA, GLU of serum and liver, and increased the content of serum HDL-C, serum LPL and liver HL activity. The optimal supplemented dose was adding 0.15% taurine in this experiment.