The effect of feed consumption levels on growth performance and apparent digestibility of nutrients in White Pekin ducks

Abstract

An experiment was designed to contain eight feed consumption levels (ad libitum, 300, 330, 360, 390, 420, 450, 480 g/day/bird) to evaluate the effects of feed consumption levels on growth performance and apparent digestibility of nutrients for White Pekin ducks from 35 days to 42 days of age. Ninety-six 35-day-old male Pekin ducks were randomly assigned into eight treatments, each containing six replicate pens with two birds per pen. All birds of the treatment group 1 as the control group was fed ad libitum and the birds of the treatment groups from 2 to 8 were quantitatively fed by force-feeding. The feed intake was 300, 330, 360, 390, 420, 450, 480 g/day/bird for treatment groups 2 through 8, respectively. Results of growth performance showed that feed consumption levels affected final body weight and average daily gain significantly (P < 0.05) but not feed/gain (P > 0.05). Based on the broken-line regression model analysis with body weight gain data, the optimum feed consumption level for Pekin ducks was 414.2 g/day, which was close to group 6 (420 g/day) that achieved the best growth performance as compared with other groups. Apparent digestibility of nutrients did not differ significantly among the groups at the first 2 days of the experimental period (P > 0.05), whereas apparent digestibility of dry matter and crude protein significantly decreased (P < 0.05) with increasing feed consumption level at the final 2 days of experimental period. Therefore, the results indicated that excess feed consumption could not improve body weight gain further but make apparent digestibility of nutrients decline in overfed Pekin ducks.

Keywords:

• Pekin duck
• growth performance
• feed consumption level
• nutrient digestibility

View correction statement:

Corrigendum

1. Introduction

In the last decade, the world production of meat-type ducks has strongly increased from about 1.7 to 3.31 million tons. Asia is the biggest producer of meat-type ducks in the world (Evans 2004), and China is the largest producer of meat-type ducks in Asia (Pingel 2011). The White Pekin duck is one of the modern meat-type ducks and has high capacity for fatty acid deposition in breast muscle and abdominal adipose tissue as compared with Mule and Muscovy ducks during the force-feeding period (Chartrin et al. 2005; Chartrin et al. 2006b; André et al. 2007). In practice, force-feeding Pekin ducks is followed by the most farmers that produce ducks for roast in China because overfed ducks result in a well-known delicacy with a delicate texture and delicious flavor due to high levels of unsaturated fatty acids, which will improve the nutritive value of ducks (Bernacki & Adamski 2001). Roasting the overfed Pekin duck is a kind of cooking culture in China like foie gras in France, and there is a large number of roasted ducks in production every year. During the force-feeding period, for the sake of increasing fat deposition quickly, excess feed is overfed into the intestinal tract of Pekin ducks. However, excessive feed input in waterfowls negatively affects nutrients digestibility, absorption and utilization (Zhang et al. 2007), which results in a large amount of waste especially manure and litter, accumulation of these wastes causes pollution problems (Yokota 1976; Yokota & Ueda 1981). In fact, the focus of force-feeding ducks should be on maximizing duck production with minimum feed cost. Quantification of feed consumption during the force-feeding period is important to improve economic benefit through better feed utilization and less feed cost. At present, the optimal amount of feed consumption is not clear in overfed Pekin ducks and experimental data for the optimal feed consumption level during the force-feeding period is limited.

Therefore, the objective of this study was to investigate the effects of feed consumption levels on growth performance and apparent digestibility of nutrients in Pekin ducks to determine the optimum amount of feed consumption that should be followed to maximize the growth performance during the force-feeding period in roast duck production.

2. Materials and methods

The present research was approved by the Animal Care and Welfare Committee of the Institute of Animal Sciences in the Chinese Academy of Agricultural Sciences.

2.1. Preparation of diets

Male White Pekin ducklings hatched on the same day were obtained from Pekin ducks conservation base in China. They were fed a common starter diet containing 205 g protein/kg and 11.76 MJ ME/kg from hatching to 14 days and a grower diet containing 167.7 g protein and 12.14 MJ ME/kg from 15 to 35 days of age. All birds were force-fed an experimental diet based corn–soybean from 35 to 42 days of age. The experimental diet was formulated to include 134.7 g protein/kg diet, 12.43 MJ ME/kg diet and an external marker (Cr₂O₃ at 5.0 g/kg). Composition of the common diet and experimental diet are shown in Table 1.

Table 1. Composition and nutrient levels of experimental diets (% as-fed basis).

Item	Common starting diet (0- to 14-day-old)	Common growing diet (14- to 35-day-old)	Overfeeding diet (35- to 42-day-old)
Corn	62.20	72.00	80.80
Soybean meal	34.00	24.20	15.00
Dicalcium phosphate	1.50	1.00	1.30
Limestone meal	1.00	1.00	1.10
Premix^a	1.00	1.50	1.00
Sodium chloride	0.30	0.30	0.30
Chromic oxide	–	–	0.50
Total calculated values	100.00	100.00	100.00
Metabolizable energy^b, MJ/kg	11.76	12.14	12.43
Crude protein	20.50	16.77	13.47
Calcium	0.83	0.96	0.94
Available phosphorus	0.41	0.40	0.36
Methionine	0.48	0.42	0.24
Lysine	1.05	0.82	0.59

^a Premix provided the following per kg of diets: Cu (CuSO₄ 5H₂O), 10 mg; Fe (FeSO₄ 7H₂O), 60 mg; Zn (ZnO), 60 mg; Mn(MnSO₄ H₂O), 80 mg; Se(NaSeO₃), 0.2 mg; I (KI), 0.2 mg; choline chloride, 1000 mg; vitamin A (retinyl acetate), 3 mg; vitamin D₃ (cholecalciferol), 0.075 mg; vitamin E (DL-α-tocopheryl acetate), 20 mg; vitamin K₃ (menadione sodium bisulphate), 2 mg; thiamin (thiamin mononitrate), 2 mg; pyridoxine hydrochloride, 4 mg; cobalamin, 0.02 mg; calcium-D-pantothenate, 20 mg; nicotinic acid, 50 mg; folic acid, 1 mg; riboflavin 8 mg; biotin, 0.2 mg.

^b Values were calculated according to the AME of chicken's feed ingredients.

2.2. Animals and experimental design

Three hundred male White Pekin ducklings were conventionally reared on the floor for the first 5 weeks. During this period, the birds had free access to feed, and drinking water and lighting were continuous. The temperature was kept at 33°C from 1 to 3 days of age, and then it was reduced gradually to room temperature until 35 days of age. At 35 days of age, all ducks were weighed individually, and 96 birds with similar weights were selected from these ducks and were allotted to 48 raised wire-floor pens (1 m × 2 m) with two birds per pen according to similar pen weight. Ninety-six birds were allotted to dietary treatment by completely randomized design and there were eight dietary treatments, each containing six replicate pens with two birds per pen. All birds of the treatment group 1 as the control group was fed ad libitum and the birds of the treatment groups from 2 to 8 were quantitatively fed by force-feeding. The feed intake was 300, 330, 360, 390, 420, 450, 480 g/day/bird for treatment groups 2 through 8, respectively. Feed intake of treatment groups from 2 to 8 in the first 2 days was the same 260 g/bird at 35 days and 300 g/bird at 36 days of age. The main purpose was to initiate metabolic adaptation to force-feeding. Force-feeding was performed four times a day at 06.00, 12.00, 18.00 and 23.00 h. The diet was mixed with tap water (1:1.2) and introduced into the crop of ducks in the force-feeding room, temperature was 20∼24°C, and humidity was 65∼75%.

2.3. Growth performance and apparent nutrient digestibility

At the end of the 7-day force-feeding period, all the ducks were fasted overnight for 12 h and provided with water. The following morning, all ducks were weighed individually for measuring body weight gain and feed/gain of ducks. Apparent digestibility of nutrients was determined with chromic oxide (Cr₂O₃) as an external indicator. In the experimental diet, 0.5% of Cr₂O₃ was added and mixed to facilitate the determination of nutrients digestibility. The excreta from each replicate pen was collected for 2 consecutive days: from day 1 to day 2 for initial force-feeding period and from day 6 to day 7 for final force-feeding period. Excreta was collected every 8 h. Contamination (e.g., feathers) was carefully removed and the excreta was stored in containers at −20°C. Samples were collected from each replicate pen during the 2 day of excreta collection and then blended, dried at 65°C, ground to a homogenous powder with a disintegrator and then sieved using a 1-mm screen prior to analysis. The Cr₂O₃ content in the samples of the diets and excreta was analysed in duplicates spectrophotometrically after acid digestion (Divakaran et al. 2002). Energy, crude protein and moisture of diets and faeces were determined according to the Association of Official Analytical Chemists (AOAC 1984). Energy was determined using an adiabatic calorimeter (HR-15A adiabatic calorimeter, Changshan, China). Crude protein (N × 6.25) was determined using the Kjeldahl method after an acid digestion using an Auto Kjeldahl System (1030-Auto-analyzer, Tecator, Sweden). Moisture was determined by oven drying at 105°C for 24 h. The results presented on a dry matter basis. Apparent digestibility of dry matter, crude protein and gross energy of diets and faeces were calculated as follows:

2.4. Statistical analysis

Data were analysed as a completely randomized design by one-way ANOVA procedure of SAS software. When dietary treatment was significant (P < 0.05), means were compared using Duncan's multiple comparison procedure of SAS software (SAS Institute 2003). In study, broken-line regression model analysis (Robbins et al. 2006) was used to estimate the optimum amount of feed consumption based on body weight gain data using the NLIN procedure of SAS software (SAS Institute 2003). The model is as following:

where Y = growth performance (such as body weight gain), X = feed consumption level, R = the abscissa of the breakpoint, and R is taken as the estimated optimum force-feeding levels, L = growth index response to optimum feed consumption level and U = the slope of model.

3. Results

3.1. Growth performance

Table 2 shows the effects of feed consumption levels on growth performance of Pekin ducks. Initial live body weights ranged between 2522.58 g and 2559.25 g and were no significant difference among treatments (P > 0.05). The average daily feed intake of control group was 259.6 g/day. The final mean body weight and body weight gain were significantly higher in the force-fed groups compared with control group (P < 0.05). Final mean body weight and body weight gain increased significantly with increasing feed consumption level below the ration of 420 g/day (P < 0.05) and showed no significant differences above the level (P > 0.05). Feed/gain was not significantly different between the force-fed groups and the control group (P > 0.05). Broken-line analysis was used to estimate the optimum feed consumption level of Pekin ducks according to growth performance, the optimum feed consumption level for optimal body weight gain [Y = 107.7−0.2531 × (414.2−X), P = 0.0019, R² = 0.956] was 414.2 g/day (Figure 1).

Table 2. Effects of feed consumption levels on growth performance of Pekin ducks.^A

Treatment group	Feed consumption levels (g/day/bird)	Initial body weight (g/bird)	Final body weight (g/bird)	Body weight gain (g/day/bird)	Feed/gain (g/g)
Control	Ad libitum (259.6)	2522.58	3034.92^e	73.19^e	3.61
Group 1	300	2524.83	3082.25^d^e	79.63^d^e	3.73
Group 2	330	2533.50	3114.67^d	83.02^d	3.86
Group 3	360	2527.27	3221.30^c	98.43^c	3.44
Group 4	390	2538.67	3237.25^b^c	99.80^b^c	3.64
Group 5	420	2529.17	3286.67^a^b^c	108.22^a	3.53
Group 6	450	2533.17	3279.00^a^b	106.55^a^b	3.79
Group 7	480	2559.25	3329.09^a	108.43^a	3.91
SEM		4.42	12.75	1.65	0.04
P-value		0.5457	<0.0001	<0.0001	0.0573

^A Data were based on all ducks (n = 2 birds/pen; n = 6 pens/treatment); the experimental feeding period lasted 7 days from 35 to 42 days of age.

SEM: pooled standard error of the mean.

^a–e Mean values in the same column with no common superscript differ significantly (P < 0.05).

Figure 1. Relationship between body weight gain and feed consumption level using a broken-line regression model analysis. The break point is labelled with an arrow. It indicates the optimum feed consumption level.

3.2. Apparent nutrient digestibility

Apparent digestibility of dry matter, energy and crude protein of Pekin ducks are presented in Table 3. Apparent digestibility of dry matter, energy and crude protein of Pekin ducks were not significantly different in the first 2 days (P > 0.05). For the final force-feeding period, apparent digestibility of energy was not significantly different (P > 0.05), but there were significant differences in apparent digestibility of dry matter and crude protein of Pekin ducks (P < 0.05), and they decreased gradually with increasing feed consumption level.

Table 3. Effects of feed consumption levels on apparent nutrient digestibility of Pekin ducks.^A

		Day 1 to day 2			Day 6 to day 7
Treatment group	Feed consumption levels (g/day/bird)	Dry matter (%)	Energy (%)	Crude protein (%)	Dry matter (%)	Energy (%)	Crude protein (%)
Control	Ad libitum (259.6)	80.84	83.94	80.08	83.04^a	86.36	80.50^a
Group 1	300	80.80	84.20	76.26	82.34^a^b	85.60	76.14^a^b
Group 2	330	81.50	84.60	78.26	82.25^a^b	85.45	75.82^a^b^c
Group 3	360	81.06	84.13	76.50	82.16^a^b	85.62	78.36^a
Group 4	390	81.10	84.17	78.13	82.16^a^b	85.72	77.56^a
Group 5	420	81.37	84.49	79.61	81.66^b	85.43	71.60^b^c
Group 6	450	80.47	83.97	76.47	81.46^b^c	85.23	70.40^c^d
Group 7	480	81.24	84.59	78.06	80.32^c	84.51	65.49^d
SEM		0.096	0.08	0.45	0.17	0.14	0.89
P-value		0.1523	0.2082	0.2686	0.0054	0.1399	<0.0001

^A Data were based on all ducks (n = 2 birds/pen; n = 6 pens/treatment); the excreta from each pen was collected for 2 consecutive days: from day 1 to day 2 for initial force-feeding period and from day 6 to day 7 for final force-feeding period.

SEM: pooled standard error of the mean.

^a–e Mean values in the same column with no common superscript differ significantly (P < 0.05).

4. Discussion

The main purpose of force-feeding is to increase body fat deposition and produce ‘foie gras’ in ducks and geese. Overfeeding can cause a dramatic increase in body weight (Zanusso et al. 2003; Saez et al. 2009). Saez et al. (2009) and Hermier et al. (2003) reported that the different ducks genotypes (Pekin, Muscovy and Mule ducks) presented different susceptibility to overfeeding. Pekin ducks exhibited greater ability to synthesize fatty acid in Pectoralis major muscle and abdominal adipose tissue as compared to Muscovy ducks and Mule ducks (Chartrin et al. 2006a). This characteristic of overfed Pekin ducks was well utilized in the roast ducks production in China. Most studies suggested that overfeeding had a positive effect on growth performance in waterfowl (Fournier et al. 1997; Davail et al. 2000; Su et al. 2009). This study found similar results. In the present study, the final body weight and body weight gain were significantly higher in the force-fed groups than those in the control group (P < 0.05). The results showed that overfeeding resulted in an improvement in final body weight and weight gain, which was in agreement with other reports (Zanusso et al. 2003; Chartrin et al. 2005; Molee et al. 2005). However, body weight gain increased significantly with increasing feed consumption level below the ration of 420 g/day (P < 0.05) and showed no significant differences above the level (P > 0.05). The results indicated that excessive feed consumption could not improve body weight gain further in overfed Pekin ducks. The reason may be that apparent digestibility of dry matter and crude protein of Pekin ducks decreased gradually with increasing feed consumption level (Table 3). This was consistent with previous studies performed in poultry (Zhang et al. 2007). Previous results and our results indicated that increasing feed consumption until optimum level had a positive effect on growth performance in all species. We applied the regression model analysis that had been widely used for determining quantitative nutrient requirements in animal nutrition (Luo et al. 2006; Yuan et al. 2010; Zhu et al. 2012) to estimate the optimum amount of feed consumption for Pekin ducks in the roast ducks production. In this trial, based on the broken-line regression model analysis with the body weight gain data, the optimum amount of feed consumption for Pekin ducks was 414.2 g/day.

To our knowledge, no reports have been published in the literature regarding the effects of feed consumption levels on nutrient digestibility in waterfowl. Generally, high-feed consumption levels leads to high passage rate of the dietary material through the digestive tract, low digestibility and low absorption of nutrients (Puvanendran et al. 2003). In the present study, as we expected, apparent digestibility of dry matter, energy and crude protein of Pekin ducks were not significantly different between each force-feeding group and the control group in the first 2 days. But for the final force-feeding period, there were significant differences in apparent digestibility of dry matter and crude protein of Pekin ducks and they decreased gradually with increasing feeding level, whereas apparent digestibility of energy did not significantly differ. This result was contrary to the finding of Zhou et al. (1989), who observed that digestibility of nutrients was almost normal in Pekin ducks force-fed twice the amount of ad libitum intake. Different feeding practices have a great impact on nutrient digestibility of animals. Generally speaking, the nutrient digestibility would decrease when animals were overfed several fold the amount of ad libitum intake (Hogendoorn 1983). Our study suggested that the absorption rate would decline when Pekin ducks were fed with excessive feed. In fact, the decreased apparent digestibility of dry matter might have negative impact on the environment by increasing excretions of solids into water. The apparent nutrient digestibility of lipid was not considered because lipid content in the faeces was very low; thus, small analytical and/or sampling errors could greatly exaggerate the calculated nutrient digestibility of experimental ingredients.

5. Conclusion

Feed consumption levels had significant effect on growth performance of Pekin ducks, and excessive feed consumption could not improve body weight further but make apparent digestibility of nutrients decline in Pekin ducks. The optimum feed consumption level for Pekin ducks in the roast ducks production was 414.2 g/day by using regression analysis.

Funding

This work was supported by the Earmarked fund for the Modern Waterfowl Industry Technology System of China [CARS-43] and the Agricultural Science and Technology Innovation Program [ASTIP-ISS09].

Additional information

Funding

Funding: This work was supported by the Earmarked fund for the Modern Waterfowl Industry Technology System of China [CARS-43] and the Agricultural Science and Technology Innovation Program [ASTIP-ISS09].