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Poult Sci 2007. 86:720-726
© 2007 Poultry Science Association
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METABOLISM AND NUTRITION

The Effect of Low-Density Diets on Broiler Breeder Development and Nutrient Digestibility During the Rearing Period

H. Enting*,1, A. Veldman*, M. W. A. Verstegen{dagger} and P. J. van der Aar2

* Schothorst Feed Research, PO Box 533, 8200 AM Lelystad, the Netherlands; and{dagger} Wageningen University, Animal Nutrition Group, PO Box 338, 6700 AH Wageningen, the Netherlands

2 Corresponding author: pvdaar{at}schothorst.nl


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
Low-density diets might help to reduce hunger feeling in restricted-fed broiler breeders. Effects of low-density diets on nutrient digestibility and bird development were studied in Cobb 500 broiler breeder hens from 4 wk of age until the onset of the lay (wk 26). The experiment included 4 treatments. The control treatment was a normal density diet (ND; 2,600 kcal/kg). Treatments 2 and 3 had a 12 and 23% lower nutrient density than ND (LD12 and LD23, respectively) through inclusion of palm kernel meal, wheat bran, wheat gluten feed, and sunflower seed meal. Treatment 4 also had a 12% lower nutrient density than ND but included oats and sugar beet pulp (LD12OP). Total daily intake of energy, digestible lysine, calcium, retainable phosphorus, sodium, and linoleic acid was kept constant in the low-density dietary treatments. Animal performance and development of the intestinal tract and reproductive tract were determined in addition to digestibility and feed passage rate. The LD12OP provided a lower AME and nutrient digestibility than calculated and was related to lower live weights. Birds given LD23 and LD12OP showed a faster ovarian and oviduct development between wk 24 and 26 compared with ND. At 22 wk of age, LD23 and LD12OP diets resulted in higher empty jejunum and ileum weights. Low-density diets did not affect intestinal tract contents and decreased mean retention time of the contents. It was concluded that low-density diets can affect live weight and development of digestive and reproductive tracts.

Key Words: broiler breeder • nutrient density • welfare • digestibility


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
To prevent or reduce health and reproductive disorders, broiler breeders with a high growth potential are feed-restricted during the rearing and laying period (Katanbaf et al., 1989a; Hocking et al., 1994). However, restriction of feed intake is particularly severe during the rearing period and can result in increased corticosterone levels and increased heterophil to lymphocyte (H/L) ratios in blood plasma of broiler breeders (Savory et al., 1996; De Jong et al., 2002). Furthermore, nutrient intake restriction can cause stereotypic object pecking, hyperactivity, and an increased feed intake motivation (De Jong et al., 2003). These changes indicate the occurrence of chronic stress and of hunger feeling (Gross and Siegel, 1983, 1986; Hocking et al., 1993; Savory et al., 1996; De Jong et al., 2003).

Feed restriction can be quantitative or qualitative. The latter has drawn specific interest because restriction of nutrient intake at higher levels of feed intake may alleviate or reduce welfare problems in broiler breeders. In this way, fatness can be avoided and reproductive performance can be maintained. Studies with pigs (Brouns et al., 1994; Ramonet et al., 2000) showed that dilution of diets by inert materials or low energy feedstuffs might reduce chronic stress and hunger feeling. De Leeuw (2004) found no effects of low-density diets at higher feed intake levels on sow performance. However, very few systematic studies in broiler breeders in this field have been done, and results were contradictory.

Zuidhof et al. (1995) diluted broiler breeders diets with 15 or 30% oat hulls and found a reduction in stereotypic behavior and H/L ratios compared with birds on similar nutrient intake levels from normal density diets. Hocking et al. (2004) observed decreased spot pecking in birds fed diets with 5% sugar beet pulp and 20% oat hulls. However, Savory et al. (1996) and Savory and Lariviere (2000) concluded on the basis of bird behavior and H/L ratios that diets diluted with different fiber-rich feedstuffs or softwood sawdust did not affect broiler breeder welfare.

In a recent unpublished experiment, A. C. J. M. Smulders (Schothorst Feed Research) and H. Enting (unpublished data) found a significant reduction in H/L ratios at 9 wk of age by lowering the nutrient density in broiler breeder diets by 12 and 23%. Reduced mortality of offspring was also found when low-density diets were provided. This suggests that chronic stress levels can be decreased by applying low-density diets. Therefore, a study was carried out in which effects of low-density diets with different fiber sources on stress, behavior, performance, and offspring vitality were examined. Breeder pullet growth performance and nutrient digestibility are also presented.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 REFERENCES
 
Stocks and Management
The protocol for the experiments was in agreement with standards for animal experiments and was approved by the Ethical Committee of Schothorst Feed Research. A total of 2,700 1-d-old Cobb 500 female broiler breeders (Cobb Europe, Putten, the Netherlands) were used. Animals were randomly placed in 30 floor pens of 4.5 x 3 m each with 90 chickens per pen. These pens were located in 2 identical light-tight compartments (15 pens per compartment) and had wood shavings (5 cm depth) as litter. Each of 4 treatments (see below) was applied from 4 to 24 wk of age, with pen as a block. Treatment 2 included the double amount of replicates because this treatment was followed by 2 different treatments during the laying period. Thus, there were 6 pens per treatment per compartment for treatment 2 and 3 pens per treatment per compartment for the other treatments.

Light and temperature schedules were according to recommendations of the breeder. Lights went on at 0745 h and were turned off as the recommended day length was reached. A light intensity of 5 lx was applied at animal level. Birds were vaccinated according to the standard vaccination program (De Kuikenaer Opfok, Delden, the Netherlands), and beaks were trimmed at 4 d of age.

Feed was provided at 0800 h each day. Five feeders were available per pen. The amount of feed given to the birds was in accordance with breeder recommendations. Water was available via 1 bell-type drinker per pen. Water was given from half an hour before feed supply until half an hour after feed was consumed in the pen with the longest feed consumption time.

In wk 20, in total 120 female broiler breeders were selected at random and placed in digestibility cages in another light-tight compartment. There were 2 birds per cage, 3 cages per replicate, and 5 replicates per treatment in the digestibility study. Water intake was restricted to 2.5 times the feed intake in the digestibility study.

Dietary Treatments
The experiment included 4 treatments. From wk 0–3, all birds were given the same standard phase 1 diet. After that the treatment diets were given. In treatment 1, normal density (ND) phase 1 and phase 2 diets were given in wk 4 to 6 and in wk 6 to 26, respectively. In treatments 2 and 3, the nutrient density of the diets was lowered by 12 (LD12) and 23% (LD23), respectively. This was done by inclusion of palm kernel meal, wheat bran, wheat gluten feed, and sunflower seed meal in these diets. The lower densities were chosen on the basis of preliminary studies. In treatment 4 the nutrient density of the diet was decreased by 12% using oats and sugar beet pulp (LD12OP). Feeds were provided in mash form. Compositions and calculated contents of the diets are presented in Table 1Go. In the digestibility study, 3% insoluble ash and 0.15% Cr2O3 were used as markers in the diets presented in Table 1Go.


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  		Table 1. Composition and calculated contents of the experimental diets (g/kg)
 
In the low-density diets, digestible lysine, calcium, available phosphorus, sodium, and linoleic acid were lowered to the same extend as AME. The amount of feed offered in treatments 2, 3, and 4 was increased by the same percentage as the dietary AME content was decreased compared with treatment 1. In this way, a similar daily intake of first limiting nutrients was obtained for the different treatments.

Measurements
Live weight of birds was determined every 3 wk, and mortality was recorded daily. From wk 18 onward, 2 birds per room were killed at random per week to determine the time at which the ovary and oviduct started to develop. In wk 24 and 26, 2 birds per replicate (12 per treatment) were killed by cervical dislocation, and the weights of the bird, oviduct, and ovary were recorded, as was oviduct length.

After an adaptation period of 2 wk starting at 20 wk of age, excreta were collected semiquantitatively in the digestibility study conducted for 4 consecutive days. Excreta were collected twice a day, and samples were pooled per replicate. During the period of excreta sampling, feed samples were taken every day. These samples were pooled for 4 d. In feeds and excreta, dry matter, crude protein, crude ash, crude fat, crude fiber, acid insoluble ash, and gross energy were determined according to ISO 6496 (ISO, 1999b), ISO/DIS 16634 (ISO, 2004), ISO 5984 (ISO, 1978), ISO 6492 (ISO, 1999a), NEN 5417 (NNI, 1988), ISO 5985 (ISO, 1978a), and ISO 9831 (ISO, 1998).

At the end of the excreta collection period, all 6 birds per replicate were killed between 1 and 7 h after feeding by injection of 0.5 mL T61 (Intervet, Boxmeer, the Netherlands) in the wing vein. The alimentary tract was removed after euthanasia. Crop, proventriculus and gizzard, duodenum, jejunum, ileum, ceca, and colon were separated and weighed. Contents were collected, and empty parts of the alimentary tract were weighed. Intestinal contents of 2 birds were pooled so that 3 samples per replicate were obtained. Mean retention time of the feed in the different sections of the alimentary tract was calculated according to Weurding et al. (2001).

Statistical Analysis
Data were analyzed by ANOVA with block and treatment as factors and replicates as experimental units (GLM procedure of GenStat 7.1, GenStat Committee, 2003). Output data were expressed as means with standard error of means. Treatments were compared by least significant differences (Snedecor and Cochran, 1967). Parameters were tested for normal distributions before analyses. Differences between treatments were considered significant at P ≤ 0.05.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
REFERENCES
 
Bird Performance
Results of live weight and feed intake of broiler breeder hens are presented in Table 2Go. At 22 and 26 wk of age, the target weights of respectively 2,550 and 3,110 g were reached in birds given ND, LD12, and LD23. In wk 6, 12, and 18, live weight in hens given LD23 was higher than in hens fed ND. The LD12OP supported a lower live weight at the end of the rearing period compared with the 3 other treatments, although feed intake was increased by 2.5% compared with the target after 18 wk of age. Mortality was low during the entire rearing period (2.2%) and almost absent during the first 6 wk (0.1%, data not shown).


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  		Table 2. Effect of low-density diets on live weight and feed and AME intake in different treatments during the rearing period1
 
Digestibility
Digestibility coefficients of all nutrients and AME contents were lower when nutrient density of the diets decreased (Table 3Go). The LD12OP provided lower digestibility coefficients for organic matter, crude fat, and N-free extract compared with LD12. Also, the determined AME content of LD12OP was lower than that of LD12. This lower AME content resulted in a 4% lower AME intake in comparison with ND, which explains the lower live weight at the end of the rearing period. The determined AME levels of ND, LD12, and LD23 were higher than the calculated levels. This can be attributed to the fact that calculated AME levels for growing birds were used for diet formulation, and these are lower than the calculated AME levels for adult birds (CVB, 2003). Although hens fed LD12 had a 3.1% higher total AME intake compared with hens given ND, no differences in live weight were observed between these treatments. This is probably due to a similar total intake of first limiting digestible amino acids in birds provided LD12 and ND.


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  		Table 3. Effect of low-density diets on digestibility coefficients of organic matter, crude protein, crude fat, and N-free extract (NFE) and AME content of the experimental diets1
 
Rogel et al. (1987) observed an increased starch digestibility when oat hulls were included in the feed. Svihus and Hetland (2001) found a similar positive effect on starch digestibility when diets were diluted with cellulose. Combined with the results of the present study, it appears that the inclusion of some fiber rich feedstuffs may result in higher digestibility coefficients and thus higher AME content than expected. The observed differences in determined AME content between treatments emphasize the importance of digestibility studies when effects of low-density diets on performance are studied. These differences may have carry over effects on laying performance (H. Enting, T.A.M. Kruip, Animal Sciences Group, Wageningen University, Lelystad, the Netherlands, and P. J. van der Aar, unpublished data).

Feed Passage Rate
Within the different components of the alimentary tract, the largest amounts of chyme, expressed as percentage of live weight, were found in proventriculus and gizzard (Table 4Go). The duodenum content was lower in LD23 as compared with all other treatments and was lower in LD12 than in ND. In treatment LD12OP, a higher ileum content was found compared with ND or LD23. Low-density diets resulted in shorter mean retention times in almost all sections of the alimentary tract (Table 5Go). These differences were significant in jejunum and colon. According to results of Leeson et al. (1991), the shorter mean retention times seem to be related to an increase in the insoluble fiber content of the low-density diets. Compared with LD12, LD12OP gave a longer mean retention time in the ceca. This effect can be attributed to the higher viscosity of these diets or to an increased fermentation of this fibrous diet (Smits, 1997).


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  		Table 4. Effect of low-density diets on contents (% of live weight) of different parts of the alimentary tract in wk 221
 

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  		Table 5. Effect of low-density diets on mean retention times (min) of chyme in different parts of the alimentary tract in wk 221
 
In pigs, an increase in gut contents is associated with increased satiety (Brouns et al., 1994; Ramonet et al., 2000). Therefore, the small changes in alimentary tract contents and the reduction of the mean retention time with low-density diets that were observed in this study might indicate that these diets do not differ in satiety. However, De Jong et al. (2005) found a significant reduction in stereotypic pecking behavior and a significant increase in the time spent sitting in hens given LD23 during the first half of the rearing period. Furthermore, they found that birds on LD23 consumed less energy in the feed intake motivation test compared with birds given ND, and LD12OP birds consumed less than birds fed LD12. These findings indicate that LD23 and LD12OP diets may increase satiety. For the latter diet, this is also supported by findings of Hocking et al. (2004), who concluded that ratios containing sugar beet pulp can improve satiety and welfare. They related this to a higher water content in the intestinal tract and to higher water holding capacity of the diet.

It might be possible that a higher degree of satiety of low-density diets is more pronounced in an ad libitum feed intake situation like in the feed intake motivation test used by De Jong et al. (2005) and at relatively high feed intake levels compared with the ad libitum feed intake capacity. De Jong et al. (2005) found no effects of low-density diets on behavior when feed intake levels during rearing were below 1.5 times the maintenance requirement for energy.

Anatomical Composition
The empty weight of the jejunum and the ileum, expressed as percentage of live weight, was higher in birds given LD23 or LD12OP compared with birds on ND or LD12 (Table 6Go). The colon weight in LD12OP was higher in comparison with all other treatments. The increased weights might be related to an increased transport of the diet through the intestinal tract, as Svihus et al. (1997) observed with whole barley, or to an increased fermentation (Gaskins et al., 2002).


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  		Table 6. Effect of low-density diets on weight of empty parts (% of live weight) of the digestive tract in wk 221
 
Reproductive organ weights, expressed as percentage of live weight, at 24 and 26 wk of age are presented in Table 7Go. At wk 24, the oviduct weight was lower in hens given LD12OP diets compared with pullets on LD12 and LD23. The length of the oviduct in hens given LD12OP was shorter in comparison with all other treatments in this week. At 26 wk of age, no differences in ovary weight and oviduct weight and length among treatments were found. The increase in ovary weight between wk 24 and 26 was higher when LD23 or LD12OP were fed instead of ND or LD12. Increases in oviduct weight and length were higher on LD12OP compared with ND or LD12 and all other treatments, respectively.


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  		Table 7. Effect of low-density diets on ovary weight and oviduct weight (% of live weight) and length (cm per kg of live weight) in different treatments at 24 and 26 wk of age1
 
The delay in onset of growth of the reproductive tract on low-density diets resembles the delay in onset that has been obtained with a more restricted feed intake or day length during rearing (Kwakkel et al., 1995; Hocking, 1996; Bruggeman et al., 1999; Hocking and Robertson, 2000). Katanbaf et al. (1989b) observed a higher oviduct weight at onset of laying when feed intake of broiler breeders had been restricted more severely. Fattori et al. (1990, 1993) showed that even small reductions in feed intake can delay the development of the reproductive tract, which might explain the delayed onset of growth of the reproductive tract in hens given LD12OP compared with hens fed ND. However, this cannot explain the delayed onset in birds given LD23 because AME intake was equal to that in birds fed ND. On the basis of the results of the digestibility study, the digestible crude protein intake in LD23 hens was higher than in ND birds, but the total digestible lysine and methionine+cystine intakes were similar between these treatments. Therefore, it may be possible that a larger proportion of protein was used for energy in birds given LD23, resulting in a lower net energy intake compared with hens on ND.

Kwakkel et al. (1991, 1995) found that differences in the development of different tissues in rearing birds due to differences in nutrient intake without clear differences in live weight can affect laying performance. This implies that feeding of low-density diets during rearing might have an effect on performance during the laying period.

Based on the results obtained in this study, it can be concluded that low-density diets can affect live weight and development of the digestive and reproductive tracts of broiler breeders. The changes in these parameters can be related to a lower than expected digestibility and lower utilization of digested nutrients on low-density diets.


   ACKNOWLEDGMENTS
 
This project was funded by the Ministry of Agriculture, Nature and Food Quality, the Product Board for Livestock and Eggs, and the Product Board for Animal Nutrition.


   FOOTNOTES
 
1 Present address: Nutreco PRRC, Casarrubios del Monte, Spain. Back

Received for publication March 27, 2006. Accepted for publication October 9, 2006.


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 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
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