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Poult Sci 2007. 86:850-856
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METABOLISM AND NUTRITION

The Effect of Low-Density Diets on Broiler Breeder Performance During the Laying Period and on Embryonic Development of their Offspring

H. Enting*,1, T. A. M. Kruip{dagger},2, M. W. A. Verstegen{ddagger} and P. J. van der Aar*,3

* Schothorst Feed Research, 8200 AM Lelystad, the Netherlands; {dagger} Animal Sciences Group, Wageningen University, 8200 AB Lelystad, the Netherlands; and {ddagger} Animal Nutrition Group, Wageningen University, 6700 AH Wageningen, the Netherlands

3 Corresponding author: pvdaar{at}schothorst.nl


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
The effect of low-density diets on bird performance, egg composition, and embryonic development was studied with 2,100 female and 210 male Cobb broiler breeders from 25 to 60 wk of age. The experiment included 5 treatments. These included a control group with a normal density diet (ND, 2,800 kcal of AME/kg). Treatments 2 (LD11) and 3 (LD21) had a 11 and 21% lower nutrient density. Treatment 4 (LD11OP) had a 11% less dense diet, which was obtained by inclusion of other feed ingredients. In these 4 treatments similar diets were given during the rearing and the laying period. Treatment 5 combined LD12 in the rearing period and ND diets during the laying period (LD12-ND). Egg composition and embryonic development were measured in eggs of ND and LD21 birds at 29 and 41 wk of age. During the laying period from wk 25 to 60, live weights did not differ among treatments, except that birds fed LD11OP had lower live weights. A significantly higher rate of lay was provided by LD11 compared with ND. Egg weights were significantly higher when low-density diets were fed, particularly in LD11OP. Percentage of fertile eggs did not differ among treatments. Compared with the other treatments, LD11OP provided a significantly lower hatchability. We found that LD21 resulted in a better development of the area vitellina externa and heart and embryo weight at 29 wk of age. It was concluded that this was related to a higher egg weight and egg white proportion. This suggests that the amount of egg white in eggs of hens fed ND was limiting for embryonic development, particularly in eggs of young broiler breeders.

Key Words: broiler breeder • nutrient density • welfare • egg composition • embryonic development


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Weight gain is an important trait in selection programs for broiler chicken parent stock. This parameter has, however, a negative relation with reproductive performance (Hocking et al., 1994). Increased weight gain and fat deposition during the rearing period can lead to reproduction disorders during the laying period. To prevent this, feed intake is restricted in broiler chicken parent stock. The current levels of feed restriction can induce hunger feelings, and this may impair animal welfare (Hocking et al., 1993; Savory et al., 1996; De Jong et al., 2003). The daily energy intake during rearing can be restricted to a maximum of 1.3 to 1.4 times maintenance (our unpublished data). This equals about one-third of the ad libitum feed intake (Savory et al., 1996; De Jong et al., 2003). During the laying period, daily energy intake is restricted to 1.6 times maintenance as an average, which equals about 70 to 100% of the ad libitum feed intake (De Jong et al., 2003).

To alleviate effects of feed restriction on hunger feelings of broiler breeders, low-density diets have been used during the rearing period. So far, contradictory effects of these diets on animal welfare have been reported (Zuidhof et al., 1995; Savory et al., 1996; Savory and Lariviere, 2000; De Jong et al., 2005), and effects of low-density diets on animal welfare and performance during the laying period have been studied on a limited scale (Zuidhof et al., 1995; De Jong et al., 2005).

It was observed by A. C. J. M. Smulders (Schothorst Feed Research, Lelystad, the Netherlands) and H. Enting (unpublished data) that increased weights of eggs and day-old chicks were found when broiler breeders were given low-density diets during the rearing and laying period. Broiler chickens originating from these eggs had a higher initial growth rate and a significantly lower mortality rate compared with broiler chickens from parents given normal-density diets. Embryo production studies in dairy cattle and sheep have shown that growth conditions can affect performance, vitality, and mortality of offspring (Walker et al., 1992, 1996; Farin and Farin, 1995; Kruip and Den Daas, 1997). Wilmut and Sales (1981) and Kleemann et al. (1994) found that fetal development and animal health in dairy cattle and sheep can be influenced by growth conditions in the uterus. Based on these observations, it is hypothesized that egg size and egg composition can affect embryonic development and subsequent broiler chicken performance and mortality. Therefore, an experiment with various low-density broiler breeder diets was performed to investigate egg weight, egg composition, and embryonic development in addition to broiler breeder performance.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Birds and Housing
The protocol for the experiment was in agreement with standards for animal experiments and was approved by the Ethical Committee of Schothorst Feed Research. The experiment involved a total of 2,100 Cobb 500 female and 210 Cobb 500 male broiler breeders. The female birds were raised at Schothorst Feed Research. Male birds, 25 wk old, were obtained from a rearing company (De Kuikenaer Opfok, Delden, the Netherlands). During rearing, light, temperature, live weight, and feed allocation schedules of the breeder (Cobb Europe, Putten, the Netherlands) were used for both female and male birds.

During the laying period, birds were housed in 30 floor pens of 4.5 x 3 m each, with 70 female and 7 male birds per pen. These pens were in 2 identical light-tight compartments (15 pens per compartment). Each pen was equipped with 4 collective laying nests of 95 x 32 x 34 cm. Each treatment included 6 pens with 1 treatment pen per block.

Wood shavings were used as floor material (5-cm depth). Light and temperature schedules were according to the management guide of the breeding company (Cobb Europe). Lights were switched on at 0745 h and were turned off as the recommended day length was obtained. Birds were vaccinated for Newcastle disease and infectious bursal disease during the laying period according to a standard vaccination program (De Kuikenaer Opfok).

Feed and Water Supply
Feed was given to female birds by 1 automatic feeding line of 3.9 m in length per pen, fitted with 5 feed pans. Males received feed by 1 male feeder per pen. Feeds were given once a day at 0800 h at levels as recommended by the breeder (Cobb Europe).

Per pen, water was available by 1 bell-type drinker from 30 min before feed allowance until 30 min after the last pen had consumed the amount of feed given. In treatments with low-density diets, extra feed was supplied to provide the same AME intake in all treatments.

Dietary Treatments and Diet Composition
Table 1Go presents the treatments included in the experiment. In treatment 1 (ND), a standard broiler breeder diet was given with a calculated AME content of 2,800 kcal/kg. Treatments 2 (LD11) and 3 (LD21) had a 11 and 21% lower AME density. The density of first limiting nutrients in the diet of these treatments was also decreased by 11 and 21%, respectively. These lower densities were selected because of a preliminary study [A. C. J. M. Smulders (Schothorst Feed Research) and H. Enting (unpublished data)]. The lower nutrient densities were obtained by the inclusion of palm kernel meal, wheat bran, wheat gluten feed, and sunflower seed meal in the diet. Treatment 4 (LD11OP) also included a 11% lower density diet as in treatment 2, in which the nutrient density was decreased by inclusion of oats and sugar beet pulp. In our preliminary study, no effect on egg weight and offspring mortality were found when low-density diets were given during the laying period only [A. C. J. M. Smulders (Schothorst Feed Research) and H. Enting (unpublished data)]. Therefore, 1 additional treatment was included (LD12-ND). In this treatment, a low-density diet was given during the rearing period only, followed by a normal density diet during the laying period.


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  		Table 1. Overview of treatments during the rearing1 and laying period
 
The composition and calculated contents of the diets are given in Table 2Go. The composition of LD11 diets was intermediate to those of ND and LD21. In all low-density diets, the content of the first limiting nutrients, digestible Lys, Ca, retainable P, Na, and linoleic acid content, was decreased with the same ratio as the AME content. Feeds were provided in mash form and were milled with a 3-mm screen to obtain a similar particle size in all diets.


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  		Table 2. Composition and calculated contents of the experimental diets1
 
Measurements
Feed intake, rate of lay, egg weight, and mortality were recorded daily. Live weight of birds was recorded at 25, 30, 40, 50, and 58 wk of age. Fertility and hatchability of eggs were determined every 2 wk when birds were 25 to 58 wk of age. Each time, 150 eggs per replicate were hatched at a commercial hatchery (Cobroed, Lievelde, the Netherlands). In addition, at a breeder age of 29 and 41 wk, 40 eggs per replicate of birds on treatments ND and LD21 were incubated (Animal Science Group, Lelystad, the Netherlands). After 24, 36, 48, 72, 84, and 264 h of incubation, the development of the embryos was measured according to Hamilton (1952) in 8, 8, 6, 6, 6, and 8 eggs per replicate, respectively. The development of the area vitellina externa, the area vasculosa, and heart and embryo weights were measured. In eggs in which the embryonic development was measured, the white:yolk was determined as well.

Statistical Analysis
Data that were obtained from the broiler breeders in the laying period were analyzed by ANOVA (GLM procedure of GenStat 7.1, GenStat Committee, 2003). Block and treatment were used as factors in the statistical model for breeder performance data. The statistical model for egg composition and embryonic development parameters included incubation time besides block and treatment. Parameters were tested for normal distributions before analyses. Embryonic development data were analyzed on a logarithmic scale. Output data were expressed as means with SEM. Significant differences among treatments were indicated by a least significant differences procedure (Snedecor and Cochran, 1967). Differences among treatments were considered significant at P ≤ 0.05.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Bird Performance
Live weights of female and male birds are given in Table 3Go. Low-density diets gave a significant reduction in live weight of females in wk 30 when these diets were fed during both the rearing and laying period. No significant differences in live weight were found in wk 25 and 58 among hens on LD11, LD21, and ND. We found that LD11OP provided significantly lower live weights in female birds compared with all other treatments.


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  		Table 3. Effect of low-density diets on live weights of female and male broiler breeders during the laying period1 (g)
 
Male live weights were significantly lower with LD21 compared with ND in wk 30. In wk 25 and 30, male bird weight was significantly lower when LD11OP was given in comparison with ND. We found that LD12-ND and ND provided similar live weights for both female and male birds.

Laying Performance and Percentage of Fertile and Hatched Eggs
We found that LD11 provided a significantly higher rate of lay than ND (Table 4Go). Peak production in birds given LD21 was reached at a significantly higher age compared with birds on LD11 and ND. Egg weight increased significantly with LD11 and LD21 compared with ND. We found that LD11OP provided a significantly lower peak production than ND. The rate of lay during the entire laying period did not differ between these 2 diets. Compared with all other treatments, egg weight of birds given LD11OP was significantly higher. The rate of lay of birds on LD12-ND was intermediate to that of LD11 and ND birds. We found that LD11 and LD12-ND provided similar egg weights. From wk 25 to 30, the difference in egg weight was significant between these 2 treatments.


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  		Table 4. Effect of low-density diets on feed intake, egg production traits, and percentage of fertile and hatched eggs of broiler breeders from 25 to 60 wk of age1
 
The percentage of fertile eggs was similar in different treatments (Table 4Go). We found that LD11OP provided a significantly lower percentage of hatched eggs than LD11, LD12-ND, and ND.

Egg Composition and Embryonic Development
Results of egg content weights during incubation are given in Table 5Go. After 24 h of incubation, egg content weights were similar in eggs from birds given LD21 and ND. But from 36 h of incubation, however, egg content weight in LD21 birds was significantly higher than in eggs of ND birds. This indicates a lower weight loss in eggs from birds given LD21. We found that LD21 provided significantly higher eggshell weights than ND in wk 29 (P < 0.02) and in wk 41 (P < 0.05; results not given).


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  		Table 5. Weight of the egg contents of ND and LD21 in wk 29 and 41 during incubation (until 264 h)1
 
Eggs from LD21 hens had a higher white:yolk at 29 and 41 wk of age compared with hens on ND (Table 6Go). The difference in white:yolk in eggs of LD21 and ND hens was larger at 29 wk of age than at 41 wk of age. White:yolk of eggs from 41-wk-old hens were lower than of eggs from hens of 29 wk of age (P < 0.01).


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  		Table 6. White:yolk of eggs of ND and LD21 in wk 29 and 41 during the first 72 h of incubation1
 
Table 7Go presents the surface of the area vitellina externa during the early incubation process. Eggs from hens given LD21 showed a significantly larger area vitellina externa both at 29 and 41 wk of age compared with eggs from hens given ND. The largest differences were observed in eggs of 29-wk-old hens. We found that LD21 and ND provided a similar area vasculosa surface at 29 and 41 wk of age (data not shown).


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  		Table 7. Surface area of the area vitellina externa of embryos in eggs of ND and LD21 in wk 29 and 41 during the first 48 h of incubation1
 
At 29 wk of age, LD21 provided significantly higher heart and embryo weights compared with ND (Table 8Go). No differences were observed among the eggs of hens of different treatments at 41 wk of age. Heart and embryo weights were higher in eggs of broiler breeders of 41 wk of age compared with 29 wk of age.


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  		Table 8. Heart and embryo weights in eggs of ND and LD21 in wk 29 and 41 after 264 h of incubation1
 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
Low-density diets did not affect live weight of female birds during the laying period, when palm kernel meal, wheat bran, wheat gluten feed, and sunflower seed meal were used as components to lower the diet density. The use of oats and sugar beet pulp in the low-density diet (LD11OP), however, provided a significantly lower live weight, indicating that fiber type in oats and sugar beet pulp can affect live weight. We (unpublished data) found a lower-than-expected digestibility of the LD11OP diet.

Hens on LD11 showed a higher rate of lay compared with ND hens. A similar increase had been observed by Zuidhof et al. (1995) when broiler breeder diets were diluted with 15% oat hulls. In our LD21 birds and in birds given diets diluted with 30% oat hulls (Zuidhof et al., 1995), no increase in rate of lay was found. The higher-than-expected digestibility and AME content of LD11 (Enting et al., unpublished data) indicate that relatively small changes in the nutrient intake of broiler breeders affect performance. This was also found by Fattori et al. (1990, 1993), Attia et al. (1995), and Robinson et al. (1998).

Low-density diets provided a significant increase in egg weight. The largest increase in egg weight was observed when hens were given LD11OP. According to Al Bustany and Elwinger (1987), Shafer et al. (1996), Schutte et al. (1994), and Whitehead et al. (1991, 1993), amino acid and linoleic acid intake can have a strong effect on egg weight. Because LD11OP did not contain more digestible amino acids and linoleic acid than LD11, the increased egg weight cannot be related to this. In treatment LD12-ND, in which ND diets were given during the laying period in addition to LD11 during rearing, an increase in egg weight was observed compared with birds given ND. In an earlier study [A. C. J. M. Smulders (Schothorst Feed Research) and H. Enting (unpublished data)], no increase in egg weight was found when low-density diets were given during the laying period only. This indicates that feeding low-density diets during the rearing period can affect egg weight. We found a delay in the development of the reproductive tract when low-density diets were given during rearing, particularly when hens were given LD11OP (our unpublished data). The delay in development of the reproductive tract was also reflected in the higher age at which peak production was achieved on LD11 and LD11OP. In general, a delay in the onset of laying gives higher egg weights (Kwakkel et al., 1991; Hocking, 1996; Bruggeman et al., 1999). The results of this experiment indicate that low-density diets given during rearing increase egg weight, which is associated with a delay in reproductive tract development.

When birds were given LD11OP, a significant lower hatchability was observed in comparison with the other treatments. Morris et al. (1968) and Szczerbinska and Zubrecki (1999) found a lower hatchability with increasing egg weights. Therefore, the lower hatchability of eggs of birds given LD11OP might be the consequence of the higher egg weight, which can limit gas exchange during incubation.

Data of the incubation studies showed that the increased egg weight of hens on LD21 was due to an increase in egg white weight, giving a significantly higher white:yolk. The differences between white:yolk in eggs of hens given ND and LD21 cannot be related to differences in intake of first limiting nutrients during the laying period. Therefore, the origin of the differences in white:yolk probably has the same origin as the differences in egg weight. This indicates that differences in the development of the reproductive tract can affect egg composition.

The higher egg weight and white:yolk in eggs of hens on LD21 related to a higher growth of the area vitellina externa and heart and embryo weights during incubation. The largest effects were observed in eggs from young broiler breeders. The higher weight of the egg itself probably did not directly cause the increased growth rate of the area vitellina externa and the embryo in eggs from birds given LD21, because Hassan and Nordskog (1971), Washburn and Guill (1974), and Al Murrani (1978) found no positive relationship between egg weight and embryo weight until d 14 of incubation. Shanawany (1984) observed that an increased flock age was related to a faster embryo development rate and higher embryo weight. This was also found in the present experiment and by Yannakopoulos and Tserveni-Gousi (1987), Applegate and Lilburn (1996), and Christensen et al. (1996) in quail and turkeys. Based on the differences between white:yolk and embryonic development in eggs from hens given ND and LD21, it can be hypothesized that the amount of white in eggs of particularly young broiler breeder hens is a limiting factor in the development of the embryo. According to Noble et al. (1986a, b), Yaffei and Noble (1990), and Vajda et al. (1994), embryos from young broiler breeders suffer from a lowered lipid transfer from the yolk to the embryo and a lower metabolism of these yolk lipids. Because the higher amount of white in eggs from hens given LD21 was associated with a better development of the area vitellina externa, it can be hypothesized that more egg white might give a better yolk utilization. This may overcome negative effects in the development of embryos from young broiler breeders. However, because higher weight losses in eggs from hens given ND during incubation went together with a lower eggshell weight compared with eggs from hens on LD21, this can also play a role in the observed differences in embryonic development (Peebles et al., 2001).

From the results from this study, it can be concluded that low-density diets can improve laying performance and increase egg weight. The increase in egg weight is due to an increase in the amount of egg white. Low-density diets improve embryonic development, which is associated with an increase in egg weight due to an increased amount of egg white.


   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

2 Theo A. M. Kruip passed away on January 21, 2004. Back

Received for publication March 27, 2006. Accepted for publication October 7, 2006.


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 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
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L. F. Romero, M. J. Zuidhof, R. A. Renema, A. N. Naeima, and F. Robinson
Effects of maternal energetic efficiency on egg traits, chick traits, broiler growth, yield, and meat quality
Poult. Sci., January 1, 2009; 88(1): 236 - 245.
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