Schothorst Feed Research, Lelystad, The Netherlands
In an experiment with 1,440 Cobb 500 female broiler breeders in the rearing period and with 1,260 Cobb 500 female and 126 Cobb 500 male broiler breeders in the laying period, the effect of low density feeds on performance of broiler breeders, egg composition, embryonic development and offspring performance were studied. The experiment included 3 treatments of 6 replicates each: a control group with practical AME-levels (treatment 1) and 2 groups in which the AME content of both rearing and laying feeds was decreased by 1.26 (treatment 2) or 2.51 (treatment 3) MJ/kg.
Results showed no differences in live weight of broiler breeders between treatments at the end of the rearing period. There was a tendency for a delayed development of the reproductive tract at the lowest AME level. During the laying period, treatment 2 gave a significantly higher laying percentage compared to treatment 1 and 3. Egg weight significantly increased with decreased AME. The increase in egg weight was accompanied by a significantly higher albumen/yolk ratio and a significantly better development of the area vitellina externa. Weight of day old chickens was also higher at lower AME levels and mortality was significantly lower with low density feeds at 60 weeks of age. It was hypothesised that increased egg weights, albumen/yolk ratios and embryonic development were due to changes in reproductive development and that changes in offspring performance were related to this.
I. Introduction
Due to the high growth potential, broiler breeders are fed restrictedly during the rearing and laying period in order to prevent health and reproduction disorders (Katanbaf et al., 1986; Hocking et al., 1994). The restriction in nutrient intake is particularly strong during the rearing period. In current feeding programmes for broiler breeders, the daily energy intake is restricted to 1.3 times the maintenance requirement in the period from week 12 to 15. This can result in chronic stress and hunger feeling (Gross and Siegel, 1983, 1986; Hocking et al., 1993; Savory et al., 1996; De Jong et al., 2002).
In order to reduce hunger feeling in broiler breeders, qualitative instead of quantitative restriction of feed and nutrient intake has been studied. In studies with pigs, it was found that dilution of feeds by inert materials or low energy feedstuffs might reduce chronic stress and hunger feeling (Brouns et al., 1994; Ramonet et al., 2000). However, studies in broiler breeders in this field have been limited and results were contradictory (Zuidhof et al., 1995; Savory et al., 1996; Savory and Lariviere, 2000).
Smulders and Enting (unpublished) reduced nutrient levels in broiler breeder feeds by 11 and 23 % by changing the feed composition. They found a significant reduction in heterophil/lymphocyte HL-ratios at six weeks of age and a significant reduction in mortality of broiler chickens from broiler breeders that were given low-density feeds. Based on these observations, a second experiment was carried out to get more insight of the effect of low density feeds on broiler breeder and offspring performance. This paper presents results of this second experiment.
II. Material and methods
(a) Animals and housing
In total 1,620 Cobb 500 day old female broiler breeders were bought from a breeding company (Cobb Europe, Putten, The Netherlands). Day old chickens were placed in 18 floor pens of 4.5 x 3 m with 90 chickens per pen. Each pen was fitted with laying nests that were closed during the rearing period. Each treatment was replicated in 6 pens.
In week 22, the number of female broiler breeders was reduced to 70 per pen and 7 male Cobb 500 broiler breeders were placed in each pen. Light, temperature and feeding schedules were according to guidelines of the breeding company. Feed levels were adjusted when live weight of the birds deviated more than 5 % from the recommended live weights. Birds were vaccinated according to the standard vaccination programmes and beaks were trimmed at day 4.
(b) Dietary treatments
The experiment included three treatments. In treatment 1, standard broiler breeder diets were given with an AME content of 10.88 MJ/kg in the rearing period and 11.72 MJ/kg in the laying period. In treatment 2 and 3, the AME content of the feeds was lowered by 1.26 and 2.51 MJ/kg respectively by inclusion of low density feedstuffs in the feeds (palm kernel meal, wheat bran, lucerne, wheat gluten feed and sunflower seed meal). In the low-density feeds, digestible lysine, calcium, retainable phosphorus and linoleic acid were lowered to the same extend as the AME content. The intake of first limiting nutrients was kept constant between treatments by increasing the feed allowance to the same extend as the AME content was decreased.
(c) Measurements
Live weight of the birds was determined every 3 weeks. Feed intake, laying percentage and egg weight were recorded on a daily basis. In week 24 and 26, 2 birds of every replicate were sacrificed by cervical dislocation and animal, oviduct and ovary weight were recorded, as was oviduct length. Albumen/yolk ratio and embryonic development were determined in 440 eggs of treatment 1 and 3 at week 29 and 41 weeks of age. Embryonic development was measured after 24, 36, 48, 72 and 264 hours of incubation according to stages published by Hamilton (1952).
(d) Statistical analysis
Data were statistically analysed by the analysis of variance method. Treatment means were compared by least significant differences (Snedecor and Cochran, 1967). The generalised model used in the analyses of variances included mean, block, treatment and residual variation. Differences between treatments were considered significant at P<0.05. Linearity between the AME content of feeds and performance parameters was tested with generalised model including mean, block, AME, AME2 and residual variation.
Results of the embryonic development were subjected to Student's t-test to find significant differences.
III. Results and discussion
During the rearing period, no significant differences in live weight were observed between treatments. At the end of the rearing period, the target weight of 2,550 grams was almost reached. In Table 1, the development of the reproductive organs between week 24 and 26 is given. In week 24, treatment 3 gave the lowest ovary and oviduct weights, which were not significantly different from treatments 1 and 2. The changes in oviduct and ovary development between week 24 and 26 gave significant differences between treatments. The faster growth of the reproductive tract between week 24 and 26 resembled a delay in the onset of the development of the reproductive tract when feed intake or day length is more restricted during rearing (Hocking, 1996; Bruggeman et al., 1999). This would indicate less efficient utilisation of the low density feeds.
Low density feeds did not have a negative effect in laying percentage (Table 2). In treatment 2, laying percentage was significantly higher compared to treatment 1. A similar effect was found by Zuidhof et al. (1995) when feeds were diluted with 15% oat hulls. During the laying period, no differences in live weight of the birds were observed. Egg weight increased when low density feeds were given. There was a significant linear relationship between the AME content of the feed and egg weight (P=0.002). The higher egg weight might be related to the higher growth rate of the reproductive tract between week 24 and 26. Smulders and Enting (unpublished) did not find an increase in egg weight when low density feeds were given only during the laying period.
Table 3 presents the effects of low density feed on albumen/yolk ratio and embryonic development.
The higher egg weight that was obtained with the low density feed was associated with a higher albumen/yolk ratio. The low density feed resulted in significant increase in the growth of the area vitellina externa and the embryo in eggs of 29 week old hens. In week 41, these differences were less clear. Day-old chicken weight was significantly higher for the low density diet in week 41. These results support the findings of Latour et al. (1996) and Ohta et al. (1998) that egg composition can affect embryonic and chick development. At the end of the growing period, the only significant differences in live weight of broiler chickens were observed with young breeders (Table 4). Mortality rate was significantly lower in broiler chickens of 60 week old broiler breeders when low density diets were given.
Based on the results of this study, it can be concluded that low density feeds can affect the development of the reproductive tract, egg production, egg size and composition, embryonic development and broiler performance. Differences in egg production may be related to digestibility of feeds. Egg size and egg composition seem to have an effect on embryonic development. It is hypothesised that differences in egg size and egg composition are due to differences in reproductive tract development.
References
Brouns, F., Edwards, S.A. and English, P.R. (1994).Applied Animal Behavior Science, 39: 215-223.
Bruggeman, V. (1998). PhD Thesis nr. 367, Catholic University Leuven, Belgium
De Jong, I. C., Van Voorst, S., Ehlhardt, D. A. and Blokhuis, H. J. (2002). British Poultry Science, 43: 157-168.
Gross, W.B. and Siegel, H.S. (1983). Avian Diseases, 27: 972-979.
Gross, W.B., and Siegel, P.B. (1986). Avian Diseases, 30: 345-346.
Hamilton, H.L. (1952). Lillie's development of the chick. Third edition. Henry Holt and Company, New York.
Hocking, P.M., Maxwell, M.H. and Mitchell, M.A. (1993). British Poultry Science, 34: 443-458.
Hocking, P.M., Bernard, R., Wilkie, R.S. and Goddard, C. (1994). British Poultry Science, 35: 299-308.
Latour, M.A., Peebles, E.D., Boyle, C.R., Doyle, S.M., Pansky, T. and Brake, J.D. (1996). Poultry Science, 75: 695-701.
Katanbaf, M.N., Dunnington, E.A. and Siegel, P.B. (1986). Poultry Science, 68: 352-358.
Ohte, Y., Tsushima, N., Koida, K., Kidd, M.T. and Ishibasi, T. (1999). Poultry Science, 78: 1493-1498.
Ramonet, Y., Bolduc, J., Bergeron, R., Robert, S. and Meunier-Salaun, M.C. (2000). Applied Animal Behaviour Science, 66: 21-29.
Savory, C.J., Hocking, P.M., Mann J.S. and Maxwell, M.H. (1996). Animal Welfare, 5: 105-127.
Savory, C.J. and Lariviere, J.-M. (2000). Applied Animal Behavior Science, 69: 135-147.
Snedecor, G.W. and Cochran, W.G. (1967). Statistical methods. Ames, Iowa, Iowa State University Press.
Zuidhof, M.J., Robinson, F.E., Feddes, J.J.R., Hardin, R.T., Wilson, J.L., McKay, R.I. and Newcombe, M. (1995). Poultry Science, 74: 441-456
From Proceedings of the "17th Australian Poultry Science Symposium", New South Wales, Australia.
