1ITAVI, Paris, 2INRA, Surgères, 3INRA SRA, Nouzilly, 4 ITERG, Pessac, 5CETIOM, Pessac, 6PRIMEX, Languidic, 7CYBELIA, Paris
France
Since the banning of animal products from poultry feed, the oily fat problem has been exacerbated by the exclusive use of vegetable oils and, from now, should be taken into account when formulating feed. The synthesis of five experiments has made possible to relate the fatty acid profile of the abdominal fat and dietary fats with the carcass presentation.
The abdominal fat fatty acid profile was highly correlated with the lipids found in the diet. The more unsaturated the fats, the softer and oilier carcasses seemed. Polyunsaturated fatty acid contents accounted well for the visual scoring of carcasses (r2 = 0.64, ETR = 0.50, n = 27).
Introduction
In broiler chickens, the oily fat problem encountered in slaughterhouses causes technological incidents. Today, this problem is exacerbated by the exclusive use of vegetable oils resulting from the recent banning of animal fats and should be taken into account, from now, when formulating feed. Generally, the fatty acid profile of chickens' tissues reflects the composition of the ingested lipids. Significant correlations between the nature of dietary lipids and that of fatty and muscle tissues have been demonstrated, particularly for unsaturated fatty acids (Pinchasov et Nir, 1992; Caudron et al., 1993; Scaife et al., 1994). The main effect of an unsaturated dietary fat or oil is to induce the deposition, in body lipids, of polyunsaturated fatty acids that are not synthesized by chickens, namely linoleic and linolenic acids in fatty and muscle tissues, and long-chain polyunsaturated fatty acids in muscles (Lessire, 1995).
Changes in the fatty acid profile of fat deposits in chickens result in a modification of the carcasses' aspect. Carcasses scores indicate they are firmer and drier when feeds are supplemented with tallow (Edwards et al., 1973; Caudron et al., 1993). Conversely, chickens fed on unsaturated oils show carcasses with softer fats (Caudron et al., 1993).
As part of the ACTA-ICTA program, "Dietary lipids and quality of fatty and muscle tissues in broiler chickens", a series of experiments showed that the composition of the fatty acids incorporated in the muscle triglycerides and phospholipids is closely linked to that of dietary lipids (Gandemer et al., 1999 ; Viau et al., 1999). The increase in n-3 PUFAs in intramuscular lipids has low impact on their sensitivity to oxidation. This good oxidation stability allows the use of diets with high linoleic acid proportions (7% of total fatty acids) with no impairment of chicken organoleptic qualities (Viau et al., 2001).
The work presented here aims to define feed composition criteria in order to obtain an acceptable presentation of chicken carcasses at the slaughterhouse.
Material and Methods
Five successive experiments were carried out with a view to establish correlations between the fatty acid profile of the feed distributed to birds from day 22 to slaughter and the abdominal fat profile and visual quality of the carcass, following the distribution described in Table 1.
Feeds
The same starter feed (with a 5% corn oil content) was given to all birds, followed by a feed containing 8% of various fats: tallow, palm and copra oils, sunflower, oleic sunflower, corn and linseed (Table 2).
Feeds were manufactured at the "Station de Recherches Avicoles (INRA)" for experiments 1, 4 and 5, and in Sourches (Cybelia) for experiments 2 and 3. For experiment 1, eight experimental diets were distributed, each characterized by its fatty acid profile: A, B, C, D, E, F, G, and H (Table 3). The saturated/unsaturated fatty acid ratio varied in the first 7 treatments with the modification of the relative proportions of the two main dietary polyunsaturated fatty acids: linolenic acid, which varied from 2 to 10% and linoleic acid, which was kept to 40% (treatments A to D). Linoleic acid varied from 20 to 60% in substitution for oleic acid and linolenic acid was maintained to 2% (treatments E to G). A tallow-based diet, supplemented with saturated fatty acids and depleted in linoleic acid (15%), was used as a reference (H). The feeds tested for the following experiments are listed in Table 2. Additional diets were introduced to obtain intermediate profiles (I, M, J and K), which were slightly less saturated than H and reflected more the practice (prior to November 14, 2000).
In the last experiment, C16:0 intakes were maximized with the use of palm and copra oils (O, P, Q and R).
Monitoring and measures
Birds were weighed collectively by pen at day 21 and individually before slaughter. Feed consumption was monitored by pen. The various fatty acid profiles were determined by ITERG (Pessac) for oils, feed and abdominal fat mixtures sampled on 20 birds per treatment according standardized methods. Carcasses were systematically scored by several trained persons, from 1 (soft and oily fat) to 5 (firm and dry fat). A linear regression step by step was carried out to explain the carcasses score according to the polyunsaturated fatty acid contents.
Results and discussion
Growth performances barely changed with the nature of the lipids ingested. The abdominal fat percentages did not show significant variations between treatments. The abdominal fat fatty acid profiles were highly correlated with the lipids found in the feed, particularly with C16:0 (r = 0.97), C18:2 (r = 0.98) and C18:3 (r = 0.97), and to a lesser extent with C18:0 (r = 0.92) and C18:1 (r = 0.92) (Figures 1 to 3).
The carcass presentation score was correlated with the C16:0 content (r = 0.78) and with total polyunsaturated fatty acids (C18 :1 + C18 :2 + C18 :3) (r = -0,78). The more unsaturated the fats, the softer and oilier carcasses seemed. Therefore, polyunsaturated fatty acid contents in the feed account for the carcass scoring:
Carcass score = 5.756 - 0.11 C18:3 (%) - 0.04 C18:2 (%) - 0.03 x C18:1 (%)
r= 0.80, ETR = 0.50, n=27
The carcass scoring also depended on a polyunsaturated fatty acid synthetic variable (PUFA = C18:1 + C18:2 + C18:3):
Carcass score = 5.812 – 0.039 PUFA (%)
r= 0.78, ETR = 0.50, n=27
This evaluation was approximately equivalent. However, this equation gave less importance to C18:3 and did not take into account the proportion of polyunsaturated fatty acids between them. In order to obtain a proper carcass presentation (score > 3, moderately firm non-dry fat), the polyunsaturated fatty acid content should not exceed 72% of the dietary fat.
Conclusion
Thus, it is possible to use such equations when formulating feed in order to take into account the carcasses' visual and technological quality. The current practice, which consists in using 1 to 2% of palm oil in the feed, permits to meet these criteria and obtain good carcass presentations while maintaining a body fatty acid profile relatively unsaturated, therefore beneficial for the consumer.
References
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Gandemer G., Viau M., Maillard N., Lessire M., Juin H., 1999. Lipides alimentaires et qualité de la viande de poulet : influence de l'apport de quantité croissante d'acide linolenique (18 :3 n-3). 3èmes Journées de la Recherche Avicole, St Malo (France), 23-25/03/99, 403-406.
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Pinchasov Y. And Nir I., 1992. Effect of dietary polyunsatured fatty acid concentration on performance, fat deposition, and carcass fatty acid composition in broiler chickens. Poultry Sc., 71(9), 1504-1512.
Scaiffe J.R., Moyo J., Galbraith H., Michie W., Campbell V., 1994. Effect of different dietary supplemental fats and oils on the tissue fatty acid composition and growth of female broilers. Br. Poultry Sci., 35 (1), 107-118.
Viau M., Gandemer G., Meunier F., Lessire M., Juin H.,1999. nLipides alimentaires et qualité de la viande de poulet: influence de l'apport de quantité croissante d'acide linoléique (18 :2n-6). 3èmes Journées de la Recherche Avicole, St Malo (France), 23-25/03/99, 359-362.
Viau M., Juin H., Metro B., Le Borgne C., Meynier A., Bouvarel I., 2001. Lipides alimentaires et qualité de la viande de poulet : influence de la teneur en 18 :3n-3 des lipides alimentaires sur la stabilité à l'oxydation du muscle pectoralis major. èmes Journées de la Recherche Avicole, Nantes (France), 27-29/03/01, 265-268.
Project led by ITAVI, jointly financed by the research envelop of ACTA/MAP/MENRT, ONIDOL and ANDA, and carried out by the following organizations and companies : CETIOM, ITERG, INRA, CEMAGREF, EVIALIS, CCPA, CYBELIA, PRIMEX, INZO° and ONIDOL
From Proceedings of the "XVI European Symposium on the Quality of Poultry Meat" and the "X European Symposium on the Quality of Eggs and Egg Products", Saint-Brieuc Ploufragan, France.
