The use of animal by-products available in Portugal in diet formulations for rainbow trout

Abstract

The chemical composition and the potential nutritive value of two Portuguese Animal by-products. Poultry by-product and hydrolysed feather meal and Meat and bone meal were evaluated in diets for rainbow trout replacing fish meal protein at levels of up to 100%. In addition six Portuguese Brown fish meals produced by different fish meal processing plants were also evaluated. Their effects on growth performance, feed utilization efficiency, liver somatic index, blood parameters, and carcass composition of fish fed diets containing these products were assessed. Based on the results of these experiments a further trial was carried out in order to evaluate the three Animal by-products in a compound diet containing different combinations of these products. A commercial trout ration produced on a small scale in Portugal was used as an additional control.

In conjunction with these feeding trials monthly samples of the Poultry by-product and hydrolysed feather meal. Meat and bone meal and the six Brown fish meals were analysed over a one year period in order to evaluate their degree of variability.

The Poultry by-product and hydrolysed feather meal successfully replaced up to 80% to 90% of the fish meal protein without any loss of performance and feed utilization efficiency although a significant alteration in fish carcass composition was indicated for fish fed diets containing this by-product. It was apparent however that the fish meal used in this initial trial was not of a particularly high quality. Nevertheless, in a subsequent trial the performance of fish fed a ration where Poultry by-product and hydrolysed feather meal replaced half of the fish meal protein was slightly better than that of fish fed a control ration based on a good quality fish meal. Furthermore the year long survey indicated that the chemical composition of this by-product was consistent.

Five of the six Brown fish meals evaluated proved to be of low quality and only one gave similar results compared with a control ration based on the bacterial SCP "Pruteen". Furthermore a wide variation in the chemical composition of all six Brown fish meals was also Indicated during the one year survey. A good quality fish meal was eventually located which contained a locally produced meal but which was blended with an imported high quality fish meal. This meal was subsequently used to produce control rations in the last two feeding trials.

The Meat and bone meal successfully replaced up to 80% of a good quality fish meal protein without any significant loss of growth performance and feed utilization efficiency although the partial removal of the bone material during pretreatment produced a meal with the characteristics of a meat meal rather than a meat and bone meal. In the final feeding trial where this pretreatment was not carried out, it was apparent that the maximum inclusion level of this product was less than 30% of the protein component. As had been the case with the Poultry by-product and hydrolysed feather meal the chemical composition of different batches of the Meat and bone meal was consistent.

The evaluation of the three Animal by-products alone or in different combinations indicated that Poultry by-product and hydrolysed feather meal is a good protein source that can replace a large proportion of a good quality brown fish meal without any loss of growth performance and feed utilization efficiency. By contrast growth performances and feed utilization efficiencies decreased with increasing Inclusion levels of Meat and bone meal and therefore inclusion levels below 30% of the protein are recommended in diets for rainbow trout. The best growth performance and feed utilization efficiency where the three Animal by-products were used in different combinations was indicated for a diet containing these products in the ratio 1.3 Brown fish meal; 1 Poultry by-product and hydrolysed feather meal: 1 Meat and bone meal.

An economical appraisal of the diets produced in the four growth trials using the three Animal by-products was carried out. The costs of the three protein sources, the diets containing these products and finally the cost of fish production using these rations were compared. The Poultry by-product and hydrolysed feather meal and the Meat and bone meal were 19% and 35% respectively, less expensive than Portuguese Brown fish meals and therefore significant savings could be expected where these products are included in diet formulations. However, based on the cost of a Kilogramme of fish production only certain formulations containing Poultry by-product and hydrolysed feather meal. Meat and bone meal or combinations of these animal by-products were cheaper than the fish meal control rations. The implications of the results obtained in this study for commercial production of trout rations in Portugal are discussed.