Using lupins and lupin products in aquaculture diets

Western Australia is the world's largest producer of lupins. The narrow-leaf sweet lupin, Lupinus angustifolius, is the main species of lupin grown, though other varieties such as the yellow lupin (L. luteus) and white lupin (L. albus) are also grown.

Each of the lupin species differ subtly in their composition (see composition table). The removal of the seed coat to produce a kernel also alters the composition of the resultant kernel meal, which has considerable advantages over whole-seed meal when included in fish diets. A comparative assessment of these different varieties when fed to rainbow trout, and an assessment of the implications of the variability of L. angustifolius kernel meals, is available in a downloadable report.

Significant nutritional advantages of using lupins in diets for fin-fish, particularly salmonids, have been identified through this research. In addition, the inclusion of lupin products in formulations has been shown to have important influences on pellet extrusion characteristics.

Much of our work in this area has been funded by the grains industry through the Australian Grains Research and Development Corporation (GRDC) and the Western Australian Grains Research Committee. This work is being done in collaboration with several groups including the Department of Agriculture.

A comprehensive review on the use of lupins in aquaculture diets is available in a downloadable document.

Chilean Fish Meal: Prime anchovy fish meal sourced from Chile.
Soybean Meal: HiPro, solvent-extracted soybean meal.
White lupin kernel: Lupinus albus.
Yellow lupin kernel: L. luteus.
Sweet lupin seed: Whole seed meal from L. angustifolius.
Sweet lupin kernel: L. angustifolius kernel.
Lupin protein concentrate: derived from L. angustifolius.
Lupin protein isolate: derived from L. angustifolius.

Digestible protein and energy values are determined from digestibility assessments made from faeces stripped from rainbow trout.

Abstract

The nutritional value of the kernel meals of three species of lupin (Lupinus albus, L. angustifolius and L. luteus) was compared against each other and a reference ingredient of solvent extracted soybean meal, when fed to rainbow trout (Oncorhynchus mykiss). Each lupin kernel meal was included in test diets at 300 g/kg and also at a greater level, representing 50% of the total protein content in the diet. The digestibility of protein of all lupin kernel meals was better than for the soybean meal. The highest protein digestibility was that from L. luteus kernel meal at 30% inclusion (100%), which at similar inclusion levels was better than that from kernel meals of both L. albus (96.7%) and L. angustifolius (95.3%) and also the soybean meal (86.7%). The digestibility of dietary energy from each of the lupin kernel meals (range from 70.1% to 74.2%) was less than that obtained from soybean meal (79.8%). However, the higher gross energy content of the lupin kernel meals still resulted in both L. luteus and L. albus providing greater levels of digestible dietary energy with their inclusion in the diet than the inclusion of soybean meal would provide. Digestibility of organic matter and the nitrogen-free extractives (NFE) was poorer from each of the lupin kernel meals relative to that from the soybean meal. In most cases, the increased inclusion of each of the lupin kernel and soybean meals in the diet also resulted in a decrease in the level of organic matter and NFE digestion. Phosphorus digestibility was better in all lupin kernel meals than that from the soybean meal. Highest phosphorus digestibility was obtained from L. angustifolius kernel meal (53.8%) and lowest from the soybean meal (28.5%).

The influence of variability in the protein level of lupin (L. angustifolius) kernel meals when fed to rainbow trout was also examined. It was identified in this study that there was a strong correlation between protein content of a lupin kernel meal and the nutritional value of that protein. Notably the strongest correlation was that between kernel meal protein content and nitrogen digestibility (R2 = 0.981). The strong correlation between kernel meal protein content and its nitrogen digestibility had a direct effect on the relationship with energy digestibility. Notably, the kernel meal protein content had more influence on its energy digestibility than that of the nitrogen digestibility. There was a close relationship between NFE and dry matter digestibilities of the lupin kernel meals. The demonstrated relationship between lupin kernel meal protein content and its nutritional value provides a good support for the promotion of grain segregation by protein content and commodity pricing also according to protein content. More specifically this valuation should focus on the value per unit of digestible protein when used as an ingredient for fish diets. On this basis, some L. angustifolius kernel meals clearly warrant premium pricing. This basis of superior nutritional value as a function of protein content would also support promoting the increased production of L. luteus as a premium grain. Indeed based on digestible protein value, L. luteus kernel meals should be commanding at 26% premium compared with a 21% premium when determined on crude protein content of the kernel meal.