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In terms of food production, the application of modern biotechnology to livestock falls into a area of animal production.
Fish:
The projected increasing demand for fish suggests that GM fish may become important in both developed and developing countries. Enhanced-growth Atlantic salmon containing a growth hormone gene from Chinook salmon is likely to be the first GM animal on the food market.
These fish grow 3-5 times faster than their non-transgenic counterparts, to reduce production time and increase food availability. At least eight other farmed fish species have been genetically modified for growth enhancement. Other fish in which genes for growth hormones have been experimentally introduced include grass carp, rainbow trout, tilapia and catfish.
In all cases, the growth-hormone genes are of fish origin. To address some of the practical problems of aquaculture, research attempts are seeking to improve disease resistance by producing Atlantic salmon with a rainbow trout lysozyme cDNA.
Lysozyme has antimicrobial properties against fish pathogens such as Vibrio, Aeromonas and Yersinia. Another type of antimicrobial protein (silk moth cecropin) is under investigation in catfish. This would improve catfish resistance to diseases such as enteric septicaemia.
The farming of carnivorous fish species, such as trout and salmon, has led to overfishing of sand eels and capelin. To tackle this problem, research is looking into the possibility of altering the metabolism of these species by improving their digestion of carbohydrates, to enable a shift to a more plant-based diet.
Lack of cold tolerance in warm-water species such as the common carp and tilapia can lead to significant stock losses in winter. The suggestion of work in this area is to alter the molecular conformation of lipids, thus increasing membrane fluidity.
To extend the geographical range of fish farming, an antifreeze gene from one fish species is transferred to the species of interest. Although freeze-resistant strains of Atlantic salmon have been produced, the level of antifreeze protein secreted by the salmon was insufficient to have a significant impact on the freezing point of blood.
The issues concerned in the identification of hazards and the assessment of risks that could be associated with the release of GM fish are still being addressed. One of these aspects involves the production of sterile GM fish to minimise the environmental risk of releasing them into wild populations.
Livestock and Poultry:
Foods derived from GM livestock and poultry are far from commercial use. Several growth-enhancing novel genes have been introduced into pigs that have also affected the quality of the meat, i.e. the meat is more lean and tender.
This research was initiated over a decade ago, but owing to some morphological and physiological effects developed by the pigs, these have not been commercialised. Many modifications to milk have been proposed that either add new proteins to milk or manipulate endogenous proteins.
Recently, researchers from New Zealand developed GM cows that produce milk with increased levels of casein protein. Use of such protein-rich milk would increase the efficiency of cheese production. Other work aims to reduce the lactose content of milk, with the intent of making milk available to the population of milk-intolerant individuals.
Other applications of genetic modification in animal production in the early stages of R&D include improvement of disease resistance, increased birth rates in sheep, altered sex ratio in poultry, increased egg production in poultry by creating two active ovaries, and improved feed conversion in the ‘enviropig’ (environmentally friendly pigs that excrete less phosphorus).
Most of this work is still theoretical and therefore estimates of time frames for possible commercial introductions of any of these applications are unavailable.
Microorganisms:
Currently, there are no known commercial products containing live genetically modified microorganisms (GMMs) on the market. In the United Kingdom, GM yeast for beer production has been approved since 1993, but the product was never-intended to be commercialised.
Other microorganisms used in foods (which are in the R&D phase) include starter fermentation cultures for various foods (bakery and brewing), and lactic acid bacteria in cheese.
R&D is also aimed at minimising infections by pathogenic microorganisms and improving nutritional value and flavour. Attempts have been made to genetically modify ruminant microorganisms for protecting livestock from poisonous feed components.
Microorganisms improved by modern biotechnology are also under development in the field of probiotics, which are live microorganisms that, when consumed in adequate amounts as part of food, confer a health benefit on the host.
Many enzymes used as processing aids in food and feed production are derived through the use of GMMs. This means that the GM microorganisms are inactive, degraded or removed from the final product. GM yeasts, fungi and bacteria have been in commercial use for this purpose for over a decade.
Examples include: alpha- amylase for bread-making, glucose isomerase for fructose production, and chymosin for cheese-making. Most of the microorganisms modified for food processing are derivatives of microorganisms used in conventional food biotechnology.
GMMs are also permitted in a number of countries for the production of micronutrients, such as vitamins and amino acids used for food or dietary supplement purposes.
An example is the production of carotenoids (used as food additives, colourants or dietary supplements) in GM bacterial systems. In the future, complete metabolic pathways could be integrated in GM microorganisms, enabling them to produce new compounds.
For animal husbandry, veterinary products such as bovine somatropin, used for increasing milk production, have been developed using genetic engineering. Bovine somatropin has been on the market in several countries for over a decade.
The technique of protein engineering aims at altering the genetic, and thus amino acid, sequence of enzymes. Hitherto, protein engineering has not been used extensively in enzyme production.
R&D in this area aims to change enzyme characteristics, e.g. improve temperature or pH stability. Enzymatic processing often replaces existing chemical reactions. In many instances, this results in lowered energy consumption and less chemical waste.