Upgrading plant amino acids through cattle to improve the nutritional value for humans: effects of different production systems.

Efficiency in animal protein production can be defined in different ways, for example the amount of human-digestible essential amino acids (HDEAA) in the feed ration relative to the amount of HDEAA in the animal products. Cattle production systems are characterised by great diversity and a wide variety of feeds and feed ration compositions, due to ruminants' ability to digest fibrous materials inedible to humans such as roughage and by-products from the food and biofuel industries. This study examined the upgrading of protein quality through cattle by determining the quantity of HDEAA in feeds and animal products and comparing different milk and beef production systems. Four different systems for milk and beef production were designed, a reference production system for milk and beef representing typical Swedish production systems today and three alternative improved systems: (i) intensive cattle production based on maize silage, (ii) intensive systems based on food industry by-products for dairy cows and high-quality forage for beef cattle, and (iii) extensive systems based on forage with only small amounts of concentrate. In all four production systems, the quantity of HDEAA in the products (milk and meat) generally exceeded the quantity of HDEAA in the feeds. The intensive production models for beef calves generally resulted in output of the same magnitude as input for most HDEAA. However, in beef production based on calves from dairy cows, the intensive rearing systems resulted in lower output than input of HDEAA. For the extensive models, the amounts of HDEAA in meat were of the same magnitude as the amounts in the feeds. The extensive models with beef calves from suckler cows resulted in higher output in meat than input in feeds for all HDEAA. It was concluded that feeding cattle plants for production of milk and meat, instead of using the plants directly as human food, generally results in an upgrading of both the quantity and quality of protein, especially when extensive, forage-based production models are used. The results imply that the key to efficiency is the utilisation of human-inedible protein by cattle and justifies their contribution to food production, especially in regions where grasslands and/or forage production has comparative benefits over plant food production. By fine-tuning estimation of the efficiency of conversion from human-edible protein to HDEAA, comparisons of different sources of protein production may be more complete and the magnitude of amino acid upgrading in plants through cattle more obvious.