1. Introduction
Due to various negative side effects together with the intensification process in conventional pig production, there is an increasing interest of consumers in pork from organic and low-input production systems [1]. Introduction of the wholesomeness concept in meat production, most often represented by organic production, is mainly due to a wish for re-establishing a positive meat sector image, including eating quality, food safety and animal welfare aspects [2] and [3]. Consumers draw a whole range of positive inferences from the label ‘organic’, and these do not only refer to concerns about the environment and health, but also about animal welfare and a better taste [4]. The organic concept refers to the whole farm as the base of a comprehensive system where the production process is intended to ensure quality production rather than maximum production. Labelling meat as being ‘organic’ identifies the products as deriving from a production method defined by guidelines that clearly go beyond other brand label programmes [5].
Organic pig production is based on organically grown feedstuffs. The ingredients of a diet should derive in the first place from home-grown feedstuffs. The restriction of organically produced feedstuffs, however, limits the availability of feedstuffs with high quality protein[6] and [7]. Due to a limited availability of high quality protein feed, it is clearly more difficult in organic pig production than in conventional pig production to formulate diets that accurately meet the requirements of high-yielding animals.
As a high level of meat quality does not necessarily emerge from specific regulations or a low-input production method, it is a real challenge in organic farming to adapt pig production to a limited availability of nutrients while simultaneously optimizing product quality.
While a pig's potential for growth is ultimately determined by its genotype [8], growth is accomplished by cellular hyperplasia early in life and cellular hypertrophy thereafter [9]. Quantitative and qualitative aspects of postnatal nutrition have a major effect on muscle development through their effect on growth rate and body composition. The dietary impact can vary depending on the stage of development and age of the pig. Additionally, myofibre characteristics play a critical role in the determination of final meat composition.
In the past, various studies have shown that diets low in amino acids have the potential to increase intramuscular fat (IMF) content, a prominent criterion for eating quality without causing an overly fat pig [10] and [11]. The IMF content is well known for enhancing softness, tenderness and overall liking of pork [12] and [13]. The authors consider IMF contents of 2–2.5% as a minimum level to influence sensory properties. The non-consideration of this trait and the unidirectional selection for lean meat in conventional production results in IMF contents averaging clearly below the desirable IMF values[14] and [15]. The relative growth rates of different fat depots vary with the stage of maturity of the animal, with the intramuscular depot being the slowest and the perirenal depot the fastest growing in pigs. Thus, the age of the animal will affect the distribution of fat [16]. A low postnatal growth rate via restricted dietary protein intake is associated with a lower muscle fibre diameter and more intramuscular lipid in the porcine longissimus muscle [17]. As an imbalanced supply of amino acids is characteristic of organic diets based on organic cereals and home-grown grain legumes, this feeding strategy may provide an appropriate tool for organic farmers to manipulate meat quality in order to meet specific market demands.
So far only few studies have been conducted on the quality of pork produced under organic conditions. The QualityLowInputFood project (QLIF, http://www.qlif.org) has addressed this issue in its fourth sub-project on organic livestock production, aimed to develop strategies that could lead to an improvement of the eating quality of pork. Two experiments were conducted to assess potentials and limitations in quality production of pork based on a restricted availability of limited amino acids (AA).
The objective of the first experiment (Experiment 1) was to test the hypothesis that pigs with different genetic potential for protein accretion react differently to an imbalanced amino acid diet in the grower and the subsequent finisher phase, thereby causing different effects on the quality traits of pork. The second experiment (Experiment 2) was conducted to validate the hypothesis that pigs with different birth weights react differently to an imbalanced amino acid diet in the growing and the subsequent finishing phase, thereby affecting pork quality.