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Low profit margins in the pig producing market are common since several years, due to the relative high feed costs compared to the market value of pigs. For biological and economical efficient meat production, pigs should attain their slaughter weight with a good growth rate and an efficient conversion of nutrients into body tissues. Moreover, the carcasses should contain a high lean meat percentage and a large proportion of the higher valued cuts. These criteria, growth rate, feed conversion, lean meat percentage and body conformation determine the profit of the pig producer, and are highly dependent on a number of factors. This study focused on three manageable and critical points which may offer possibilities to reduce costs efficiently and to upgrade quality of the pig production process: diet composition, genetic lines and disease control. Feed is the major production input to the swine production system, making it economically interesting to attain a higher efficiency of nutrient use in growing pigs. The objective of the study described in Chapter 3, was to explore the effect of feeding ad libitum an increased Lysine:Net energy (Lys:NE) during five subsequent growing phases on the growth performance and final carcass quality in Belgian Piétrain crossbreds. During the first phase after weaning, all pigs were fed the same commercial starter diet. Afterwards, the pigs were randomly assigned either to the standard or the concentrated diet. Feeding the concentrated diet had a positive effect on daily gain, feed efficiency and energy efficiency (expressed as the ratio between body weight gain and energy intake) from 12 to 20 kg and from 20 to 40 kg. After 40 kg, daily gain was unaffected by treatment, but feed and energy efficiency were positively affected when feeding the standard diet. Final carcass quality, being valued as the lean meat content, was unaffected by treatment. This study emphasized the need to accurately adjust nutrient density to pigs' genetic capacity to grow, in order to maximize profitability in relation to feed cost. A negative effect of an increased dietary concentration on growth was observed during the last growing phases, which could be explained as a possible effect of oversupply of nutrients. In conclusion, investing in a higher quality diet during the early phases may be very cost effective as growth performance may be increased. During the later phases, on the other hand, feed cost is a very deciding factor because of the lower feed efficiency in comparison with the earlier phases. As a result, feeding a higher quality diet during the later growing phases does not improve the growth performance and leads to unnecessary costs for the farmer as this diet is more expensive. A detailed characterization of different genetic lines in terms of growth performance, body composition and carcass quality is crucial for choosing the right terminal sire adapted to the pig farmers’ objectives. Such characterization has been investigated several times in literature for unrelated breeds. In contrast, our study focused on the characterization of three sire lines within one breed, the Piétrain breed (Chapter 4) in combination with one line of hybrid sows. The three crossbreds could be differentiated based on measures of body composition, body conformation and meat quality, whereas growth performance was similar: Belgian Piétrain crossbreds had higher weights of higher valued cuts (ham and loin), higher loin muscle depth and similar backfat depth in comparison to the other crossbreds. Furthermore, the presence of the halothane gene was mostly related to a higher risk to develop an aberrant meat quality.The relationship between energy intake and protein deposition for the three crossbreds was studied in Chapter 5. The aim of this study was to investigate the capacity of growing Piétrain crossbreds to deposit protein and fat during three growing phases between 20 and 105 kg body weight under ad libitum feeding conditions. A general accepted model to describe the relationship between energy intake and protein deposition is the linear-plateau model, consisting of a linear part where the slope describes the quantity of deposited protein per extra unity of energy intake and a plateau part representing the maximal rate of protein deposition (PDmax). In our study, no PDmax could be detected, suggesting that the Piétrain crossbreds did not reach their maximal protein deposition capacity. However, some differences between the slopes of protein deposition of the three growing phases were seen, as well as between the three crossbreds. Firstly, a higher slope of protein deposition for the Belgian Piétrain crossbred was observed, whereas the slope of fat deposition was similar across all crossbreds, regardless the growing phase. Secondly, a steeper slope for protein deposition was found for pigs weighing between 20 and 40 kg compared to the later growing phases. Moreover, an increasing slope for fat deposition with increasing age was found. These results indicate a high potential to deposit lean tissue during the first phases and an increasing lipid deposition with age, which was common for all crossbreds. The negative impact of disease outbreaks on growth performance of pigs was demonstrated in Chapter 6. It is commonly known that disease outbreaks in a herd are an important threat to the profitability of the pig industry. Still, many farmers focus on therapeutic measures and consequently promote the resistance of pathogens against antibiotics. Thus, alternative ways to suppress the outbreaks of infections should be developed and this study aimed to deliver an important contribution to the research of disease prevention as an alternative to solely disease treatment. We focused on the administration of vaccinations against all clinical and subclinical pathogens, present in an existing herd prior to the start of the experiment, in combination with an elaborate biosecurity protocol. The developed strategy was successful at suppressing a clinical Actinobacillus Pleuropneumoniae (APP) infection which was establishedduring the former trials. However, a reduction in growth performance was observed during the growing phase in which most vaccinations were administered to the pigs. It was concluded that solely focusing on the clinical pathogens present at the farm may be more efficient to control disease outbreaks without negatively affecting growth performance.Hence, the main overall conclusions of this thesis are that adjusting diet composition to the genetic capacities of a pig line is crucial in order to optimize growth performance and body composition of pigs. Secondly, different lines within one breed can be distinguished based on economical important factors, such as lean meat percentage and body conformation. Finally, a new strategy of vaccination and biosecurity may be promising to prevent disease outbreaks. Therefore, a proper follow-up of the health status of a herd is essential.