Alimentació de semiprecisió de porcs d'engreix sense castració

Resumen

Conventional swine feeding systems usually aim to feed the average pig, or slightly higher nutrient levels to ensure that the overall population growth is not limited. To feed pigs in accordance with their requirements, most swine operations use phase feeding during the grow-finishing phase to match the diminishing dietary nutrient concentration for an increased feed intake at greater age and body weight. However, within a population of pigs there are factors that can modify protein deposition and feed intake potential (body weight variability, sex, sire line…), and consequently influence nutrient requirements. For instance, body weight variability constitutes a challenge in all-in all-out swine production systems not only for the issue of pigs with a low body weight at marketing, but also because it entails an inefficiency and inaccuracy of phase feeding strategies. Therefore, the purpose of this thesis was to describe the responses to varying nutrient levels and confirm whether these responses vary in pigs grouped for having different growth performance or tissue deposition rate. Afterwards, analyze the economic and environmental feasibility of semi-precision feeding systems consisting in feeding those groups differently. Initially, the influence of factors such as sire-line, sex, carcass weight and marketing day on growth performance and carcass composition was analyzed (Chapter 3). Synthetic sired pigs grew faster and had a higher feed intake compared to Pietrain sired pigs, which also resulted in fatter carcasses. Increasing carcass weight increased carcass fatness, but indistinctly, boars were leaner than gilts. Besides, increasing marketing day, as an indicator of body weight variability, reduced carcass fatness. Afterwards, the effect of increasing standardized ileal digestible lysine to net energy ratio (SID Lys:NE) was compared between pigs of different initial body weight (Chapter 4) and sex (Chapters 5 & 6). Growing pigs (30-60 kg) sorted by their initial body weight showed a different response to increasing dietary lysine. The lightest ones growth performance showed a greater linear improvement when increasing SID Lys:NE than the heavier ones. Moreover, from 70 to 100 kg body weight, increasing SID Lys:NE improved linearly growth performance and carcass composition of boars in a greater manner than in gilts. Consequently, boars required around 0.5 g SID Lys/Mcal NE more than gilts to maximize their greater potential growth performance. Reducing dietary net energy concentration 190-250 kcal/kg from a 2,450-2,550 reference diets did not impair growth performance when pigs could reach a sufficient energy intake (Chapter 7). However, if grow-finishing pigs could not overcome the reduced energy density by increasing sufficiently feed intake it resulted in impaired growth and reduced carcass fatness. Summarizing, the present PhD. dissertation provides evidence of the potential of semi-precision feeding to improve the growth performance of the lightest pigs in the growing phase (30-60 kg) whether improve boars performance in the finishing phase (70-100 kg) in a context of non-castration. In addition, in Chapter 8 the economic benefits of semi-precision feeding over conventional strategies in specific raw materials cost scenarios are shown and discussed. Finally, it shows the potential benefits to reduce nitrogen excretion by feeding gilts lower SID Lys:NE without much worsening their growth performance. In conclusion, semi-precision feeding by initial body weight or sex might be a feasible strategy to improve the sustainability of swine production in specific contexts.