Development of new feeding systems and strategies for lamb meat production

Tesis doctoral de la Universidad de León y el Instituto de Ganadería de Montaña (IGM-CSIC). Leída el 19 de mayo del 2017.[EN] Lamb meat production and consumption in Spain has experienced a significant decrease in the last decade. There are several factors that can definitely affect this sector, some of which are economic (production costs) whereas others are of social nature (the image of this product from the point of view of the consumers together with changes in their habits). Given this situation, the lamb meat production sector faces the need to evolve through changes in the production systems to improve competitiveness and meet the new market demands. Feeding is a key element that can directly influence production costs, meat characteristics and added value, as well as the public image of the production system in terms of animal welfare and environmental impact. In Spain, sheep meat comes mainly from suckling lambs and lambs slaughtered with weights between 25 and 30 kg. The latter are bred in intensive systems where they are traditionally fed on ad libitum supply of concentrated feed and cereal straw. Separate straw administration from the concentrate entails an additional cost to the value of the feed itself, derived from its storage and distribution. One of the possible alternatives to this feeding system is the use of pelleted total mixed rations, in which forage and concentrate are mixed together and pelleted before being supplied. This type of rations allows optimization of feed storage (hoppers) and distribution (pellets can be automatically delivered to animals). However, the use of this type of rations in young fattening lambs has not been evaluated in depth. Therefore, it is necessary to set the scientific basis for their adequate formulation, particularly with regard to the proportion of forage that must be included for a balance between animal performance, environmental impact and animal welfare. Furthermore, the use of lipid supplements is a common practice when formulating rations for fattening ruminants due to several reasons. On the one hand and from a performance point of view, lipids increase the energy density of the rations without increasing the risk of acidosis. On the other hand, lipid supplements can reduce the methanogenic potential of the ration and, consequently, reduce the environmental impact of the production system. Last, from a nutritional point of view, lipids open up the opportunity of enhancing meat fatty acid composition towards a healthier profile. Among the lipid supplements, soapstocks are in general terms cheaper than the vegetable oils from which they come after refinement. Hence their use in animal feed contributes to the reuse of these by-products in the food chain as an alternative to vegetable oils. For all these reasons, the present research work was raised with the overall objective of studying the effect of new feeding strategies (pelleted total mixed rations with different proportions of barley straw and sunflower soapstocks) for fattening lambs. We assessed feed intake, digestibility, animal performance and welfare, environmental impact and carcass and meat quality for the different feeding strategies. To achieve this objective, different experimental trials were carried out, whose results were published in 5 scientific articles, corresponding to the 5 chapters of this dissertation.Chapter I corresponds to the article entitled "Concentrate plus ground barley straw pellets to replace conventional feeding systems for light fattening lambs", which describes the effect of using different proportions of straw in total mixed rations on feed intake, digestive utilization, animal performance and carcass and meat characteristics. For this purpose, 40 merino lambs with an initial body weight of 14.1 ± 0.17 kg were used. Animals were housed in individual pens and assigned at random to one of the following experimental groups (ten lambs per treatment): CONTROL (ad libitum pelleted concentrate feed and long straw in different feeding troughs), B05 (ad libitum pelleted total mixed ration including 5% of straw in the pellet), B15 (ad libitum pelleted total mixed ration including 15% of straw in the pellet) and B25 (ad libitum pelleted total mixed ration including 25% of straw in the pellet). The animals received the daily ration early in the morning and had free access to fresh water. During the days 22 to 26 of the experimental period a digestibility trail was carried out by housing 4 lambs per group in cages that allowed the separate collection of faeces and urine. The lambs were slaughtered when they reached 27 kg of body weight. The weight of different organs and the hot and cold carcass (after 24 h chilling) were recorded. Commercial cuts were obtained from the left carcass, each piece being weighed to calculate its proportion on the carcass. Meat quality was evaluated in the longissimus thoracis et lumborum muscle. The pH was measured at 0 hours and 45 minutes postmortem at the level of the sixth rib. After chilling (24 h) this muscle was removed from the carcass and sectioned to measure pH and color, and samples to analyze cooking losses, texture and chemical composition analysis were taken. Straw, total dry matter, crude protein, FAD and FND intake increased linearly (P0.05) with none of the lipid supplements and inclusion levels evaluated, but fermentation pattern was modified, acetic acid proportion decreased linearly (P<0.05) as olive and sunflower soapstocks percentage increased, whereas acetic acid proportion increased with the level of soybean soapstock. Propionic acid proportion increased linearly with the proportion of soapstock (olive, sunflower and soybean) added. In spite of these variations in the fermentation pattern, all soapstocks reduced methane production per gram of incubated dry matter or mol of volatile fatty acids produced (P