The effects of dietary fat supplementation on grower/finisher pig performance and digestibility

Cereals have traditionally been used in the pig industry as the main source of energy in pig diets. However, due to variable composition, differences in nutritive value between cereal types and the availability and price of cereals, alternative sources of energy have been considered, for example, the addition of fat. The use of fat as an energy source for pigs has been shown to increase digestibility of nutrients (Asplund et al., 1960; Berschauer, 1984; Jones et al., 1992; Lewis and Southern, 2001) and (or) improve growth rate (Myer and Combs, 1991; Bauden et al., 2003; Campbell, 2005; Philpotts et al., 2008; Collins et al., 2009a), however, studies on the effects of adding fat to swine diets have yielded variable results. Nevertheless, some recent information (Campbell, 2005; Philpotts et al., 2008; Collins et al., 2009a) has shown that added fat can be of benefit to growing/finishing pigs under commercial situations where there are often a number of constraints, such as increased stocking density and decreased feeder access (Campbell, 2005), that might create conditions where added fats in diets is beneficial because of its higher energy concentration. A review by Pettigrew and Moser (1991) concluded that there was a consistent improvement in growth rate and reduction in feed intake and improvement in feed:gain when fat is added to the diet of growing/finishing pigs. In addition to the level of fat per se in the diet influencing production and digestibility, the type of fat (i.e., saturated versus unsaturated fat), and the ratio of fat types are also likely to influence any responses (Mu, 2007). Differences in the fatty acids composition and the ratio of unsaturated:saturated fatty acids (UFA:SFA) in the fat source are also likely to cause variations in production and digestibility (Stahly, 1984). To date and to my knowledge, comprehensive studies investigating these factors that link production measurements to estimates of digestibility have not been conducted. With this in mind, the overall aims of this thesis were as follows; 1. Determine whether the use of added fat, either as beef tallow (BT) or canola oil (CO), to increase the digestible energy (DE) content in diets above current recommendations would improve measures of production and an estimate of the cost of any production gain; 2. Determine the optimum feeding strategy for diets containing different types and levels of added fat in the growing/finishing period; 3. Determine the effects of fat type, either as BT or CO, the level of fat in the diet and the dietary UFA:SFA ratio acids on estimates of digestibility of selected nutrients and diet components when assessed at the ileum and in the faeces. The specific hypotheses examined in this thesis were as follows; 1. Supplementing grower/finisher diets with up to 8% added fat would improve feed conversion ratio (FCR) and growth performance without being detrimental to carcass quality (P2 backfat thickness); 2. Feeding supplemental fat only in the finisher period would enhance production and lower costs, as no supplemental fat would be necessary in the grower period. However, eliminating fat in the finisher period, if already present in a grower diet, would be detrimental to growth performance; 3. Pigs fed diets with added CO would have a higher digestibility (ileal and total tract) than pigs fed diets containing BT; 4. A higher UFA:SFA ratio would significantly improve nutrient digestibility; 5. Increasing dietary fat level would slow rate of passage