Total Backfat and Individual Backfat Layer Changes of Primiparous Sows During Late Gestation and Lactation

Purdue University 1998 Swine Research Report. Modern gilt genotypes often reach puberty and conceive their first litter before their body reserves (muscle and fat) have matured. This lack of body reserves at breeding can result in extended wean to estrus intervals and decreased conception rates in parity 1, and reduced litter size in parity 2 (Mullan and Williams, 1989). Under-developed body reserves at breeding may also compromise sow longevity, as many gilts are culled from the breeding herd for locomotion or reproductive problems (Dourman et al., 1994; Rozeboom et al., 1996). Gestation is the only phase of production during which sows can replenish lost body reserves. The amounts of energy and protein supplied to the sow during gestation are the limiting factors in the development of body reserves (Dourmad et al., 1996). Development of fat reserves during gestation is necessary for satisfactory reproductive performance, but excessive fat deposition can have negative effects on reproduction. It is well established that high levels of body fat deposition during gestation can decrease feed intake during lactation (Revell et al., 1994; Weldon et al., 1994). However, body fat reserves are necessary for adequate milk production and to limit body weight loss during lactation (Ranford et al., 1994). Thus, there is an optimal range of backfat that is necessary to sustain reproduction. Over the past three years, we have observed that pig genotypes differ not only in the total amount of backfat, but also in the relative amounts of the three individual backfat layers – outer, middle and inner (Figure 1). While it is apparent from carcass evaluations that these layers differ in chemical, structural and textural properties, their relative contributions to growth and physiology in the live animal remain unknown. At the present time, we are analyzing the growth of individual backfat layers in market hogs, and further characterizing each layer in terms of cellularity, fatty acid composition and gene expression. This trial is a preliminary investigation of how the energy demands of gestation and lactation affect growth and depletion of individual backfat layers. Preliminary data from other trials indicate that consideration of these layers to be three separate tissues may enhance pork quality and carcass composition. We are currently investigating whether such a consideration could enhance reproductive management as well. Monitoring backfat development may provide an insight into relationships between individual fat layers and reproductive traits. The main objective of this study was to monitor changes in both total 10th rib backfat depth and individual backfat layer thickness during gestation and lactation. We also wanted to relate these changes in total backfat and backfat layers to gestational dietary treatments, reproductive performance during the subsequent lactation, and sire line of the litter.