Effects of feeding patterns of low lysine diets added with sweet-potato crumbs on growth performance and intramuscular fat content in longissimus dorsi muscle of growing-finishing pigs

We conducted a feeding trial with different levels of dietary lysine in order to control growth performance and intramuscular fat (IMF) content in longissimus dorsi (l. dorsi) muscle of growing-finishing pigs. We prepared diets of two lysine levels: control diets meeting the requirement of lysine (C diet) and low lysine diets the lysine content of which is approximately 70% of the requirement (L diet). The diets are prepared for the growing period (30 to 70 kg body weight) and for the finishing period (70 to 120 kg body weight), thus, in terms of lysine levels, four diets in total were prepared: C diets for the growing and finishing periods and L diets for the growing and finishing periods. In addition, sweet-potato crumbs as food co-products from a factory of local sweets were added at the level of 10% to the diets for the finishing periods in order to investigate the effects of sweet-potato crumbs on quality of longissimus dorsi (l. dorsi) muscle. There were four patterns of lysine feeding: pigs given the C diet throughout the feeding trial (CC), pigs given the C diet during the growing period and thereafter given the L diet during the finishing period (CL), pigs given the L diet during the growing period and thereafter given the C diet during the finishing period (LC), pigs given the L diet throughout the feeding trial (LL). Further, the halves of the pigs were given the diets with sweet-potato crumbs during the finishing period (IMO+) and the rest were given the diets without sweet-potato crumbs during the finishing period (IMO-). Sex of the pigs was also considered. We used in total thirty two crossbred ((Landrace x Large White) x Duroc) pigs where fourteen gilts and 18 barrows were assigned to a 4 x 2 x 2 factorial design. The trial started when body weight of the pigs reached to 30 kg. The pigs were allowed free access to the diets and water until their body weight reached to 120 kg. At the end of the trial, carcass traits were measured and IMF contents, cooking loss, and share value of l. dorsi muscle were determined. Feeding the low lysine diets throughout the trial tended to decrease growth rates of the pigs (p0.1). Patterns of lysine feeding affected IMF contents in l. dorsi of pigs (p0.05) : it was the highest in the LL group (5.7%), followed by LC group (3.9%) and CC, LC group (3.5%). Patterns of lysine feeding tended to affect share values of l. dorsi muscle (p0.1) : it was the lowest in the LL group (1.9 kgf), those of the CC and CL groups were similar (2.4 kgf), and the LC group had the highest value (2.5 kgf). Although growth rates and feed intake of the LC group during the growing period were lower than those of the other groups, both growth rates and feed intake were recovered during the finishing period. As a result, average growth rate of the LC group throughout the trial was as high as 998g/d. However, back fat depth of the LC group tended to be larger than the other groups (p0.1). Adding sweetpotato crumbs to diets during the finishing period did not affect IMF contents and other traits of l. dorsi muscle. These results indicate that growth performance, growth rate in particular, and IMF content in l. dorsi muscle can be controlled by pattern of lysine feeding in growing-finishing pigs.