Metabolic changes and tissue responses to selection on residual feed intake in growing pigs1, 2

Abstract

Previous selection experiments using residual feed intake (RFI) to select pigs with a high feed efficiency have reported that a low RFI was associated with a reduced body fat content and a greater muscle glycogen content. In the current study, growing Large White female piglets from 2 lines divergently selected for RFI were used to determine the changes in energy and protein metabolisms in key tissues and their cross talks in response to selection. Pigs of low RFI (RFI(-); n = 26) or high RFI (RFI(+); n = 36) selection lines were offered free access to feed during postweaning and growing periods. Pigs of each line were then slaughtered at 19 kg (n = 8 per line) or 115 kg BW (n = 14 to 18 per line). A third group of pigs of the RFI(+) line was offered feed at the same level per metabolic BW (BW0.60) as RFI- pigs (group RFI+R, n = 14). Regardless of the growth period considered, G:F was less in RFI(+) pigs than in RFI(-) pigs. At 19 kg BW, RFI(+) and RFI(-) pigs had a similar body composition and tissue lipid content. The fractional rate of protein synthesis and proteasome activity were decreased (P < 0.090) in the livers of RFI(+) pigs compared with RFI(-) pigs whereas activities of energy catabolic enzymes did not differ in the liver and LM samples. Plasma insulin was conversely greater (P = 0.049) in RFI(+) pigs at this stage. At 115 kg BW, enzyme activities of protein catabolism in the liver and in the LM did not differ (P > 0.10) between RFI(+) pigs and RFI(-) pigs. Both lactate dehydrogenase activity participating in glucose metabolism and hydroxylacylCoA dehydrogenase activity involved in fatty acid oxidation were greater (P < 0.05) in the liver and LM of RFI(+) pigs compared with RFI(-) pigs. In the liver, contrary to the LM, those differences in enzyme activities were directly associated with selection on RFI regardless of ADFI. Increased backfat depth and content and greater lipid content and adipocyte hypertrophy (P < 0.05) in subcutaneous adipose tissue were reported in RFI(+) pigs compared with RFI(-) pigs at 115 kg BW without marked changes in key lipogenic enzyme activities; these changes were directly associated with ADFI. In conclusion, the present study shows an increase of catabolic pathway activities in the liver and muscle of RFI(+) pigs at market weight that is likely to generate more ATP compared with RFI(-) pigs.

Evidence of decreased muscle protein turnover in gilts selected for low residual feed intake1

“…Hence, gilts from the low RFI line are more efficient, at least in part, because of decreased protein degradation. These results are dissimilar to those of Le Naou et al (2012), who documented no differences in total calpain activity in the LM or liver of either weaned or market weight Large White pigs selected for reduced or high RFI. This disparity may be due to differences in techniques used to measure activity; Le Naou et al (2012) used a fluorometry technique that measured combined μ-and m-calpain activity of a sample extract whereas the current study used chromatography techniques to isolate the individual proteases (μ-and mcalpain) and their endogenous inhibitor (calpastatin) followed by determining their activities.…”

“…Proteasome activity in the LM was decreased by 24% in the low RFI pigs (Table 4) compared with high RFI pigs and was positively correlated with RFI index values (r = 0.60, P < 0.05; Table 5). These results are in contrast to those reported by Le Naou et al (2012), who observed that proteasome activity tended to be increased (P = 0.08) in the liver of weaned (19 kg) Large White pigs selected for reduced RFI although no differences were found in the LM of these pigs. However, market weight pigs (115 kg) from the same study had no differences in proteasome activity in either tissue.…”

“…However, market weight pigs (115 kg) from the same study had no differences in proteasome activity in either tissue. The pigs in the current study were intermediate to the above study at 65 kg BW; it may be that the differences observed by Le Naou et al (2012) are only evident during the early stages of growth. It is also possible that differing methods allowed more sensitive characterization of proteasome activity in the current study; again Le Naou et al (2012) used fluorometry techniques that determined overall proteasome activity whereas the methods of the current study specifically measured 20S proteasome activity.…”

Effect of inflammation stimulation on energy and nutrient utilization in piglets selected for low and high residual feed intake

“…In our experiment, the HP due to physical activity did not differ between the two lines, even though the size of the cage in which the animals were housed allowed for more movement than in the previous studies conducted in the same laboratory. In contrast to these studies, feed intake in our study was similar for the two lines, thus feed restriction was more pronounced for RFI+ than for RFI− piglets (feed intake equaled respectively 64% and 74% of voluntary feed intake based on the results of Le Naou et al, 2012). Figure 1 Effects of complete Freund's adjuvant (CFA) injection on the respiratory quotient (CO 2 /O 2 ) in piglets selected for a low or a high residual feed intake (RFI− and RFI+, respectively; n = 13).…”

“…The way that genetic selection for RFI affects protein utilization is unclear (Le Naou et al, 2012;Cruzen et al, 2013) but our results indicate that, at least when animals were fed the same restricted level, genetic selection for RFI did not affect protein utilization. Considering that protein catabolism and protein synthesis rate do not differ in the muscle of RFI+ piglets compared with RFI− piglets when fed ad libitum (Le Naou et al, 2012), differences in feed efficiency between both lines may be related to differences in their feed intake and energy metabolism, that is the way the animal manages its energy balance and homeostasis. Because equivalent amounts of N were excreted in the urine, the ratio between ME and DE was also similar in both lines of pigs.…”