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Genetic selection on residual feed intake (RFI) can be used as an alternative method to G:F to improve feed efficiency in pigs. The objective of this study was to determine the effects of selection for RFI on digestive and metabolic utilization of energy in 2 lines of purebred French Large White castrated male pigs obtained from a divergent selection experiment over 6 generations. The [RFI.sup.+] (high RFI) line consumed more feed than predicted from performance compared with the [RFI.sup.-] (low RFI) line. Digestibility of energy and nutrients, total heat production (HP), HP related to physical activity, and energy and N balance were measured in respiration chambers for a 6-d period in pigs offered feed ad libitum. Pigs remained in the chamber for an additional day and did not receive any feed to estimate the fasting HP and calculate the thermic effect of feeding. Five pairs of 2 littermates from the same farrowing batch were used in each line. Because 2 respiration chambers were available for the trial, pigs were measured regularly during the 25- to 95-kg growing period. Two pigs per chamber were used until pigs reached 45 kg of BW, and 1 pig per chamber was used thereafter. Individual feed intake and BW gain were measured continuously from weaning to the end of the trial. Pigs were fed 3 diets with decreasing CP contents during the 25 to 45 (period 1), 45 to 65 (period 2), and 65 to 95 (period 3) kg of BW periods. Average daily feed intake was greater in [RFI.sup.+] pigs than in RFI pigs between 25 and 65 kg of BW (2,128 vs. 1,891 g/d; P < 0.01) and G:F was 8% greater in RFIpigs compared with [RFI.sup.+] pigs (P < 0.01). There was no line effect on digestibility coefficients or N retention, irrespective of the experimental period studied. Nitrogen retention was 31.2, 28.7, and 20.8 g/d at periods 1, 2, and 3, respectively (P < 0.001). The HP was greater in [RFI.sup.+] pigs than in [RFI.sup.-] pigs (1,497 vs. 1,383 kJ x kg of [BW.sup.-0.60] x [d.sup.-1]; P < 0.01), with no subsequent line effect on energy retention. The activity-related HP tended to be greater in [RFI.sup.+] pigs than in [RFI.sup.-] pigs (250 vs. 218 kJ x kg of [BW.sup.-0.60] x [d.sup.-1]; P = 0.09), and the fasting HP was 10% greater (P = 0.04) in [RFI.sup.+] pigs than in [RFI.sup.-] pigs (846 vs. 771 kJ x kg of [BW.sup.-0.60] x [d.sup.-1]). The thermic effect of feeding, expressed as a percentage of ME intake, was the same for both lines of pigs (average, 14.7%). In conclusion, the [RFI.sup.+] pigs are energetically less efficient because of their greater HP related to physical activity and basal metabolic rate. Key words: energy utilization, fasting heat production, growing pig, heat production, residual feed intake doi: 10.2527/jas.2009-2395

Most studies concerning the Ile requirement in pigs have been carried out using blood products as a protein source, and these have a relatively low Ile content relative to the other branched-chain AA (BCAA). There are indications that an excess supply of one BCAA can affect the utilization of the other BCAA. Little information is available concerning the Ile requirement in pigs when the supply of the other BCAA is moderate (e.g., in cereal- and soybean mealbased diets). The objective of the present study was to evaluate the response of piglets to Ile supplementation under different nutritional conditions. In all experiments, piglets were housed individually and had ad libitum access to feed during a 3-wk period. The first experiment was carried out to study the response of piglets to an increasing Ile supply by using 2 sources of L-Ile differing in degree of purity. Piglets received either a control diet with 48% standardized ileal digestible (SID) Ile:Lys or 1 of 4 other diets containing graded levels of either source of L-Ile to provide 52 or 56% SID Ile:Lys. All diets were formulated to provide 1.00% SID Lys in the diet. Feed intake and growth were not affected by Ile level or Ile source. Experiment 2 was performed to exclude a possible interaction between Ile and Lys supply. In a 2 x 2 factorial arrangement, 2 levels of Lys (1.00 and 1.15% SID Lys) and 2 levels of Ile (48 and 60% SID Ile:Lys) were used. Growth and G:F were 8 and 7% greater in piglets receiving the diet with the greater Lys content, but the Ile:Lys did not affect performance. No interactions were observed between the Lys and Ile supplies. In Exp. 3, a 2 x 2 factorial arrangement was used to test the effect of protein source (spray-dried blood cells or corn gluten meal) and Ile supply (50 or 65% SID Ile:Lys) on performance in piglets. Both protein sources had an elevated BCAA content but differed in Leu and Val contents. Protein source or Ile supply did not affect feed intake, growth, or G:F in the piglets. Plasma concentrations after an overnight fast reflected the difference in AA concentrations of the diets. In conclusion, the results of these experiments indicate that the SID Ile:Lys requirement may be not greater than 50% in piglets receiving cereal-and soybean meal-based diets with a moderate BCAA content. In contrast to other studies, we could not confirm that the Ile requirement was affected by BCAA content of the diet. Key words: branched-chain amino acid, feed intake, growth, isoleucine, pig, requirement doi: 10.2527/jas.2009-1964

Voluntary feed intake in sows after parturition may be related to the capacity of the sow to cope with the numerous changes occurring around farrowing. This experiment was undertaken to investigate whether the feed intake during lactation was related to the reactivity of the sow during gestation and plasma Trp and cortisol concentrations. On d 58 of pregnancy, 37 sows were individually placed in a novel environment, and their behavior was observed during a 5-min open-field test. This test allowed the selection of 12 reactive (R) and 8 nonreactive (NR) sows for the study. Sows were fed 3 kg of a standard gestation diet/d before farrowing and a standard lactation diet ad libitum thereafter. The behavioral reactivity of sows when a human touched their neck in the farrowing crate was evaluated on d 72 of gestation, and their behavior during farrowing was analyzed. Sows were catheterized on d 70 of gestation, and blood samples were taken after an overnight fast on d 37 before farrowing, daily during the week before and the week after parturition, and on d 14 and 21 of lactation for plasma Trp and cortisol determination. The NR sows were less reactive to human contact (P = 0.02), had a shorter farrowing duration (P = 0.02), and tended to have a shorter birth interval between piglets (P = 0.09) than the R sows. Feed intake was greater for the NR sows than for the R sows during wk 1 of lactation (P = 0.02), as well as during the whole lactation (P = 0.03). Plasma cortisol concentration was maximal on the day after farrowing (P = 0.01) and returned to basal concentration within 4 d postpartum. No relationship was observed between sow behavior and plasma concentration of cortisol. For both groups of sows, plasma concentrations of Trp between d 2 and 4 postpartum were less than during gestation (P < 0.05). The NR sows had decreased plasma Trp concentrations compared with the R sows during wk 1 of lactation (P = 0.02). A low reactivity during gestation was associated with behavior of the sow that was favorable to piglet survival during farrowing, increased feed intake, and decreased plasma Trp concentration during wk 1 of lactation. Further research is needed to elucidate whether Trp or Trp metabolites are related to reactivity and ADFI of the reproducing sow. Key words: feed intake, lactation, reactivity, sow, tryptophan

Little knowledge on the digestive and metabolic utilization of solid feed in veal calves is available. The objectives of the study were to determine the effects of 2 solid feeds offered at 2 feeding levels (FL90 and FL105) in addition to a milk replacer on heat production (HP) and protein and fat deposition in veal calves. Sixteen calves (148.0 [+ or -] 3.7 kg) received milk replacer (75% of a reference DE allowance) and solid feeds that consisted of corn grain and pelleted hydrolyzed wheat gluten without (CO) or with (CS) chopped wheat straw. The solid feed supply provided 15 or 30% of the reference DE allowance to achieve FL90 or FL105, resulting in 4 treatments: CO90, CS90, CO105, and CS105. A fifth treatment consisted of using the milk replacer alone at FL90 (treatment M90) and was measured in 4 other calves. All calves were kept individually for 7 d in a respiration chamber to estimate energy and N balances and fasting HP. The digestibility coefficients of DM, OM, GE, and major nutrients were at least 94% for M90 and decreased when solid feed was added (P < 0.05). Methane production was negligible in M90 calves and increased when solid feed was given (ranging 8 to 23 L/d between CO90 and CS105, P < 0.01), indicative of ruminal fermentation. The provision of increasing amounts of solid feed decreased urinary energy in connection with a tendency (P = 0.09) for a reduction of urinary glucose excretion. The metabolizability of DE was greater with the milk replacer (95.6%) and decreased when straw was added (P < 0.01). Neither CO90 or CS90 affected HP and total energy retention (P > 0.05). Dietary treatment had no effect (P > 0.05) on activity HP (53 kJ/kg of [BW.sup.0.85] daily) but did affect thermic effect of feeding; efficiency of utilizing ME for maintenance and growth was greatest for the M90 calves (84.5%, P = 0.02). Fasting HP tended (P = 0.09) to increase at the greatest FL (308 vs. 298 kJ/kg of [BW.sup.0.85] daily). Maintenance ME requirement increased (P = 0.04) from 364 to 382 kJ/ kg of [BW.sup.0.85] daily when feeding level increased (P = 0.04) but was not affected by ingestion of solid feed. The provision of solid feed to veal calves was associated with a reduced efficiency of N retention (P = 0.04), and energy retained as protein tended to decrease (P = 0.08), probably as a result of an imbalanced AA supply of the solid feeds. The data were used to calculate the energy contents of solid feed. The utilization of energy from solid feed differed from that of milk replacer. Key words: digestibility, heat production, protein and fat retention, solid feed, veal calf

To reduce the impact of animal production on the environment, the CP content of the diet can be reduced by limiting the excess supply of AA. Improving the balance between AA relative to the requirement of the animal implies that we need to have accurate knowledge of the requirement of individual AA. The purpose of this study was to determine the Val requirement in postweaned piglets (12 to 25 kg) because Val is considered to be potentially limiting to performance after Lys, Met (and Cys), Thr, and Trp. The first experiment was carried out to identify a diet limiting in Lys supply. In this experiment, piglets were offered 1 of 3 diets: a low-CP diet containing low or adequate Lys concentrations [providing 1.0 and 1.2% standardized ileal digestible (SID) Lys, respectively] or a normal-CP diet with 1.2% SID Lys. Average daily gain of piglets receiving the diet containing 1.0% SID Lys was significantly less than that of piglets receiving diets containing 1.2% SID Lys at low or normal CP (486 vs. 522 g/d, respectively; P < 0.01). In Exp. 2, four diets with 1.0% SID Lys were used in a 2 x 2 factorial design, in which diets contained 57 or 70% SID Val:Lys in combination with 50 or 60% SID Ile:Lys. Independent of the Ile supply, feed intake and daily BW gain were, respectively, 15 and 20% less in piglets receiving diets providing 57% SID Val:Lys compared with piglets receiving 70% SID Val:Lys (P < 0.001). The Ile content of the diet did not affect feed intake or daily BW gain (P > 0.10). Experiment 3 was conducted to evaluate the response of piglets to an increasing Val supply provided by 2 sources of L-Val differing in the degree of purity. Increasing the Val supply from 58 to 66% SID Val:Lys resulted in a linear increase in both feed intake and daily gain by 24 and 30%, respectively (P < 0.001). No difference was observed between both sources of L-Val (P > 0.10). Experiment 4 was a dose-response study using 5 concentrations of Val supply (ranging from 60 to 80% SID Val:Lys). The estimated SID Val:Lys requirements for maximizing ADFI, ADG, and G:F were, respectively, 74, 70, and 68% using a linear-plateau model, and 81, 75, and 72% using a curvilinear-plateau model. Plasma Val, plasma [alpha]-ketoisovaleric acid, Ile, and Leu concentrations after an overnight fast increased with increasing Val supply (P < 0.001). The results of these experiments indicated that the SID Val:Lys was at least 70%, which was slightly greater than the current NRC recommendation. Key words: branched-chain amino acid, feed intake, growth, pig, requirement, valine

The impact of dietary fiber on fecal digestion is well-known and provides a comprehensive approach toward nutrient digestibility and availability. Little quantitative information is available on digestion of fiber in the different segments of the gastrointestinal tract (GIT). The objectives of this study were to obtain a method allowing the quantification of the digestive process in different segments of the GIT and to study the impact of dietary fiber on nutrient digestibility. Six barrows (average initial BW of 30 kg and fitted with a simple T-cannula at the proximal duodenum and caudal ileum) were used in a replicated 3 x 3 Latin square design. In each period, pigs were offered 1 of 3 diets differing in fiber content (low, medium, and high). Differences in fiber content were created by replacing wheat and barley with wheat bran. Titanium dioxide was included in the diet as an indigestible marker to determine the apparent digestibility coefficients in different segments of the GIT. The apparent digestibility of ash, CP, DM, and OM increased in the different segments of the GIT. Duodenal digestibility coefficients were negative for ash (e.g., -39.9% for the mediumand high-fiber diets), indicating important endogenous mineral secretions by the stomach and digestive glands. The duodenal digestibility of other nutrients and OM were positive but close to zero and numerically lower in the diets with the greater fiber contents. The fiber content in the diet did not affect the apparent ileal digestibility of nutrients. Increasing the fiber content in the diet affected the fecal digestibility of CP, ether extract, and energy (P < 0.01). The method used for studying sites of digestion in the digestive tract provides promising results, but it is limited due to the high variability that is likely caused by sampling limitations and variation between animals. Key words: dietary fiber, digestion, endogenous secretion, pig

An experiment was carried out to evaluate the metabolic utilization of energy in crossbred barrows during feed restriction and subsequent refeeding. Ten pigs, initially weighing 52 kg, were used in 5 blocks of 2 littermates each. A 7-d adaptation period (P1) was used in which pigs were offered feed at 2.60 MJ of ME*kg of B[W.sup.-0.60] x [d.sup.-1]. This adaptation period was followed by a 7-d period (P2), in which 1 pig of each block continued to receive feed at the same level of feeding, whereas for its littermate a 40% reduction in feed intake was imposed (i.e., 1.55 MJ of ME*kg of B[W.sup.-0.60] x [d.sup.-1].). During the subsequent 7-d period (P3), both pigs were offered feed at 2.60 MJ of ME*kg of B[W.sup.-0.60] x [d.sup.-1]. After P3, pigs were fasted for 1 d. Heat production (HP) was measured for all pigs during the last 3 d of P1 and on all days for P2 and P3. Heat production was measured using an open-circuit respiration chamber. Energy and N balances were determined for P1, P2, and P3. The HP was partitioned into HP due to physical activity, the short-term thermic effect of feeding, and resting HP. Feed restriction during P2 decreased (P < 0.01) total HP, resting HP, short-term thermic effect of feeding, and retained energy, whereas HP due to physical activity was not affected by feed restriction (P = 0.50). Likewise, fecal and urinary N loss, protein gain, lipid gain, and ADG were reduced during feed restriction (P < 0.01). There were no differences in components of HP and metabolic utilization of energy between the 2 groups during P1 and P3. Nevertheless, urinary N loss was decreased (P < 0.05) and ADG increased (P < 0.01) during P3 for pigs that were restricted in P2. Compensatory growth after a period of feed restriction does not seem to be related to a change in the metabolic utilization of energy for gain but more likely is due to gain in water and gut contents. Key words: compensatory growth, feed restriction, heat production, pig

A study was conducted to compare utilization of ME for growth vs. maintenance in rainbow trout and Atlantic salmon. Fish were hand-fed to satiation one of four isoenergetic diets (DE = 20 MJ/kg, as-fed basis) with different digestible protein (DP) to DE ratios (24, 22, 20, and 18 g/MJ). Intake of ME (kJ/ d), energy deposited as protein (PD, kJ/d), and energy deposited as lipid (LD, kJ/d) were determined by a comparative slaughter technique. Data were analyzed by a factorial approach or by multivariate analysis of PD and LD on ME. Maintenance energy requirements ([ME.sub.m]) and efficiency of ME utilization for PD ([k.sub.p]) and LD ([k.sub.f]) were estimated with both approaches. For the multivariate analysis, an additional parameter, the fraction of ME intake above maintenance used for PD (X) was defined as linear function of BW, with slope (d) and intercept (c) estimated simultaneously with the above parameters. Estimates were highly dependent on the approach and assumptions used. The [ME.sub.m] and [k.sub.p] values were higher and less accurate with the factorial approach than with multivariate analysis. The factorial approach estimated unrealistic [k.sub.f] values ([k.sub.f] > 1). With the multivariate analysis, [ME.sub.m] did not differ between species (20 kJ*[d.sup.-1]*[kg.sup.-0.8]). On the other hand, [k.sub.p] was significantly higher (e.g., 0.52 [+ or -] 0.06 vs. 0.43 [+ or -] 0.06; P < 0.05) for salmon than for trout and independent of diet, but [k.sub.f] was 0.81 ([+ or -] 0.13) regardless of species or diet. The ME intake above MEre used for PD (c) was higher in salmon than trout (57 vs. 55%; P < 0.05). The change in partitioning of ME for PD due to the change in BW was negative for trout (d = -0.18), but positive for salmon (d = 0.16). The d values agreed well with the increase of LD:PD ratio with BW for trout and the decrease of LD:PD with BW for salmon, which may have been related to the maturation status of this fish and the associated loss of body lipid observed by maturing salmon. In conclusion, [ME.sub.m] and cost of LD were similar for rainbow trout and Atlantic salmon, but the cost of PD was lower for salmon than for trout. Key Words: Energy Efficiency, Energy Requirements, Oncorhynchus mykiss, Salmo salar

Twelve multiparous sows with an average initial weight of 182 kg were used in a randomized complete block design to determine the effects of feeding Carnichrome (50 mg of carnitine and 200 [micro]g of chromium picolinate per kilogram of feed, as fed) on energy and nitrogen utilization in early, mid-, and late gestation. All sows were fed a diet with or without Carnichrome for the preceding 28-d lactation, the weaning-to-estrus period, and for the duration of gestation. Daily feeding allowances over pregnancy were based on calculated energy and nutrient requirements to achieve a target sow maternal weight gain of 20 kg and remained constant throughout gestation. Heat production (HP) and its partitioning (activity, thermic effect of feeding short term [TE[F.sub.st]], basal) were determined in early (wk 5 or 6), mid- (wk 9 or 10), and late (wk 14 or 15) pregnancy using indirect calorimetry. Net maternal weight gain and total number of fetuses averaged 21.6 kg and 16.4, respectively. Organic matter and energy digestibility for the Carnichrome diet was greater (P < 0.05), which resulted in greater DE and ME contents (0.6%, P < 0.05) compared with the control diet. The digestibility coefficient of energy in the current experiment for a typical corn and soybean meal diet (92%) was greater than that predicted from DE values of corn and soybean meal in feeding tables (88%). Carnichrome had no effect on total HP, energy retained as protein or lipid, and maternal energy retention in early, mid-, or late gestation. Heat production in late gestation increased linearly (4.0 kJ/[kg B[W.sup.0.75]xd]) for each additional day from d 90 to 110, despite the reduction of ME intake per unit of B[W.sup.0.75]. Metabolizable energy requirement for maintenance was 405 kJ/(kg B[W.sup.0.75]xd). On average, activity HP was 116 kJ/(kg B[W.sup.0.75]xd), which was equivalent to 20% of ME intake; however, this value ranged from 11 to 37% between sows, which corresponds to duration of standing ranging from 210 to 490 min/d. Energy cost of standing activity averaged 0.30 kJ/(kg B[W.sup.0.75]xmin). In conclusion, Carnichrome had no effect on the components of heat production and maternal weight gain during gestation, although it improved energy and organic matter digestibility of the diet. Key Words: Carnitine, Chromium, Gestation, Heat Production, Sows

The effects of reducing CP level in combination with an increase in ambient temperature (29 vs 22 [degrees] C) on performance and carcass composition were studied in a factorial arrangement of treatments involving 66 Pietrain x (Landrace x Large White) barrows from 27 to 100 kg BW. Animals were fed at each temperature one of three experimental diets that provided 0.85 or 0.70 g of digestible lysine per megajoule of NE, in the growing (27 to 65 kg) and the finishing (65 to 100 kg) phases, respectively. Diet 1 was a corn, wheat, and soybean meal diet formulated without crystalline AA; CP levels were 20.3 and 17.6% for the growing and the finishing phases, respectively. In Diets 2 and 3, CP level was reduced by substituting part of the soybean meal with corn and wheat (Diet 2), or with corn, wheat, and 4% fat (Diet 3). Diets 2 and 3 were supplemented with AA and balanced according to the ideal protein concept. The CP levels of Diets 2 and 3 were, respectively, 15.8 and 16.3% in the growing phase, and 13.4 and 13.8% in the finishing phase. Pigs were housed individually and had free access to feed and water. The ADFI was measured daily, and animals were weighed weekly. Carcass composition was measured at slaughter (100 kg BW). Increasing ambient temperature from 22 to 29 [degrees] C resulted in a 15% reduction in ADFI and 13% lower ADG. Leaner carcasses (P < 0.01) were obtained at 29 [degrees] C (22.8 vs 24.8% carcass fat). At 22 [degrees] C, ADFI was lower (P < 0.05) for the low-CP diets, but daily NE intake, ADG, and carcass composition were not affected (P > 0.05). At 29 [degrees] C, ADFI was not different (P > 0.05) between diets and daily NE intake was higher (P < 0.05) with Diet 3 than with Diet 1, and the difference was more important during the finishing period than during the growing period. Using the model ADFI = a B[W.sup.b], estimates of b were 0.65, 0.53, and 0.53 at 22 [degrees] C and 0.50, 0.44, and 0.50 at 29 [degrees] C, for Diets 1, 2, and 3, respectively. The higher NE intake for Diet 3 at 29 [degrees] C did not improve ADG (P > 0.05) but increased mainly fat deposition. These results indicate that a 4 percentage unit reduction of dietary CP level reduces N excretion (minus 37%) but does not affect growth and carcass composition as long as the ratio between essential AA and NE are kept optimal. In addition, diets with reduced CP limit the effect of high ambient temperature on ADFI. Finally, our results demonstrate the significance of using NE, rather than DE or ME, for formulating diets. Key Words: Body Composition, Dietary Fat, Dietary Protein, Growth, Heat Stress, Pigs