Tryptophan requirement of pregnant sows.

Amino acid requirements of sows may change from early to late gestation due to the accelerated growth of products of conception after d 70 of pregnancy. The objective of this study was to determine the Trp requirement, Phe kinetics, and energy expenditure in early (d 35 to 53) and late (d 92 to 111) pregnancy using the indicator amino acid oxidation method and indirect calorimetry. The same 6 second parity sows were fed 6 diets in a Latin square design in both early and late pregnancy. The diets based on corn, corn starch, and sugar provided 20 to 120% of the current recommended Trp intake (2.5 g/d) in early pregnancy and 60 to 180% in late pregnancy. Feed allowance was constant for each sow at 2.41 kg/d (SE 0.029). Expired air and blood were collected every 30 min for 5 1/2 h. After three 30-min periods to determine background (13)C enrichment in expired CO2 and plasma Phe, L[1-(13)C]Phe was given orally at a rate of 2 mg/(kg BW · h) with 8 1/2 hourly meals. Expired air and plasma were analyzed for (13)CO2 and (13)C-Phe enrichment, respectively. Requirements were determined as the breakpoint of 2-phase linear models. Sows grew from 167.7 kg (SE 3.93) at breeding to 211.9 kg (SE 5.18) post-farrowing and had litters of 14.5 piglets (SE 0.43) weighing 19.0 kg (SE 1.41) at birth. The Trp requirement was 1.7 g/d (SE 0.29, P = 0.001) in early pregnancy and 2.6 g/d (SE 0.37, P = 0.013) in late pregnancy, or 0.7 g/kg and 1.1 g/kg diet of total Trp, respectively, for a feed allowance of 2.4 kg/d. The Trp requirement in late pregnancy tended (P = 0.056) to be greater than in early pregnancy. Quantitative Phe kinetics were not affected by Trp intake except for a quadratic response of Phe oxidation and retention (P < 0.1) to Trp intake in early pregnancy. In late pregnancy, sows oxidized less Phe and retained more Phe (P = 0.001) than in early pregnancy, indicating that young, growing pregnant sows increase the efficiency of utilizing AA in late pregnancy to maintain protein synthesis in both maternal and fetal tissues. Oxidation and body protein breakdown contributed less to Phe flux in late than early pregnancy while protein synthesis contributed more (P < 0.01). Heat production and energy retention were not affected by Trp level or stage of gestation. To meet both energy and AA requirements in late gestation, a phase feeding program with 2 diets is recommended. The feed allowance in late pregnancy should be greater than in early pregnancy to account for the increased energy expenditure.

Isoleucine requirement of pregnant sows.

The objective of this study was to determine the Ile requirement in early (d 39 to 61) and late (d 89 to 109) pregnancy using the indicator AA oxidation method. The same 7 Large White × Landrace sows in their fourth parity were used in early and late pregnancy. Each sow received 6 diets based on corn, corn starch, and sugar in both early and late pregnancy at constant feed allowances (2.5 kg/d). Diets provided Ile at 20, 40, 60, 80, 100, and 120% of the Ile requirement (6.2 g/d based on the 1998 NRC) in early and 60, 80, 100, 140, 160, and 180% in late pregnancy. After determination of (13)C background in expired CO2 and plasma free Phe for 1.5 h when confined in respiration chambers, sows were fed the tracer, L[1-(13)C]Phe, a rate of 2.0 mg/(kg BW·h) over 4 h divided into eight 30-min meals. Expired CO2 and plasma free Phe were analyzed for (13)C enrichment above background. Requirements were determined as the breakpoint in 2-phase nonlinear models. Sow BW was 246.5 kg in early and 271.6 kg in late pregnancy. Daily gain of the 6 sows was similar in early (344 g/d) and late pregnancy (543 g/d). During pregnancy, sow maternal gain was 19.1 ± 4.4 kg and litters of 17.7 ± 0.8 piglets weighed 22.6 ± 0.9 kg at birth. The Ile requirement was 3.6 ± 1.2 g/d (P = 0.001) in early pregnancy with a Phe retention (-0.59 g/d) and energy retention (-0.31 MJ/d) that were not different from 0. This indicates that the fourth parity sows had requirements close to maintenance in early pregnancy. The Ile requirement in late pregnancy was 9.7 ± 1.9 g/d (P = 0.001) when sows retained 3.30 g/d of Phe and -1.45 MJ/d of energy. The greater Ile requirement in late pregnancy was probably caused by the increased conceptus growth after d 70 of pregnancy. Phenylalanine flux, oxidation, and nonoxidative disposal increased (P < 0.1) from early to late pregnancy, but body protein breakdown did not. Phenylalanine oxidation, nonoxidative disposal, and retention increased (P < 0.01) with increasing Ile intake in early pregnancy but were not affected by Ile intake in late pregnancy. Body protein breakdown did not respond to Ile intake in early or late pregnancy. Although energy retention was similar in early and late pregnancy, the respiratory quotient decreased (P = 0.047) from early (1.05) to late pregnancy (0.98), indicating lipid mobilization in late pregnancy when Ile was at or above the requirement. The results of this study show that the Ile requirement of sows increases from early to late pregnancy.

Protein intake but not feed intake affects dietary energy for finishing pigs.

The effects of dietary protein and feeding levels on dietary metabolizable (ME) and net energy (NE) content were determined in 24 pigs, each offered two diets at 2.0 times the energetic maintenance requirement or for ad libitum intake between 55 and 95 kg body weight. Within feeding levels, pigs received, in random order, low-protein (LP; 11.2% CP, 0.61% lysine) or high-protein (HP; 20.2% CP, 0.61% lysine) diets of similar digestible energy content. Dietary NE was calculated from heat production based on 24-h indirect calorimetry following a 7-day N-balance period. Feed intake was greater for LP than HP when fed for ad libitum intake (p = 0.001). Protein level did not affect daily gain (p > 0.1) but HP improved gain: feed (p = 0.003). Dietary ME and NE were not significantly affected by feeding level but were decreased by high protein intake (p < 0.07). Reducing dietary protein reduced urinary energy losses and increased energy retention but did not affect heat production. The effect of dietary protein restriction was already evident on the ME level and carried over to a similar degree to the NE level because the utilization of ME was not affected by protein level. Dietary ME and NE decreased by 0.012 MJ/kg (p = 0.014) and 0.018 MJ/kg (p = 0.062), respectively, for each gram per day N intake. The results suggest that although there was an effect of protein level on NE, the greatest effect occurred at the level of ME. However, the prediction of both ME and NE may be improved by adopting energy values for dietary protein that changes with dietary protein content.

Dietary lysine requirement of sows increases in late gestation.

Current AA recommendations for sows are to provide a fixed amount of AA intake throughout gestation; however, the demand for nutrients changes from maternal lean tissue in early gestation (EG) to fetal and mammary growth in late gestation (LG). The objective of this study was to determine the Lys requirement in EG (d 24 to 45) and LG (d 86 to 110) using the indicator AA oxidation method with simultaneous determination of heat production. Each of 7 Large White × Landrace sows received 6 diets in random order in both EG and LG. Three semisynthetic diets (14.0 MJ ME/kg) based on corn were formulated and mixed to produce a basal diet (60% of 1998 NRC Lys requirement) and high diets for EG and LG (150% and 185% of 1998 NRC Lys requirements, respectively). The 6 test diets provided Lys intakes of 7.5 to 19.3 g/d in EG and 8.1 to 23.7 g/d in LG. Sows were placed in respiration chambers, and expired air and blood were collected every 30 min for 5.5 h. The tracer AA, l-[1-(13)C]Phe, was given orally at a rate of 2 mg/(kg BW ⋅ h) over the last 4 h, divided into 8, 0.5-h meals. Expired air was measured for (13)CO(2) enrichment, and plasma was measured for l-[1-(13)C]Phe enrichment and free Lys concentration. Background (13)CO(2) was subtracted from plateau (13)CO(2) enrichment. Requirements were determined using a 2-phase nonlinear model. Mean maternal BW gain in gestation (43.7 kg; pooled SE, 1.2 kg), litter size (14.6 total born piglets; pooled SE, 0.8), and litter weight (19.4 kg; pooled SE, 0.9 kg) did not differ between parities. Sow weight gain and BW was greater (P = 0.001) in LG than EG. Lysine requirement was 9.4 and 17.4 g/d in EG and LG, respectively. Phenylalanine retention in LG was maximized at a Lys intake of 17.7 g/d. Heat production was more (P = 0.069) and energy retention less (P = 0.019) in LG than EG. Energy retention in LG was not different from 0. Quantitative Phe kinetics in EG were not affected by Lys intake. In LG, Phe retention increased with Lys intake (P = 0.004), whereas Phe oxidation decreased (P = 0.005). The Lys requirement was determined to be less than current recommendations in EG and more than current recommendations in LG. To meet the change in requirements, diets with increased lysine content are needed in LG. Increasing the feed allowance in LG is necessary to maintain a positive energy balance throughout gestation.

The threonine requirement of sows increases in late gestation.

Current AA recommendations for sows are to provide a fixed amount of AA intake throughout gestation based on the assumption that there is a constant demand for AA; however, the demand for nutrients changes from maternal lean tissue in early gestation to fetal and mammary growth in late gestation. The objective of this study was to determine the Thr requirement in early (d 35 to 53 and 25 to 55 for Exp. 1 and 2, respectively) and late (d 92 to 110 and 81 to 111 for Exp. 1 and 2, respectively) gestation using the indicator AA oxidation (IAAO) method with l-[1-(13)C]Phe as the tracer AA. A total of 14 multiparous sows were used: 6 in Exp. 1 and 8 in Exp. 2. Each sow received each of 6 diets in random order in both early and late gestation. A basal diet was formulated to contain Thr at 60% of the 1998 NRC recommendation in Exp. 1 and 20 and 60% of the 1998 NRC in Exp. 2 for early and late gestation, respectively. Crystalline l-Thr was added to create additional diets with approximately 10% incremental increases in Thr. Sows were placed in respiration chambers, and expired air and blood were collected every 30 min for 5.5 h. Tracer Phe [mg/(kg of BW·h)] was given orally over the last 4 h divided into eight 0.5-h meals. Expired air and plasma were measured for (13)CO(2) enrichment and free Thr concentration, respectively. Background (13)CO(2) was subtracted from plateau (13)CO(2) enrichment. Data were analyzed using a 2-phase nonlinear Mixed model. The overall litter size and litter weight were 13.5 ± 3.1 and 20.5 ± 3.9 kg, respectively. Based on IAAO, the Thr requirement in early gestation was 6.1 g/d (R(2) = 0.59, Exp. 1) and 5.0 g/d (R(2) = 0.71, Exp. 2). In late gestation, the Thr requirement based on IAAO was 13.6 g/d (R(2) = 0.60, Exp. 1) and 12.3 g/d (R(2) = 0.58, Exp. 2). Based on plasma Thr, the Thr requirement in early gestation was 7.0 g/d (R(2) = 0.90, Exp. 1) and 3.9 g/d (R(2) = 0.90, Exp. 2). In late gestation, the Thr requirement based on plasma Thr was 10.5 g/d (R(2) = 0.67, Exp. 2). There was a linear response to increasing Thr intake in late gestation in Exp. 1. Feeding a single amount of AA throughout gestation results in overfeeding AA in early gestation and underfeeding AA in late gestation. The 2-fold increase in Thr requirement in the last third of gestation suggests that phase feeding sows in gestation will more closely meet the demands for nutrients and that the requirement for essential AA in gestating sows should be re-evaluated in early and late gestation separately.

Methionine-hydroxy analogue was found to be significantly less bioavailable compared to dl-methionine for protein deposition in growing pigs.

When methionine (Met) is limiting in swine diets, it is commonly supplemented by using anhydrous dl-methionine (DLM, 99% purity) or liquid dl-methionine-hydroxy analogue free acid (MHA-FA, 88% purity). The objective of this experiment was to test the null hypothesis that the bioavailability of DLM and MHA-FA were not different for growing pigs, using the indicator amino acid (AA) (phenylalanine, Phe) oxidation (IAAO) method in a slope-ratio assay. Six barrows (mean BW during study: 21.1 kg) received seven dietary treatments with all pigs receiving all diets in random order at an intake of 95 g/kg BW0.75. The basal diet (BD) contained analyzed content of 15.1% CP, 0.20% Met, 0.73% Phe and all other AA in excess of requirement. The BD was supplemented with three graded levels of DLM or MHA-FA on an equimolar basis. Dietary treatments only varied in Met content and included: (i) BD, (ii) BD + 0.034% DLM, (iii) BD + 0.054% DLM, (iv) BD + 0.086% DLM, (v) BD + 0.029% MHA-FA, (vi) BD + 0.078% MHA-FA and (vii) BD + 0.107% MHA-FA, as analyzed. Indicator AA oxidation was determined during 4 h studies, where pigs were fed half-hourly meals each equal to 1/32 of their daily feed allowance. Each meal was mixed with 258.7 kBq (s.e. 2.6) of l-[1-14C]Phe with a prime of 3.5 times the half-hourly dose added to the first meal. The slope of the decrease in IAAO calculated by linear regression analysis was greater (P = 0.012) for DLM supplementation (9.87 ± 1.450 per g, 1.488 ± 0.215% per mmol) than for MHA-FA (6.48 ± 0.89 per g, 1.107 ± 0.152% per mmol). The ratio of slopes indicated a bioavailability of MHA-FA on a product basis, relative to DLM, of 65.7%. Bioavailability on an equimolar Met basis, calculated from the ratio of the slopes was 74.4% for MHA-FA, relative to DLM. In conclusion, these results indicate that the metabolic bioavailability of MHA-FA for growing pigs is appreciably lower than that of DLM on both an equimolar and a product basis.

An estimate of the methionine requirement and its variability in growing pigs using the indicator amino acid oxidation technique.

Although AA requirements for the mean of a population of growing pigs have been established using traditional methods, there are no estimates of the variability within the population and whether this variation differs among AA. With the increased use of supplemental Lys in pig diets, there will be an increased need to supplement Met, commonly the second or third limiting AA in corn-soybean diets. The indicator AA oxidation method allows repeated measurements in a short period of time so that the AA requirement can be determined for individual pigs at a similar physiological stage. The objective of this study was to determine the mean Met requirement in individual gilts and to estimate the related variability. Six individually housed female pigs (initial BW = 8.8 kg, SD 1.5) each received diets providing 6 levels of dl-Met. The isonitrogenous and isoenergetic diets contained 0.187, 0.250, 0.290, 0.320, 0.350, and 0.377% Met (analyzed, as-fed basis). Cysteine (0.48%) and Lys (1.44%) concentrations were similar for all diets. Pigs were adapted for 6 d to the basal corn-soybean meal diet (0.187% Met), which was offered at 95 g/kg(0.75) of BW to ensure complete consumption of the test diets. During 4-h oxidation studies, 313.4 kBq, (SD 35.6) of L-[1-(14)C]Phe was mixed with each of 8 half-hourly meals, and expired CO(2) was collected. The breakpoint in Phe oxidation, representing the Met requirement, and its variability, was determined using 2-phase linear regression. Phenylalanine oxidation decreased as the Met content increased from 0.187 to 0.29%. Phenylalanine oxidation was not different (P > 0.2) for diets ranging from 0.320 to 0.377% Met. The dietary Met requirement varied from 0.320 to 0.373% for individual pigs. The mean Met requirement for individual pigs was determined to be 0.340% of diet (SD = 0.024%, CV= 7.1%), with 0.340, 0.364, and 0.388% covering the requirement of 50, 66, and 95% of the population, respectively. The present mean population estimate was similar to the recommended dietary Met concentration of 0.325% for pigs of this BW and feed intake. To maximize profitability, Met levels in starter pig diets should be determined, depending on the cost of crystalline Met and the fraction of the population whose requirement is to be met.

Relationship between bicarbonate retention and bone characteristics in broiler chickens.

Determination of the bicarbonate retention factor (BRF) is an important step during development of the indicator amino acid oxidation technique for use in a new model. A series of 4-h oxidation experiments were performed to determine the BRF of broilers aged 7, 14, 21, 28, 35, and 42 d using 4 birds per age group. A priming dose of 1.2 microCi of NaH(14)CO(3), followed by eight half-hourly doses of 1 microCi of NaH(14)CO(3) were given orally to each of 4 birds per age. The percentage of (14)C dose expired by the bird at a steady state was measured. These birds, as well as 12 additional birds matched for age and BW, were killed, and femur bone mineral density was measured by quantitative computed tomography to determine the relationship between bone development and bicarbonate retention at each age. There was a correlation (r = 0.50; P < 0.05) between total cross-sectional femur bone mineral density and bicarbonate retention at each age. A prediction equation (Y = 6.95 x 10(-2)X - 3.51 x 10(-5)X(2) + 27.58; P < 0.0001, R(2) = 0.79) where Y = bicarbonate retention and X = BW was generated to predict Y as a function of X. Bicarbonate retention values peaked at 28 d, during the stage of the most rapid bone deposition and the highest growth rate. A constant BRF was found from 1,900 to 2,700 g of BW of 35.15 +/- 1.095% (mean +/- SEM). This retention factor will allow the accurate correction of oxidation of (14)C-labeled substrates in broilers of different ages and BW in future indicator amino acid oxidation studies.

Estimate of the variability of the lysine requirement of growing pigs using the indicator amino acid oxidation technique.

Although AA requirements for the mean in a population of growing pigs are well established, there are no direct estimates of their variability within the population. The indicator AA oxidation method allows repeated measurements in a short period of time so that the AA requirement can be determined for individual pigs. The objective was to determine the Lys requirement in individual pigs to derive a first estimate of the population mean requirement and its variability. Nine individually housed barrows (15 to 18 kg) were surgically implanted with venous catheters for isotope infusion. Pigs were offered, in random order, isonitrogenous and isoenergetic diets with one of seven Lys concentrations (4.8 to 15.5 g of Lys/kg diet, as-fed basis). The pigs were fed twice daily, except for study days when they received one-half of the daily allowance in eight equal hourly meals. After a validated minimum adaptation period, indicator (Phe) oxidation was determined for each dietary Lys level during a 4-h primed, constant infusion of L-[1-(14C)]Phe at a rate of 464 kBq/h. The Lys requirement was calculated using a two-phase linear regression crossover analysis within individual pigs. For each pig, Phe oxidation decreased linearly (P < 0.02) as the dietary Lys concentration increased until the requirement was reached; thereafter, Phe oxidation was not different. The true ileal digestible Lys requirement ranged from 7.5 to 10.6 g/kg of diet (as-fed basis) for the nine animals. The mean requirement for all pigs was 9.1 g/d (CV, 11.6%) or 93.9% (CV, 9.8%) of the predicted (NRC, 1998) requirement based on each pig's mean BW and energy intake. The measured and predicted requirements did not differ. The indicator AA oxidation method gave values for Lys requirement similar to conventional methods. The short (< 3 wk) experimental period allows, for the first time, the estimate of population variability, which provides for more accurate calculation of the effect of altering Lys intake on herd performance and production economics. This method is suitable to use with all dietary indispensable AA.

Influence of dietary protein content of efficiency of energy utilization in growing pigs.

The objective of this trial was to quantify the influence of a varied dietary crude protein content supplying equal amounts of limiting essential amino acids on parameters of energy metabolism. A total of 16 castrated male pigs were allocated to four dietary treatments and subjected to measurements of N-balance and gas exchange at approximately 65 and 85 kg live weight. Two ratios formulated to be isoenergetic differed in crude protein content (CP) and were offered at two feeding levels. At 85 kg, rations with a lower CP content were used. Multiple regression analysis was used to determine the effects of CP and those of live weight and metabolizable energy intake (IME). A rise in CP significantly increased energy losses via urine and the energy retained as protein (RPE), while the energy retained as fat was significantly reduced. Energy retention tended (P < 0.1) to decrease, while related to IME the reduction was non significant. The proportion of RPE in energy gain was significantly improved. Possible mechanisms for this shift towards reduced fat and energy retention at higher protein intakes are discussed. It is concluded that in practical feeding, rations with a lower CP content should be fed restrictively or be reduced in energy content to avoid excessive carcass fatness.