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.     

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.     

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.     

Effect of phytase-xylanase supplementation to wheat-based diets on energy metabolism in growing–finishing pigs fed ad libitum

The effects of dietary protein and phosphorus level, and phytase and/or xylanase addition on performance, nutrient digestibility and energy metabolism in finisher pigs were determined. Protein reduction increased nutrient digestibility, pig performance and dietary net energy. Phosphorus reduction increased heat production, and tended to negatively affect all parameters. Phytase increased daily gain and dietary metabolizable energy. Xylanase improved digestibility of nutrients and energy, but had no effect on dietary net energy. Phytase and xylanase addition were not additive.     

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.     

Metabolic availability of lysine in feedstuffs determined using oral isotope delivery

Using the indicator amino acid oxidation technique in a standard curve assay, the availability of lysine in feedstuffs for pigs was determined using oral isotope delivery. In 8 barrows, 20 kg initial weight, indicator oxidation responded linearly to increasing levels of free lysine at 50, 60, 70 and 80% of requirements. The availability of lysine in peas was reduced from 75.8% to 68.3% after heating. Adding back the lysine lost during heating restored the availability to 76.5%. Using this method, the availability of lysine in soybean meal (87.5%) was similar to reported true ileal digestibility, while that in canola meal (71.4%) and cottonseed meal (75.1%) was lower and greater, respectively. The results for peas demonstrate that this method responds sensitively to small changes in lysine availability. Therefore, using oral isotope delivery with this method is suitable to determine the bioavailability of amino acids in feedstuffs for pigs.     

小麦基础日粮中添加植酸酶-木聚糖酶对肥育猪能量代谢的影响

本试验研究了日粮中蛋白和磷含量、植酸酶和/或木聚糖酶的添加对生长肥育猪生长性能、养分消化率以及能量代谢的影响。减少日粮蛋白质含量可提高养分的消化率、猪的生长性能以及日粮净能。降低磷水平可以提高试验猪的产热,并且对所有参数具有负面影响的趋势。添加植酸酶可提高日增重和日粮能量代谢率。添加木聚糖酶可提高养分和能量的消化率,但对日粮净能没有影响。同时添加植酸酶和木聚糖酶并没叠加效应。