Effect of dietary potassium on absorption of magnesium and other macroelements in sheep fed different levels of magnesium

Two metabolism trials were conducted with 24 crossbred wether lambs. Two levels of Mg (.1 and .2%) and four levels of K (.6, 1.2, 2.4 and 4.8%) were fed in a 2 x 4 factorial arrangement of treatments. Each trial consisted of a 10-d preliminary period followed by a 10-d collection of feed, feces and urine. Increasing levels of dietary K resulted in a linear increase in fecal Mg excretion and a linear decrease in Mg absorption. A large depression in Mg absorption occurred when K was increased from 1.2 to 2.4% with a further decrease when K was increased to 4.8%. Lambs fed the high level of Mg (.2%) absorbed and retained more (P less than .05) total Mg (g/d, but not percentage of intake) compared with the low magnesium level (.1%). Dietary Mg did not affect the amount of K excreted, absorbed or retained. Increasing the level of dietary K resulted in a linear increase in urinary, fecal and total K excreted, absorbed and retained (P less than .05).     

Effects of dietary potassium and sodium on magnesium utilization in sheep

Two metabolism trials were conducted to determine the effect of altering dietary Na and K on Mg availability. Three dietary treatments (normal K-normal Na, high K-normal Na and high K-high Na) were imposed upon nine crossbred wether lambs in a randomized block design. Each trial consisted of a 5-d diet adjustment, a 10-d preliminary period and a 5-d collection of feed, feces and urine. Increasing K and Na intake increased the percentage of Mg excreted in feces. Both elevated K and K-Na depressed (P less than .10) urinary Mg excretion, primarily a reflection of depressed Mg absorption in animals fed these diets. Apparent K absorption and retention increased when animals were supplemented with K. Addition of Na to the diet did not alter absorption or retention of K. Apparent K and Na availability increased when K and Na supplements were included in the diet. This increased availability resulted from increased total absorbed K and Na compared with a fixed endogenous excretion. Calcium balance in lambs was not affected by addition of K or Na. Lambs were able to absorb enough Mg from their respective diet to maintain normal serum Mg levels. Addition of Na to a diet high in K did not enhance Mg absorption in lambs.     

Effect of dietary electrolyte balance on nutrient digestibility determined at the end of the small intestine and over the total digestive tract in growing pigs

A replicated 4 x 4 Latin square digestion trial was conducted to determine the effect of electrolyte balance (EB = Na + K - Cl meq/kg of the diet) on apparent nutrient digestibilities in pigs fitted with ileal T-cannulas. Experimental diets were composed of corn and soybean meal with dietary EB altered by the substitution of CaCl2 for CaCO3, or NaHCO3 for corn and soybean meal. Electrolyte balance levels examined were -50, 100, 250 or 400 meq/kg of the diet. Increasing dietary EB concentration linearly increased (P less than .05 to P less than .02) apparent ileal digestibility of N, energy, DM and all amino acids, except alanine and methionine. However, nutrient and amino acid digestibilities measured over the total digestive tract were similar (P greater than .16) among EB levels. Increasing dietary EB resulted in a linear and quadratic (P less than .03) effect on daily urinary N excretion, resulting in a linear (P less than .05) improvement in N retention expressed both as a percentage of N intake and of absorbed N. Blood pH, total CO2, HCO3 and base excess concentrations increased linearly (P less than .02 to P less than .001) with increasing dietary EB. Dietary EB concentrations influenced nutrient and amino acid absorption measured near the end of the small intestine. Additionally, the N balance data per unit of N intake or N absorbed are indicative of an improved N utilization in pigs fed increasing dietary EB concentrations from -50 to 400 meq/kg.     

Estimation of the isoleucine and aromatic amino acid requirements of pregnant swine

The requirements of the pregnant gilt for isoleucine (Ile), total aromatic amino acids (TAAA), phenylalanine (Phe) and the replacement of Phe with tyrosine (Tyr) were investigated in these studies. Five balanced 6 x 6 latin-square arrangements of treatments and time periods were conducted with six pregnant gilts in each trial. Each diet treatment was fed (1.8 kg once daily) for 10 d beginning on d 40 of pregnancy. Nitrogen balance trials were conducted from the 6th to 10th d during each period. Blood samples were obtained from each gilt before and 2 h after the last feeding in each period. Based on the titration trials, the L-Ile requirement was satisfied at .23% of the diet. Assuming that crystalline L-Ile was 100% available, the L-Ile requirement for pregnant gilts fed a corn-soybean meal diet is estimated at .25%. A dietary requirement of no more than .43% satisfied all the criteria measured in the L-TAAA trial. Adjustment for availability of crystalline L-Phe used in the diets would increase the requirement to about .48% dietary L-TAAA. About 42% of the L-TAAA requirement for pregnancy should be supplied by L-Phe.     

日粮不同磷水平和钙磷比例对香猪钙磷代谢的影响

３６ 头香猪生长阶段去势公猪,通过３ ×３ 交叉分组设计,随机分配到９ 个处理中,每个处理４个重复,每个重复１ 头猪。试验两个因子中日粮磷３ 个水平分别为０ ．３ ％ 、０ ．６ ％ 和０ ．９ ％ ,日粮钙磷比的３ 个水平为１ １ 、１ ．２５ １ 和１ ．５ １ 。试验基础日粮由玉米、豆粕、血粉和苜蓿粉组成,各处理日粮磷水平和钙磷比用分析纯ＣａＣＯ３ 、Ｎａ２ＨＰＯ４ 和ＣａＨＰＯ４ 调配。两期钙磷代谢试验结果表明,提高日粮磷水平线性增加香猪钙磷采食量、粪钙磷和尿磷（Ｐ＜ ０ ．０１） ,０ ．６ ％ 的日粮磷水平在两期试验中表现出最高的磷存留量和磷表观利用率。随日粮钙磷比增加,钙的采食量、粪钙磷和尿钙逐渐增加（Ｐ＜ ０ ．０１） ,而尿磷逐渐减少（Ｐ＜ ０ ．０１） 。在体重７ｋｇ 时,当钙磷比为１ ．２５ １ 时,钙的表观消化率和表观利用率显著高于１ １组（Ｐ＜ ０ ．０５） 。在体重１７ｋｇ 时,钙磷的存留量、钙的表观利用率和磷的表观消化率在日粮钙磷比１ １ 时表现最大值（Ｐ＜ ０ ．０１） ,并且日粮磷和钙磷比互作效应显著影响粪钙磷、尿磷、钙磷存留量、磷的表观消化率和钙磷表观利用率（Ｐ＜ ０ ．０１）     

Influence of oscillating dietary crude protein concentration on performance, acid-base balance, and nitrogen excretion of steers

Decreasing dietary N inputs into beef cattle feeding operations could potentially decrease environmental concerns relating to air and water quality. Previous studies with sheep suggest that oscillating dietary CP concentrations may improve N use efficiency and thereby decrease dietary N requirements. Therefore, two studies were conducted to determine the effects of oscillating dietary CP concentrations on performance, acid-base balance, and manure characteristics of steers fed high-concentrate diets. Steers were fed to a constant backfat thickness in both studies. In the first trial, 92 steers (mean BW = 408 +/- 2.8 kg; four pens/treatment) were fed the following diets: 1) constant 12% CP, 2) constant 14% CP, and 3) 10 and 14% CP oscillated at 2-d intervals. Steer performance and carcass characteristics were measured. In the second trial, 27 steers were individually fed the same three experimental dietary regimens (nine steers/treatment). Animal performance, arterial acid-base balance, plasma metabolites, and fecal characteristics were measured. In both trials, steers fed the 14% CP diet tended (P < 0.10) to have greater ADG and gain:feed than steers fed the 12% CP diet. Steers fed the oscillating CP regimen had intermediate performance. In Trial 1, steers fed the 14% CP diet tended (P = 0.09) to have smaller longissimus area and higher quality grades than steers fed the oscillating CP regimen. Protein retentions (g/d) calculated from NRC (2000) equations were greater (P = 0.04) for steers fed the 14% CP diet than steers fed the 12% CP diet. Steers fed the oscillating CP regimen tended (P = 0.08) to have greater calculated protein retention (g/d) than steers fed the 12% CP diet. Steers fed the 14% CP diet had greater (P < 0.05) calculated urinary N excretion than steers fed the 12% CP or oscillating CP regimens. Venous plasma concentrations of urea N were greater (P < 0.001) in steers fed the 14% CP diet than in steers fed the 12% CP diet; steers fed the oscillating CP regimen were intermediate but fluctuated over days. Based on arterial blood gas concentrations, acid-base balance was not significantly affected by dietary CP regimen. Results of these trials suggest that the CP requirement of steers in these studies was greater than 12% of the diet DM, and/or that the degradable CP requirement was greater than 6.3% of diet DM. However, the effects of oscillating dietary CP were minimal.     

Effects of dietary protein concentration on the response of growing chicks to methionine.

1. Experiments were conducted independently at two stations to measure the requirement for methionine in chick diets with crude protein (CP) varying in 8 steps from 140 to 280 g/kg diet (experiment 1) or from 90 to 300 g/kg (experiment 2). 2. Protein composition was the same at all protein concentrations within a trial. The diet was designed to be first-limiting in methionine and DL-methionine was added to provide 5 ratios of methionine to CP at each protein concentration. 3. Methionine required for maximum growth rate or maximum efficiency of food utilisation was estimated at each protein concentration by fitting a quadratic regression equation to the relevant data. The requirement was also estimated by fitting the Reading model to data for growth rate and methionine intake. 4. In both trials and by all three methods of estimation, the methionine requirement (g/kg diet) for maximum performance increased as a linear function of dietary CP concentration and nearly in direct proportion to CP. 5. It is concluded that diets which contain surplus protein, beyond that needed to maximise growth rate or food efficiency, need supplementation with methionine beyond that required when dietary protein is just adequate. A suitable rule for practical formulation is that methionine concentration in chick diets should be not less than 0.025 times the dietary CP concentration.     

生长猪饲粮磷水平对磷酸氢钙中磷真消化率评定的影响

本试验旨在研究生长猪饲粮磷水平对磷酸氢钙(DCP)中磷的全肠道真消化率评定的影响。选用56头体重为(25.90±0.25)kg的杜×长×大杂交去势公猪,根据体重随机分为7个处理组,每组8个重复,每个重复1头猪。对照组饲喂未添加DCP的基础饲粮,6个处理组在基础饲粮中分别添加0.64%、1.28%、1.92%、2.56%、3.20%、3.84%DCP。使用全收粪法测定磷的表观全肠道消化率。结果表明:生长猪总磷的表观全肠道消化率随饲粮DCP水平提高呈线性和二次增加(P0.05);随着DCP添加水平的提高,由差量法测得无机磷的全肠道真消化率呈二次上升的趋势(P0.1),具体表现为无机磷的全肠道真消化率随饲粮DCP水平提高呈现出先增加后降低的趋势;通过线性回归法发现,生长猪饲喂低DCP饲粮后测得磷的全肠道真消化率显著高于饲喂高DCP饲粮(P0.05)。由此可见,饲粮磷水平显著影响差量法和线性回归法测得DCP的全肠道真消化率;使用差量法测定饲粮原料磷的全肠道真消化率时应将饲粮磷水平维持在接近磷需要量的水平,使用线性回归法测定磷的全肠道真消化率时应将饲粮磷水平控制在低于磷需要量的范围内。     

Calcium and phosphorus requirement of swine from weaning to market weight: I. Development of response curves for performance

Three trials using 300 pigs were conducted to establish response surfaces for effects of calcium and phosphorus (Ca/P) levels and of time on postweaning pig performance. Five dietary Ca/P levels (70, 85, 100, 115 and 130% of the NRC [1979] estimated dietary Ca and P requirements) were fed from weaning to market weight. Twelve replicates, each consisting of five pigs, were used across the three trials, and one pig per replicate was slaughtered every 4 wk following the start of the trials. Efficiency of feed utilization (G:F) was insensitive to diet within the range of Ca/P levels used, whereas ADG and average daily feed intake (ADFI) were linearly (P less than .01) and quadratically (p less than .01) related to both diet and weigh period. Asymptotic models relating continuous effects of total Ca + P intake (average grams per day of Ca + P) relative to the NRC estimated Ca + P intake and days on test at the midpoint of each weigh period were fitted to the data and used to derive response surfaces for ADG and ADFI. Ninety, ninety-five and ninety-eight percent of maximum ADG, ADFI and G:F also were determined; 98% of maximum ADG was reached with a Ca and P intake of 99.8% of NRC Ca/P estimates, whereas Ca and P intakes of 95.3 and 83.5% of NRC estimates were required to produce 98% of maximum ADFI and G:F, respectively.     

Note on the effects of protein concentration on responses to dietary lysine by chicks

1. This paper gives further analyses of data from previously reported trials in which chicks were fed diets with protein concentrations ranging from 140 to 280 g/kg diet, with the lysine content varied at each protein concentration. 2. Alternative methods of estimating the lysine requirement, at each concentration of protein, are investigated. 3. Although these methods produce rather different estimates of requirement, they do not change the conclusion that the lysine needed for maximum growth or maximum efficiency of food utilisation is a linear function of dietary protein concentration throughout the range from 140 to 280 g crude protein/kg. 4. It is concluded that lysine requirements for growing chicks should be specified as a proportion of the protein and not as a proportion of the diet.     

Effect of supplemental potassium in the receiving diet and form of antibiotic on feeder pig performance

In five separate trials 901 feeder pigs (769 purchased and 132 university-raised) were used to determine the effect of level of dietary K (.64 vs 1.00 vs 1.40%), form of neoterramycin (feed-grade vs water-soluble) and a long-lasting oxytetracycline injection on subsequent performance. Purchased pigs fed a 28-d receiving diet with 1.00% K gained faster (P less than .05) than the control pigs fed a .64% K diet (.64 vs .60 kg) during a 1980 summer trial. Feed efficiency was not affected by level of dietary K. Three additional trials conducted during January, July and October of 1981 failed to substantiate this beneficial effect on rate of gain. Feeder pig performance was not different (P greater than .05) when either feed-grade or water-soluble neoterramycin was used as a 14-d receiving treatment at preventative levels. However, in one trial nearly twice as many pigs on the medicated feed diet required additional treatment for sickness compared with pigs receiving water medication (14.5 vs 7.9%; P less than .1). Giving pigs an injection of a long-lasting oxytetracycline (LA-200) either at the market or upon arrival at the finishing facility had no effect on performance; however, the pigs were home-raised rather than purchased; consequently, their health was excellent.     

Histidine requirement of the young pig

A histidine (HIS)-deficient, feather meal-corn-dried whey basal diet (19% protein and 3,200 Kcal ME/kg), supplemented with lysine, methionine and tryptophan, was employed to determine the HIS requirement of the growing pig between 10 and 20 kg live weight. Using a chick bioavailability growth assay, the HIS-deficient basal diet was found to contain .19% bioavailable HIS. A preliminary pig study established that the HIS-deficient basal diet was capable of supporting good growth of pigs when supplemented with sufficient L-HIS.HCl.H2O. In the second pig experiment, crossbred pigs with an average initial weight of 10 kg were kept in individual metabolism crates and were fed to appetite in two feedings the HIS-deficient basal diet supplemented with 0, .06, .12 or .18% L-HIS. Rate and efficiency of weight gain increased linearly between 0 and .12% supplemental HIS, but the highest supplemental level of HIS did not improve performance further. Plasma HIS increased, whereas plasma urea-N remained unchanged, as the level of dietary HIS increased. The third pig experiment employed narrower increments of .06, .09 or .12% supplemental HIS, and a linear response in both gain and feed efficiency occurred. Viewing all experiments together, the bioavailable HIS requirement of the 10- to 20-kg pig was .31% of the diet. Assuming an 85% bioavailability of HIS in commercial diets based on corn and soybean meal, the total HIS level needed in practice would be .36%.     

Adaptation of protein oxidation to protein intake in the domestic cat

It is well-accepted that cats require more dietary protein than omnivores and herbivores. Work on hepatic enzyme activities showed that cats lack the ability to regulate the urea cycle enzymes in response to the dietary supply of protein. It was thus hypothesized that the high protein requirement of cats is due to an inability to regulate these enzymes, limiting adaptation to a low protein diet. We used indirect respiration calorimetry to assess the in vivo ability of cats to adapt substrate oxidation to different levels of dietary protein, including one below their protein requirement. In random order, eight cats consumed each of four semi-purified diets containing 7.7% (LP), 14.6% (AP), 27.3% (MP) and 51.1% (HP) of ME from protein. Cats consumed each diet for at least 14 days and then completed a 5-day nitrogen balance trial and at least 2, 12-hour indirect calorimetry measurements. The data were analyzed by anova using the Mixed procedure of SAS and are expressed as mean ± SEM. There was a significant effect of diet on protein oxidation (p < 0.0001), measuring 9.8 ± 0.5%, 13.4 ± 0.9%, 23.5 ± 0.8% and 49.0 ± 1.8% of total energy expenditure on the LP, AP, MP and HP diets, respectively. The ratio of protein oxidation/protein intake was significantly higher with the LP diet (1.27 ± 0.07) than the other three diets (AP, 0.92 ± 0.06; MP, 0.86 ± 0.03; HP, 0.96 ± 0.04; p < 0.0001), indicating a net loss of protein on the LP diet. Thus, cats adapted to a wide range of dietary protein concentrations, but were unable to fully adapt to the LP diet.     

Estimation of dietary lysine requirement using plasma amino acid concentrations in mature thoroughbreds

Four experiments were conducted to estimate dietary lysine (Lys) requirements using plasma amino acid concentrations as a criterion in mature thoroughbreds. In each experiment four adult thoroughbreds were used. The changes in plasma Lys concentration after feeding were observed in Experiment 1. Blood samples were taken from the cervix vein 0.5 h before, and 1, 3, 5.5, and 10 h after feeding. The plasma Lys concentration increased and remained constant until 3 h after feeding, decreased until 5.5 h and remained constant after then. Therefore, the bleed was done at 3 h after feeding in all later experiments. To make sure of the response speed of the plasma Lys to changes of dietary Lys levels, dietary Lys levels were changed from high to low, and low to high levels in Experiment 2. Blood samples were taken just on the changing day and 1, 2 and 3 days after changing diets. The plasma Lys concentration decreased until 2 days after changing the diet, and then remained constant with advancing days after changing the diet from high Lys to low Lys. On the other hand, the plasma Lys increased until one day after changing the diet, and then remained constant with advancing days after changing dietary Lys levels. Thus, blood samples were taken 3 days after feeding in the next experiments. The possibility of estimating the Lys requirement for maintenance using plasma Lys concentration was elucidated by two methods in Experiments 3 and 4. In Experiment 3, the horses were fed a diet containing 0.33 percent Lys for 3 days. After this the diet was changed to diets containing higher levels of Lys to 0.40, 0.47, 0.54, and 0.61 percent every third day. The Lys requirement was estimated to be 0.46 percent of diet from the response of plasma Lys concentration of five Lys levels. In Experiment 4, a 4 × 4 Latin square design was used for four dietary Lys levels. The Lys requirement was estimated to be 0.47 percent of the diet with a plasma Lys concentration of four Lys levels.     

日粮不同精粗比对肉羊氮沉积和尿嘌呤衍生物排出量的影响

本试验旨在研究肉羊在不同日粮精粗比条件下氮沉积和尿嘌呤衍生物的排出规律。选择12只体况健康的9月龄、体重(47.21±3.35)kg杜×寒杂交绵羊公羊,试验日粮为12种不同精粗比的全混合颗粒饲料,采用12×4不完全拉丁方设计,进行4期消化代谢试验,试验每期19 d,其中预试期14 d,正试期5 d,采用全收粪、尿法。结果表明:随日粮精粗比的提高,尿氮排出量和氮沉积量均显著提高(P<0.05),日粮精粗比对粪氮排出量的影响不显著(P>0.05),氮沉积量与氮采食量之间存在线性相关(R2=0.72,P<0.05);尿中尿囊素排出量和总尿嘌呤衍生物排出量均随日粮精粗比升高而显著升高(P<0.05),尿囊素、尿酸、黄嘌呤和次黄嘌呤排出量占总尿嘌呤衍生物排出量的比例变化范围分别为69.92%~84.76%、2.89%~7.58%和9.39%~25.04%。日粮精粗比对粪氮与尿氮有不同的影响,对尿嘌呤衍生物排出量影响显著;尿嘌呤衍生物排出量与尿氮排出量存在着线性相关,相关方程为Y=0.429X+0.324(R2=0.85)。     

Physiological effects of feeding high levels of magnesium to sheep

The effects of feeding high levels of Mg to sheep on animal health, nutrient digestibility, metabolism of macro-minerals, blood and tissue mineral concentrations and hematological and histological tissue changes were evaluated. Six lambs were allotted to each of four diets supplemented with MgO to attain .2, .6, 1.2 or 2.4% Mg. Total fecal and urinary collections were made for the initial 20 d and last 10 d of a 50 d study. Diarrhea was noted in lambs fed the two highest Mg levels. Apparent digestibility of DM, ADF and CP decreased linearly (P less than .01) with increasing Mg levels. Dietary Mg levels did not affect (P greater than .05) rectal temperature, respiration rate or pulse rate. Apparent absorption and retention of Mg (g/d) were lowest in lambs fed 2.4% Mg until 15 d on trial, after which values increased linearly (P less than .01) with dietary Mg. Phosphorus absorption and retention decreased linearly (P less than .01) with increasing Mg levels. Increasing dietary Mg resulted in a linear increase (P less than .01) in serum Mg and variable increases (P less than .05) in erythrocyte Mg. Serum Ca was decreased linearly (P less than .05) and quadratically (P less than .05) by added Mg during the d 1 to 30 and 40 to 50 periods, respectively. Serum inorganic P was elevated consistently in lambs fed 2.4% Mg. A linear response to increasing dietary Mg (P less than .05) occurred in the Mg content of liver, kidney, rib bone and femur bone. Dietary Mg did not alter (P greater than .05) other criteria.(ABSTRACT TRUNCATED AT 250 WORDS)     

Determination of the selenium requirement in kittens

The purpose of this study was to determine the selenium (Se) requirement in kittens. Thirty-six specific-pathogen-free kittens (9.8 weeks old) were utilized in a randomized complete block design to determine the Se requirement in cats with gender and weight used as blocking criteria. Kittens were fed a low Se (0.02 mg/kg Se) torula yeast-based diet for 5 weeks (pre-test) after which an amino acid-based diet (0.027 mg Se/kg diet) was fed for 8 weeks (experimental period). Six levels of Se (0, 0.05, 0.075, 0.10, 0.20 and 0.30 mg Se/kg diet) as Na2SeO3 were added to the diet and were used to construct a response curve. Response variables included Se concentrations and Se-dependent glutathione peroxidase activities (GSHpx) in plasma and red blood cells (RBC) as well as plasma total T3 (TT3) and total T4 (TT4). No significant changes in food intake, weight gain or clinical signs of Se deficiency were noted. Estimates of the kitten's Se requirement (i.e. breakpoints) were determined for RBC and plasma GSHpx (0.12 and 0.15 mg Se/kg diet, respectively), but no definitive breakpoint was determined for plasma Se. Plasma TT3 increased linearly, whereas plasma TT4 and the ratio of TT4 : TT3 decreased in a quadratic fashion to dietary Se concentration. The requirement estimate determined in this study (0.15 mg Se/kg) for kittens is in close agreement with other species. As pet foods for cats contain a high proportion of animal protein with a Se bioavailability of 30%, it is recommended that commercial diets for cats contain 0.5 mg Se/kg DM.     

Site of magnesium and other macromineral absorption in steers fed high levels of potassium

Six Angus x Simmental steers, surgically equipped with abomasal and ileal cannulae, were used during three metabolism trials. Steers were blocked according to weight ad were allotted to three dietary K levels (.6, 2.4 and 4.8% dry basis) for each trial with the restriction that no animal would receive the same level during two successive trials. Each trial consisted of a 5-d transition, a 10-d preliminary period, a 7-d collection of feed, feces and urine and a 6-d sampling of feed, feces and abomasal and ileal fluid. Chromic oxide (.5%) was used as an indicator to measure flow through the digestive tract. Magnesium absorption decreased linearly (P less than .05) with increasing level of dietary K. The primary site of Mg absorption was the preintestinal region followed by a net secretion into the small intestine. Preintestinal Mg absorption was decreased 39% when 4.8% K was fed. Serum Mg was lower at high levels of dietary K. Potassium absorption increased linearly when expressed as g/d and curvilinearly when expressed as percentage of intake, with increasing levels of dietary K. When .6% K was fed, the primary site of K absorption was the small intestine, but with the high levels of K, the preintestinal region was also an important site of absorption. The effect of high K level on Mg absorption in steers was similar to that observed previously in sheep.     

Isoleucine requirement for late-finishing (87 to 100 kg) pigs

Three pig trials were carried out to determine the true digestible Ile requirement for maximal weight gain and minimal plasma urea nitrogen (PUN) of late-finishing (87 to 105 kg) pigs. In Exp. 1, an Ile-deficient basal diet was developed and confirmed to be markedly deficient in Ile, yet fully efficacious when fortified with surfeit Ile. This diet contained corn and dried red blood cells (RBC) as Ile sources, and was analyzed to contain 10.5% CP, 0.25% Ile, and 0.63% lysine; ME was calculated to be 3,475 kcal/kg. True digestibility of Ile in the basal diet was 88% based on previous digestibility trials in ileal-cannulated pigs and cecectomized roosters. Experiment 2 was a growth trial that involved five graded levels of crystalline Ile supplementation (0.02%) to generate five dose levels of true digestible Ile (0.25 to 0.33%), Diets 1 through 5, respectively. Gain and feed efficiency showed a linear response to incremental doses of Ile (P = 0.003 and 0.036, respectively), with an apparent plateau at 0.31% true digestible Ile. In Exp. 3, a replicated 5 x 5 Latin square, five barrows (Square 1) and five gilts (Square 2) were used in five 4-d feeding periods, with five levels of true digestible Ile (0.22 to 0.30%). Using feed intake as a covariate, a linear decrease in PUN occurred in gilts (8.9, 8.6, 8.0, 7.0, and 5.5; P = 0.004) and in gilts and barrows combined (9.5, 9.2, 9.2, 8.5, and 7.6; P = 0.006) as Ile increased incrementally. The PUN results for barrows (10.5, 10.0, 10.2, 9.9, and 9.7) were not affected by dietary Ile (P = 0.417). The results of these experiments suggest that the factorial requirement estimate of 0.30% true digestible Ile for high-lean, late-finishing pigs suggested by the NRC Subcommittee on Swine Nutrition is accurate.     

Mineral absorption in the black rhinoceros (Diceros bicornis) as compared with the domestic horse

To test whether mineral recommendations for horses are likely to guarantee adequate mineral provision for black rhinoceroses (Diceros bicornis), we investigated the apparent absorption (aA) of macro- and microminerals in eight black rhinoceroses from three zoological institutions in a total of 32 feeding trials with total faecal collection, with additional data from three unpublished studies (18 feeding trials). Feeds and faeces were analysed for Ca, P, Mg, Na, K, Fe, Mn, Cu, Zn and Co. The resulting aA coefficients, and the linear relationships of apparently absorbable dietary mineral content to total dietary mineral content [per 100 g dry matter (DM)], were compared with data for domestic horses. Rhinoceroses had significantly higher aA coefficients for Ca and Mg (because of a higher calculated 'true' absorption), and lower ones for Na and K (because of calculated higher endogenous faecal losses). High absorption efficiency for divalent cations is hypothesized to be an adaptation to a natural diet of particularly high Ca:P ratio (approximately 14:1); an effective removal of Ca from the ingesta guarantees sufficient P availability at the fermentation site in the hindgut. Higher faecal losses of Na and K are hypothesized to be linked to a higher faecal bulk per DM intake in black rhinoceroses as compared with horses because of a generally lower digestive efficiency. There were no relevant differences in the absorption patterns of microminerals. In particular, there were no discernable differences in Fe absorption within the rhinoceroses for diets with and without tannin supplementation. Several of the zoo diets assessed in this study were deficient in Cu, Mn or Zn, and most contained excessive levels of Fe when compared with horse requirements. The findings of this study indicate that differences in mineral absorption between occur even between species of similar digestive anatomy; that in particular, Ca absorption might vary between hindgut fermenters with Ca:P ratio in their natural diet; that Na might be a particularly limiting factor in the ecology of free-ranging rhinoceroses; that moderate doses of tannins do not seem to markedly influence mineral absorption; and that diets for captive animals should contain adequate, but not excessive mineral levels.