猪氮代谢及其调控的研究进展

当前集约化猪场随粪尿排出的氮对环境的污染已成不容忽视的问题,本文对影响猪氮(氨基酸)排放量的主要因素以及猪氮(氨基酸)代谢与调控研究方法进行综述,就降低猪饲粮中氮排放及提高氮利用率做了探讨,以促进其进一步研究应用。     

不同比例低蛋白氨基酸平衡日粮对断奶仔猪生长性能及氮平衡的影响

为了解不同比例低蛋白氨基酸平衡日粮对断奶仔猪生长性能及氮平衡的影响,试验将96头初始体重9.8 kg左右的杜×长×大断奶仔猪随机分成4个处理,每个处理分别饲喂含不同蛋白水平的玉米-豆粕型饲粮(20%CP、19%CP、18%CP和17%CP),通过补充合成氨基酸,使各处理组的氨基酸与要求相一致。正式试验期为28 d,测定断奶仔猪生长性能、氮平衡指标。结果表明,日粮蛋白水平降至18%时,不会影响断奶仔猪生长性能,且显著降低尿氮、粪氮和总氮排放量(P<0.01);但随着日粮蛋白水平进一步降至17%时,显著降低仔猪平均日增重(P<0.01),显著增加料重比(P<0.01);18%CP组与17%CP组总氮排放量、氮表观利用率、氮表观生物学效价差异不显著(P>0.05)。说明添加合成氨基酸满足断奶仔猪需要,将日粮蛋白水平降至18%,不仅不会影响仔猪生长性能,而且还会降低氮排放,减少环境污染。     

α-酮戊二酸对肥育猪生长性能、氮沉积及氮排放的影响

酮戊二酸(AKG)是连接碳和氮代谢的重要枢纽,对动物氮代谢具有重要作用。本试验旨在研究α-酮戊二酸对肥育猪生长性能、氮沉积及氮排放的影响。选取36头(54.21±2.95)kg杜×长×大杂交肥育猪,随机分到4个组,每组3个重复.每个重复3头猪。4个组分别饲喂添加0%(对照组)、0.5%、1.0%、1.5%的α-酮戊二酸的低蛋白(CP 10.99%)日粮。结果表明:添加α-酮戊二酸提高肥育猪的生长性能,氮沉积提高了10.42%,总氮排放量降低了26.16%。低蛋白日粮中添加1.0%和1.5%AKG可促进肥育猪生长,并有效降低血液尿素氮的含量,氮排放量可降低26.16%,氮沉积最高可提高10.42%。     

精准营养下低排饲粮对生长猪生长性能、骨骼特性及氮平衡的影响

试验旨在研究基于理想氨基酸模型,精准营养下低排饲粮对生长猪生长性能、骨骼特性及氮平衡的影响,为指导低排饲粮的推广应用提供依据。试验选取体重相近、健康的约20 kg杜×长×大三元杂交生长猪72头,随机分为2组,即对照组和试验组,每组6个重复,每个重复6头,分别饲喂基础饲粮和低排饲粮,试验期36 d。结果表明:相比对照组,低排饲粮对生长猪的生长性能无显著影响(P>0.05);低排饲粮对生长猪的骨骼发育无显著影响(P>0.05);低排饲料显著降低总氮摄入量、粪氮、尿氮和总氮排放量(P<0.05),显著提高氮沉积率和氮消化率(P<0.05)。在氨基酸平衡条件下,低排饲料对生长猪的生长性能和骨骼发育无显著影响,但能够降低氮排放,提高蛋白质的利用率。     

不同粗蛋白和粗纤维水平对肥育猪生产性能及氮排泄的影响

为探讨氨基酸平衡日粮中粗蛋白和粗纤维水平对肥育猪生产性能及氮排泄的影响,试验选取36头体重接近[(65.77±1.08)kg]的三元杂交(杜×长×大)阉公猪,采用2(CF:4%、6%)×3(CP:15.5%、14%、12.5%)两因子完全交叉试验设计。试验共设6个处理,每个处理2个重复,每个重复3头猪。试验结果表明:不同粗蛋白和粗纤维水平对肥育猪平均日增重(ADG)、平均日采食量(ADFI)和料肉比(F/G)均无显著影响(P>0.05);饲喂6号日粮(CP:12.5%、CF:6%)的F组经济效益最佳,每千克增重成本为5.59元;降低日粮粗蛋白水平减少了尿氮(P<0.05)、粪氮(P>0.05)和总氮(P<0.05)的排泄量;日粮粗蛋白水平平均每降低一个百分点,尿氮、粪氮和总氮排泄量分别减少3.58%、1.56%和2.53%;增加日粮粗纤维水平也减少了尿氮(P<0.05)、粪氮(P<0.01)和总氮(P<0.01)排泄量。     

低蛋白补充合成氨基酸日粮对仔猪氮排泄的影响

试验选用32头断奶仔猪,初始体重为6.8kg,共进行14d,其中适应期9d,正式收粪尿期为5d。试验全面研究了不同蛋白水平补充合成氨基酸对仔猪氮排泄的影响。研究发现,降低蛋白水平并按照理想蛋白模式补充合成氨基酸,显著降低了粪尿排放量(P=0.01),线性降低了氮排泄(P<0.001),同时日氮沉积绝对量也呈现线性下降(P<0.001);平均每降低一个百分点的仔猪日粮蛋白水平,可减少8.4%的氮排泄量。     

色氨酸的营养研究及其在家禽生产中的应用

色氨酸作为肉鸡的第三限制性氨基酸,不仅参与体蛋白质合成,还是一种具有代谢活性的氨基酸,它是5-羟色胺、褪黑激素、烟酸等的重要前体物质,对节约蛋白质饲料资源、减少粪氮排泄量及控制环境污染具有重要意义。本文就日粮中色氨酸的营养代谢作用及在家禽生产中的应用效果进行了综述。     

猪低污染日粮技术研究进展

最大限度地发挥每头猪的生产性能一直是生产者和营养学家共同追求的目标。因而,一般的日粮配合很少或根本不考虑营养物质的排出,结果使过量的营养素 (主要是氮和磷 )随粪尿排出。近年来,公众对环境的关注日益强烈。通过营养学技术,提高猪的饲料转化效率,减少排污 (粪尿 ),已成为当前养猪学及营养学研究的一个热点。通过补充合成氨基酸,降低日粮蛋白质水平 (2％～ 4％ ),能使氮的排出量显著减少。日粮蛋白质水平每降低一个百分点,氮排出量大约减少 8％。在日粮中添加植酸酶,可提高磷的利用率,减少日粮中无机磷的添加量,从而降低磷的排出。此外,抗生素、益生素、单细胞蛋白和酵母、有机铬等在减少猪营养物质方面亦有一定作用。     

行业

印遇龙：低蛋白质配方技术有助减少养殖业氮排放 ＂通过低蛋白质配方技术可以减少养猪业的氮排放量。＂11月10日,中国工程院院士、动物营养学家印遇龙在湘潭参加＂畜产品质量与食品安全＂研讨时指出,现在工厂化养猪的蛋白质水平从16%降低到13%时,发现猪的生产性能没有影响,差异不显著。降低3个百分点的蛋白质水平,可以使粪便里面的总氮排放量降低30%。蛋白质水平越高,猪粪便里面的氮排放量就越高。     

低蛋白质日粮对育肥猪生产性能、氮代谢及血液生化指标的影响

本研究旨在探讨低蛋白质日粮对育肥猪生产性能、氮代谢及血液生化指标的影响。试验选用初始体重为60kg左右的"长×大"杂交育肥猪84头,随机分为3组,每组4个重复,每个重复7头猪。对照组育肥猪饲喂正常蛋白质水平日粮(蛋白质含量为14.80%),试验组育肥猪饲喂低蛋白质日粮(蛋白质含量分别为13.86%和12.86%)。结果表明,降低育肥猪日粮蛋白质水平1~2个百分点,对育肥猪生长性能和养分表观消化率均没有产生显著影响(P0.05);另外,饲喂低蛋白质日粮后,育肥猪的摄入氮、吸收氮、总氮排出量、尿氮以及血清中尿素水平均呈现出降低的趋势(P0.05);氮的表观生物学价值和血清肌酐含量随日粮蛋白质水平的降低而升高(P0.05)。试验结果表明日粮蛋白质水平降低1~2个百分点对育肥猪生产性能和健康状况无不利影响,同时降低日粮成本和增重成本,还可显著降低氮的排放,有助于缓解养殖业对环境造成的污染。     

Advances in low-protein diets for swine

Recent years have witnessed the great advantages of reducing dietary crude protein(CP) with free amino acids(AA)supplementation for sustainable swine industry, including saving protein ingredients, reducing nitrogen excretion, feed costs and the risk of gut disorders without impairing growth performance compared to traditional diets. However, a tendency toward increased fatness is a matter of concern when pigs are fed low-protein(LP) diets. In response, the use of the net energy system and balanced AA for formulation of LP diets has been proposed as a solution. Moreover, the extent to which dietary CP can be reduced is complicated. Meanwhile, the requirements for the first five limiting AA(lysine, threonine, sulfur-containing AA, tryptophan, and valine) that growing-finishing pigs fed LP diets were higher than pigs fed traditional diets, because the need for nitrogen for endogenous synthesis of non-essential AA to support protein synthesis may be increased when dietary CP is lowered. Overall, to address these concerns and give a better understanding of this nutritional strategy, this paper reviews recent advances in the study of LP diets for swine and provides some insights into future research directions.     

Injection of porcine growth hormone releasing hormone gene plasmid in skeletal muscle increases piglets'' growth and whole body protein turnover

The aim of the current study was to investigate the effects of a porcine growth hormone releasing hormone (pGHRH) gene plasmid injection in piglets on growth performance and whole body protein turnover. Sixty male Canadian Landrace × Chinese Taihu piglets were assigned to an intramuscular injection of 0 (control), 0.25, 0.5, 1 and 2 mg. All pigs were fed with the same diet (crude protein: 239.8 g/kg, digestible energy: 14.28 MJ/kg) at ad libitum intake. Protein turnover was determined on the 22nd day with a three-pool model by using a single-dosage, end-product analysis method with ¹⁵ N-glycine as a tracer. Injection of the pGHRH gene plasmid increased the piglets' growth rate, altered feed intake and decreased feed conversion ratio. It increased plasma growth hormone releasing hormone (GHRH), growth hormone (GH), insulin-like growth factor-I (IGF-I) and somatostatin but reduced serum urea and triglyceride. It reduced the urinary nitrogen excretion and led to higher nitrogen retention as well as the efficiencies of nitrogen retention and digestible N utilization. It increased the rates of protein synthesis, protein breakdown and net protein gain. Excretion of endogenous urinary nitrogen was reduced and nitrogen reutilization rate was improved. Conclusions: Injection of the pGHRH gene plasmid in skeletal muscle stimulated GHRH, GH and IGF-I excretion in piglets. Protein deposition was increased by an increase in protein synthesis and a smaller increase in protein breakdown, which was accompanied by reducing amino acid oxidation and increasing nitrogen reutilization.     

Transfer of blood urea nitrogen to cecal microbial nitrogen is increased by fructo‐oligosaccharide feeding in guinea pigs

The present study was conducted to determine the mechanism by which nitrogen (N) availability is improved by fructo‐oligosaccharide (FOS) in guinea pigs. Adult male guinea pigs were fed a commercial pellet diet (50 g/day) with either 5% glucose or 5% FOS for 7 days in individual metabolism cages. After 7 days of feeding the diet, ¹⁵N‐urea was administered intravenously 1 h before slaughter under anesthesia. The amount and concentration of total, protein, bacterial, ammonia and urea N and the ¹⁵N atom % excess were measured in blood, liver, gut contents and urine. The ¹⁵N atom % excess of total and protein N, and the amount of total, protein and bacteria N and ¹⁵N in the cecum were significantly increased by the consumption of FOS. Furthermore, the concentration and amount of short‐chain fatty acids were significantly increased by the consumption of FOS. In contrast, the amount of urinary ¹⁵N was significantly decreased by the consumption of FOS. These results suggest that consumption of FOS increases transfer of blood urea N into the large intestine for bacterial N synthesis, which is subsequently re‐absorbed by cecotrophy, and contributes to the increase of N utilization in guinea pigs.     

Effects of dietary protein and fermentable fiber on nitrogen excretion patterns and plasma urea in grower pigs

Effects of dietary protein concentration (high, 18.5; low, 15.7%) and fermentable fiber (control; soyhulls, SH; and sugar beet pulp, SBP) on N excretion patterns and plasma urea were tested in a 2 x 3 factorial arrangement. The objectives were: 1) to determine if reduced dietary protein together with fermentable fiber would reduce urinary N excretion further than a single diet manipulation, 2) to determine if effects of diet manipulations were similar between pigs with restricted and free access of feed, and 3) to further develop predictions of urinary N excretion using plasma urea. Diets were formulated to 3.30 Mcal digestible energy (DE)/kg and 2.4 g of digestible lysine per Mcal DE, and supplemented with lysine, methionine, tryptophan, threonine, isoleucine, leucine, or valine to ensure meeting an ideal AA profile. Pigs (30.5 +/- 3 kg; n = 36) were housed in metabolism crates with restricted access to feed (3 x 110 kcal DE/kg BW(0.75)) from d 1 to 18, and free access from d 19 to 26. Feces and urine were collected from d 15 to 18 and d 23 to 26, and blood was sampled on d 17 and 25. With restricted access to feed, urinary N was reduced 28% and N retention was reduced 12% for the low- compared to high-protein diet (P < 0.01; as g/d). Fecal N was increased 4% units for SH and 6.5% units for SBP (P < 0.01; as % of N intake) and urinary N was reduced 5% units for SH (P < 0.10) and 9% units for SBP (P < 0.05) compared to the control. With free access to feed, urinary N was reduced 27% (P < 0.05; as g/d) and N retention was reduced 7% (P < 0.10) for the low- compared to high-protein diet. Fecal N was increased 5% units for SH and 9% units for SBP (P < 0.001; as % of N intake), and urinary N was reduced 9% units for SH and 10% units for SBP (P < 0.01) compared to the control. For either restricted or free access to feed, fermentable fiber did not affect N retention (P > 0.10). A protein x fiber interaction was not observed for urinary N excretion (P > 0.10), indicating that reducing dietary protein and including fermentable fiber reduced urinary N excretion in an additive manner. Daily urinary N excretion was related positively and linearly with plasma urea in pigs with free access to feed (R2 = 0.71; at 0800). In summary, reduction of dietary protein reduced urine N excretion, and fermentable fiber shifted N excretion from urine to feces. Effects of dietary protein and fermentable fiber on reducing urinary N excretion are additive.     

非常规蛋白饲料原料对泌乳山羊氮代谢和微生物蛋白合成的影响

文章旨在研究不同蛋白质来源精饲料对泌乳山羊氮代谢及微生物蛋白合成的影响。试验选择平均初始体重为(43.62±2.35)kg的泌乳期山羊72头,随机分为3组,每组4个重复,每个重复6头。各组分别饲喂以豆粕、大豆浓缩蛋白和豆科植物(银合欢)为基础的精料,试验为期8周。结果:大豆浓缩蛋白组尿液和尿素氮排泄量较豆科植物组显著提高21.41%和23.31%(P<0.05),但大豆浓缩蛋白和乳尿素氮排泄量最低(P<0.05)。大豆浓缩蛋白组尿液和尿素氮排泄量占体重的比例也显著高于豆科植物组(P<0.05)。大豆浓缩蛋白组氮摄入量最低(P<0.05)。大豆浓缩蛋白组尿氮含量显著高于豆粕和豆科植物组(P<0.05)。豆科植物组微生物氮、微生物蛋白量及合成效率也显著高于豆粕组(P<0.05)。结论:在本研究条件下,以大豆浓缩蛋白为蛋白源的精饲料饲喂哺乳期山羊,尿液氮排泄量更大,导致负氮平衡,而以豆科植物(银合欢)为蛋白源时,可以提高乳山羊瘤胃微生物蛋白合成能力。     

纤维和蛋白质对肠道健康和环境的影响

由于膳食纤维和蛋白质对肠道健康和环境都有潜在的有益或有害影响,因此,膳食纤维和蛋白质在猪肠道中的发酵是一个值得关注的问题。本文综述了近年来有关膳食纤维和蛋白质发酵对猪肠道环境的影响及其对猪粪和猪舍含氮气体和异味排放的影响,同时探讨了蛋白质发酵和相关代谢化合物的生产,与膳食纤维发酵、对肠道健康、细菌蛋白质合成和氮排泄的影响。生产上可以采用不同的营养策略来应对集约化养猪生产对环境的的负面影响,如降低日粮粗蛋白质水平减少氮排泄。总的来说,日粮纤维和蛋白质水平是影响猪肠道发酵、氮排泄和环境影响的一个有效策略。     

Effect of nitrogen source in high-concentrate, low-protein beef cattle diets on microbial fermentation studied in vivo and in vitro

In Exp. 1, four Holstein heifers (112+/-5.5 kg BW) fitted with ruminal cannulas were used in a 4 x 4 Latin square to evaluate the effects of N source on ruminal fermentation and urinary excretion of purine derivatives. A 2 x 2 factorial arrangement of treatments was used; the factors were the type of protein source (soybean meal, SBM, vs a 50:50 mixture of fish meal and corn gluten meal, FMCGM) and the partial substitution of protein source by urea (with vs without). Heifers were allowed to consume concentrate and barley straw on an ad libitum basis. Barley straw:concentrate ratio (12:88) and average ruminal pH (6.25) were not affected (P > 0.05) by treatment. Ruminal NH3 N concentration and urinary excretion of purine derivatives were not affected (P > 0.05) by supplemental N source. In situ CP degradability of supplemented SBM was very low (50%). In Exp. 2, eight dual-flow continuous-culture fermenters were used to study diet effects on microbial fermentation and nutrient flow, using forage:concentrate ratio, solid and liquid passage rates, and pH fluctuation to simulate in vivo conditions. The treatment containing SBM without urea reached the greatest total VFA concentration (P < 0.01), molar percentage of acetate (P < 0.05), and NH3 N concentration (P < 0.05), followed by treatments with partial substitution of protein source by urea, and finally by the treatment containing FMCGM. True OM digestion tended to increase (P = 0.13) in treatments containing SBM. These results suggest that amino N from SBM and NH3 N concentration stimulated nutrient digestion. Microbial protein synthesis was lowest in treatments with FMCGM and without urea, indicating that rapidly available N limited microbial growth. The low CP degradability of SBM observed may have contributed to the limitation in N supply for microbial growth. Efficiency of microbial protein synthesis increased in treatments containing urea (P < 0.05). Protein source affected total (P < 0.05) and essential AA (P < 0.10) flows, which were greater in treatments containing FMCGM. Partial replacement of protein supplements by urea did not affect total and essential AA flows. Because mean dietary protein contribution to total N effluent was 46%, the AA profile of supplemental protein sources had a great impact on total AA flow and its profile.     

Growth hormone increases whole-body protein turnover in growing pigs.

Ten pigs with an average initial live weight of 65 kg were used to investigate the effects of daily exogenous porcine pituitary growth hormone (pGH; .1 mg.kg-1.d-1) for a 13-d period on N retention and whole-body protein turnover. Feed intake was restricted to both the control (treated with excipient) and pGH-treated groups to ensure that animals in each group consumed equal amounts. Whole-body protein turnover was estimated from the excretion of 15N in urinary urea and ammonia after a single oral dose of [15N]glycine. Nitrogen balance and whole-body N flux were increased by 35 to 40% with pGH treatment (P less than .001). Protein synthesis and breakdown were increased by 56 and 59% (P less than .001), respectively, in pGH-treated pigs relative to controls. These higher rates of protein turnover seemed to lower slightly the efficiency of the metabolic process for protein deposition. However, the absolute increment in protein synthesis rate was greater than that for breakdown, leading to the increased net N retention. Thus, pGH treatment improved the utilization of dietary amino acids for protein deposition.     

Tracer studies of urea kinetics in growing pigs: II. The effect of starch infusion at the distal ileum on urea recycling and bacterial nitrogen excretion.

Six gilts, with an average BW of 70 kg, were fitted with a simple T-cannula at the distal ileum to study the effect of continuous starch infusion on urea kinetics by means of a radioisotope dilution technique. The pigs were fed twice daily 600 g of a cornstarch-based diet formulated to contain 16% CP by supplementation with isolated soy protein. Infusion of starch, compared with water, decreased (P < .05) plasma urea concentration, urea pool size, and entry, excretion, and degradation rates; urea turnover rate and urea space were not affected (P > .05). Expressed as a percentage of total entry rate, approximately 40% of urea was recycled into the digestive tract in both infusion treatments. The stimulation of microbial fermentation in the large intestine resulted in an increase (P < .05) in fecal N excretion, which was mainly due to an increased excretion of bacterial N. This increase could not be attributed to a greater secretion of urea into the large intestine and its subsequent utilization by the intestinal microflora. The increased bacterial N assimilation after starch infusion led to a reduction in ammonia absorption from the large intestine, which in turn was reflected by a reduced urinary N excretion. As a result, the overall N balance was not affected. In a second experiment, two barrows, with an average BW of 80 kg, were fed twice daily 1.4 kg of a cereal-based diet. The body urea pool of both pigs was labeled with a single injection of 1 g and 2 g of [15N]urea, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dietary lactulose decreases apparent nitrogen absorption and increases apparent calcium and magnesium absorption in healthy dogs

To study the effect of lactulose on the route of nitrogen excretion, we fed six healthy, adult dogs on diets containing either 0, 1 or 3 g lactulose/MJ metabolizable energy according to a 3 × 3 Latin square design. The results were analysed to identify statistically significant linear trend effects of lactulose. Faecal pH was significantly lowered by lactulose. Faecal ammonium and nitrogen excretion tended to be raised by lactulose feeding whereas urinary urea excretion was significantly reduced. Lactulose feeding significantly lowered apparent nitrogen digestibility. It is concluded that lactulose feeding shifts nitrogen excretion from urine to faeces in dogs which may be beneficial for liver patients. The data are in line with the concept that lactulose stimulates bacterial growth in the colon which in turn enhances faecal nitrogen excretion and lowers the entry of colonic ammonia into the bloodstream, leading to a lesser workload for the liver and less urinary nitrogen excretion. Lactulose consumption was also found to produce a dose-dependent increase in the apparent absorption of calcium and magnesium, but not phosphorus.