生长肥育阉牛饲料蛋白质转化效率的研究

用３个不同梯度氮进食量的１０种日粮的研究结果表明,可消化氮进食量与氮沉积之间呈线性相关（ｒ＝０．９６０１）。当沉积氮为零时,可消化氮为０．３９８２ｇ／Ｗ０．７５。沉积氮／可消化氮与沉积氮量之间呈线性相关（ｒ＝０．９６１５）,实测的沉积氮（ｇ／Ｗ０．７５）范围为０．０１１至０．３７６,沉积氮／可消化氮的范围为０．０２３５至０．４７９。维持的可消化氮需要为０．３９８２ｇ／Ｗ０．７５,内源尿蛋白氮为２．４４ｇ／Ｗ０．７５。     

磷对奶牛红细胞膜脂质的影响

对１５例临床上有明显低磷血症的奶牛血清磷、红细胞膜脂质成分进行了测定。结果表明，低磷血症奶牛血清磷、红细胞膜磷脂明显降低；红细胞膜胆固醇及膜胆固醇／磷脂摩尔比值（ｎｃｈ／ｎｐｌ）明显升高，与健康对照组牛相比差异极显著（Ｐ＜０．０１）；直线相关分析表明，血清磷与红细胞膜磷脂之间呈极显著正相关（ｒ＝０．９１７，ｙ＝１０．８５２ｘ＋３．１９６，Ｐ＜０．０１）；与红细胞膜胆固醇以及ｎｃｈ／ｎｐｌ之间分别呈显著负相关（ｒ＝－０．９４０，ｙ＝２．８５０ｘ－１．０７２，Ｐ＜０．０１；ｒ＝－０．９２０，ｙ＝１．９６８ｘ－１．４０１，Ｐ＜０．０１）。此外，红细胞膜微粘度与膜磷脂之间呈显著负相关（ｒ＝－０．９５４，ｙ＝１９．１２２ｘ－４．３８４，Ｐ＜０．０１），而与膜胆固醇以及ｎｃｈ／ｎｐｌ之间呈显著正相关（ｒ＝０．９８８，ｙ＝０．９２７ｘ＋０．９６４，Ｐ＜０．０１；ｒ＝０．９７８，ｙ＝－０．２９３ｘ＋１．１１３，Ｐ＜０．０１）。结果表明，磷是红细胞膜脂质成分改变的先决因素，而后者又是红细胞膜流动性及膜结构、功能发生变化并导致膜损伤的一个重要因素。     

瘤胃灌注不同比例的混合VFA对肉牛血液相关代谢指标影响规律的研究

以装有瘤胃瘘管的成年肉用阉牛（体重３９０±３０ｋｇ）喂１００％羊草的基础日粮,通过瘤胃瘘管灌注４种不同摩尔比例（乙酸：丙酸：丁酸分别为７５：１５：１０,６５：２５：１０,５５：３５：１０和４５：４５：１０）的混合ＶＦＡ,按４×４拉丁方试验设计测定了灌注后血液ＣＯ２结合力、血液总酮体水平、血糖及胰岛素水平。结果如下：瘤胃灌注４种不同比例的ＶＦＡ对血液ＣＯ２结合力、血液总ＶＦＡ浓度和血液总酮体水平无显著影响（Ｐ＞００５）。瘤胃液中的丙酸比例超过１８５５％时,血液中葡萄糖和胰岛素水平显著增加（Ｐ＜００５）,血液中葡萄糖（Ｙ,ｍｍｏｌ／Ｌ）和胰岛素（Ｙ,μｇ／Ｌ）水平分别与瘤胃液中的丙酸比例（ｍｏｌ／１００ｍｏｌ）存在线性正相关,回归方程式分别为：Ｙ＝１７１０＋００７８Ｘ（ｒ＝０９６７,ｎ＝４）;Ｙ＝７２１２＋００２０Ｘ（ｒ＝０９２２,ｎ＝４）。ＶＦＡ转化为体脂肪的效率（ｋｆ,Ｙ,％）和可消化氮转化为沉积氮的效率（ＲＮ／ＤＮ,Ｙ,％）分别与血液中葡萄糖水平（Ｘ,ｍｍｏｌ／Ｌ）呈线性正相关,回归方程分别为：Ｙ＝－２８４９９＋２１４４４Ｘ（ｒ＝０９６９,ｎ＝４）;Ｙ＝－１６６４１＋１４５１３     

长×荣杂交猪体蛋白沉积模型及氨基酸需要量的预测

以长×荣二元杂交猪为研究对象，通过饲养试验和屠宰试验，测定了试验猪２０～３５、３５～５０、５０～８０、８０～１００ｋｇ阶段的生产性能和胴体无脂瘦肉生长指数（胴体无脂瘦肉沉积速度）。试验结果表明：试验猪全期日增重平均为７６２ｇ，平均日采食量２１５３ｇ，饲料报酬（Ｆ／Ｇ）２．７８７，各生产性能公母间差异不显著（Ｐ＞０．０５）；日增重与体重的回归方程为ＡＤＧ（ｇ／ｄ）＝２９３．０３＋１５．１ＢＷ－０．１　０３４ＢＷ２（Ｒ２＝０．９９８８）；试验猪全期胴体无脂瘦肉生长指数为２２７ｇ／ｄ；体蛋白沉积模型Ｙ（ｇ／ｄ）＝７２．２１１－１．５２７５ＢＷ＋０．０６４８ＢＷ２－０．０００５ＢＷ３（Ｒ２＝０．９５５）；真可消化赖氨酸需要模型Ｙ（ｍｇ／ｄ）＝８６６５．４１－１８３．３ＢＷ＋７．７７８８ＢＷ２－０．０６１２ＢＷ３＋３６ＢＷ０．７５，据此模型推算出２０～５０、５０～８０、８０～１００ｋｇ阶段真可消化赖氨酸需要量分别为９．６７、１３．６３和１１．６１ｇ／ｄ，总赖氨酸需要量为１１．１２、１５．７６和１３．４２ｇ／ｄ，真可消化赖氨酸按占风干日粮的百分比表示为０．６１％、０．５６％和０．４１％，总赖氨酸需要量按占风干日粮的百分     

饲粮粗蛋白质水平对泌乳水牛产奶量及氮代谢的影响

本试验旨在研究饲粮粗蛋白质水平对泌乳水牛产奶量及氮代谢的影响。试验采用４×４拉丁方试验设计,选用 １６头体况良好、上期泌乳量相近、产犊胎次 ２～３胎、健康的泌乳前期水牛,随机分为４组,进行动物饲养试验和消化代谢试验。将４组泌乳水牛随机分配到４个梯度的饲粮粗蛋白质水平组,即 １６．０％、１５．２％、１４．４％、１３．６％ ４个组,每组 ４头,进行 ４期饲养试验,每期 ２１ｄ,共 ８４ｄ。按照 ４×４拉丁方设计给各期各组泌乳水牛饲喂不同粗蛋白质水平的饲粮,每期试验预试期 ７ｄ。在第 ２期和第 ４期饲养试验的最后 ４ｄ开展 ２期氮消化代谢试验。结果表明,总采食氮、可消化氮、乳氮／进食氮以及氮表观消化率在部分组间差异显著（Ｐ＜０．０５）;乳氮、粪氮、尿氮在各组间差异不显著（Ｐ＞０．０５）。饲喂不同粗蛋白质水平饲粮对水牛产奶量、乳蛋白率、乳脂率、乳非脂固形物率和乳糖率均无显著影响（Ｐ＞０．０５）。血清总蛋白和尿素氮含量各组间差异不显著（Ｐ＞０．０５）。以试验期间进食氮水平（ｇ／ｄ）为横坐标（ｘ）,标准乳产量（ｋｇ／ｄ）为纵坐标（ｙ）,获得进食氮水平与标准乳产量的二次曲线关系,即 ｙ＝－０．００１６ｘ２＋０．９５５６ｘ－１２９．９１。由此可见,饲粮粗蛋白质水平对泌乳水牛生产性能及血液生化指标影响不显著,根据进食氮水平与标准乳产量的二次曲线关系可得,当进食氮水平为 ２９８．６２５ｇ／ｄ时,得到水牛标准乳产量最大值为 １２．７７３ｋｇ／ｄ。     

高效液相色谱法测定FQS-110的含量

用Ｉｒｒｅｇｕｌａｒ－Ｈ Ｃ１８色谱柱,以０．０５ｍｏｌ／ｌ柠檬酸溶液（以三乙胺调ｐＨ４．０）：乙腈（８１：１９,ｖ／ｖ）为流动相,以邻氨基苯甲酸为内标,于２７３ｎｍ波长处,测定ＦＱＳ－１１０含量,药物浓度（ｘ）与药物峰面积和内标峰面积之比（ｙ）呈良好的线性关系,线性方程为ｙ＝０．０８７５ｘ－０．０９３３,ｒ＝０．９９９４,线性范围为４￣４０μｇ／ｍｌ,日内与日间变异系数分别为０．６４％和０．６７     

真胃内灌注不同水平的葡萄糖和酪蛋白对高乙酸比例VFA增重效率调控的研究

3头带有瘤胃和真胃痿管的肉牛(375±25kg)饲喂全羊草以满足其维持需要 ,设计3个对比试验 ,每一试验均向瘤胃内持续灌注高乙酸摩尔比(75 %)的混合VFA。试验一 :真胃每天持续灌注100g、250g和400g 的葡萄糖 ;试验二 :真胃每天持续灌注200g、300g 和400酪蛋白 ;试验三 :真胃每天持续灌注葡萄糖和酪蛋白的混合物分别为250g±200g ,250g +300g以及250g +400g。连续7天持续灌注后用农大KB -1型呼吸测热室测定产热和能氮平衡。试验结果表明 ,①试验一、二、三均能明显降低代谢产热率(HP/ME ,P<0.05) ,增加能量沉积效率(Kf值 ,P<0.05) ,并促进体脂肪和体蛋白的沉积(P<0.05)。试验一和试验二的HP/ME和Kf值十分接近 ,表明在降低代谢产热率和提高Kf值方面真胃灌注葡萄糖和酪蛋白混合物的效果是一样的。但从体组织沉积的组成来看 ,灌注酪蛋白肉牛沉积的蛋白质质量比灌注葡萄糖时高68.47 %。②试验三的HP/ME比试验一下降了4.53个百分点(P<0.05) ,比试验二下降了5.17个百分点(P<0.05) ;Kf值比试验一提高了4.78个百分点 ,比试验二提高了4.56个百分点 ,表明真胃灌注葡萄糖和酪蛋白混合物的效果要优于单独灌注其中之一。本试验条件下 ,在降低HP/ME ,增加Kf值方面 ,真胃单独灌注250g葡萄糖和300g 酪蛋白以及250g葡萄糖与20     

日粮降解氮转化为瘤胃微生物氮效率影响因素的研究

用１０种不同氮源日粮（４种糊化淀粉尿素日粮、常规尿素日粮、豆饼日粮、甲醛及非甲醛新保护剂保护豆饼日粮）在５头装有瘤胃和真胃瘘管的阉牛中分别进行６×５和４×４两个拉丁方试验，用体内法测定日粮的蛋白质和有机物质的降解率、微生物蛋白质产量及瘤胃氨浓度。同时用瘤胃尼龙袋法测定蛋白质和有机物质降解率。结果表明：不同氮源日粮间降解氮转化为微生物氮的效率差异明显（Ｐ＜０．０１）：降解氮转化效率与瘤胃平均氨浓度有限高曲线负相关（ｒ＝－０．９１９２），与降解氮同体内法测定的瘤胃可消化有机物（ＲＤＯＭ）及瘤胃尼龙袋法测定的瘤胃２４小时可发酵有机物（ＦＯＭ）的比率均有同种类型的曲线负相关（ｒ＝－０．８７９６，ｒ＝－０．９０３７）。说明降解氮转化为微生物氮的效率受饲料蛋白质降解量、降解速度及降解氮与微生物可利用能平衡的影响。     

生长期牦牛蛋白质需要量的研究

将１８头１．５岁生长牦牛分为Ⅰ、Ⅱ、Ⅲ三组，分别饲喂含ＣＰ６．７１％，１０．１４％，１３．４３％的日粮，用比较屠宰试验、消化代谢试验和饲养试验相结合的方法研究其氮代谢。结果表明：Ⅰ、Ⅱ、Ⅲ组日增重分别为５４．０６ｇ，１９３．６７ｇ，２４７．４７ｇ，其中Ⅱ组与Ⅰ组差异显著（Ｐ＜０．０５），Ⅲ组与Ⅰ组差异极显著（Ｐ＜０．０１），而Ⅲ组与Ⅱ组差异不显著（Ｐ＞０．０５）；相应的尿氮（ＵＮ）排出（ｇ／ｄ·Ｗ￣（０．０５２））分别为０．５６２，１．２９１，１．７６２，其中Ⅱ、Ⅲ与Ⅰ差异极显著（Ｐ＜０．０１），Ⅱ与Ⅲ差异显著（Ｐ＜０．０５）；在氮沉积（ＮＲ）、采食氮利用效率方面，三组均无显著差异（Ｐ＞０．０５）。生长牦牛的维持需要量ＲＤＣＰｍ＝６．０９３Ｗ￣（０．５２），增重需要量ＲＤＣＰｇ＝（１．１５４８／△Ｗ＋０．０５０９／Ｗ￣（０．５２））￣（－１）。得出的三个回归方程均呈强直线相关（Ｐ＜０．０１）：１．ＵＮ与进食氮（ＮＩ）的回归方程ＵＮ（ｇ／ｄ）＝－０．１１Ｗ￣（０．５２）＋０．４７３２ＮＩ（ｎ＝９，ｒ＝０．９２８）２．粪氮（ＦＮ）与干物质进食量（ＤＭＩ）及ＮＩ的回归方程ＦＮ（ｇ／ｄ）＝－０．７５１０（１＋０．８     

近交系小鼠的生长曲线拟合

通过４３６０只近交系小鼠体重分析,得出生长曲线：雄性ｒ＝２５．２４１７／１＋４．７８０３ｅ＾－０．４００４１ｘ,相关系数Ｒ＝０．９８９８,相关指数Ｒ＾２＝０．９７９７。雄性ｙ＝２３．７６４５／１＋３．９６４５ｅ＾－０．３３３９７ｘ,Ｒ＝０．９８２５,Ｒ＾２＝０．９６５２。     

Studies on nitrogen retention in growing pigs

Nitrogen retention (RN) was measured in 60 barrows of Danish Landrace and a total of 470 balance periods was carried out during the growth period from 20 to 85 kg live weight. In the first serie (Expt A) six different feed compounds of high biological value (HBV) were fed to 48 barrows, while in the second serie (Expt B) 12 barrows were measured on feed compounds of HBV or low biological value (LBV). Three different levels of gross energy were used in Expt B. Individual differences of 10-20% in the pigs capability for nitrogen retention were observed. Nitrogen retention increased from 12 to 21 g N/d on the HBV-compounds and was not influenced by increasing nitrogen or energy intake. Nitrogen retention was curvilinear in relation to metabolic live weight (kg0.75) in both series. A parabolic function on kg0.75 gave the best fit to the data with the following regression equations: Expt A + B: RN, g/d = 1.48 LW, kg0.75 - 0.027 LW, kg1.50 (HBV) Maximum = 20.5 g RN/d at 84 kg LW Expt B: RN, g/d = 1.03 LW, kg0.75 - 0.013 LW, kg1.50 (LBV) Maximum = 20.4 g RN/d at 133 kg LW     

瘤胃灌注不同比例的混合VFA对肉牛瘤胃发酵、能量和氮代谢的研究

以装有瘤胃瘘管的肉牛（３９０±３０ｋｇ）饲喂全羊草的基础日粮，瘤胃灌注４种不同摩尔比例的混合ＶＦＡ（乙酸：丙酸：丁酸为７５∶１５∶１０，６５∶２５∶１０，５５∶３５∶１０和４５∶４５∶１０），按４×４拉丁方试验设计测定了灌注后代谢产热率（ＨＰ／ＭＥ），ＶＦＡ转化为体脂肪的效率（Ｋｆ）和可消化氮转化为沉积氮的效率。结果表明，随着灌注混合ＶＦＡ中丙酸比例超过２５％，ＨＰ／ＭＥ明显降低（Ｐ＜００５），Ｋｆ值极显著地增加（Ｐ＜００１）；可消化氮转化为沉积氮的效率显著增加（Ｐ＜００５）；ＨＰ／ＭＥ与瘤胃中乙酸比例、Ｋｆ值与瘤胃液中丙酸比例均呈线性正相关。     

不同氮硫比对安哥拉兔营养物质利用、产毛性能和血液指标的影响

选取24只体重3.5kg左右的健康安哥拉兔,随机分为3组,分别饲喂氮硫比为9.991、7.911和5.971的全价日粮,研究了不同氮硫比对安哥拉兔营养物质利用、产毛性能和血清尿素氮及胆固醇含量的影响。试验结果表明:氮硫比为7.911时,日粮干物质(DM)和有机质(OM)的消化率最高,氮硫比为9.991时,日粮酸性洗涤纤维(ADF)的消化率最高;随着氮硫比的降低,沉积氮、可消化氮转化为沉积氮的效率和氮的表观消化率均下降(P<0.05),以氮硫比为9.991组最高,分别为1.24g/d、50%和62%;日粮氮硫比为9.991时,安哥拉兔产毛性能最好,估测年产毛量为862.67g,平均毛长为5.44cm,血液尿素氮含量最高为131.11mg/DL;随着日粮氮硫比的降低血清尿素氮含量有降低的趋势(P>0.05)。日粮中不同氮硫比胆固醇含量水平无规律性变化。     

Nitrogen balance in lambs fed a high-concentrate diet and infused with differing proportions of casein in the rumen and abomasum

Twenty-five wether lambs (34 +/- 0.9 kg) fitted with ruminal and abomasal infusion catheters were used in a completely randomized design to determine the effects of differing proportions of ruminal and abomasal casein infusion on N balance in lambs fed a high-concentrate diet (85% corn grain, 1.6% N; DM basis) for ad libitum intake. Wethers were infused with 0 (control) or 10.4 g/d of N from casein with ruminal:abomasal infusion ratios of 100:0, 67:33, 33:67, or 0:100% over a 14-d period. Feed, orts, feces, and urine were collected over the last 5 d. Total N intake and excretion were greater (P < 0.01) in lambs infused with casein than in controls; however, N retention did not differ in lambs infused with casein compared with controls, suggesting that N requirements were met without casein supplementation. Total N intake and total N excretion did not differ among casein infusion treatments. Urinary N excretion decreased linearly (P = 0.07) with decreasing ruminal infusion of casein. Site of casein infusion quadratically (P = 0.06) influenced N retained (g/d), with the greatest retention observed in the 33:67 ruminal:abomasal infusion treatment. Dry matter intake from feed decreased from 1,183 to 945 g/d (P = 0.02) in lambs infused with casein compared with controls, but apparently digested DM did not differ among treatments. These data indicate that decreasing the ruminal degradability of supplemental protein above that required to maximize N retention results in decreased urinary excretion of N without greatly affecting apparent diet digestion.     

Nitrogen balance in lambs fed low-quality brome hay and infused with differing proportions of casein in the rumen and abomasum

Twenty wether lambs (46 +/- 2 kg) fitted with ruminal and abomasal infusion catheters were used in a completely randomized design to determine the effects of differing proportions of ruminal and abomasal casein infusion on N balance in lambs fed low-quality brome hay (0.8% N, DM basis) for ad libitum intake. Wethers were infused with 0 (control) or 10.7 g/d of N from casein with ratios of ruminal:abomasal infusion of 100:0 (100R:0A), 67:33 (67R:33A), 33:67 (33R:67A), or 0:100% (0R:100A), respectively, over a 12-d period. Total N supply (hay N intake + N from casein infusion) was greater (P = 0.001) in lambs receiving casein infusion than in controls. Urinary N excretion (g/d) was greater (P = 0.001) in lambs receiving casein infusion than in controls. Urinary N excretion decreased as casein infusion was shifted from 100R:0A to 33R:67A and then slightly increased in lambs receiving 0R:100A (quadratic, P = 0.02). Total N excretion was greater (P = 0.001) in lambs receiving casein infusion than in controls and decreased linearly (P = 0.005) as casein infusion was shifted to the abomasum. Retained N (g/d, % of N intake, and % of digested N) was greater (P = 0.001) in lambs receiving casein than in controls. Retained N increased as infusion was shifted from 100R:0A to 33R:67A and then slightly decreased in lambs receiving 0R: 100A (quadratic, P < 0.07). Based on regression analysis, the predicted optimum proportion of casein infusion to maximize N retention was 68% into the abomasum. The regression suggests that supplementation with undegradable intake protein had an additional benefit over supplementation with ruminally degradable intake protein (100R:0A) and that changing the percentage of ruminally undegradable intake protein in supplemental protein from 33 to 100% resulted in minimal differences in N retention. Apparent N, DM, OM, and energy digestibility (% of intake) was greater (P < 0.03) in lambs infused with casein than controls but did not differ among casein infusion groups. These data suggest that feeding protein supplements containing a portion (greater than 0%) of the crude protein as ruminally undegradable intake protein, as compared to 100% ruminally degradable intake protein, to lambs consuming low-quality forage increases N retention and the efficiency of N utilization without influencing total-tract nutrient digestion.     

Sulfur-containing amino acid requirement of rapidly growing steers

Eight ruminally cannulated steers (294 kg, ADG = 1.3 kg/d) were used in a N retention study (8 x 8 latin-square design) to evaluate sulfur-containing (S) amino acid (AA) requirements for growth. Treatments were abomasal infusions of seven levels of L-methionine (0, 3, 6, 9, 12, 15 and 18 g/d) and one level of DL-methionine (6 g/d). All steers were fed a semipurified diet based on ammoniated corn cobs (DMI = 6.56 kg/d) and were abomasally infused with 400 g/d dextrose and 296.4 g/d of crystalline AA that simulated the non-S-AA pattern of casein. Infusion of 3 g/d supplemental L-methionine maximized N retention in steers. Intestinal flows of absorbable S-AA were determined to be 1.89 g/kg DMI. Breakpoint analysis of retained N as a function of total absorbable S-AA yielded a total S-AA requirement of 14.7 g/d. Nitrogen retention for DL-methionine (36.4 g/d) was not different (P greater than .05) from that for 6 g/d L-methionine (38.8 g/d), but because this value was not in the linear response range, the efficacy of DL-methionine in meeting S-AA needs could not be evaluated. Plasma methionine concentrations increased linearly (P less than .05) in response to L-methionine infusion and were greater (P less than .05) for steers infused with 6 g/d DL-methionine (45.3 microM) than for steers receiving 6 g/d L-methionine (30.5 microM). Plasma cystine increased when up to 9 g/d L-methionine was infused.(ABSTRACT TRUNCATED AT 250 WORDS)     

Glycolytic potential of red, soft, exudative pork longissimus muscle

Red, soft, exudative (RSE) pork is red as "normal" pork and exudative as PSE pork. The origin of RSE quality is unknown. In the present study, we determined whether the occurrence of RSE pork is related to the presence of the RN (Rendement Napole) gene. A glycolytic potential [= 2 x (glucose + glycogen + glucose-6-phosphate) + lactate] of > 180 micromol lactate/g of meat was used as indicator for presence of the RN gene. At 1 d postmortem, pork loin samples were collected at a commercial slaughter plant, and meat quality characteristics and glycolytic potential were determined. Glycolytic potential of RSE pork (n = 42) was higher (P < .01) than that of RFN (red, firm, nonexudative) pork (n = 25): 137 vs 110 micromol lactate/g of muscle. The glycolytic potential of PSE pork (n = 28) was 161 micromol lactate/g of muscle, which was higher (P < .01) than the glycolytic potential of RFN or RSE pork. Using a glycolytic potential of 180 micromol lactate/g of muscle as suggestive for the presence of the RN gene, four (10%) of the RSE samples were from RN carriers. By the same criterion, the PSE group contained nine (32%) RN gene carriers. These results suggest that the occurrence of RSE quality is not related to the presence of the RN gene.     

The effect of abomasal methionine supplementation on nitrogen retention of growing steers postruminally infused with casein or nonsulfur-containing amino acids

An experiment was conducted to develop a system useful for measuring methionine requirements of growing steers. Seven ruminally cannulated steers (312 kg, gaining .91 kg/d) were fed a diet based on ammoniated corn cobs, corn starch, molasses and urea. Quantities of N and sulfur-containing amino acids disappearing from the small intestine were 96.0 and 14.8 g/d, respectively. Postruminal infusions of Na-caseinate (CAS) resulted in linear (P less than .01) increases in N retention with values increasing from 30.1 g/d with no postruminal CAS infusion to 39.3, 50.8 and 59.2 g/d (averaged across methionine supplementation) when 100, 200 and 300 g/d CAS were infused. Postruminal infusions of a mixture of crystalline L-amino acids (simulating the nonsulfur-containing essential amino acid pattern of casein; SIM) at levels of 100, 200 and 300 g/d also led to linear increases (P less than .01) in N retention with steers retaining 30.9, 38.9 and 50.5 g N/d (averaged across methionine supplementation), respectively. Postruminal infusion of 12 g/d L-methionine across CAS and SIM infusions improved (P less than .01) N retention by 7.6 g/d but infusion of SIM, which is devoid of sulfur amino acids, also increased N retention. Responses to methionine supplementation was greatest when 200 or 300 g/d SIM were abomasally infused. The data are interpreted to demonstrate that, for steers fed a diet containing little true protein, postruminal supplementation with nonsulfur-containing amino acids tended to increase the ability of growing steers to respond to methionine supplementation.     

Effects of ruminal casein and glucose on forage digestion and urea kinetics in beef cattle

Effects of supplemental glucose and degradable intake protein on nutrient digestion and urea kinetics in steers (Bos taurus) given ad libitum access to prairie hay (4.7% CP) were quantified. Six ruminally and duodenally cannulated steers (initial BW 391 kg) were used in a 4 × 4 Latin square with 2 extra steers. Treatments were arranged as a 2 × 2 factorial and included 0 or 1.2 kg of glucose and 240 or 480 g of casein dosed ruminally once daily. Each period included 9 d for adaptation, 4 d for total fecal and urine collections, and 1 d for ruminal and duodenal sampling. Jugular infusion of (15)N(15)N-urea with measurement of enrichment in urine was used to measure urea kinetics. Glucose reduced forage intake by 18% (P < 0.01), but casein did not affect forage intake (P = 0.69). Glucose depressed (P < 0.01) total tract NDF digestion. Glucose supplementation decreased ruminal pH 2 h after dosing, but the effect was negligible by 6 h (treatment × time; P = 0.01). Providing additional casein increased the ruminal concentration of NH(3), but the increase was less when glucose was supplemented (casein × glucose; P < 0.01). Plasma urea-N was increased (P < 0.01) by additional casein but was reduced (P < 0.01) by glucose. Microbial N flow to the duodenum and retained N increased (P ≤ 0.01) as casein increased, but neither was affected by glucose supplementation. Urea-N entry rate increased (P = 0.03) 50% with increasing casein. Urinary urea-N excretion increased (P < 0.01) as casein increased. The proportion of urea production that was recycled to the gut decreased (P < 0.01) as casein increased. Glucose supplementation decreased (P < 0.01) urinary urea excretion but did not change (P ≥ 0.70) urea production or recycling. The amount of urea-N transferred to the gut and captured by ruminal microbes was less for steers receiving 480 g/d casein with no glucose than for the other 3 treatments (casein × glucose interaction, P = 0.05), which can be attributed to an excess of ruminally available N provided directly to the microbes from the supplement. Overall, the provision of supplemental glucose decreased forage intake and digestibility. Increasing supplemental casein from 240 to 480 g/d increased urea production but decreased the proportion of urea-N recycled to the gut.     

Pancreatic exocrine secretion and plasma concentration of some gastrointestinal hormones in response to abomasal infusion of starch hydrolyzate and/or casein

Eight Angus steers (290 +/- 8 kg), surgically prepared with pancreatic pouch-duodenal reentrant cannulas and abomasal infusion catheters were used in a replicated 4 x 4 Latin square experiment to investigate the effects of abomasal infusion of starch hydrolyzate (SH) and/or casein on pancreatic exocrine secretion and plasma concentration of hormones. Steers were fed a basal diet of alfalfa (1.2 x NEm) in 12 equal portions daily. Abomasal infusion treatments (6-L total volume infused per day) were water (control), SH [2.7 g/(kg BW x d)], casein [0.6 g/(kg BW x d)], and SH + casein. Periods were 3 d for adaptation and 8 d of full infusion. Pancreatic juice and jugular blood samples were collected over 30-min intervals for 6 h on d 11. Weight and pH of pancreatic samples were measured, and a 10% subsample was composited and frozen until analysis of total protein and pancreatic enzyme activities. The remaining sample was returned to the duodenum. Plasma was harvested and frozen until analyzed. Pancreatic juice (67 mL/h) and protein (1.8 g/h) secretion rates were not affected by nutrient infusion. There were SH x casein interactions for all pancreatic enzyme secretions (U/h; alpha-amylase, P < 0.03; trypsin, P < 0.08; and chymotrypsin, P < 0.03) and plasma insulin concentration (P < 0.10). Secretion of pancreatic enzymes was increased by SH (trypsin) and casein (alpha-amylase, trypsin, and chymotrypsin) but not when SH + casein were infused together. Glucose (P < 0.10) and cholecystokinin octapeptide concentrations (CCK-8; P < 0.05) were increased by SH, but glucagon was decreased (P < 0.10). Casein decreased (P < 0.10) plasma CCK-8 concentrations. These data indicate that positive effects of postruminal casein on enzyme secretion were inhibited by SH, emphasizing the complexity of the regulatory mechanisms involved in dietary adaptation of pancreatic exocrine secretion. Changes in hormone concentration may not relate directly to changes in enzyme secretion.