一年生黑麦草青贮料和玉米青贮料中添加蒸汽压片玉米和破碎玉米对奶牛生产性能的影响

选用24头泌乳期荷斯坦奶牛进行为期6周的奶牛饲养试验,采用2×2因素随机区组试验设计,研究以一年生黑麦草青贮料(RS)或以50∶50混合的一年生黑麦草青贮料和玉米青贮料组成的混合料(BLEND)为基础日粮,添加饲喂破碎玉米(GC)或蒸汽压片玉米(SFC)对奶牛生产性能的影响。试验日粮包含49.6%的粗饲料,以全混合日粮的形式饲喂,1次/d,试验期4周,预饲期2周。处理之间没有发现交互作用。饲喂BLEND组比饲喂RS组的奶牛的干物质(DM)、有机物(OM)、中性洗涤纤维(NDF)和酸性洗涤纤维(ADF)的采食量高。但饲喂RS组的OM、NDF和ADF的总消化率高于饲喂BLEND组。测定第4周营养物质消化率,未发现各组间营养物质采食量有差异,但SFC组的DM和OM的消化率要高于GC组。饲喂BLEND的奶牛比饲喂RS的奶牛生产更多的能量校正乳,表现为提高了生产效率。当日粮中添加SFC时,奶牛干物质采食量减少,产奶量增多,但乳中乳脂率较低。与饲喂GC相比,饲喂SFC乳蛋白生成量和生成效率较高。各组间血糖和乳尿素氮生成量相似,但饲喂GC的奶牛比饲喂SFC的奶牛血尿素氮水平要高。本试验的结果表明,与只饲喂黑麦草青贮料相比,饲喂一年生黑麦草青贮料和玉米青贮料效果更好。日粮中添加SFC与GC相比,奶牛生产性能和效率均有一定的提高。     

不同饲粮模式对奶牛乳腺长链脂肪酸摄取的影响

本试验旨在研究不同饲粮模式对奶牛乳腺长链脂肪酸摄取的影响。选用健康且胎次、体重[(554±21)kg]、泌乳期[(120±4)d]和产奶量[(24.30±1.47)kg/d]相近的荷斯坦奶牛30头,采用随机区组设计,分为3组,每组10头。3组奶牛饲喂不同模式的饲粮,即以苜蓿、羊草和全株玉米青贮为粗饲料的饲粮(MF组)、营养水平约同MF组但以单一玉米秸秆为粗饲料的饲粮(CS1组)和粗饲料比例等同MF组但以单一玉米秸秆为粗饲料的饲粮(CS2组)。试验期90 d,分3期进行,每期30 d,在每期的最后2 d采集饲粮样、乳样和血样进行检测分析。结果表明:1)不同饲粮模式对奶牛的体重和干物质采食量均无显著影响(P0.05),但对奶牛的产奶量、乳脂率和日乳脂产量均有显著影响(P0.05)。MF组的产奶量和日乳脂产量均显著高于CS1组和CS2组(P0.05),而CS1组则显著高于CS2组(P0.05);MF组的乳脂率显著高于CS1组(P0.05)。2)不同饲粮模式对奶牛动、静脉血浆中C16∶0、C18∶0、C18∶2cis-6、C18∶1 cis-9和总长链脂肪酸的浓度均无显著影响(P0.05)。3)不同饲粮模式对奶牛的血流量造成了显著的影响(P0.05),呈现出CS1组MF组CS2组。不同饲粮模式影响了奶牛动脉对总长链脂肪酸的供给量,表现为MF组和CS1组显著大于CS2组(5 629.51、6 605.02 g/d vs.3 878.91 g/d)(P0.05)。4)不同饲粮模式影响了奶牛乳腺对总长链脂肪酸的摄取率,表现为MF组和CS2组显著高于CS1组(10.99%、10.84%vs.7.39%)(P0.05)。5)不同饲粮模式影响了奶牛乳腺对总长链脂肪酸的摄取量,表现为MF组(618.69 g/d)CS1组(487.87 g/d)CS2组(420.56 g/d),组间差异显著(P0.05)。本研究揭示了在低质粗饲料条件下,增加精料浓度并不能有效提高奶牛乳腺对长链脂肪酸的摄取。     

围产前期奶牛日粮中添加过瘤胃脂肪对其干物质采食量和泌乳性能的影响

文章旨在研究围产前期奶牛日粮中添加过瘤胃脂肪对其初乳质量、干物质采食量和泌乳性能的影响。试验选择30头产前3周的中国荷斯坦奶牛,随机分为对照组、试验Ⅰ组和试验Ⅱ组,每组10头牛。3组奶牛在产前饲喂含不同脂肪添加量的日粮,对照组不添加额外脂肪,试验Ⅰ组添加2%干物质基础的脂肪酸钙盐,试验Ⅱ组添加3%干物质基础的脂肪酸钙盐。脂肪酸钙盐主要成分为大豆油。3组奶牛饲喂相同的泌乳日粮。试验期从产前3周至泌乳12周。奶牛产犊时,测定初乳产量,测定初乳成分及Ig G含量。每周记录采食量,每天记录产奶量,每周采集奶样测定乳成分。试验结果表明,产前3周奶牛日粮中添加脂肪对其初乳产量和乳成分无显著影响(P0.05),显著增加了初乳中Ig G含量(P0.05)。试验Ⅱ组奶牛初乳中Ig G含量最高,分别比对照组和试验Ⅰ组奶牛高32.04%和12.40%(P0.05)。产前3周奶牛日粮中添加脂肪对产前奶牛的干物质采食量无显著影响(P0.05),显著增加了产后奶牛的干物质采食量,而且与脂肪添加剂量呈线性相关(P0.05)。试验Ⅱ组奶牛和试验Ⅰ组奶牛的产奶量显著高于对照组(P0.05),而且以试验Ⅱ组奶牛具有最高的产奶量(P0.05)。因此,本试验结果表明,产前奶牛日粮中添加脂肪可以提高初乳质量,增加奶牛产奶量,本试验中以3%的添加剂量为宜。     

不同粗饲料组合混合日粮对奶牛泌乳性能的影响

本试验通过给奶牛饲喂不同粗饲料组合的TMR日粮,探讨日粮中不同粗饲料组合对奶牛泌乳性能的影响.结果表明,日粮鲜重的精粗比从30∶70提高到40∶60后,奶牛的干物质采食量有显著地增加（P＜0.05）.随着精料比例增加,其能量水平、蛋白含量和乳蛋白率增加.同时,蛋白含量和产奶量都有所提高.在试验二组中用青贮代替了全贮,提高了奶牛的采食量和泌乳性能.说明,奶牛全混合日粮（TMR）可以提高日粮养分表观消化率、产奶量和改善乳蛋白质水平.青贮饲料的蛋白质的降解和利用更容易被瘤胃微生物降解和吸收,从而提高奶牛的泌乳性能,取得较高的经济效益.     

不同饲喂模式对奶牛采食和瘤胃发酵的影响

为采用4头体重(600±50)kg、装有永久性瘤胃瘘管的中国荷斯坦经产奶牛进行试验,比较传统精粗分开饲喂向全混合日粮(TMR)转换时泌乳奶牛的采食、瘤胃发酵及生产性能的变化。试验动物所用日粮组成在整个试验期完全相同。前17 d采用精粗饲料分开饲喂的模式,后13 d则采用TMR进行饲喂。在由传统的精粗分开饲喂向TMR饲喂转换过程中,试验牛的日粮干物质采食量(DMI)、中型洗涤纤维进食量(NDFI)差异极显著(P<0.01),而与之相对应的采食时间差异不显著;全天的瘤胃pH值试验期前后比较无明显差异,但pH曲线但有趋于平稳的趋势,瘤胃中氨态氮浓度在试验期结束时差异极显著(P<0.01)。     

复方中草药添加剂对围产期奶牛泌乳性能和初乳品质的影响

本试验旨在探讨不同剂量的复方中草药对围产期奶牛干物质采食量、产奶性能和初乳品质的影响。选择年龄、胎次、预产期和上一个泌乳期产奶量相近的围产期荷斯坦奶牛40头,随机分为对照组、处理Ⅰ组、处理Ⅱ组和处理Ⅲ组。对照组奶牛饲喂常规日粮,在常规日粮基础上,处理Ⅰ组、Ⅱ组、Ⅲ组分别添加50、150 g/d·头和300 g/d·头剂量的复方中草药,饲喂时间为产前21 d至产后21 d,共42 d。试验结果表明,从产前7 d到分娩,处理Ⅰ组、Ⅱ组和Ⅲ组奶牛的干物质采食量分别比对照组显著提高1.11、1.98 kg/d和2.44 kg/d(P0.05)。复方中草药添加剂对提高围产期奶牛的产奶量和乳成分含量,改善初乳品质具有重要的促进作用,而且具有显著的剂量效应,处理Ⅲ组的饲喂效果最好(P0.05)。因此,在奶牛围产期饲料中补充添加复方中草药可显著提高奶牛干物质采食量,提高产奶量,改善乳品质,以300 g/d·头剂量效果最佳。     

NFC/RDP水平对围产期奶牛干物质采食量和血液生化指标的影响

试验旨在研究围产期日粮不同NFC/RDP水平对奶牛干物质采食量及血液生化指标的影响。选择2～5胎、产奶量、体重和体况评分值相近的围产期荷斯坦奶牛48头,随机分为6组,每组8头,于产前第28天开始,各组分别饲喂NFC/RDP为5.14(Ⅰ)、3.46(Ⅱ)、4.00(Ⅲ)、5.12(Ⅳ)、3.33(Ⅴ)、2.87(Ⅵ)的日粮。分娩后各组均饲喂相同的产奶日粮,至产后第56天结束。结果表明:饲喂NFC/RDP为4.00(Ⅲ)的日粮,显著提高了奶牛产后的干物质采食量(P<0.05),且奶牛血液生化指标浓度的变化幅度较小。在本试验条件下,NFC/RDP为4.00(Ⅲ)的日粮饲喂效果最佳。     

产前日粮碳水化合物来源和莫能菌素对经产奶牛围产期代谢和泌乳的影响

选用85头经产荷斯坦奶牛随机设计,评估产前碳水化合物来源及莫能菌素对围产期奶牛干物质采食量、血液参数和泌乳性能的影响。日粮处理按照2×2阶乘排列设计,包括传统的干奶料(CONV)和不含有草料纤维来源的干奶料(NFFS),补充或不补充330 mg/d.头莫能菌素。CONV日粮包括70%的草料,NFFS日粮28%的草料用棉籽壳和大豆壳替代。在整个干奶期(产前60 d)饲喂试验日粮(CONV和NFFS)。在预期产犊日期之前的28 d开始每天追加一次莫能菌素直到分娩。分娩后,所有奶牛饲喂相同的泌乳期奶牛料。结果发现,在妊娠的最后28 d,与饲喂CONV日粮相比,饲喂NFFS产前日粮干物质采食量(15.8 vs 11.9 kg/d)、干物质采食量体重百分比(2.1%vs1.6%体重)、血糖(67.4 vs 64.6 mg/dl)和血清胰岛素浓度(0.59 vs 0.45 ng/ml)更高,非酯化脂肪酸浓度(185 vs 245μEq/L)较低。在泌乳的前56 d,产前CHO、莫能菌素或两者混合效应对平均产奶量或乳成分没有明显的影响。但随着时间的延长,产前碳水化合物来源有影响产奶量的趋势。产前28 d补给莫能菌素对围产期产奶量没有影响。产前日粮对产后干物质采食量、血糖、非酯化脂肪酸、胰岛素浓度或肝脏甘油三酯没有影响。研究结果表明,在干奶期日粮中用NFFS部分替换传统日粮碳水化合物提高或维持了产前干物质采食量,因此增强了分娩前代谢水平。产前更高的干物质采食量可能潜在增加泌乳早期的产奶量。     

日粮-淀粉酶对过渡期奶牛生产性能和代谢的影响

24头经产荷斯坦奶牛(体重759kg,SD=30kg;体况指数3.2,SD=0.13)采用随机分组设计确定α-淀粉酶对过渡期奶牛瘤胃发酵、主要代谢产物和泌乳性能的影响。奶牛分别饲喂对照日粮和在对照基础上按0.1%DM水平添加了α-淀粉酶的处理日粮(662个真菌淀粉酶单位/g,AMA)。在产前21d和泌乳期头21d饲喂试验日粮,泌乳的第22~70d,所有奶牛都饲喂泌乳期日粮。处理组产前和产后的平均DM采食量分别为12.4和17.8kg/d,差异不显著;但产前最后1周处理组DM采食量的下降幅度相对于对照组比产前第2周大。处理组产前瘤胃中丁酸盐的比例有上升趋势,但产后不出现此现象。处理组的血浆胰岛素、肝脂肪和肝糖原的浓度与对照组相比差异不显著。饲喂AMA的牛在产前其血浆β-羟基丁酸盐和非酯化脂肪酸浓度均高于对照组,且产后血糖浓度上升。血浆中β-羟基丁酸盐和非酯化脂肪酸增加的现象出现在产前而不是产后,并且产后血糖有上升趋势,表明饲喂α-淀粉酶的奶牛由脂肪代谢向碳水化合物代谢转换。     

粗饲料水平对奶牛健康及生产性能影响的研究进展

高品质的粗饲料可以提高奶牛的生产性能,合理的日粮精粗比更对奶牛生产有着重要的作用。研究表明,日粮中的精粗比过低,会降低奶牛采食量,导致奶牛养分摄入不足,产奶量和乳脂率降低。日粮中的精粗比过高则会破坏瘤胃内环境稳定导致瘤胃pH值降低,影响微生物蛋白、氨态氮和VFA的合成,严重导致瘤胃酸中毒,致使奶牛淘汰或死亡,降低生产效益。综合分析,探寻高品质粗饲料以及最佳的日粮精粗比是奶业发展的重中之重。本综述主要叙述粗饲料的品种与长度以及奶牛日粮中粗饲料添加水平对奶牛的健康以及生产性能的影响。     

Effects of corn straw or mixed forage diet on rumen fermentation parameters of lactating cows using a wireless data logger

The objective of this study was to evaluate the effect of two different forage types on rumen fermentation parameters and profiles using a wireless data logger. Eight lactating cows were randomly assigned to one of two dietary treatments with a low forage diet with corn straw (CS) or a high forage diet with mixed forage (MF) as the forage source, respectively. Dietary physically effective neutral detergent fiber (peNDF) content was 11.3% greater in CS. Dry matter intake and milk fatty acid content decreased upon CS (P < 0.05). Ruminal pH, temperature and oxidation reduction potential (ORP) were monitored for 14 weeks. The CS group had significantly higher pH but lower temperature and ORP compared to MF (P < 0.01). With the CS diet regime, pH at the time before morning feeding, rumination and post‐ingestion were significantly higher than those in the MF group (P < 0.05). However, times with the ruminal pH below 6.0 and 5.8 were significantly reduced (P < 0.05), whereas ruminal pH below 5.6 tended to be lower (P = 0.07). The results indicated that rumen fermentation parameters were affected by forage types and dietary peNDF content might be predominant in ruminal pH regulation.     

Effects of feeding alkaline hydrogen peroxide-treated wheat straw-based diets on intake, digestion, ruminal fermentation, and production responses by mid-lactation dairy cows.

The objective of this experiment was to determine the effects of feeding different levels of alkaline hydrogen peroxide-treated wheat straw (AHP-WS) in the diet on feed intake, nutrient digestion, ruminal fermentation, and production responses in mid-lactation dairy cows. Eight Holstein cows, averaging 147 d postpartum, were used in two replications of a 4 x 4 Latin square design. Complete mixed diets consisted of 70% forage and 30% concentrate (DM basis) with various levels of AHP-WS, alfalfa haylage, and corn silage as forage sources. Treatments contained 0 (control), 20.0, 40.1, or 60.0% AHP-WS in the diet. A quadratic effect (P = .08) of AHP-WS level on DMI was noted, with values of 2.16, 22.3, 20.8, and 18.9 kg/d for the control, 20.0, 40.1, and 60.0% AHP-WS treatments, respectively. Apparent digestibilities of DM, OM, CP, and ADF were not affected (P greater than .10) by replacing haylage and corn silage with increasing amounts of AHP-WS in the diet, but there was a linear increase (P = .03) in NDF digestibility (44% for control vs 59% for the 60.0% AHP-WS diet) and a parallel decrease (P less than .05) in cell content digestibility (82 vs 70% for these two diets). Yields of milk and 4% fat-corrected milk (FCM) were decreased (quadratic; P = .0001) as the level of AHP-WS increased in the diet. The addition of AHP-WS to the diet decreased the milk fat percentage from 3.72 to 3.60% (quadratic; P = .05) and decreased milk protein percentage from 3.27 to 3.13% (linear; P = .0001). Cows fed the higher levels of AHP-WS had linear increases (P = .0001) in ruminal concentrations of total VFA (128.0 mM for control vs 136.0 mM for the 60.0% AHP-WS treatment) and molar proportion of acetate, resulting in a quadratic effect (P less than .0001) on the acetate:propionate ratio. These data indicate that feeding the 40.1 and 60.0% AHP-WS diets lowered digestible DM and OM intakes, which resulted in reduced 4% FCM yield as nutrient intakes were decreased compared with cows fed the 20.0% AHP-WS diet or the control diet containing alfalfa haylage and corn silage. Although substituting AHP-WS for haylage and corn silage increased NDF digestibility and tended to increase digestible NDF intake, milk production was depressed because digestible DMI decreased.     

Effect of energy source and ruminally degradable protein addition on performance of lactating beef cows and digestion characteristics of steers

Two trials were conducted to determine the effect of energy source (ENG) and ruminally degradable protein (RDP) on lactating cow performance and intake and digestion in beef steers. In Trial 1, 78 cow-calf pairs were used in a 2 x 2 factorial design to determine the effect of ENG (corn or soyhulls; SH) and RDP (with our without sunflower meal) to a forage diet for lactating beef cows. The basal diet consisted of 75% grass hay (11.5% CP) and 25% wheat straw (7.4% CP). Supplement treatments and predicted RDP balances were corn (-415 g of RDP/d); SH (-260 g of RDP/d); corn plus RDP (0 g of RDP/d); or SH plus RDP (0 g of RDP/d). Data were analyzed as a split-plot in time, with pen as the experimental unit (two pens per treatment). No interaction between ENG and RDP was present (P > 0.08) for any response variable. No differences (P > 0.39) due to ENG or RDP were noted for BW, BCS, or milk yield; however, final calf weight tended to increase with ENG (P = 0.06). In Trial 2, a 5 x 5 Latin square was used to determine effects of ENG and RDP on intake and digestion in steers (686 +/- 51 kg BW). Treatments were arranged as a 2 x 2 plus one factorial and comprised a control (CON; grass hay, 7% CP), grass hay plus 0.4% BW SH, grass hay plus 0.4% BW SH and 0.15% BW sunflower meal, grass hay plus 0.4% BW corn, and grass hay plus 0.4% BW corn and 0.2% BW sunflower meal. Preplanned contrasts included main effects of ENG and RDP, ENG x RDP interaction, and CON vs. supplemented (SUP) treatments. Supplementation increased total DMI compared with CON (P = 0.001), but forage DMI was greater (P = 0.001) for CON than for SUP. An ENG x RDP interaction occurred for forage DMI (P = 0.02); addition of RDP to corn decreased forage intake, whereas addition of RDP to SH had no effect. There was an ENG x RDP interaction (P = 0.001) for ruminal pH; pH tended to increase with RDP addition to SH (P = 0.07), but decreased with RDP addition to corn (P = 0.001). Supplementation increased ruminal ammonia compared with CON (P = 0.001). Likewise, RDP increased ruminal ammonia (P = 0.001). An interaction occurred for OM disappearance (OMD; P = 0.01). The RDP addition to SH numerically decreased OMD (P = 0.23), whereas RDP addition to corn numerically increased OMD (P = 0.14). Intake and digestion seem to respond differently to RDP addition depending on supplemental energy source. Both corn or SH seem to be suitable supplements for the quality of forage used in this trial. Addition of supplemental protein did not improve cow or calf performance.     

玉米秸秆饲粮条件下阴外动脉灌注氨基酸混合物对奶牛乳腺内短链脂肪酸摄取规律的影响

本试验采用动静脉血插管技术,以泌乳中期荷斯坦奶牛为研究对象,研究玉米秸秆饲粮条件下阴外动脉灌注氨基酸(AA)混合物对奶牛产奶性能、尾动脉血和乳静脉血中短链脂肪酸(SCFA)浓度及其比例以及乳腺内SCFA摄取规律的影响。采用2×2交叉试验设计,将体况良好、体重相近、日乳产量为(20.17±1.28)kg的8头经产(2~3胎)荷斯坦奶牛随机分为采食不同饲粮的2组[苜蓿组(MF组)和玉米秸秆组(CS组)],每组4头。2组奶牛饲喂的饲粮精粗比均为45∶55,精饲料组成相同,粗饲料组成不同,MF组粗饲料由苜蓿干草、玉米青贮和羊草组成,CS组以单一的玉米秸秆全部替代MF组饲粮中的粗饲料。试验分为2个阶段,每个阶段20 d,均分为饲粮适应期(预试期)14 d,载体灌注期3 d,正式灌注期3 d。在第1阶段,在载体灌注期,MF组奶牛接受载体灌注(阳性对照组1),CS组奶牛也接受载体灌注(对照组);在正式灌注期,MF组奶牛继续接受载体灌注(阳性对照组2),CS组奶牛接受AA混合物灌注;在第2阶段,将2组动物互换后处理方法同第1阶段。每个正式灌注期的最后2 d采集乳样和血样。结果显示:CS组奶牛阴外动脉灌注AA混合物可显著提高乳蛋白率(P0.05),对乳产量、4%乳脂校正乳(FCM)产量、乳脂率、乳脂产量、乳蛋白产量有一定促进效果,但部分指标仍然显著低于MF组(P0.05)。CS组奶牛阴外动脉灌注AA混合物可趋于显著地提高乳静脉血中乙酸的浓度(P=0.09),显著降低乳腺内乙酸的动静脉差(P0.05),缩小CS组与MF组奶牛在乳腺对乙酸的摄取量和摄取效率方面存在的差距。CS组奶牛阴外动脉灌注AA混合物对提高尾动脉血中乙酸/丙酸、(乙酸+丁酸)/丙酸有一定的促进效果(P0.05)。由此得出,以玉米秸秆为粗饲料的奶牛阴外动脉灌注AA混合物可显著提高乳蛋白率,增加乳静脉血中的乙酸浓度,同时缩小与以苜蓿干草、玉米青贮和羊草为粗饲料的奶牛在乳腺对乙酸的摄取量和摄取效率方面存在的差距。     

Effects of haylage and monensin supplementation on performance, carcass characteristics, and ruminal metabolism of feedlot cattle fed diets containing 60% dried distillers grains

The objectives of this research were to determine the interaction of monensin and haylage supplementation for steers fed 60% dried distillers grains (DDGS) on 1) mineral status, performance, and carcass characteristics, and on 2) ruminal pH, H(2)S, and short-chain fatty acid concentrations. In Exp. 1, Angus-cross steers (n=168; BW=277 ± 67 kg) were blocked by BW and allotted in a 2 × 2 factorial arrangement of treatments to 24 pens. Dietary treatments were 1) 0 mg of monensin/kg of diet + 0% haylage, 2) 33 mg of monensin/kg of diet + 0% haylage, 3) 0 mg of monensin/kg of diet + 10% haylage, and 4) 33 mg of monensin/kg of diet + 10% haylage. The remainder of the diet was 60% DDGS, 10% corn silage, 15% supplement, and corn (either 5 or 15%) on a DM basis. When supplemented with 0 mg of monensin/kg of diet, added haylage increased ADG by 5.7%, whereas when supplemented with 33 mg of monensin/kg of diet, added haylage increased ADG by 13% (P < 0.01). No interactions of monensin and haylage were observed for DMI or G:F (P ≥ 0.36). Haylage inclusion increased (P < 0.01) DMI and decreased (P < 0.01) G:F. No interactions (P > 0.05) on plasma mineral concentrations were observed; however, over time, plasma Cu concentrations decreased (P < 0.01), whereas plasma ceruloplasmin and S concentrations increased (P < 0.01). There were no treatment effects (P ≥ 0.08) on carcass characteristics. Cattle fed the 60% DDGS diets benefitted from increased dietary forage, and the effects of monensin and forage were additive for ADG and final BW. In Exp. 2, ruminally fistulated steers (n=8; BW = 346 ± 34 kg) were used in a replicated 4 × 4 Latin square design and were randomly assigned to the diets used in Exp. 1. Haylage inclusion increased ruminal pH from 1.5 through 12 h postfeeding, and the effects of monensin supplementation were additive (P < 0.05). From 1.5 through 9 h postfeeding, steers fed 33 mg of monensin/kg of diet tended to have reduced (P ≤ 0.10) concentrations of H(2)S when compared with steers fed 0 mg of monensin/kg of diet. Acetate:propionate ratios at 6 h postfeeding were 0.94, 0.93, 1.29, and 1.35 for diets 1 to 4, respectively (P < 0.01); total lactate was decreased regardless of treatment (range: 0.94 to 1.42 μmol/mL). Sulfuric acid in DDGS, not ruminal short-chain fatty acids, may be responsible for the low rumen pH observed and may influence the maximum inclusion of DDGS in cattle diets. Monensin supplementation decreased H(2)S concentration and may decrease the risk of polioencephalomalacia for cattle fed high-DDGS diets.     

Effect of dietary carbohydrate and monensin on expression of gluconeogenic enzymes in liver of transition dairy cows

Thirty-four multiparous Holstein cows were used in a randomized block design to evaluate the effects of feeding nonforage fiber sources (NFFS), monensin, or their combination on expression of gluconeogenic enzymes in the liver during the transition to lactation. The addition of 0 or 300 mg/d of monensin to a conventional (CONV) or NFFS prepartum diet was evaluated in a 2 x 2 factorial arrangement of treatments. The NFFS diet was formulated by replacing 30% of the forage component of the CONV diet with cottonseed hulls and soyhulls. The CONV and NFFS basal diets were fed at dry-off and continued through parturition. Monensin was fed from -28 d relative to calving (DRTC) through parturition. At calving, all cows were placed on the same diet. Liver biopsy samples obtained at -28, -14, +1, +14, and +28 DRTC were used to determine pyruvate carboxylase (PC) and cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C) mRNA expression. Feeding NFFS resulted in greater (P < 0.05) prepartum DMI compared with the CONV diet. There was no effect of prepartum diets on postpartum DMI or average milk production to 56 d of lactation. Expression of PC mRNA was elevated (P < 0.05) at 1 d postpartum, but there was no effect of NFFS or monensin on PC mRNA abundance. Expression of PEPCK-C mRNA at calving was increased (P < 0.05) with prepartum monensin feeding. The data indicate that feeding monensin to transition cows induces hepatic PEPCK-C mRNA expression before calving. The increased expression of hepatic PEPCK-C mRNA with monensin feeding suggests a feed-forward mechanism of metabolic control in ruminants that links molecular control of gluconeogenesis with the profile of rumen fermentation end products.     

Effects of forage-to-concentrate ratio in prepartum diet on the dry matter intake and milk yield of periparturient cows during hot weather

The objective of this experiment was to study the effect of prepartum diets on dry matter intake (DMI) around parturition and on milk production in early lactation during a hot summer. Nine cows due to calve in July or August were assigned to two groups and fed either control (group C; four cows) or high‐concentrate (group H; five cows) diets to meet 110% of their energy requirements from 18 days before the expected calving date to parturition. The proportion of concentrate in the control diet was 35%, and that in the high‐concentrate diet was 45%. For 21 days after parturition, all cows were fed the same diets for lactation ad libitum. The DMI of cows in group H almost met their energy requirements. In group C, the DMI was decreased relative to group H and the concentration of plasma non‐esterified fatty acids was significantly higher (P < 0.05) before parturition. Therefore, the cows in group C were thought to be energy deficient before parturition. After parturition, there were no significant differences in DMI between the two groups. The milk yield of cows in group H tended to be higher than that of cows in group C at 21 days after parturition. Milk protein yield was significantly higher (P < 0.05) in group H 21 days after parturition relative to group C. There were no significant differences in milk composition between the two groups.     

Effect of dietary potassium and anionic salts on acid–base and mineral status in periparturient cows

Dry cow diets based on grassland forage from intensive production contain high amounts of K and could be responsible for a reduced ability to maintain Ca homoeostasis. The aim of this study was to determine whether a moderate anionic salt supplementation to a forage‐based pre‐calving diet with varying native K content affects the mineral and acid–base status in transition cows. Twenty‐four dry and pregnant Holstein cows, without antecedent episodes of clinical hypocalcemia, were assigned to two diets during the last 4 weeks before estimated calving date. Twelve cows were fed a hay‐based diet low in K (18 g K/kg DM), and 12, a hay‐based diet high in K (35 g K/kg DM). Within each diet, six cows received anionic salts during the last 2 weeks before the estimated calving day. After calving, all cows received the high K diet ad libitum. Blood samples were taken daily from day 11 pre‐partum to day 5 post‐partum. Urine samples were taken on days 7 and 2 pre‐partum and on day 2 post‐partum. The anionic salt did not alter feed intake during the pre‐partum period. Serum Ca was not influenced by the dietary treatments. Feeding pre‐partum diets with low K concentrations induced a reduced metabolic alkalotic charge, as indicated by reduced pre‐partum urinary base–acid quotient. Transition cows fed the low K diet including anionic salts induced a mild metabolic acidosis before calving, as indicated by higher urinary Ca, lower urinary pH and net acid–base excretion. Although serum Ca during the post‐partum period was not affected by dietary treatment, feeding a low K diet moderately supplemented with anionic salts to reach a dietary cation–anion difference close to zero permitted to obtain a metabolic response in periparturient cows without altering the dry matter intake.     

热应激条件下粗饲料组合对奶牛氮素利用的影响

为了研究粗饲料组合对热应激奶牛氮素利用的影响,试验选取20头胎次和泌乳天数相似的健康荷斯坦奶牛,随机分成2组,每组10头,分别饲喂2种粗饲料组合饲粮:玉米青贮+苜蓿(0.92∶1.00,AF组)和玉米秸秆(CS组)。2组饲粮精料相同,精粗比均为63.7∶36.3。预试期1周,正试期8周。结果表明:1)与CS组相比,AF组奶牛产奶量及能量校正乳、4%脂肪校正乳、乳蛋白和乳糖产量显著或极显著升高(P0.01或P0.05)。2)奶牛对AF组饲粮粗蛋白质表观消化率极显著高于CS组(P0.01)。3)与CS组相比,AF组瘤胃微生物蛋白产量显著升高(P0.05),而尿液和血液尿素氮浓度极显著降低(P0.01)。4)与CS组相比,AF组氮摄入量和乳中氮产量极显著升高(P0.01),但氮转化效率显著降低(P0.05)。结果提示,与玉米秸秆相比,玉米青贮+苜蓿的组合能提高饲粮粗蛋白质水平,增加热应激奶牛粗蛋白质表观消化率,促进瘤胃微生物蛋白和乳蛋白的合成,但氮的转化效率有待提高。