Background

It is estimated that 50%of the cows in extensive beef systems do not receive adequate nutritional management,and this is a main reason for low fertility rates in tropical herds[1].

Among the factors affecting the reproductive performance of beef cattle,nutrition has perhaps the highest impact[2].Supplementation to grazing animals is a practice that can be adopted under tropical conditions to increase animal performance.Because the last third of gestation usually coincides with the dry season and,consequently,with low quantity and quality of forage,producers in tropical conditions,as in Brazil,are usually oriented to supplement pregnant cows for the last 90 d of gestation.

The objective with this experiment was to study whether this period of supplementation could be reduced to avoid extra labor and,consequently,reduce feeding costs.Therefore,we conducted a study to evaluate the effects of different supplementation strategies for pregnant beef cows in the last third of gestation,receiving supplementation for 90,60 or 30 d pre-partum.

Methods

The two experiments were conducted at the Department of Animal Science-Universidade Federal de Viçosa,Brazil,from July to December 2012.All animal care and handling procedures were ethically standardized and approved by the Animal Care and Use Committee of the Universidade Federal de Viçosa,Brazil.

Experiment 1-Performance

Thirty-five multiparous,at an average age of five years old,single pregnant Nellore cows with 491.88±55 kg of body weight(BW),a body condition score(BCS)of 4.7±0.58 and 200±15 d of gestation were used.Cows were housed in an experimental area of Brachiaria decumbens divided into four paddocks of 5.0 ha each,and had unlimited access to water,feeders and mineral salt(8.7%calcium,9.0%phosphorous,18.7%sodium,9.0%sulfur,2,400 mg/kg of zinc,800 mg/kg of copper,1,600 mg/kg of manganese,40.0 mg/kg of iodine,8.00 mg/kg of cobalt and 8.16 mg/kg of selenium).To avoid any effects of paddock on the responses,treatments were rotated among paddocks every 10 d.

Animals were assigned to a completely randomized design with four treatments.There were nine cows each in the control group,60-d and 90-d supplemented groups,and eight cows in the 30-d supplemented group.Supplement was fed in a collective feeder,which is experimental handling closer to what is normally observed in beef production systems due to cattle gregarious behavior.As the evaluations in Experiment 1 were focused on individual performance,and these measurements were collected individually,the animal was considered the experimental unit,as recommended by Detmann et al.[3].

Supplement was composed of corn,sorghum and soybean meal,and formulated to contain approximately 20%crude protein(CP;Table 1).The level of supplementation adopted for the 90-d treatment corresponds to the daily supply of 1 kg of supplement to approximately 23%of the requirements of CP and 17%of the daily energy requirements of a pregnant Nellore cow,with average BW of 465 kg and expected calf birth BW of 32 kg[4].The other supplemented treatments were based on the supply of the same total amount of energy and CP,but offered in a reduced period of feeding.

Cow BW was recorded at the beginning of the experiment,approximately 90 d prior to the day of calving,at the week before the expected date of parturition(calving BW),and 31 d after parturition.Cow BCS was recorded at the beginning of experiment,prior to calving and in the first day of the breeding season on a scale ranging from 1 to 9,as recommended by NRC[5]by two experienced technicians.Calf BW was also recorded at birth.Shrunk BW(SBW)was calculated using adjustments proposed by Gionbelli et al.[6]for Nellore cows as follows:

After calving,cows were managed as a single herd until after pregnancy was diagnosed.During this period,all cows grazed the same pasture and received mineral supplement ad libitum.

Table 1　Ingredients and chemical composition of supplements

aOM-organic matter;CP-crude protein;apNDF-neutral detergent fiber corrected for ash and protein residue

Itema　Supplement Ingredients,%as-fed basis Corn 33 Sorghum　33 Soybean meal　34 Chemical composition,g/kg OM 971 CP　208 apNDF　164

Twenty-one and 31 d after calving,blood samples were taken from the jugular vein using vacuum tubes with clot accelerator and gel for serum separation(BD Vacuntainer®SST II Plus,São Paulo,Brazil).Immediately after collection,the samples were centrifuged at 3,600×g for 20 min.Then,the serum was frozen at-20°C and subsequently analyzed for progesterone by the chemiluminescent method using Access Progesterone Reagent Kit(Ref.Number 33550,Beckman Coulter®,Brea,USA)in the Access 2 Immunoassay System(Beckman Coulter Inc.,Brea,USA).

Pasture chemical composition(Table 2)was assessed by hand-plucked samples every two weeks.In the middle of every experimental month,a second pasture sample was also collected to estimate forage potentially digestible dry matter(pdDM)as proposed by Detmann et al.[5].Four subsamples were randomly collected in each plot by cutting it close to the ground using a metal square(0.5 m×0.5 m).Samples were weighed and oven dried at 60°C for 72 h.After that,samples were mill grinded to pass through a 2-mm screen for indigestible neutral detergent fiber(iNDF)analysis[7].A sub portion of 20 g of each sample was grinded to pass through a 1-mm screen for analyses of dry matter(DM),ash,crude protein(CP)and neutral detergent fiber(NDF).

格拉斯说，“在中国，由于老龄化加剧和医保体系尚未完善，阿尔茨海默病的防治将要面对更为复杂的困境，这是任何公共卫生专家和政策制定者都需要着力应对的局面。”

Samples of forage were analyzed following procedures described by Detmann et al.[7]for DM(index INCTCA G-003/1),CP(index INCT-CA N-001/1),ash(index INCT-CA M-001/1),NDF corrected for contaminant ash and protein(apNDF;index INCT-CA F-002/1,INCT-CA M-002/1,and INCT-CA N-004/1).The iNDF was evaluated using F57 filter bags(Ankom®)by a 288-h in situ incubation procedure[7].

Table 2　Potentially digestible forage mass and chemical composition of forage in Experiment 1

apdDM-potentially digestible forage dry matter;OM-organic matter;CP-crude protein;NDIN-neutral detergent insoluble N;apNDF-neutral detergent fiber corrected for ash and protein residue;iNDF-indigestible neutral detergent fiber bpdDM was estimated for forage sampled in the area delimited by a metal square 0.5 m×0.5 m;chemical composition was evaluated in the handplucked forage sample

Itema,b　Experimental month 1 2 3 pdDM,kg/hm2　4820　4050　3410 OM,g/kg　912　913　922 CP,g/kg　77.4　66.6　65.2 NDIN,%of total N　6.94　7.54　9.18 apNDF,g/kg　618　628　679 iNDF,g/kg　225　251　272

The potentially digestible dry matter(pdDM)was estimated using the second sample collected in each month,as described previously,using the following eq.[5]:

Abbreviations

In the breeding season,cows were synchronized using the following protocol:on d 0,an intravaginal device of progesterone release(Tecnopec Primer®,São Paulo,Brazil)was inserted,and an i.m.injection of 2.0 mg of estradiol benzoate(Tecnopec RIC-BE®,São Paulo,Brazil)was performed.On day seven,the intravaginal device was removed and cows received a 2-mL injection of cloprosterol sodium(MSD Saúde Animal Ciosin®,São Paulo,Brazil).Finally,on day eight,cows received 0.5 mL of estradiol cypionate i.m.(Zoetis-Pfizer E.C.P.®,Campinas,Brazil).Fixed time artificial insemination(FTAI)was performed 46-52 h following intravaginal device removal(day nine).Semen from five Nellore sires were randomly assigned to each cow.The protocol was repeated once more in a way that cows that did not conceive were inseminated again 32 d after the first FTAI.Pregnancy diagnosis was determined via trans-rectal ultrasonography 30 d after each FTAI.The number of days from parturition to re-conception was calculated for each cow.

Response variables were analyzed using GLIMMIX in SAS 9.4.Initial BW of cows was used as a covariate for data analysis.Treatments were compared using orthogonal contrasts,contrasts were constructed in order to evaluate the effects of supplementation,and the linear and quadratic effects of days receiving supplementation(30,60 and 90 d).For the variables which didn’t present supplementation effect but a linear or quadratic effect was significant,a Dunnett’s test was performed to identify whether a supplemented treatment differed from the control.Significance was considered at P＜0.05.

All treatments in the present study presented acceptable calving intervals,but cows receiving higher amounts of supplement per day for a reduced number of days had lower calving intervals(30-d and 60-d vs.90-d).

In order to evaluate the effects of the amounts of supplement offered daily in Experiment 1 on intake and metabolism,a second experiment was conducted simultaneously.Four multiparous,five years old,single pregnant Nellore cows with 488±22 kg of BW,BCS of 4.7±0.3,and 210±10 d of gestation were assigned to a 4×4 Latin square design,with experimental periods of 15 d each.

Cows were individually housed in an experimental area of Brachiaria decumbens divided into four paddocks of 0.34 ha each,with free access to water,mineral salt and feeders.Experiment 2 started 15 d later than Experiment 1.

The experimental treatments evaluated were:3.0 kgcows received 3.0 kg of supplement daily;1.5 kg-cows received 1.5 kg of supplement daily;1.0 kg-cows received 1.0 kg of supplement daily;and 0.0 kg-no concentrate supplement was fed.The supplement used was the same used in Experiment 1(Table 1).

Pasture chemical composition(Table 3)was assessed by hand-plucked samples,collected on the eighth day of each experimental period.On the same day,a second pasture sample was also collected to estimate forage pdDM.Samples were collected and processed as described in Experiment 1.

After six days of adaptation to treatments in each period,a nine-day intake trial was carried out.To estimate fecal excretion,chromium oxide(Cr2O3)was used as an external marker in the amount of 15 g per animal.The chromium oxide was packed in paper cartridges and delivered via the esophagus with a metal probe once daily,at 10:00.To estimate DM intake,iNDF was used as an internal marker.Once the intake trial had started,six days were allowed for stabilization of Cr2O3excretion;and,after that,fecal samples were collected at 1500 h on the seventh day,at 1100 h on the eighth day,and at 0700 h on the ninth day of the intake trial(13th,14th　and　15th　d　of　each　experimental　period,respectively).

Fecessampleswere　collected　directly　from　the rectum of cows,at amounts of approximately 200 g,dried(60°C/72 h)and mill grinded as described for forage samples.Ground samples were proportionally combined to a pooled three-day sample per animal per period.

The microbial N produced(g/d),the efficiency of microbial N produced in relation to N ingested and the efficiency of microbial N produced in relation to OM digested were not different among levels of supplementation(P＞0.10;Table 7).Level of SUN was also similar among treatments(P＞0.10),but ureic nitrogen excreted(g/d,UUN)tended to increase linearly with level of supplementation(P＜0.10).

There was a linear effect of number of days of supplementation on cow BW at calving(Table 4;P＜0.05).Body weight at calving ranged from 508 kg for cows in the 30-d strategy to 531 kg for cows in the 90-d strategy.Supplemented treatments did not differ from the control by Dunnett’s test as well.Looking at the individual means of each treatment,can be observed that,actually,control cows had a BW at calving intermediate compared to the supplemented cows.It possibly reflects the small numbers of animals used in this study coupled with the variability of the variable in question.Birth BW of calves averaged 34.4 kg and was not different among supplementation strategies used for their mothers in the last third of gestation(P＞0.10).

Table 3　Potentially digestible forage mass and chemical composition of forage in Experiment 2

apdDM-potentially digestible forage dry matter;OM-organic matter;CP-crude protein;NDIN-neutral detergent insoluble N;apNDF-neutral detergent fiber corrected for ash and protein residue;iNDF-indigestible neutral detergent fiber bpdDM was estimated for forage sampled in the area delimited by a metal square 0.5 m×0.5 m;chemical composition was evaluated in the handplucked forage sample

Itema,b　Experimental period 1 2 3 4 pdDM,kg/hm2　4320　3740　3245　1640 OM,g/kg　925　917　922　938 CP,g/kg　68.1　75.7　59.8　52.3 NDIN,%of total N　10.4　10.4　12.3　10.9 apNDF,g/kg　652　644　712　719 iNDF,g/kg　257　239　312　345

Fecal excretion(FE)was estimated by the ratio of chromium oxide and its concentration in the feces.Dry matter intake(DMI)was estimated by using iNDF as an internal marker and calculated by the following equation:

模型预测，在情景1下，2018年出口总额(现价美元值，下同)将增长11.83%，比2017年提高5.21个百分点；进口总额将增长20.00%，比2017年提高3.87个百分点。2019年，出口总额和进口总额增速则分别为5.96%和10.70%，较2018年均有所回落。而在情景2下，2018年出口总额将增长11.48%，以进口总额将增长19.86%，增速较情景1下略有降低。2019年，出口总额和进口总额增速则分别为5.05%和9.89%，贸易摩擦的冲击更加明显。

针对当前中小企业发展过程中财务会计管理工作中存在的问题，新时期要想循序渐进地改善财务会计管理工作的基本情况，促进综合管理效能的提高，就要加强对中小企业财务会计管理工作的重视，制定更为科学的财务会计管理方案，为企业实现持续稳定发展的目标创造理想化的条件，发挥中小企业的重要作用，维护我国市场经济的稳定发展，为经济强国的构建奠定基础。

where FE is the fecal excretion(kg/d);iNDF feces is the concentration of iNDF in the feces(kg/kg);iNDF supplement is the iNDF in the supplement(kg/d);iNDF forage is the concentration of iNDF in forage(kg/kg)and SI is DM supplement intake.

图3给出了算法对远场目标定位的均方根误差和偏差情况.可以看出，算法同样表现出了优于其它三种算法的定位性能.在测量误差较小时，仅本文算法可以达到CRLB.Group-2WLS算法无法达到CRLB的原因在于其分组优化的方式导致其无法达到全局最优解.文献[24]的3WLS算法无法达到CRLB的原因在于其在第二步WLS中仅利用了第一步WLS估计中辅助参数估计，而忽略了对目标位置粗估计值的利用，导致了第二步WLS中有用信息的丢失和方程数量的减少，从而降低了定位精度.与近场目标相比，相同的测量误差条件下，算法对远场目标的定位误差较大.

At the 15thd of each period,two blood samples were collected immediately before and 4 h after supplementation,to　estimate　insulin　levels　pre-　and　postsupplementation,respectively.Blood was collected in tubes with clot activator and gel for serum separation(BD Vacuntainer®SST II Plus,São Paulo,Brazil),centrifuged at 3,600×g for 20 min and serum was immediately frozen at-20°C in duplicate until further analysis.The same blood collected 4 h after supplementation was used for quantification of serum urea concentrations.

Insulin was analyzed by the chemiluminescent method using Access Ultrasensitive Insulin Reagent(Ref.Number 33410,Beckman Coulter®,Brea,USA)in the Access 2 Immunoassay System(Beckman Coulter Inc.,Brea,USA).Urea was quantified by an enzymatic-colorimetric method using reagents provided by commercial kits(Ref.Number K056,Bioclin®Quibasa,Belo Horizonte,Brazil)in an automatic biochemistry analyzer(Mindray BS200E,Shenzhen,China).Serum urea N(SUN)was estimated as 46.67%of total blood urea.

Spot urine sampling at the 15thday of each experimental period(collected immediately before the 4 h after supplementation blood sampling)was used to assess the excretion of urinary nitrogenous compounds[9].Urine volume was estimated using creatinine concentration as a marker and assuming a daily creatinine excretion(mg/d)of 34.5×SBW0.9491[10].Microbial N synthesis was estimated by using the technique of the purine derivatives in urine.Allantoin was estimated by colorimetry[11].The urinary concentrations of creatinine and uric acid were obtained　bycolorimetricand　enzymatic-colorimetric methods,respectively.The analyses of creatinine and uric acid　were performed in an　automaticbiochemistry analyzer(Mindray BS200E,Shenzhen,China)using commercial kits(Ref.Number K067 for creatinine and K139 for uric acid,Bioclin®Quibasa,Belo Horizonte,Brazil).

Excretion of the purine derivatives in urine was calculated by the sum of the allantoin and uric acid excretions,which were obtained by the product between their concentrations in urine by the daily urinary volume.Absorbed purines were calculated from the excretion of purine derivatives[12],as follows:

where Y=absorbed purines(mmol/d),x=excretion of purine derivatives(mmol/d),0.8=recovered absorbed purines.The 0.301×BW0.75value=endogenous excretion of purine derivates.

Ruminal synthesis of nitrogen compounds was calculated as a function of the absorbed purines[12]:

where Z=ruminal synthesis of nitrogen compounds(g/d),Y=absorbed purines(mmol/d),70=purine N content(mg/mol),0.93　=　purine　digestibility　and 0.137=relation of purine N:total N of microorganisms.

Linear,quadratic and cubic effects of amount of supplement fed daily were analyzed using GLIMMIX in SAS 9.4.Animal and period were considered as random effects.Significance was assumed at P＜0.05.

Results

Experiment 1

出口资讯图安装于站厅付费区，即站台往站厅层上扶梯或楼梯附近的墙面（玻璃栏杆）处，保证为乘客出站时行经或可注意到的位置。

Samples of forage,feces and supplement were analyzed for DM,CP,ash,apNDF,and iNDF following procedurespreviously described for Experiment 1.Fecal samples were also analyzed for levels of chromium by atomic absorption spectrophotometry(index INCT-CA M-005/1)and titanium dioxide by colorimetry(index INCT-CA M-007/1),as recommended by Detmann et al.[8].

马克思指出，人们的“需要即他们的本性”，“你自己的本质即你的需要”。所以说，需要是工程师恪守工程伦理，进行工程创新的动力，是他们实现全面发展的源泉。工程师从事工程活动不仅为了满足自己生活资料的需要，而且也是为了满足精神层面和社会层面的需要。基于此，在工程伦理教育中，要偏重于精神的需要，培养工程师的“普世”情怀，让他们在工程活动中心系“广大民众”，以民众的最大福祉为工程活动的出发点。让他们的心理需要和心理特征与大众融合，让他们的活动迎合社会的基本价值观念，使工程活动在满足人类需要的同时，实现工程最大的“善”，即工程与人、自然、社会的和谐共生。这才是工程伦理教育最终的归宿。

Table 4　Cow BW and BCS,calf BW,cow progesterone concentrations and reproductive performance

aBW-body weight;BCS-body condition score;FTAI-fixed time artificial insemination bTreatments:30-d-cows received 3.0 kg of concentrate supplement beginning 30 d prior to calving;60-d-cows received 1.5 kg of concentrate supplement beginning 60 d prior to calving;90-d-cows received 1.0 kg of concentrate supplement beginning 90 d prior to calving;and control-no concentrate supplement was fed cS-effect of supplementation,supplemented treatments compared to the control;L and Q-effects of linear and quadratic order of supplement delivery strategy(30,60 or 90 d).*Means statistically different from the control by Dunnett’s test

Itema　Treatmentb　SEM　P-valuec 30-d　60-d　90-d　Control　S　L　Q Supplement fed,kg/d　3.00　1.50　1.00　-Cow BW,kg,cow BCS and calf BW,kg Initial BW 494　517　503　503　18.0　0.95　0.74　0.43 Initial BCS　4.66　4.65　4.54　4.87　0.20　0.28　0.65　0.85 Calving BW　508　515　531　522　6.79　0.56　0.02　0.55 Calving BCS　4.74　4.83　4.83　4.82　0.15　0.95　0.70　0.82 Calf birth BW　33.8　31.7　35.8　36.2　1.93　0.28　0.43　0.10 Cow BW 31 d after calving　468　490　482　465　7.73　0.09　0.21　0.15 BW change from parturition to day 31 post-calving　-46.7　-24.9　-53.5　-62.1　8.24　0.04　0.58　0.03 Breeding season BCS　5.00　5.11　4.83　5.03　0.21　0.84　0.57　0.43 Progesterone concentration,ng/dL 21 d after calving　0.27*　0.21　0.12　0.14　0.06　0.34　0.05　0.82 31 d after calving　1.24　0.70　0.69　0.14　0.37　0.08　0.29　0.55 Cow reproductive performance,%Calving to conception,d　57.2　63.1　84.2*　64.1　5.85　0.53　0.01　0.30

At 21 d post-calving,progesterone concentration linearly reduced with an increase in days of supplementation(P=0.05),cows in the 30-d strategy had higher progesterone concentration compared to control cows.Ten days later,at 31 d post-calving,supplemented cows tended to have greater progesterone concentration compared to cows receiving no supplement(P＜0.10).

循此，论文不揣谫陋，探讨“绿色原则”向《民法典》“物权编”辐射过程中生发的上述课题，以助推“物权编”编纂的顺利展开。

A significant linear effect on interval from parturition to conception(P＜0.05)was observed,with the highest calving to conception interval being observed for cows in the 90-d strategy.

Experiment 2

高校要围绕创新创业教育建构立体式课程体系，以专业亲近产业，开展多学科交叉与融合教学，拓宽理论基础，强化实践训练，增强学生的就业竞争力和社会适应能力。在课程建设方面，高校一方面要紧紧围绕职业教育，开设与工匠精神培养密切相关的创新创业类通识教育课程，坚持理论与实践并举，着力培养学生的职业技能和就业创业能力[8]；另一方面要改进专业结构，紧跟产业变革，以工程问题为线索建构交叉学科专业课程体系，课程内容和目标要全面涵盖价值观、知识和能力三个维度，并通过跨学科融合优化课程内容，使学生掌握复合型知识，养成创新性思维，培养创造能力，全面提高职业综合素质。

Level of supplementation linearly increased DM intake(kg/d and g/kg of BW),DM digested(kg/d and g/kg of BW),OM(kg/d and g/kg of BW)and OM digested(kg/d),and crude protein(g/d-Table 5;P＜0.05).There was also a cubic effect of the level of supplementation on intake of crude protein(g/d;P＜0.05).There was no effect of the level of supplementation on intake(g/d and g/kg BW)of forage DM,forage OM,forage apNDF,apNDF and iNDF.

根据系统胺液总量和脱盐前后HSS的浓度差进行计算，累计脱除热稳定盐43.45 t。脱盐期间能耗主要有除盐水、电、氢氧化钠溶液和少量盐酸(清洗膜堆)，产生含胺废水217 t，具体数据见表1。由表1可知，每去除1 t HSS的平均能耗为5332.7 MJ，消耗30%(w)的NaOH溶液0.3 t，并产生含盐、含胺废水5.0 t。废水中MDEA质量浓度为0.03 g/m L，平均每去除1 t HSS的胺液损耗为0.15 t，其原因是在电场作用下，部分MDEA因发生质子化而带电荷，从而穿过阳膜进入浓盐室，和废水一起排出。

Level of supplementation increased the digestibility of OM and CP linearly(P＜0.05;Table 6).There was also a cubic effect of the level of supplementation on digestibility of OM(P＜0.05).

从单因子污染指数法评价结果可以看出，28份荸荠土壤中锌、铜和铬的污染指数均小于1，表明研究区荸荠土壤目前未受到锌、铜和铬元素的污染。从潜在生态风险评价结果来看，锌、铜和铬3种重金属均处于轻微的潜在生态风险水平，其潜在生态危害指数平均值分别为 1.11、2.25 和 0.28，潜在生态危害由强至弱为Cu＞Zn＞Cr。总体上看锌、铜和铬还处于一个较低含量水平，污染风险程度较低，基本符合荸荠安全种植的要求。

Pre-supplementation levels of insulin were not different according to the level of supplementation(P＞0.10;Table 8),but insulin levels 4 h after supplementation increased linearly with the amount of supplement fed(P＜0.05).

Table 5　Intake according to amount of supplement fed to cows in the last third of gestation

aDM-dry matter;OM-organic matter;apNDF-neutral detergent fiber corrected for ash and protein residue;iNDF-indigestible neutral detergent fiber;CP-crude protein bTreatments:3.0 kg-cows received 3.0 kg of concentrate daily;1.5 kg-cows received 1.5 kg of concentrate daily;1.0 kg-cows received 1.0 kg of concentrate daily;and 0.0 kg-no concentrate supplement was fed cL,Q and C-effects of linear,quadratic and cubic order of level of supplementation

Itema　Treatmentb　SEM　P-valuec 3.0 kg　1.5 kg　1.0 kg　0.0 kg　L　Q　C Intake per day,kg/d Forage DM　5.56　5.69　6.00　5.61　0.72　0.96　0.73　0.86 DM　8.03　6.92　6.82　5.61　0.72　0.05　0.94　0.15 DM digested　4.00　2.97　2.76　2.08　0.45　0.01　0.67　0.08 Forage OM　5.11　5.26　5.55　5.22　0.65　0.90　0.72　0.89 OM　7.51　6.46　6.35　5.22　0.65　0.05　0.95　0.15 OM digested　4.03　3.01　2.83　2.13　0.41　0.01　0.68　0.06 Forage apNDF　3.70　3.89　4.11　3.85　0.48　0.83　0.66　0.94 apNDF　4.11　4.09　4.25　3.85　0.48　0.72　0.71　0.68 iNDF　1.56　1.69　1.71　1.60　0.19　0.88　0.53　0.95 CP,g/d　882　613　556　359　58.8　　＜0.01　0.48　　＜0.01 Intake per kg BW,g/kg BW Forage DM　9.95　9.78　10.15　9.58　1.22　0.84　0.88　0.77 DM　14.35　11.92　11.53　9.58　1.23　0.03　0.85　0.12 DM digested　7.16　5.09　4.68　3.55　0.77　0.01　0.54　0.07 Forage OM　9.14　9.05　9.39　8.92　1.12　0.89　0.87　0.81 OM　13.42　11.13　10.74　8.92　1.13　0.03　0.84　0.12 OM digested　5.06　4.74　4.75　6.25　0.95　0.24　0.20　0.39 Forage apNDF　6.64　6.70　6.94　6.59　0.84　0.97　0.81　0.87 apNDF　7.36　7.05　7.17　6.59　0.84　0.54　0.88　0.61 iNDF　2.81　2.93　2.87　2.74　0.33　0.89　0.70　0.99

Table 6　Coefficients of digestibility(%)according to amount of supplement fed

aDM-dry matter;OM-organic matter;apNDF-neutral detergent fiber corrected for ash and protein residue;CP-crude protein bTreatments:3.0 kg-cows received 3.0 kg of concentrate daily;1.5 kg-cows received 1.5 kg of concentrate daily;1.0 kg-cows received 1.0 kg of concentrate daily;and 0.0 kg-no concentrate supplement was fed cL,Q and C-effects of linear,quadratic and cubic order of level of supplementation

Itema　Treatmentb　SEM　P-valuec 3.0 kg　1.5 kg　1.0 kg　0.0 kg　L　Q　C OM　53.87　45.94　44.44　39.57　3.30　　＜0.01　0.42　0.01 apNDF　52.39　49.52　50.22　48.77　2.55　0.18　0.69　0.25 CP　48.12　39.14　36.54　17.70　8.98　0.03　0.53　0.11

Discussion

Nutritional status at calving is the most important factor that influences the interval from parturition to conception in beef cows.Postpartum nutrient intake can modulate the duration of the postpartum anestrous interval;however,if thin cows gain great amounts of weight after calving,ovulation occurs later than for cows that calve in good body condition and maintain body weight[2].

Cabral et al.[13]supplemented pregnant cows grazing pastures in similar conditions to the present study,but with different amounts of supplement per day,and observed a quadratic pattern in performance,with cows receiving 1.0 kg of supplement daily gaining more BW.The total amount of supplement provided for the 1.0 kg treatment in Cabral’s work(84 kg)was similar to the present study(90 kg).

Based on the magnitude of post-partum BW change,supplementing cows with 1.5 kg of supplement during the last 60 d prior to calving was the most efficient strategy to lessen the post-partum negative energy balance,since cows on this strategy lost about half(-25 kg)of the BW lost in the 30-d and 90-d strategies(-50 kg).The differences found in BW changes are related to supplementing proper amounts of nutrients at key times and the effects when this supplement is removed from cow diet and its impact on cow metabolism,in addition to changes that naturally occur due to calving and lactation.Therefore,supplementing adequate amounts of nutrients at times of higher requirements(last 60 d of gestation)[4,5]seems to metabolically prepare the cow for the post-calving period,not only due to accretion in body reserves,but also due to its effects on cow metabolism later on,when supplements are no longer provided.These results provide evidence that adopting a strategy to deliver the same amount of supplement 60 d prior to calving,instead of the usually recommended 90 d,may not only be economical,but also improve cow post-partum performance.

Previous studies in cattle during late gestation[14]have provided evidence that feeding systems during the last third of gestation can alter the subsequent birth weight of the progeny,suggesting that the maternal dietary energy source may affect fetal growth[15].Although the maternal intake of protein has also been　shown　to　bean　importantfactorforfetal growth,Summers et al.[16]found no difference in calf birth BW according to the supplementation strategy applied to their mothers.Similarly,no difference was observed for calf birth BW in the present study,probably because throughout the experiment forage presented median quality(Table 2).

In tropical pastures,the use of energetic-protein supplements can impact forage intake in different ways,depending largely on forage quality,amount and quality of supplement provided[17-19].Linear increase of DM,OM and CP intake with levels of supplementation observed in the present work was simply due to the increase in supplement intake,as no difference in forage DM intake was observed in the present study.

Acknowledgements

Level of supplementation linearly increased insulin levels post-supplementation.For animals in an exclusiveforage diet,the relative amount of propionate,a glycogenic precursor,available for metabolism is low,and supplementation significantly increases the proportion of propionate produced in the rumen[20].

Table 7　Nitrogen utilization according to amount of supplement fed

aNmic-microbial N;OMD-organic matter digested;SUN-Serum urea nitrogen;UUN-Urine urea N bTreatments:3.0 kg-cows received 3.0 kg of concentrate daily;1.5 kg-cows received 1.5 kg of concentrate daily;1.0 kg-cows received 1.0 kg of concentrate daily;and 0.0 kg-no concentrate supplement was fed cL,Q and C-effects of linear,quadratic and cubic order of level of supplementation

Itema　Treatmentb SEM　P-valuec 3.0 kg　1.5 kg　1.0 kg　0.0 kg　L　Q　C Nmic,g/d　72.87　77.99　48.02　36.14　16.4　0.17　0.58　0.82 Nmic,g/g N ingested　0.747　0.788　0.605　0.533　0.20　0.45　0.76　0.93 Nmic,g/kg OMD　26.71　26.21　19.99　14.87　7.19　0.25　0.72　0.67 SUN,mg/dL　13.77　12.72　12.37　10.85　1.70　0.20　0.88　0.41 UUN,g/d　61.36　47.59　33.35　32.39　9.85　0.09　0.53　0.48

Table 8　Insulin levels(μIU/mL)according to amount of supplement fed

aTreatments:3.0 kg-cows received 3.0 kg of concentrate daily;1.5 kg-cows received 1.5 kg of concentrate daily;1.0 kg-cows received 1.0 kg of concentrate daily;and 0.0 kg-no concentrate supplement was fed bL,Q and C-effects of linear,quadratic and cubic order of level of supplementation

Item　Treatmenta SEM　P-valueb 3.0 kg　1.5 kg　1.0 kg　0.0 kg　L　Q　C Pre-supplementation　1.68　1.50　1.18　1.13　0.43　0.13　0.79　0.63 Post-supplementation　2.20　1.48　1.33　1.25　0.38　0.03　0.21　0.13

Hawkins et al.[21]have suggested that an increase in insulin,concomitant with a decrease in growth hormone(GH),is an important relationship to consider for evaluating the impact of nutrition on reproduction.Insulin is an important mediator of nutritional effects on follicular dynamics in cattle,and can stimulate the release of gonadotropin-releasing　hormone　(GnRH)from　the hypothalamus.In the ovaries,insulin may also stimulate cell proliferation and steroidogenesis[22].In accordance with these findings,in the present study,supplementing with higher amounts of supplement daily linearly increased progesterone concentrations after calving.

The interval from calving to conception greatly influences the profitability of beef production.Hence,in beef systems,it is recommended that the calving interval is no longer than 85 d in order to assure the cow will produce a calf per year.Cows that conceive early calve early,and have a better opportunity to start reproductive cycles in time to re-conceive in the next breeding season.The calving date also affects the value of offspring,demonstrating the importance of supplementation strategies to improve early re-conception.

Cushman et al.[23]and Funston et al.[24]reported that heifer calves born early tend to conceive early in their first breeding season and remain in the herd.The calving date can also impact male offspring performance;steer calves born earlier in the calving season have greater weaning BW,hot carcass weight and marbling scores[24].In this way,increasing early calving by early conception may increase progeny value at weaning,enhance carcass value of the steers and increase heifer pregnancy rates in their first breeding season.

Experiment 2-Intake and metabolism

C&C探测，对放马URL的IP进行C&C探测和协议识别，从下面的例子可发现放马URL和C&C经常在一个IP上，黑客的资源也是有限，放在一个服务器上的概率大。

Conclusions

Providing 1.5 kg of supplement during the last 60 d of gestation,instead of 90 d that are usually recommended,is a nutritional management strategy that can be adopted to improve cow performance,reducing the magnitude of BW lost after calving and reducing the number of days from calving to re-conception in the following breeding season,with no negative effect on forage intake or digestibility.

where:0.98 is the true digestibility coefficient of intracellular content;NDF is forage content of neutral detergent fiber;and iNDF is forage content of indigestible neutral detergent fiber.

apNDF:Neutral detergent fiber corrected for ash and protein residue;BCS:Body condition score;BW:Body weight;CP:Crude protein;DM:Dry matter;FTAI:Fixed time artificial insemination;iNDF:Indigestible neutral detergent fiber;NDF:Neutral detergent fiber;OM:Organic matter;pdDM:potentially digestible dry matter;SUN:Serum urea N;UUN:Urine urea N

During the intake and metabolism experiment(Table 3),average forage CP content was adequate or slightly below the minimum required by ruminal microorganisms[17].In this way,the level of supplementation did not affect apNDF digestibility or intake.

The authors thank to Fapemig and CNPq for financial support and CNPq and Capes for the scholarships provided to the first author.

Funding

This research was supported by funding from Fapemig-Fundação de Amparo à Pesquisa de MG,CNPq-Conselho Nacional de Desenvolvimento Científico e Tecnológico and Capes-Coordenação de Aperfeiçoamento de Pessoal de Nível Superior.

(5)在数组O=[ot,r]4×r的第四行中，随机改变某子批量在工序间流转过程中的搬运设备，并按照FCFS规则生成搬运设备选择相邻解。

Availability of data and materials

The data generated during the current study are available from the corresponding author on reasonable request.

Authors’contributions

AGS,conceived the study,carried out the experimental trial,performed the statistical analysis and wrote the manuscript.MFP,contributed to draft the manuscript,and coordinate the research group.ED and HJF,contributed to the statistical analysis and to draft the manuscript.LSA,REMO,contributed to designing the experiment and to draft the manuscript.VVC,JACL,FHM,MBM,JAB,carried out the experimental trial,performed the chemical analysis and contributed to draft the manuscript.All authors read and approved the final manuscript.

Ethics approval and consent to participate

This manuscript does not involve any human subject,or human data.

Consent for publication

This manuscript does not contain any individual personal data.

Competing interests

2.2.4 提取次数对综合评分的影响 在60%乙醇为提取溶剂、提取时间为2 h、液料比为15∶1（V/m，mL/g）的条件下，分别设置提取次数为1、2、3、4次。取处方配比药材样品（均粉碎，过4号筛）适量，分别进行加热回流提取，按“2.1.6”项下方法进行各指标成分含量测定并计算综合评分，结果见图2D。由图2D可知，综合评分随提取次数的增多而先增加后趋于平缓，当提取2次时综合评分已高于2.95分，故最终选择2次为提取次数。

The authors declare that they have no competing interests.

Author details

1Universidade Federal de Viçosa,Viçosa,Minas Gerais 36570-000,Brazil.2Present Address:Universidade Federal de Mato Grosso do Sul,Campo Grande,Mato Grosso do Sul 79074-460,Brazil.3Universidade Estadual de Mato Grosso do Sul,Aquidauana,Mato Grosso do Sul 79200-000,Brazil.4Biotran-Biotecnologia e Treinamento em Reprodução Animal,Alfenas,Minas Gerais 37130-000,Brazil.5Universidade Federal do Acre,Rio Branco,Acre 69920-900,Brazil.

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