Stover quality of dual-purpose sorghums: genetic and environmental sources of variation

Improvement of the nutritive value of dual-purpose sorghum (Sorghum bicolor (L.) Moench) stover is an important objective for the semi-arid tropics where sorghum crop residue is extensively used for livestock feed. To identify the relative importance of genetic and environmental sources of variation for nutritive value, leaves and stems of six diverse dual-purpose sorghum cultivars were evaluated for in vitro gas production (Gas48hr), neutral detergent fiber (NDF), acid detergent fiber (ADF), lignin, nitrogen, and ash contents under two fertility and two plant-density regimes during 2 years in India. Substantial genotypic differences were observed for stem Gas48hr (25.7 to 33.0 ml in 200 g⁻¹ dry matter (DM)) and NDF (564–687) content. Gas48hr and NDF content of stems exhibited more promise as selection criteria than those of leaves, as stems showed larger portion of variation attributed to genotypes, relatively less genotype by environment (GE) interactions, and were closely related to whole-plant values. Year, nitrogen fertilization and plant density showed very little influence on Gas48hr, NDF or ADF of leaves and stems. Gas48hr exhibited substantial GE interactions with all environmental factors, indicating the need for multi-environment testing to achieve progress.     

Age of regrowth as a factor affecting the nutritive value of hay of kikuyu grass (Pennisetum clandestinum) offered to lambs

The changes in chemical composition of hay of kikuyu grass ( Pennisetum clandestinum ) harvested at 50, 70 and 90 d of regrowth, and its effect on intake, digestibility, fermentation and microbial protein synthesis in the rumen (Experiment 1) and oxygen uptake by portal-drained viscera (PDV) (Experiment 2) were evaluated. The experiments were carried out with Polwarth × Texel crossbreed lambs with a mean live weight (s.e.m.) of 35(3·0) kg housed in metabolic cages. Organic matter (OM), neutral-detergent fibre (NDF) and nitrogen (N) intake, as well as rumen ammonia-N concentration, decreased linearly with age of regrowth ( P  <   0·05). Acid-detergent fibre (ADF) and indigestible NDF intakes were similar for all treatments. Apparent digestibility of organic matter (OM), NDF and N, as well as true digestibility of OM, microbial protein synthesis in the rumen, N retention, pH of rumen fluid and sugars, amino acids and peptide concentrations in rumen fluid were similar for all treatments. Age of regrowth also did not affect the kinetics of passage of the particulate phase through the digestive tract nor oxygen uptake by PDV. Heat production by PDV represented an average of 0·039 of digestible energy (DE) intake. Increasing the age of regrowth of kikuyu grass from 50 to 90 d did not affect digestibility nor the efficiency of DE use by PDV tissues of lambs but it reduced the nutritive value of the hay due to a lower intake of OM. Intake of hay appeared to be most limited by the ADF and indigestible NDF concentrations of the hay.     

刈割高度对多花黑麦草新品种产量和品质的影响

为探讨不同刈割高度对多花黑麦草新品种饲草产量和品质的影响,以2个多花黑麦草新品种为对象,采用5个刈割高度分别测定2个品种的鲜、干草产量、粗蛋白、可溶性碳水化合物(WSC)、中性洗涤纤维(NDF)、酸性洗涤纤维(ADF)和干物质体外可消化率(IVDMD)。结果表明:在65 cm时刈割,所获得的鲜、干草产量最高;随着刈割高度的增加,2个黑麦草品种的粗蛋白和可溶性碳水化合物含量呈抛物线趋势变化,在刈割高度为55 cm时达到最高值;中性和酸性洗涤纤维含量则随着刈割高度的增大逐渐增加;干物质体外消化率亦呈现抛物线的趋势,在刈割高度为65 cm时达到最高。2个品种的表现规律一致。     

A two-year comparison on nutritive value and yield of eight lucerne cultivars and one red clover cultivar

Red clover (Trifolium pratense) and lucerne (Medicago sativa) are among the most common legume species used for ruminant feeding systems. Besides the greater nutritive quality and first-year ley yield compared to lucerne, red clover decreases its yield over the years. However, under unfavourable soil conditions the persistency of lucerne can be compromised, not performing as expected. This study compared yield and chemical composition of eight lucerne cultivars and one tetraploid red clover cultivar, with similar growth capacity as lucerne, replicated over two years. In the second year, four lucerne cultivars and the red clover cultivar were analysed for crude protein (CP) fractions, dry matter and neutral detergent fibre (NDF) digestibility. A randomized block design was used with three field blocks per cultivar for the multiple comparisons within each year. There were differences in DM yield, concentrations of CP and NDF and CP fractions among the lucerne cultivars, but the differences were inconsistent between years and between growth cycles within year. The red clover cultivar had lower CP and NDF concentrations than a majority of the lucerne cultivars, and greater in vitro organic matter digestibility compared to all of the lucerne cultivars. Also, the red clover cultivar had greater rumen undegradable-to-degradable CP ratio but confirmed its lower yield persistency compared to the lucerne cultivars.     

Yield and nutritive value of timothy as affected by temperature,photoperiod and time of harvest

Scenarios of global climate change forecast an increase in air temperature of 3°C over the next 100 years in eastern Canada. Growth and nutritive value of cool‐season grasses are known to be affected by air temperature. It is also believed that grasses grown at high latitude have a greater nutritive value. The objectives of this study were to assess the effect of four combinations of day/night temperature and photoperiod (15 h–17/5°C; 15 h–22/10°C; 15 h–28/15°C; and 17 h‐17/5°C) on dry‐matter (DM) yield, in vitro true DM digestibility (IVTD), in vitro digestibility of neutral‐detergent fibre (NDF), and concentrations of NDF, acid‐detergent fibre (ADF), lignin, minerals and non‐structural carbohydrates (NSC) in timothy grown under controlled conditions. Furthermore, herbage was harvested in the morning and in the afternoon to assess the impact of the time of harvest. The dietary cation–anion difference [DCAD = (K⁺ + Na⁺) ? (Cl^? + 0·6 S^2?)] and the grass tetany index [GT index = K⁺/(Ca²⁺ + Mg²⁺)] were also calculated. Higher temperature regimes significantly decreased IVTD and digestibility of NDF but had a limited effect on concentrations of NDF, ADF and lignin. DM yield of herbage was less and the concentration of NSC was greater in timothy grown under a temperature regime of 28/15°C than the 17/5°C and 22/10°C regimes; this effect is mainly explained by a response to temperature stress. Values of DCAD and the GT index of herbage were also lower under the 28/15°C than the 17/5°C and 22/10°C regimes as a result of a decreased plant K concentration. Under the 17/5°C regime, an increase in 2 h of photoperiod resulted in increased DM yield, decreased concentrations of K, Ca, Mg, Cl and N, and an increased starch concentration; IVTD or digestibility of NDF were not affected, although lignin concentration was reduced. Harvesting timothy in the afternoon rather than in the morning resulted in higher NSC, mainly sucrose, concentrations, and decreased ADF and NDF concentrations. The forecasted increase in air temperature in eastern Canada over the next 100 years will result in lower yields and nutritive value of timothy.     

Production and nutritional value of sorghum and black oat forages under nitrogen fertilization

The effect of nitrogen (N) fertilization on the dry‐matter (DM) yield and nutritional value of sorghum (Sorghum sp., cv. Jumbo) and black oat (Avena strigosa cv., IPR 61) was investigated in the context of forage and livestock production in southern Brazil. Sorghum was cultivated with 0, 37·5, 75, 150, 225, 300 and 375 kg N ha^?1 during the summer crop seasons of 2010/11 and 2011/12. Black oat received 0, 40, 80, 120, 160, 200 and 240 kg N ha^?1 in the winter of 2011. According to the adjusted polynomial regression, sorghum DM yield increased in response to N up to 288 (12·9 t ha^?1) and 264 kg ha^?1 (5·6 t ha^?1) in 2010/11 and 2011/12 respectively. Crude protein (CP) content of sorghum was highest at 349 and 328 kg N ha^?1, but in vitro dry‐matter digestibility (IVDMD) was highest at 212–207 kg N ha^?1 in 2010/11 and 2011/12 respectively. Sorghum neutral detergent fibre (NDF) and acid detergent fibre (ADF) were not affected by N fertilization. In black oat, the maximum DM yield (6·0 t ha^?1) was obtained with 187 kg N ha^?1; the IVDMD, NDF and ADF were not affected by N fertilization, but the CP content increased up to 220 kg N ha^?1. It is concluded that these forage species can improve the year‐to‐year amount and quality of forage produced but high rates of N fertilizer are required to achieve high yields. Fertilizer N rates of 210–280 kg N ha^?1 in sorghum and 180 kg N ha^?1 in black oat in the crop rotation provide the greatest responses in DM yield consistent with good nutritional quality for livestock production.     

Functional dynamics of the nitrogen balance of sorghum. II. Grain filling period

Maintenance of green leaf area during grain filling can increase grain yield of sorghum grown under terminal water limitation. This ‘stay-green’ trait has been related to the nitrogen (N) supply–demand balance during grain filling. This study quantifies the N demand of grain and N translocation rates from leaves and stem and explores effects of genotype and N stress on onset and rate of leaf senescence during the grain filling period. Three hybrids differing in potential height were grown at three levels of N supply under well-watered conditions. Vertical profiles of biomass, leaf area, and N% of leaves, stem and grain were measured at regular intervals. Weekly SPAD chlorophyll readings on main shoot leaves were correlated with observed specific leaf nitrogen (SLN) to derive seasonal patterns of leaf N content. For all hybrids, individual grain N demand was sink determined and was initially met through N translocation from the stem and rachis. Only if this was insufficient did leaf N translocation occur. Maximum N translocation rates from leaves and stem were dependent on their N status. However, the supply of N at canopy scale was also related to the amount of leaf area senescing at any one time. This supply–demand framework for N dynamics explained effects of N stress and genotype on the onset and rate of leaf senescence.     

青贮玉米生物产量及营养积累规律研究

对青贮玉米不同生育阶段全株干物质与青贮营养积累规律、不同器官产量与营养转移规律、全株生物产量积累规律及水分变化规律进行了研究。结果表明,青贮玉米乳熟期鲜产量最高,随着子粒灌浆和成熟度的提高,全株鲜产量及蛋白质含量有所下降,但蜡熟期全株具有较高的干物质产量和蛋白质总量,具有适宜青贮的最佳含水量,蜡熟期全株青贮后NDF和ADF最低,消化率最高,收获加工青贮具有较高的产量和营养价值。     

Effect of harvest date on the chemical composition and nutritive value of Cerastium holosteoides

Abstract Cerastium holosteoides is a short‐lived plant often found in small proportions on dry and mesotropic semi‐natural, species‐rich grassland communities. To obtain more information about its nutritive value, two experiments on Arrhenatheretum elatioris grassland were carried out to examine the effect of harvest date on in vitro organic matter digestibility (IVOMD), neutral‐detergent fibre (NDF), acid‐detergent fibre (ADF), acid‐detergent lignin (ADL), estimated net energy for lactation (NEL) and crude protein (CP) concentrations of C. holosteoides, and selection of this plant by dairy cows grazing on semi‐natural grassland. C. holosteoides starts flowering in spring and continuously develops new flowers on new branches throughout the summer. Harvests were made in relation to particular growth stages of Dactylis glomerata present in the sward: (A) tillering; (B) stem elongation; (C) ear emergence; (D) flowering; and (E) ripening. Chemical composition and nutritive value were evaluated in 1998 and 1999. With advancing maturity, IVOMD of C. holosteoides decreased from 0·771 at growth stage A to 0·485 at growth stage E. At the same time, CP concentration decreased from 153 to 69 g kg^?1 dry matter (DM) and estimated NEL concentration from 6·00 to 4·07 MJ kg^?1 DM. With advancing maturity, there was a significant increase in NDF, ADF and ADL concentrations. In the summer harvest season, C. holosteoides contained significantly higher NDF, ADF and ADL concentrations, lower NEL concentration and had a lower IVOMD value than in the spring. Differences between years were also found for IVOMD and for NDF, ADF, ADL and NEL concentrations. In a grazing experiment in the year 1999, at growth stage B, Simmental cows grazed an A. elatioris sward in which the main species was D. glomerata (0·092), and the proportion of C. holosteoides was 0·034. C. holosteoides was, on average, grazed by cows to the same relative extent as other species in the sward.     

收割高度对不同类型玉米饲用品质和产量的影响

在大田条件下分别对农大108和科多4号不同收割始节位(基部第1～8节间)的整株饲用品质和产量变化研究表明：随着收割始节位升高,两品种秸秆CP含量均呈直线增加趋势,NDF、ADF和ADL均呈直线下降趋势;随着收割高度的增加两品种之间的CP含量提高速率及ADL下降速率相近,科多4号的NDF下降速度快于农大108,农大108的ADF下降速率快于科多4号;玉米基部3个节间CP含量低,NDF、ADF和ADL含量高,饲用营养品质差;从第4节间收割明显改善玉米秸秆的饲用营养品质,其干物质产量损失10%以下。     

Inclusion of alfalfa improves nutritive value and in vitro digestibility of various straw–grass mixed silages in Tibet

To enlarge the feed resources and enhance the utilization efficiency of straws as ruminant feed in Tibet, four kinds of local crop straws with tall fescue (Festuca arundinacea Schreb.) based on the ratio of 40/60 (fresh weight) were ensiled with four levels (0, 10%, 20% and 30% of fresh weight) of alfalfa (Medicago sativa L.), respectively. The laboratory silos (1L) were opened after 45 days of ensiling, and the fermentation characteristics, nutritive value and in vitro digestibility of the mixed silages were analysed. The silages including alfalfa had significantly (p < 0.05) or numerically (p > 0.05) higher lactic acid and crude protein contents, lactic acid bacteria counts, in vitro digestibility of dry matter, neutral detergent fibre (NDF) and acid detergent fibre (ADF), and lower NDF and ADF contents than controls. The results suggest that inclusion of alfalfa to mixtures of straws and tall fescue had favourable effects on fermentation quality and obviously improved the nutritive value and in vitro digestibility of mixed silages. This effect was most evident when the inclusion proportion of alfalfa was 30% in oat straw mixed silage.     

Effects of monensin and increasing crude protein in early lactation on performance of dairy cows

Twenty-four Holstein dairy cows were used to evaluate the singular and combined effects of different level of crude protein and monensin treatments during the early lactation on digestion and milk yield of dairy cows. The experiment was designed as completely randomized with a 3x2 factorial arrangement of treatments. The factors were three Concentrations of CP supplement (19.5, 21.4 and 23.4% of dry matter) and two levels of monensin (0 and 350 mg per cow per day). This experiment consist of three periods and each period was 3 week in length. Monensin did not affect DMI, milk yield, lactose and SNF but it reduced milk fat and protein percentage. Monensin premix significantly decreased rumen ammonia but rumen pH and microbial protein synthesis was not affected by monensin treatment. Although, Monensin treatment increased apparent digestibility of DM, NDF, ADF, CP, but they were not significantly. Increasing dietary CP, improved milk and protein production, but did not alter the other components of milk. Digestibility of NDF, ADF, CP were improved by increasing dietary CP. Increasing diet CP from 19.5 to 21.4% did not significantly increase ruminal ammonia, but increasing to 23.4% have significant effect on it. There was a linear relationship between level of crud protein in the diet and urine volume excretion. Microbial protein synthesis was affected by increasing CP level; on this way maximum protein synthesis was achieved in 21.4% CP.     

Intercropped wheat (Triticum aestivum L.) and bean (Vicia faba L.) as a whole-crop forage: effect of harvest time on forage yield and quality

Abstract Sole crops and intercrops of wheat (Triticum aestivum L.) and bean (Vicia faba L.), at three harvest dates, representing successive growth stages, were evaluated for biomass production of whole‐crop forage and quality characteristics of crude protein (CP), neutral‐detergent fibre (NDF), acid‐detergent fibre (ADF), water‐soluble carbohydrate (WSC) concentrations and ash content. These tests were carried out for two field experiments, respectively, drilled during the spring of 1997 and autumn of 1997 on Imperial College Farm, Wye, UK. Results indicated that optimum forage yield and quality were obtained from the second to third harvest dates for the spring‐drilled experiment and the second harvest for the autumn‐drilled experiment. Wheat and bean intercrops were higher in total forage dry matter (DM) yield than either wheat or bean grown as sole crops. Field bean intercropped with wheat led to increased forage quality (CP and NDF concentrations) compared with sole wheat, and higher WSC concentrations compared with sole bean. Intercrops also enhanced weed suppression compared with sole bean. It is suggested that winter wheat–bean intercrops may have considerable potential as a moderate‐yielding, relatively high‐quality, low‐input and environmentally benign forage crop with considerable potential with regard to yield and quality and warrant further study.     

玉米自交系开花后叶片保绿度衰减特性遗传效应分析

采用ADM遗传模型对不同玉米自交系开花后叶片保绿度衰减特性遗传效应进行研究。结果表明,不同自交系叶片保绿度衰减起始时间(Ts)、最大衰减速率出现时间(TVmax)、最大衰减速率(Vmax)均存在显著的遗传与环境互作效应,自交系叶片保绿度衰减特性在不同环境条件下的表现具有明显差异。利用包括基因型与环境互作效应在内的遗传分析方法,可以更清楚地发现不同亲本叶片保绿度衰减特性的遗传效应差异,有利于筛选出具有较大遗传效应的自交系,用于玉米叶片保绿度性状的改良。     

优质青贮玉米自交系筛选与评价

以448份玉米自交系为材料,对玉米全株的品质含量指标蛋白、淀粉、中性洗涤纤维(NDF)及酸性洗涤纤维(ADF)进行评价,筛选高蛋白/淀粉、低纤维的青贮玉米自交系。结果表明,在所有供试材料中,蛋白含量变化不大,淀粉含量与纤维(NDF、ADF)含量极显著负相关。以淀粉、NDF和ADF品质含量为指标,通过聚类分析,筛选出7份高淀粉(47.50%~51.20%)、低纤维(ADF为9.08%~12.93%,NDF为26.67%~31.07%)含量的青贮玉米自交系,分别为P124-3、P125-12、P128-1、P132、13634-3、12099-2和12906-1。     

Effect of intercropping vetch (Vicia sativa L.), field pea (Pisum sativum L.) and triticale (X Triticosecale) on dry‐matter yield,nutritive and ensiling characteristics when harvested at two growth stages

This study aimed to investigate the effects of growth stage and legume proportion on the nutritive and ensiling characteristics of triticale–pea–vetch intercrop mixtures. The three‐species mixtures were sown at three seeding ratios to produce different legume proportions (low, medium and high proportions) and harvested at two growth stages. The six resulting forages were subsequently ensiled in mini‐silos. Forage dry‐matter (DM) yield, nutritive characteristics of fresh and ensiled mixtures and fermentation characteristics of silages were determined. Forage DM yield almost tripled between early‐stage harvest and late‐stage harvest. Nutritive characteristics of fresh and ensiled mixtures were affected by both growth stage and legume proportion: crude protein concentration and pepsin–cellulase digestibility decreased whereas NDF and ADF concentrations increased as growth stage advanced. Crude protein concentration and pepsin–cellulase digestibility were higher for the high‐legume treatment at both growth stages. All mixtures ensiled well, as indicated by low pH and high lactic and acetic acids contents. However, all silages had high soluble nitrogen and ammonia concentrations. This study showed that triticale–pea–vetch silages hold good potential net energy supply value for ruminants, especially at early‐stage growth and when legume proportion increases. However, protein value has to be improved by reducing protein breakdown during ensiling.     

Physio-Morphological Characters of F1 Hybrids of Rice (Oryza sativa L.) in Japonica-Indica Crosses: II. Heterosis for leaf area and dry matter accumulation

Summary

A pot experiment was conducted to investigate the heterosis for morphological characters and to examine the relationship among some characters at active tillering, flowering and dough ripe stages of 12 Fj hybrids from crosses between japonica and indica rice. Heterosis for plant height, number of tillers, green leaf area and dry matter accumulation per plant was positive at all stages. The intensity of heterosis was higher at the active tillering stage for number of tillers, leaf area and dry matter accumulation per plant. A significant positive relationship was found between tiller number and leaf area per plant at active tillering and flowering stages. Significant positive relationships between leaf area and dry matter accumulation, and between tiller number and dry matter accumulation per plant were observed at all stages. A significant positive relationship was found between leaf area per plant at an early stage and dry matter accumulation per plant at a later stage, suggesting that early development of leaf area is an important factor for higher dry matter accumulation in 1 hybrids. Although heterosis for percent dead leaf blade was positive at the flowering stage due to early leaf senescence in some Fx hybrids, a larger leaf area was also found in Fx hybrids at this stage and leaves of Fx hybrids remained green longer compared to parent cultivars up to the dough ripe stage.     

Production, survival and nutritive value of the perennial legumes Dorycnium hirsutum and D. rectum subjected to different cutting heights

Dorycnium hirsutum and D. rectum are perennial legumes which may have potential for use as pastures for the control of groundwater recharge in southern Australia. Little is known about the quality of the forage of Dorycnium species for grazing livestock or how these species respond to cutting. The effect of cutting height on plant survival, production of dry matter (DM), the proportion of leaf, edible stem (approximately <5 mm diameter) and woody stem in the DM and the nutritive value of the edible components was investigated. Biomass above five cutting‐height treatments (uncut, ground level, 5–8 cm, 10–15 cm and 15–30 cm above ground level) was removed at 8‐week intervals from plots of D. hirsutum and D. rectum from September 2002 to July 2003. In both species, plants subjected to lower cutting height treatments produced less DM above the height of the cut than those cut at higher heights. DM production declined over time in all treatments. Plants cut to ground level failed to regrow after the second harvest in D. hirsutum and the fourth harvest in D. rectum. Thus, these Dorycnium species were susceptible to high severity defoliations at 8‐week intervals. Negligible inedible woody stem was present in regrowth of both species after 8 weeks but D. hirsutum regrowth had a higher proportion of leaf (0·72) than D. rectum (0·56). Plants left uncut accumulated a large proportion of inedible woody stem in the DM (0·69 in both species) by July 2003, particularly at the base of the plant. Edible DM from regrowth of D. hirsutum and D. rectum had crude protein (CP) concentrations of 120 and 150 g kg^?1 DM; dry matter digestibility (DMD) values of 0·45 and 0·58; organic matter digestibility (OMD) values of 0·50 and 0·64; neutral‐detergent fibre (NDF) concentrations of 370 and 290 g kg^?1 DM; and acid‐detergent fibre (ADF) concentrations of 260 and 210 g kg^?1 DM, respectively. Medicago sativa, grown under similar conditions, had higher digestibility values (0·63 DMD and 0·66 OMD) and similar CP concentrations to D. rectum (140 g kg^?1 DM), but higher concentrations of NDF and ADF (410 and 290 g kg^?1 DM). Leaf material from both Dorycnium species had a higher nutritive value than edible stems, with DMD and OMD values of leaf of D. rectum being 0·68 and 0·74 respectively. Uncut plants had a much lower nutritive value of edible DM than the regrowth from cut treatments; older material was also of a lower nutritive value. The relatively low nutritive value of even the young regrowth of Dorycnium species suggests that forage quality is a major limitation to its use. Forage of Dorycnium species could be used during periods when other sources of forage are in short supply but infrequent grazing it is likely to produce forage of a low nutritive value.     

The effects of forage preservation method and proportion of concentrate on digestion of cell wall carbohydrates and rumen digesta pool size in cattle

Six bulls with ruminal and duodenal cannulae were used in a 6 × 6 Latin square design with a 2 × 3 factorial arrangement of treatments. Barn-dried grass (G) and direct-cut silage (S) from the same sward were fed together with 250 (L), 500 (M) and 750 (H) g kg^-1 total dry matter (DM) of a barley-based concentrate (barley 875 and rape-seed meal 125 g kg^-1) at the level of 80 g DM kg^-1 live weight^0·75. Rumen and total digestibility of cell wall constituents were measured by a double marker and total collection method. Rumen pool sizes of dietary constituents were estimated by emptying the rumen. Particle-associated enzyme activities were measured from rumen particulate material and feed particles incubated in nylon bags in the rumen. Neutral detergent fibre (NDF) and hemicellulose digestibility were higher (P<0·05) for G diets than for S diets while no differences were observed between the forages in acid detergent fibre (ADF) and cellulose digestibility. Both rumen and total digestibility of cell wall constituents decreased with increasing level of concentrate. The proportion of total cell wall digestion in the rumen was unaffected by the forage preservation method and the proportion of concentrate. NDF, and especially cellulose digestibility, declined quadratically with increasing level of concentrate. Dietary effects on particle-associated carboxymethylcellulase and xylanase activity were consistent with those observed in cell wall digestion. There were no differences between the forages in rumen pool size of total ingesta or any dietary constituent. Rumen pool size of total ingesta decreased with increasing level of concentrate. On the other hand, DM content of ingesta increased with the level of concentrate, while the pool size of DM, NDF and ADF declined quadratically reaching a minimum on M level of concentrate. The differences in rumen NDF pool size were mainly in the digestible fraction. Calculation of digestion kinetic parameters showed that both the rate of passage and especially the rate of digestion were markedly depressed in animals fed on the highest level of concentrate. The results suggest that a reduced fate of digestion of NDF with high concentrate diets can be partially compensated for by an increased NDF retention time in the rumen of animals fed at a restricted level of feeding.     

干旱条件下我国不同年代玉米品种保绿性比较

选用35个玉米品种(农家种4个, 双交种4个, 单交种27个), 在海南三亚设置正常浇水和花期干旱两个处理, 鉴定每个品种在干旱环境下的保绿性, 比较不同年代品种的持绿性。结果发现, 干旱导致玉米叶片叶绿素含量下降, 衰老启动时间提前, 干旱条件下品种的衰老启动时间、最大衰老速度出现时间均随年代更替而延后, 最大衰老速度均随着年代更替而下降, 即玉米的保绿性均随着年代更替而提高, 与正常浇水条件下的趋势相似。玉米保绿性与叶绿素含量均与产量呈显著相关;在干旱处理条件下, 品种保绿性均随年代更替而提高, 我国的玉米育种中已经对持绿性进行了改良, 耐旱性也得到提高。