Increasing crop competitiveness using higher seeding rates is a possible technique for weed management in low input and organic farming systems or when herbicide resistance develops in weeds. A range of wheat seeding rates were sown and resulted in crop densities between 50-400 plants/m(2) (current recommendations are 100-150 plants/m(2)) in the presence and absence of annual ryegrass (Lolitun rigidum Gaud.) in three wheat cUltivars at nine experiments in southern Australia. Wheat densities of at least 200 plants/m(2) were required to suppress L. rigidum and to a lesser extent increase crop yield across a wide range of environments (seasonal rainfall between 200-420 mm) and weed densities (50-450 L. rigidum plants/m(2)). Doubling crop density of all cultivars from 100 to 200 plants/m(2) halved L. rigidum dry weight (averaged over all experiments) from 100 g/m(2) to about 50 g/m(2). Higher crop densities gave diminishing marginal reductions in weed biomass, while cultivar differences in weed suppression were small. Grain yields ranged from 0-5 t/ha to over 5 t/ha depending on site and season. Maximum yields in the weed-free plots (averaged over environments and cultivars) were at 200 crop plants/m(2), and yield declined only slightly by 4-5% at densities up to 425 plants/m(2). In the weedy plots grain yield continued to increase up to the highest density but at a slower rate. The percentage yield loss from weed competition was of a smaller magnitude than the suppression of L. rigidum by wheat. For example, 100 wheat plants/m(2) led to an average 23% yield loss compared with 17% at 200 plants/m(2), and the probability of reduced crop grain size and increased proportion of small seeds was negligible at these densities. Cultivar differences in yield loss from weed competition were small compared with differences due to crop density. Adoption of higher wheat seed rates as part of integrated weed management is now strongly promoted to farmers.
In Sweden, deposition of organic waste will be prohibited in the year 2005. Instead, the waste will be either incinerated or source separated, processed (composted or anaerobically digested) and recycled back to arable land. In order to evaluate the biologically processed waste products as fertilizers, a field experiment was initiated in Sweden in the autumn of 1998. The main focus of the experiment was to compare compost (C) from source-separated domestic waste with biogas residues (BR) from source-separated domestic waste. Each fertilizer was applied in two combinations: in treatments C-50 and BR50, 50 kg N/ha/year originates from the waste and 50 kg N/ha/year from mineral nitrogen fertilizer, while in C-100 and BR100, the organic wastes were the only plant nutrient sources (100 kg N/ha/year). Mineral fertilizer (NPS100) and unamended were used as controls. Generally pure mineral fertilizers resulted in the highest yield, while control without nitrogen generated the lowest yield. A combination of organic fertilizer and mineral fertilizer resulted in higher yield compared with applying sole organic fertilizer. Total mineral N in the fertilizer was generally the best overall predictor/regressor for grain yield, total nitrogen yield and apparent bioavailable nitrogen. Application of biogas residue resulted in higher yield and grain quality than compost. The higher concentration of nitrogen in oats suggested that oats is a better choice when using compost as a fertilizer. In conclusion, compost and anaerobic biogas residues should not be used as sole fertilizers. Compost should be complemented with mineral N and the biogas residues with P. If compensation for the low content of mineral N in compost is made by a higher application rate, large amounts of heavy metals might be applied along with the compost.
Inclusion in the diet of concentrations of vitamin E and selenium (Se) above requirement is associated with variable improvements in animal performance and immune function. At the cellular and molecular level, research in the last decade has produced a clearer understanding of the mechanisms underlying the multiple functions of vitamin E and Se and it is apparent that these functions extend beyond antioxidant protection. This paper reviews recent research relating to the functionality of vitamin E and Se in relation to the ewe and her lambs and attempts to relate this understanding to the whole animal level. Important aspects of this improved understanding are descriptions of three groups of seleno-proteins and the appreciation that there is a hierarchy in both the distribution of selenium between tissues and in the synthesis of different enzymes within tissues. In addition, there is diversity in the effects of vitamin E and Se derivatives on immune cell function. Given this heterogeneity in function it is not surprising that published responses for the production and health of ewes and lambs to supplementary vitamin E and selenium are variable and not always positive. Coupled with information on factors influencing variability in supply of vitamin E and Se from fresh and conserved forages and concentrate supplements, this review highlights the need for greater awareness of the importance of adequate supplementation of ewe and lamb diets with vitamin E and Se.
An algorithm to fit boundary lines, using Cubic smoothing splines, was written and used to identify Yield responses to changes in soil properties. This method involves fitting a curve that represents the maximum yield response to each predictor value, which represents the yield potential at each soil property value. Boundary-line yield responses to individual soil properties were found to differ from responses found by fitting Curves through the data scatter. The effects of correlated variables appeared to be lessened using the boundary line approach. Multivariate boundary-line models, based on the Law of the Minimum, were found to be useful for the identification of site-specific causes of yield variation and Yield potentials. The boundary line was found to be a useful complement to more traditional data analysis techniques.
Mixed intercropping of spring barley (Hordeum vulgare L.) with field pea (Pisum sativum L.), faba bean (Vicia faba var. minor L.) or narrow-leafed lupin (Lupinus angustifolius L.) was compared with sole cropping in two fleld experiments at different locations, on a sandy loam soil and a sandy soil, in Denmark in 2001. Grain legumes were dominant in intercrops on the sandy loam soil, except for lupin, whereas barley was dominant in intercrops on the sandy soil site. Combined intercrop grain yields were comparable to grain yields of the respective sole cropped grain legume or sole cropped, fertilized barley on each soil site. On the sandy loam soil, pea-barley and faba bean-barley intercrops increased the proportion of plant N derived from N-2 fixation in grain legumes and increased the barley grain N concentration (from 1-7 to 2-2 mg/g) compared with sole cropping. However, the later maturity of faba bean compared with barley caused problems at harvest. The grain N concentration of intercropped barley was increased where grain legumes were the dominant intercrops and not on the sandy soil site. Lupin-barley intercrops did not show intercropping advantages to the same degree as faba bean and pea, but lupin constituted a more stable yield proportion of the combined intercrop yield over locations. Furthermore, the study indicated that the natural N-15 abundance at certain locations might not always be sufficient to ensure a reliable estimate of N-2 fixation using the N-15 natural abundance method.
Seeds of oilseed rape (Brassica napus L.) can persist in the soil over several years by becoming secondarily dormant and can then germinate to create volunteer plants in following crops. As well as agricultural impacts caused by volunteers, gene dispersal in time - particularly from genetically modified cultivars - can be another undesirable consequence. Conventionally bred and transgenic seeds were tested in 2001 and 2002 in laboratory experiments, and in a field experiment, by burying seeds in the soil to determine the variation in dormancy and persistence capacity. In the conventional group of cultivars tested in the laboratory, the level of dormancy was 13-76% in 2001, and 3-76% with an extended group in 2002. The transgenic group of cultivars was 1-31% dormant. In the burial experiments the number of viable seeds recovered in the conventionally bred cultivars ranged from 34-90% in 2001, and 7-68% in 2002. In the same studies the transgenic cultivars developed persistence levels from 12-79% in 2001, and 46-67% in 2002. Since dormancy levels of conventionally bred cultivars from 2 harvest years in the laboratory tests correlated significantly (r = 0(.)71), it appears that there is a genetic background to secondary dormancy. There was also a significant correlation (r = 0(.)61 in 2001 and 0(.)80 in 2002) between the results from laboratory and burial experiments. This indicates that the laboratory approach can simulate the situation in the field. Ageing over 6 months decreased the capacity for seed persistence to about a fifth of the level shown when freshly harvested. As a consequence of ageing and environmental impacts on persistence, only seeds from the same location and harvest year should be used for testing genetic variability. The high genetic variability among currently available rape seed cultivars gives breeding strategies a good chance of ideotyping low persistence genotypes and minimizing the risk of gene dispersal in time.
Previous investigations have shown that the long-chain fatty alcohols and long-chain fatty acids of plant waxes have potential as diet composition markers. This study was conducted to measure faecal recoveries of long-chain fatty alcohols (C-20-C-30) and long-chain fatty acids (C-20-C-32) in sheep fed mixed diets. Methodology for quantitative analysis of these compounds in feed and faeces is also presented. The method was an extension of the original n-alkane method of Mayes et al. (1986) in which separate hydrocarbon (n-alkanes, n-alkenes and branched-chain alkanes), alcohol (free + esterified) and acid (free + esterified) fractions could be obtained from a single sample. A fraction containing alcohols and sterols was eluted from the silica gel column after removal of the hydrocarbons. Sterols were removed from alcohols using aminopropyl solid-phase extraction columns. Alcohols were converted to their trimethylsilyl (TMS) ethers and run on a gas chromatograph (GC). Acids were extracted from the aqueous phase of saponification products after removal of hydrocarbons, alcohols and sterols, purified through silica gel columns and were converted into their methyl esters (FAMES) prior to analysis on a GC. Tests were carried out to evaluate the reproducibility of the results obtained from the analytical method developed for quantifying alcohols and acids. Twelve sheep, in metabolism crates, were offered (0(.)8 kg DM/animal/day) four different mixtures of hill grass (Agrostis capillaris), birch (Betula pendula) leaves and current season's growth of heather (Calluna vulgaris) and bilberry (Vaccinium in yrtillus) for 17 days. Total daily faeces and feed refusals collections were carried out over the last 7 days. Faeces collections were bulked for each animal. Representative samples of feed, refusals and faeces were analysed for alcohols and acids using the described method. Faecal recoveries of alcohols and acids were calculated from the ratio of output and input of each marker. The results showed high, though incomplete, faecal recoveries for both alcohols and acids. Alcohols had consistently higher faecal recoveries compared with acids. Mean (+/-S.E.) faecal recovery values for alcohols C-20, C-22, C-24, C-26, C-28 and C-30 were 0(.)58 +/- 0(.)04, 0(.)67 +/- 0(.)01, 0(.)72 +/- 0(.)008, 0(.)80 +/- 0(.)007, 0(.)94 +/- 0005 and 1(.)01 +/- 0(.)02, respectively, whereas those of acids C-20, C-22, C-24, C-26, C-28, C-30 and C-32 were 0(.)47 +/- 0(.)02, 0(.)57 +/- 0(.)02, 0(.)61 +/- 0(.)02, 0(.)77 +/- 0(.)017, 0(.)84 +/- 0(.)01, 0(.)79 +/- 0(.)015 and 0(.)84 +/- 0(.)013, respectively. Increasing chain-length had a significant effect (P 0(.)05) on the recoveries of alcohols and acids in faeces.
Grass-legume associations may offer a way of improving the N efficiency of dairy farming, but may also have an adverse impact on the environment by increasing leaching losses. Nitrate leaching from four cropping sequences with different grassland frequency and management (long-term grazed, long-term cut, cereals followed by 1 and 2-year grazed leys) were investigated on a loamy sand in central Jutland for both unfertilized grass-clover (perennial ryegrass (Lolium perenne L.)/white clover (Trifolium repens L.)) and fertilized perennial ryegrass (300 kg N/ha) swards during 1997-2002. Furthermore, 1 year (2001) of N2 fixation in 1-, 2- and 8-year-old grass-clover pastures was determined. Nitrate leaching from grazed unfertilized grass-clover was always considerably lower than from grazed fertilized ryegrass. The effect of grassland age on nitrate leaching was insignificant in grass-clover but clear in grazed ryegrass, where levels increased dramatically with sward age. In production years 6-8, leaching from grass-clover was only 9-13% of the comparable losses from ryegrass. Under the cutting regime grass-clover showed a significant reduction in both yield and N-removal with increasing sward age, whereas for ryegrass these figures did not show any decreasing trend. N2 fixation was lower in 8-year-old swards compared with fully established 2-year-old swards as a consequence of lower dry matter production, lower clover content and a lower proportion of clover-N derived from the atmosphere. The results from the present study indicate that the higher leaching losses observed in fertilized grass compared with unfertilized grass-clover systems were caused by (1) a reduction in N2-fixation in grass-clover over time and (2) a reduction in dry matter production in grass-clover over time, lowering the grazing intensity and the recycling of grassland N via animal excreta. [PUBLICATION ABSTRACT
The study reported presents the findings relating to commercial growing of genetically-modified Bt cotton in South Africa by a large sample of smallholder farmers over three seasons (1998/99, 1999/2000, 2000/01) following adoption. The analysis presents constructs and compares groupwise differences for key variables in Bt v. non-Bt technology and uses regressions to further analyse the production and profit impacts of Bt adoption. Analysis of the distribution of benefits between farmers due to the technology is also presented. In parallel with these socio-economic measures, the toxic loads being presented to the environment following the introduction of Bt cotton are monitored in terms of insecticide active ingredient (ai) and the Biocide Index. The latter adjusts ai to allow for differing persistence and toxicity of insecticides. Results show substantial and significant financial benefits to smallholder cotton growers of adopting Bt cotton over three seasons in terms of increased yields, lower insecticide spray costs and higher gross margins. This includes one particularly wet, poor growing season. In addition, those with the smaller holdings appeared to benefit proportionately more from the technology (in terms of higher gross margins) than those with larger holdings. Analysis using the Gini-coefficient suggests that the Bt technology has helped to reduce inequality amongst smallholder cotton growers in Makhathini compared to what may have been the position if they had grown conventional cotton. However, while Bt growers applied lower amounts of insecticide and had lower Biocide Indices (per ha) than growers of non-Bt cotton, some of this advantage was due to a reduction in non-bollworm insecticide. Indeed, the Biocide Index for all farmers in the population actually increased with the introduction of Bt cotton. The results indicate the complexity of such studies on the socio-economic and environmental impacts of GM varieties in the developing world.
Grass-legume associations may offer a way of improving the N efficiency of dairy farming, but may also have an adverse impact on the environment by increasing leaching losses. Nitrate leaching from four cropping sequences with different grassland frequency and management (long-term grazed, long-term cut, cereals followed by 1 and 2-year grazed leys) were investigated on a loamy sand in central Jutland for both unfertilized grass-clover (perennial ryegrass (Lolium perenne L.)/white clover (Trifolium repens L.)) and fertilized perennial ryegrass (300 kg N/ha) swards during 1997-2002. Furthermore, 1 year (2001) of N-2 fixation in 1-, 2- and 8-year-old grass-clover pastures was determined. Nitrate leaching from grazed unfertilized grass-clover was always considerably lower than from grazed fertilized ryegrass. The effect of grassland age on nitrate leaching was insignificant in grass-clover but clear in grazed ryegrass, where levels increased dramatically with sward age. In production years 6-8, leaching from grass-clover was only 9-13% of the comparable losses from ryegrass. Under the cutting regime grass-clover showed a significant reduction in both yield and N-removal with increasing sward age, whereas for ryegrass these figures did not show any decreasing trend. N2 fixation was lower in 8-year-old swards compared with fully established 2-year-old swards as a consequence of lower dry matter production, lower clover content and a lower proportion of clover-N derived from the atmosphere. The results from the present study indicate that the higher leaching losses observed in fertilized grass compared with unfertilized grass-clover systems were caused by (1) a reduction in N-2- fixation in grass-clover over time and (2) a reduction in dry matter production in grass-clover over time, lowering the grazing intensity and the recycling of grassland N via animal excreta.
Assessment of the stability of micronutrients is important in breeding for the enhanced nutritional quality of staple food crops as a means to alleviate malnutrition. Twenty early-maturing elite tropical maize (Zea Mays L.) genotypes were evaluated over 2 years at three locations representing three distinct agroecologies in West and Central Africa (WCA). The objectives were to analyse the pattern of genotype x environment interactions (GEI) and environmental stability of iron and zinc concentrations in grain using the Additive Main Effects and Multiplicative Interaction (AMMI) statistical modcl. Results indicated that the effects of genotypes, environments and GEI were significant (P < 0-05) for both micronutrients. The effect of GEI' was about double the contribution Of the genotypes for grain iron and more than double the effect of genotypes for grain zinc. Partitioning of GEI indicated that variety x location was the dominant source of a significant amount of GE1 for both micronutrients. Scores of the first two interaction principal component axes (IPCAI and IPCA2) from the AMMI were significant and accounted for 0 center dot 68-0 center dot 75 of the pattern of GEI for both micronutrients. About half of the genotypes evaluated were stable for grain iron and zinc concentration over the set of environments. The AMMI model identified ACR98TZEMSR-W as the most stable genotype for grain iron and MAKA-SRBC5 was the most stable for grain zinc. However, the yellow genotype, AK94-DMR-ESR-Y was the most promising, with high and moderately stable concentrations of iron and zinc in the grain. Because it is yellow, with beta-carotene content and high concentrations of iron and zinc in the grain, it might significantly contribute to an improved intake of these micronutrients in populations who rely oil maize for a major portion of their daily diet.
The Japanese rice cultivar, Akenohoshi, has numerous spikelets in a panicle (extra-heavy particle type) and achieves a large yield sink capacity. However, this cultivar, as well as other extra-heavy panicle types, does not always produce higher yields because of poor grain filling of the spikelets on the secondary branches in a particle. To determine whether the poor grain filling found in Akenohoshi was due to source-limited or sink-limited conditions, the present study examined the responses of grain-filling characteristics to several spikelet-removal treatments immediately after heading. Only when the spikelets on secondary branches remained was a significant increase in filled grain percentage in this spikelet position observed. This increase seemed to be associated with the increases in rate and duration of the grain-filling process and in single grain weight in this spikelet position. These results clearly indicate that the poor grain filling in the spikelet on secondary branches of Akenohoshi could mainly be attributed not to sink-limited conditions, but to source-limited conditions probably at specific stages of grain filling.
Visible (VIS) and near-infrared reflectance spectroscopy (NIRS) combined with multivariate data analysis was used to predict potentially mineralizable nitrogen (PMN) and nitrogen in particulate organic matter fractions (PSOM-N). Soil samples from a long-term experiment (n=24) as well as soils under commercial management (n=160) in Uruguay (South America) were analysed. Samples were scanned in a NIRS 6500 monochromator instrument by reflectance (400-2500 nm). Modified partial least square regression (MPLS) and cross validation were used to develop the calibration models between NIRS data and reference values. NIRS calibration models gave a coefficient of determination for the calibration (R-CAL(2))>0.80 and the standard deviation of reference data to standard error in cross validation (RPD) ratio ranging from 2 to 5.5 for the variables evaluated. The results obtained in the study showed that NIRS could have the potential to determine PMN and PSOM-N fractions in soils under different agronomic conditions. However, the relatively limited number of samples led us to be cautious in terms of conclusions and to extend the results of this work to similar conditions.
The rate of growth of individual seeds of soybean (Glycine max L. Merrill) is determined, in part, by the concentration of sucrose in the seed. Water stress during seed filling reduces photosynthesis, but the effect on seed sucrose concentration is not well understood. Soybean plants (cultivars Elgin 87 and Asgrow 232HS) were exposed to water stress from early in the seed-filling period until maturity in field and greenhouse experiments. Stress reduced yield (5-38%) and seed size (11-35%) but it did not affect the number of seeds. Stress accelerated leaf senescence as shown by a more rapid decline in leaf photosynthesis in both experiments. Seed-growth rate and cotyledon sucrose concentrations (expressed on a mM basis using the bulk water content of the cotyledons) during the linear phase of seed growth were not affected by stress in either experiment. Thus, water stress during seed filling had no direct effect on seed growth; its only effect was to accelerate leaf senescence, which shortened the seed-filling period and resulted in smaller seeds. Strategies to reduce yield loss from water stress during seed filling should focus on leaf senescence instead of seed growth.
An experiment was conducted to investigate the effect of grazing legumes and ryegrass on the performance of Suffolk x Mule finishing lambs in terms of growth rate, days to finish and carcass characteristics. Replicate plots (n = 2) of red clover (Trfolium pratense), lucerne (Medicago sativa), lotus (Lotus corniculatus) and perennial ryegrass (Lolium perenne) were established in May 1999 at the Institute of Grassland and Environmental Research (IGER), Aberystwyth, and maintained at a similar vegetative growth stage. From the beginning of September 1999 each forage was grazed by 10 wether lambs and 10 ewe lambs. The lambs grazed the experimental plots from weaning until they reached fat-class 3L. There was a significant decline in crude protein (CP) concentration in lucerne (-2.6 g/kg DM/day, P<0.05) and lotus (-2.5 g/kg DM/day, P<0.001) over the grazing period, while the CP concentration in red clover and ryegrass remained comparatively constant. Growth rates were highest for lambs grazing lotus compared with lambs grazing the other forages, and growth rates were significantly higher for lambs grazing red clover than for lambs grazing ryegrass. Growth rates of lambs grazing lucerne were significantly lower than lambs grazing lotus but similar to that of lambs grazing red clover and ryegrass. Lambs grazing the legume forages required significantly fewer days to finish compared with lambs grazing ryegrass. Cold carcass weight and killing out percentage were significantly higher for lambs grazing red clover compared with that for lambs grazing the other forages. Lambs grazing red clover and lucerne had significantly higher voluntary intakes, estimated using n-alkanes, than lambs grazing ryegrass, with intakes for lambs grazing lotus not significantly different. There were no treatment effects on in vivo digestibility. Levels of total protein and P-hydroxybutyrate in blood were unaffected by dietary treatment, although lambs grazing the forage legumes had significantly higher blood glucose and urea concentrations compared with lambs grazing ryegrass. Lambs grazing lotus had the highest plasma albumin. The results indicate that by grazing finishing lambs on forage legumes it is possible to increase growth rates and reduce time to finish without compromising carcass quality.
The alkane technique allows estimates of intake and diet composition. For the latter a correction for incomplete recovery of faecal alkane concentrations has to be made. Feeding level and diet proportions have been discussed as factors possibly influencing recovery. A balance trial was conducted to study these effects on faecal alkane recovery rates and their consequences on estimates of roughage intake in sheep. The diets consisted of force-dried pelleted alfalfa meal (A) and wheat whole meal (W) in three levels each (360, 480, 600 and 270, 360, 450 g/day, respectively); the wheat was partly labelled with beeswax to provide a distinctive alkane pattern. Each diet was fed to four wethers. Despite significant effects (P < 0.05) of A and W on organic matter digestibility, no such effects were observed for alkane recovery rates. Estimates of alfalfa intake were better if alkanes with a higher coefficient of variation of recovery were not included in diet composition estimates. Furthermore, in spite of the lack of significance of the dietary factors A, W and A x W, faecal alkane concentration correction based upon diet-specific faecal recoveries gave better estimates of alfalfa intake than based on overall recoveries. The estimate of alfalfa intake differed from known intake by -1.7 to -2.6%, depending on the method of estimation. The relative mean discrepancy was regarded as a tool to assess estimated intakes of individual animals. It ranged from 4.4 to 14.2% for dietary treatments and was 7.6% for all animals. The poor quality of estimates for individual animals may result from the variation of faecal recovery rates and needs further investigation.
Grass pea (Lathyrus satirits) is a potentially valuable feed and food crop in semi-arid regions. Much work has been done on lowering toxicity and on selection of low toxicity varieties, while research on the eco-physiological characteristics of grass pea is very rare. Stomatal character, photosynthetic character and seed chemical composition were measured in four varieties of L. sativus to investigate their relationships at different water availabilities. For L. sativus cv. Yongshou (YS), L. sativus cv. Dingxi (DX), L. sativus cv. Heilongjiang (HLJ) and L. sativus cv. Xide (XD), stomatal density was in the order XD > HLJ > DX > YS under both control and drought conditions. Stomatal aperture, photosynthetic rate (Pn), transpiration rate (E), and the concentrations of seed beta-N-oxalyl-L-alpha, beta-diaminopropionic acid (ODAP), protein and starch were in the order YS > HLJ > DX > XD, while the opposite order was found for water use efficiency (WUE). Under drought conditions, stomatal aperture, Pn and E were lower than those under the control, while the other parameters were higher. A significant positive correlation was observed between stomatal density and WUE, while negative correlations were found between stomatal density and the remaining parameters. Obvious positive correlations were also observed between stomatal aperture and Pn, E, the concentrations of seed ODAP, protein and starch, while a negative correlation appeared between stomatal aperture and WUE. Under drought conditions, R-2 values were more comparable with the control. Intriguingly, the R-2 values of stomatal aperture were higher than of stomatal density, especially under drought conditions. These results indicate that stomatal aperture may be more closely related to photosynthetic character and seed chemical composition in grass pea, and water deficit may enhance the correlations.
A 3-year study was set up to evaluate the influence of cow genetic potential for milk production and concentrate supplementation level on profitability of pasture based systems of milk production. In each of the 3 years, 96 cows were used in a three (genotype) x 3 (levels of concentrate supplementation) randomized block design. Cows were categorized based on their pedigree index (PD) for milk production (PDMILK) into low (LP; PDMILK less than 100 kg), medium (MP; PDMILK 100-200 kg) and high (HP; PDMILK 200-300 kg). Concentrate supplementation levels were 376, 810 and 1540 kg per cow per lactation, identified as low (LC), medium (MC) and high (HC) concentrate respectively. Three milk production scenarios were investigated using the Moorepark Dairy Systems Model (MDSM) which included: EU milk quota applied at farm level with current costs and prices (SI), EU quota applied at farm level with projected future costs and prices (S2), and EU milk quota applied at industry level (quota purchasing possible) with projected future costs and prices (S3). The effect of variation in milk price, concentrate price and opportunity cost of land were modelled using stochastic budgeting. The results suggest that where EU milk quota is applied at farm level (S1 and S2), the optimum system of milk production is where margin per unit of output is maximized. When milk quota is applied at industry level (S3) the optimum system will be where margin per cow will be maximized. The results also suggest that the optimum system for cows with lower genetic potential for milk production is low level of concentrate supplementation, while cows with higher genetic potential for milk production is high level of concentrate supplementation.
Six S-5 lines of maize, previously identified as having contrasting responses to nitrogen (N) supply, were used to carry out a complete series of diallel crosses. The resulting 15 hybrids were grown in a field at two N levels. The general combining ability (GCA) and specific combining ability (SCA) were estimated using the method 4, model 1 analysis of Griffing for grain yield kernel weight, grain number, harvest index. green leaf number, ear leaf area, N utilization efficiency, total plant N, grain N content anthesis-silking! interval, chlorophyll content and prolificacy. For the majority of the traits, GCA was more important than SCA and there was an increase of non-additive effects under low N. Significant interactions were observed between GCA and N levels for grain yield, grain number and chlorophyll content, indicating the selection of different lines for each N level. The lines with the largest effects of N Supply per se oil grain yield, were those with the largest effects of GCA for this trait. This association indicates that the response of the lines to N supply, Should be considered in breeding programmes in order to achieve acceptable hybrids for environments with both high and low N.
The effects of acetic, propionic, butyric and lactic acids (short-chain acids), and of glycerol, on the in vitro dry matter digestibility (IVDMD) of oat hay, and on cellulolysis by a protein extract of rumen fluid were studied. The objective was to gain information on the impact of increasing the concentrations of those compounds in the medium on degradative activities carried out by rumen microorganisms. Short-chain acids were assayed as sodium salts and, for all compounds, the concentrations were 50, 100, 200 and 300 mM. The volatile fatty acids (VFA: acetic, propionic and butyric acids) were tested separately or in two mixtures A and B that contained different proportions of each VFA. The IVDMD was assayed according to a modified Tilley & Terry (1963) technique while cellulolysis was assessed by the hydrolysis of carboxymethylcellulose (CMC) in 1-h incubations at 39 C. Parallel incubations with NaCl were utilized as controls for ionic strength and osmolarity changes in the incubation medium. Increases of 100-300 mM of short-chain acids decreased IVDMD between 7 and 39%. The inhibitions produced by increases of 200 and 300 mM of acetic acid were smaller than those caused by the same concentrations of either butyric or lactic acids. Increases of 100, 200 and 300 mM of glycerol reduced by 8-15% the IVDMD, and the inhibitions produced by increments of 200 and 300 mM of this compound were smaller than the ones elicited by the short-chain acids, with the exception of 200 mM of acetic acid that did not differ. The IVDMD was inhibited by NaCl only when concentrations were increased by 200 (12%) and 300 mM (26%). The degradation of CMC was reduced by 7-20% by 200 and 300 mM increases of the short-chain acids or glycerol, the exception being lactic acid that had no effect. One hundred mM increases of acetic and butyric acids inhibited the CMC degradation by 7 and 9%, respectively, whereas only butyric acid was inhibitory (7%) at 50 mM. Greater concentration increases of both VFA mixtures A and B than of the individual VFA were necessary to inhibit the hydrolysis of CMC. Cellulolytic activity was decreased 6 and 9% by increases of 200 and 300 mM of NaCl, respectively, and these drops of activity were smaller than those obtained with increases in any of the other compounds. Since osmolarity and/or ionic strength changes in the medium cannot completely account for the observed inhibitions of IVDMD and cellulolysis, it is suggested that glycerol and the anions of short-chain acids produce changes in the reaction media polarity that contribute to the inhibitory effects observed. Alterations in the media could also bring about conformational changes in the degradative enzymes leading to reduced rates of reaction and subsequent decreases in IVDMD and cellulolysis. Since most of the effects were observed with concentration increases that were larger than the physiological concentrations in the rumen, it is suggested that the compounds tested have little impact in vivo on the ruminal degradative activities that were evaluated.