The purpose of the current study was to determine the effects of dietary docosahexaenoic acid (DHA) on fatty acid deposition in egg yolk and various tissues of laying Leghorn hens, and on the expression of hepatic lipogenesis-related transcription factors. There were three treatments with 10 Leghorn hens per treatment. Diets were based on maize-soybean meal (ME: 12 MJ/kg; CP: 171 g/kg; Ca: 34 g/kg) supplemented with 0 (plus 20 g butter/kg), 5 g (plus 15 g butter/kg) or 20 g algal DHA oil/kg. The egg production of the birds was not affected by dietary DHA oil (P>0·05). The DHA content in egg yolks of the laying hens increased significantly (P<0·01) with the dietary supplementation of DHA. The DHA content of the total fatty acids in the egg yolk of laying hens was 4±16, 11±43 and 20±90 g/kg for 0, 5 and 20 g/kg DHA treatments, respectively for the first week, and 6±16, 18±49 and 31±86 g/kg for the second week. Therefore, algal DHA oil can be utilized by laying Leghorn hens to enhance egg yolk DHA content and produce high DHA eggs. The concentrations of triacylglycerol (TG) and cholesterol in plasma of laying Leghorn hens were not affected by dietary DHA treatments (P>0·005). The DHA content in plasma and livers of laying hens was increased with the addition of DHA in the diet (P<0·05). The DHA content in the skeletal muscle of Leghorn hens was also increased with the increase in dietary DHA. The data indicate that dietary DHA oil can be incorporated into plasma, egg yolks and various tissues. The mRNA concentrations of the lipogenesis-related transcription factors, sterol regulatory element binding protein 1 (SREBP1) and SREBP2, in the livers of laying Leghorn hens were not affected by the supplement of algal DHA oil for 2 weeks, suggesting that the expressions of these transcription factors are tightly controlled and not sensitive to DHA treatments in laying hens.

A 3-year field study was conducted during 1998/99–2000/01 on the effect of tillage on crop growth, yield and nutrient use in wheat (Triticum aestivum L.) grown after different methods of rice (Oryza sativa L.) seeding. Treatments comprised three methods of rice seeding, viz. direct seeding (unpuddled), manual transplanting and mechanical transplanting by self-propelled rice transplanter as main plots and three tillage levels in wheat (conventional tillage (CT), reduced tillage (RT), zero tillage (ZT)) as subplots. Results indicated that tillage significantly decreased soil bulk density (1·59 Mg/m3) over the zero tillage system (1·69 Mg/m3). Greater root density in terms of root dry weight (7·50 Mg/20 cm row length) was recorded in CT and the lowest root dry weight (5·80 Mg/20 cm row length) was obtained in ZT during 2000/01. Significantly higher dry matter accumulation (254 g/m row) and leaf area index of wheat (3·04) were consistently recorded under direct seeding of rice, which was statistically different from the other methods of seeding adopted in the preceding rice crop. CT resulted in significantly higher dry matter (253 g/m row) and leaf area index of wheat (3·02) than RT and ZT respectively, during 2000/01. The highest mean yield of wheat (6·02 Mg/ha) was obtained in direct seeding of rice, followed by mechanical and manual transplanting. Among different tillage levels, CT recorded the highest mean yield of wheat (5·90 Mg/ha) followed by RT (5·82 Mg/ha) and ZT (5·40 Mg/ha). The yield reduction was in the order of 11·28 and 6·31% under ZT and RT, respectively. Soil chemical analysis showed that available soil N, P and K contents were affected significantly due to seeding method and tillage after each cycle of rice–wheat sequence. Significantly greater available soil N, P and K were recorded under direct seeding of rice followed by manual and mechanical transplanting. CT recorded significantly lower values of available soil N and higher values of soil P and K whereas ZT recorded higher values of available soil N and lower values of available soil P and K during the 3 years of study.

The suitability of models specifically re-parameterized for analyzing energy balance data relating metabolizable energy intake to growth rate has recently been investigated in male broilers. In this study, the more adequate of those models was applied to growing turkeys to provide estimates of their energy needs for maintenance and growth. Three functional forms were used. They were: two equations representing diminishing returns behaviour (monomolecular and rectangular hyperbola); and one equation describing smooth sigmoidal behaviour with a fixed point of inflexion (Gompertz). The models estimated the metabolizable energy requirement for maintenance in turkeys to be 359–415 kJ/kg of live-weight/day. The predicted values of average net energy requirement for producing 1 g of gain in live-weight, between 1 and 4 times maintenance, varied from 8·7 to 10·9 kJ. These results and those previously reported for broilers are a basis for accepting the general validity of these models.

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 C50 and BR50, 50 kg N/ha/year originates from the waste and 50 kg N/ha/year from mineral nitrogen fertilizer, while in C100 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.

By a variety of exposure routes it is possible that the toxic heavy metals cadmium, arsenic and mercury could enter the diet of farm animals and hence contaminate food products derived from those animals. Therefore, there is a need to be able to assess the likely levels of contamination in animal tissues if exposed to contaminated feed and also to estimate how rapidly an animal will decontaminate once the source of contamination is removed from the feed. The development of dynamic models to predict changes in the degree of heavy metal contamination in tissues of ruminants have been hindered by the lack of data on the transfer and excretion rates of these metals from tissues. A study is described during which dairy cows were given a single intraruminal administration of 109Cd, 73As and 203Hg and measurements made of the subsequent concentrations of the radioisotopes in body tissues and milk. The resultant data were used to adapt previously developed compartment models describing the behaviour of the metals in sheep for use with dairy cows. Two changes were made to the sheep models: (i) a new excretion route was included to describe transfer to milk; (ii) the rate coefficients (with the exception of those involving gut absorption and transfer) were adjusted according to the ratio of the metabolic live-weights (live-weight (kg)0·75) of the sheep to that of the cattle. The models predicted levels of the metals in the cattle tissues and milk reasonably well.

Nitrogen (N) levels in the soil and N fertilization are among the major factors that affect grain protein concentration (GPC) in malting barley (Hordeum vulgare L.). The use of inherently low protein cultivars might be an advantage in conditions of excessive soil N or in situations where N is applied to maximize yield. In the present study, eight malting barley genotypes were grown under dryland and irrigated conditions to compare their response to four rates of nitrogen (N) application (0, 30, 60 and 120 kg/ha). The trials were carried out in 1998 and 1999 at a site in the Wimmera region of Victoria, Australia, which has a Mediterranean-type environment. Seasonal differences accounted for a large proportion of the observed variation in GPC, but had little influence on variation in grain yield. Nitrogen application significantly increased grain yield and GPC, and decreased kernel weight and plumpness. The rate of response for grain protein was higher under dryland than irrigated conditions, but the genotype-by-nitrogen interaction was not significant under both conditions. To further characterize genotypic response, the method of pattern analysis was used to identify groups of genotypes showing a similar pattern in their response to N application and to relate the patterns to available knowledge about the inherent GPC of their grains. The eight genotypes were clustered into three entry groups, corresponding to low, moderate and high-protein genotypes. There was little difference among groups in the rate of response to N application. However, the genotype group with inherently low GPC maintained the lower protein over those with higher grain protein at the different rates of N application. Under dryland conditions, the low-protein genotypes tended to have less plump kernels with increasing rates of N application than the respective high-protein group.

Damping-off and stem rot of cowpea is an important soil-borne disease worldwide. Cowpea fields were randomly chosen in each agro-ecological zone in Benin and surveyed in 2001 and 2002 to determine the occurrence of the diseases throughout the country. Diseased plants, prevailing environmental conditions and cowpea grower cultural practices were recorded and causal agents associated with the disease identified. Results indicated that damping-off and stem rot were distributed throughout Benin. The disease incidence was higher in the South (0·074) and Centre zones (0·063) than in the other zones (<0·02) in the country. Among factors influencing the disease incidence, cultural practices such as sole crop and no-till systems appeared to be most important. Isolated fungi included Sclerotium rolfsii, Fusarium spp., Pythium ultimum, Rhizoctonia solani, Phoma sp., Rhizopus sp. and Trichoderma harzianum. None of the Fusarium, T. harzianum or Rhizopus sp. isolates were pathogenic in the greenhouse. Pythium ultimum, R. solani and Phoma sp. were infrequently isolated and few isolates caused the disease symptoms in the greenhouse. However, this is the first report of Phoma sp. causing damping-off and stem rot of cowpea in Benin. Sclerotium rolfsii was by far the most common species isolated from all the agro-ecological zones and all isolates were pathogenic on cowpea in the greenhouse. Sclerotium rolfsii was considered to be the main causal agent of cowpea damping-off and stem rot in the Republic of Benin due to its wide distribution, high incidence and predominance on plants with damping-off and stem rot symptoms.

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 (C20–C30) and long-chain fatty acids (C20–C32) 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 myrtillus) 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 C20, C22, C24, C26, C28 and C30 were 0·58±0·04, 0·67±0·01, 0·72±0·008, 0·80±0·007, 0·94±0·005 and 1·01±0·02, respectively, whereas those of acids C20, C22, C24, C26, C28, C30and C32 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 both alcohols and acids (R2=0·808, 0·741, respectively). Different dietary plant mixtures had no effect (P>0·05) on the recoveries of alcohols and acids in faeces.

The objective of the study was to determine the chemical composition of the diet, intake and plasma concentrations of glucose, urea and non-esterified fatty acids (NEFA) during pregnancy in goats grazing a thorn scrubland of the semi-arid region of North Mexico. Additionally, monthly changes during pregnancy of plasma concentrations of luteinizing hormone (LH), growth hormone (GH), insulin (INS) and progesterone (P4) were also measured. A herd of 250 goats was bred in August and blood samples were collected from 12 goats at monthly intervals up to December to evaluate plasma glucose, urea, NEFA, LH, GH, INS and P4. Three goats fitted with oesophageal cannulae (38±1·7 kg BW) were used to obtain diet samples during pregnancy. Response variables were analysed by split-plot ANOVA for repeated measures on animals across time. When significant differences were observed among pregnancy months, multiple comparisons were performed using the PROC GLM-PDIFF option of SAS. The response variables organic matter (OM), crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF), lignin, hemicellulose and cellulose differed across pregnancy. Mean values for the whole period were (g/kg DM) 866 (OM), 149 (CP), 524 (NDF), 364 (ADF), 131 (lignin), 160 (hemicellulose), and 233 (cellulose). Mean values for dry matter intake (DMI, kg/day), metabolizable energy intake (MEI, MJ/day) and metabolizable protein intake (MPI, g/day) were 1·2, 8·9 and 74·0, respectively and were different among periods of sampling (P<0·05). Mean plasma glucose concentration was 41±4·3 mg/dl with no significant differences (P>0·05) across pregnancy. Plasma NEFA concentrations increased (P<0·05) at the end of pregnancy (August, 0·396 v. November, 1·27 mM/l). Plasma urea concentrations were higher (P<0·05) in August (26·3 mg/dl) and November (26·2 mg/dl). Serum urea concentrations were related to MPI (r=0·82, P=0·10) and to the undegraded protein absorbed from the duodenum (r=0·79; P=0·07), but not with the rumen NH3-N concentration (r=−0·25; P=0·68). Hormone plasma concentrations differed (P<0·05) across pregnancy. While the largest serum LH concentration (P<0·05) was observed in mid pregnancy (October, 7·8 ng/ml), the lowest value was depicted at the end of gestation (4·8 ng/ml). A similar pattern was observed in plasma P4, with monthly increases from August to November, and a reduction during the last month of gestation (August, 5·6 v. December 2·5 ng/ml). With respect to the metabolic hormones, a negative correlation (−0·23, P=0·05) was observed between GH and INS, with the largest plasma INS levels in mid pregnancy (October 1·9 ng/ml), the lowest INS levels in December, 0·8 ng/ml and the largest serum GH concentration in December, 20·2 ng/ml. Results from the study indicate that DMI, MEI and MPI in grazing goats are useful indicators of the nutritive value of the forage consumed by goats which allowed them to keep an important steroidogenic luteal activity during gestation (P4=5·7±0·82 ng/ml, litter size=1·44 kids). Nonetheless, the observed plasma levels of glucose, urea, NEFA, INS and GH indicate that a schedule of energy supplementation may be outlined to ensure an adequate nutritional status of goats during late pregnancy and early lactation.

The proportions of alkanes in plant cuticular waxes are influenced by sampling date, site and grazing pressure. Alkanes in organs of major wild forage grasses in Japan were evaluated to estimate the intake and diet composition of grazing animals. Samples of four grasses from a fixed site in native grassland and three grass species from different sites were collected from June to November, to test the temporal and spatial effects on alkane concentrations. Most alkane concentrations in Miscanthus sinensis Anderss, Pleioblastus chino (Franch. Et Savat.) Makino, Sasa nipponica and Zoysia japonica increased from June to July, and then decreased to mid November. Alkane concentrations in the Z. japonica sward used to test the effects of grazing pressure decreased from May to September. Although the sampling dates affected the alkane concentrations, the species effects accounted for 70–93% of the observed variation. Grazing pressure affected only the C29 (n-Nonacosane) alkane concentrations in dead aboveground materials of Z. japonica, but altered the ratios of C29[ratio ]C31 (n-Hentriacontane) in both dead and live Z. japonica. There were positive correlations between C27 (n-Heptacosane), C29 and C35 (n-Pentatriacontane) alkane concentrations in live leaves of M. sinensis and of C31 in live leaves of P. chino with growing season temperature and radiation. The concentrations of C25, C27 and C29 in dead leaves of M. sinensis and of C33 (n-Tritriacontane) and C35 in live Z. japonica were significantly correlated only with radiation. Alkane concentrations differed between the sampling sites, and considerable differences were observed between samples from Iwate and Kumamoto. Both live leaf and dead leaf samples from M. sinensis contained substantial amounts of C27, C29, C31, C33 and C35, and showed that alkane concentrations in stems were much lower during the whole growing season. Although concentrations of C29 were highest in Sasa nipponica (Makino) makino et Shibata, concentrations of C31 or C33 were highest in the other three grass species. Grazing pressures had little effect on alkane patterns, in which alkanes with odd-numbered carbon chains were predominant and most alkanes were of chain length C25 (n-Pentacosane) to C35 (n-Pentatriacontane).

Maize improvement at the International Institute of Tropical Agriculture (IITA), which began in the 1970s, built on the germplasm and experience of earlier years. The main breeding emphasis was to develop maize cultivars and hybrids with high yield potential and durable resistance to diseases and pests with specific adaptation to the different agro-ecological zones of West and Central Africa. Over the years, open-pollinated cultivars have been developed with different levels of resistance to biotic and abiotic stresses. Identification of the factors that contributed to improvements in the maize cultivars developed during the past decades may be useful to sustain the genetic gain from selection in the future. A study was conducted to quantify genetic gains in yield and associated traits of open pollinated maize cultivars released from 1970 to 1999 in the West African savannas. The genetic gain in grain yield was 0·41% per year and seems to be associated with increases in total biomass and kernel weight, and reductions in plant height and days to flowering (anthesis and silking). There was no significant change in harvest index of the cultivars.

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×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.

To assess the effect of grassland management on the ruminal digestion of silages, four lactating dairy cows, fitted with a rumen cannula, were fed diets consisting of concentrates and different grass silages. The grass silages consisted of intensively managed grass (IM) in variable proportions replaced by silages harvested from a ‘species-poor’ grassland managed to stimulate nesting of birds (SPP) or from a grassland managed to increase plant species diversity (SPR). The roughage part of the diets was composed completely of IM (100IM), or 200 g/kg (in dry matter) of IM replaced by SPP (20SPP) or 600 g/kg of IM replaced by SPP (60SPP), or SPR (60SPR). The pH in the rumen was highest on 60SPR and lowest on 100IM and 20SPP (P<0·05), whereas volatile fatty acids (VFA) concentrations were lowest on 60SPP and 60SPR and highest on 100IM (P<0·05). No differences in the ratio non-glucogenic: glucogenic volatile fatty acids were observed among the diets. The NH3 concentration was highest on 100IM and 20SPP and lowest on 60SPR (P<0·05), reflecting differences in CP intake. The concentration of uric acid in the urine (mg per kg metabolic body weight) was highest on 100IM (P<0·05). Rumen pool size of OM and DM did not differ among treatments, but pool size of NDF and IADF were highest on 60SPR (P<0·05). Passage rate was high on 100IM and 60SPR, but no significant differences with the other treatments were established. Also, no significant differences were observed in rates of degradation. Clearance rate of large particles was highest on 60SPP and differed significantly from 60SPR (P<0·05) only. No differences were observed in clearance rate of small particles. In conclusion, for most rumen fermentation characteristics measured in the study, no noticeably aberrant behaviour of the silages from semi-natural grassland was observed.

Four perennial ryegrass growth models were evaluated for their suitability to form the basis of a herbage growth model (HGM) for a decision support system (DSS). The successful candidate had to be suitable for further development to meet the specification of the DSS and following redevelopment it would then be integrated into a pasture management decision support system for dairy production. The models selected for evaluation were the Irish produced Brereton model (Brereton et al. 1996), the LINGRA model (Schapendonk et al. 1998), produced in the Netherlands, and a version of the English Johnson & Thornley (1985) model, developed for field use at the Northern Ireland Plant Testing Station (Laidlaw & Gilliland 2000). The fourth model was a version of the LINGRA model, simplistically adapted by the authors to take account of reproductive growth (LINGRARep). The performance of the models was tested using the mean squared prediction error (MSPE) against a total of 28 seasons' growth data, collected from two sites; i.e. at the former Grassland Research Institute at Hurley, England and the Northern Ireland Plant Testing Station at Crossnacreevy. The Brereton model, when validated against the Hurley dataset, had the lowest MSPE of the four models, but had the highest MSPE against Crossnacreevy data. The PTS model did not perform as well as expected considering its mechanistic basis. Equally, the performance of the LINGRA model was poor at both sites. However, the LINGRARep performed well, having the lowest MSPE at Crossnacreevy and second lowest at Hurley. The LINGRA model was selected for development as the final HGM given that it proved suitable for adaptation and by making even simple adaptations, as in LINGRARep, its performance could be substantially improved. Therefore, it was considered that it possessed the greatest potential for further development.

Reproductive performance has been reported to be declining within the UK dairy herd due to continued selection for increased milk production. The aim of the current work was to assess the influence of genetic merit for milk production (as described by PIN95, the index in use at the time), and level of herd performance on reproductive performance. Fertility records from seven commercial dairy farms over a two-and-a-half year period between August 1997 and January 2000, providing a total of 1003 cow records (with a mean genetic merit of 38·6 (±0·80) PIN95) were collected. The influence of genetic merit for milk production, herd mean 305-day milk yield and their interaction on the reproductive performance of individual dairy cattle was estimated. Additionally, 90-day milk yield, 90-day body condition score and deviation from herd mean 305-day milk yield were also investigated for their influence on fertility. A series of regression models using the Proc GLM procedure in SAS were run using data from those cows that conceived during the monitoring period (n=874) (PIN95=38·8±0·83). The models included the variables, year of calving, month of calving and parity. The results showed that days from calving to conception and services per conception increased significantly both with herd 305-day milk yield, and within herds with deviation from herd 305-day milk yield level. Calving to conception also increased with reduced body condition score of cows at 90 days postpartum. Genetic merit (PIN95) was not significantly related to these fertility measurements.

Mathematical models have been developed that describe possible sources of the free amino acids (AA) present in the red blood cells (RBC). These models reflect three hypotheses, namely (i) direct transport between plasma and RBC, (ii) enhanced direct transport by deformation of the RBC during passage through capillaries and (iii) direct exchange between tissues and RBC. The latter implies that RBC samples from appropriate blood vessels might offer an alternative to tissue biopsies in protein turnover studies.

These compartmental models were tested against data from ovine studies. For hypothesis (i), a single dose of [U-13C] AA was added to blood in vitro. The rate of disappearance of label from plasma was low (kP=0·0009–0·004 per min), indicative of slow direct transport between plasma and RBC. For hypotheses (ii) and (iii), a single dose of [1-13C] AA was administered intravenously to sheep. Label disappeared from plasma quicker (kP=0·33–0·53 per min) than in vitro, with the appearance of labelled AA in the RBC higher than could be explained from direct transport alone. The model reflecting enhanced exchange of free AA between plasma and RBC due to capillary action over-predicted RBC enrichments and pool sizes by up to five-fold. The third hypothesis, namely that AA in the RBC are predominantly derived from exchange with tissues, gave better agreement. This model suggested that at least 0·63 of the AA in the RBC might come from exchange with tissue.

To investigate whether peripheral tissues (skin and muscle) might be involved in such exchange, an additional experiment was conducted in five sheep prepared with arterio-venous catheters across the hindquarters. [1-13C,15N] leucine was continuously infused, with both blood samples and tissue biopsies taken. The ratio of [1-13C] leucine to [1-13C,15N] leucine was 1·8–2·9 fold greater in muscle and skin compared with arterial plasma, indicative of intracellular transamination. If free leucine exchanged directly between tissues and RBC then the ratio should be higher in RBC isolated from venal caval compared with arterial blood. In practice, the ratios from the RBC in aorta and vena cava were similar (P=0·30). These findings suggest that, for leucine, RBC enrichments do not form an alternative to tissue biopsies to estimate the enrichment of the precursor pool in protein turnover studies of the hindquarter. Instead, other tissues must play a more important role in the exchange of AA with the RBC.

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 (R2CAL)>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.

An experiment was carried out to evaluate the utilization of the n-alkane technique and the chromium sesquioxide (Cr2O3)/acid insoluble ash (AIA) procedure to estimate feed intake of meadow hay by two breeds of cattle. The animals were housed in individual pens, and offered known amounts of meadow hay as the sole diet component. One group of 4 Barrosã cows (average weight, 457±24 kg) and another group of 4 Holstein–Friesian cows (average weight, 635±148 kg) were dosed with intra-ruminal controlled-release capsules (CRC) that contained alkane markers or Cr2O3 in separate capsules. During intake estimation, meadow hay and faeces were sampled twice daily. There was no significant effect of grab sampling time on the meadow hay intake estimation, due to the fact that no differences were observed in the faecal marker concentrations.

The mean real intakes, measured as the difference between the dry weight of feed offered each day and the dry weight of daily feed refusal, were 5·64 and 7·76 kg DM/day for Barrosã and Holstein–Friesian cows, respectively. For Barrosã cows the mean estimated intakes when using the CRC release rates documented by the manufacturer (MRR) were 5·66, 6·59 and 6·90 kg DM/day, using the Cr2O3/AIA procedure, C31[ratio ]C32 and C33[ratio ]C32 n-alkane pairs, respectively. For Holstein–Friesian cows the same markers gave values of 7·72, 8·51 and 8·95 kg DM/day, respectively. Mean daily intake estimation was improved when the release rate calculated as the reduction rate in CRCs payload performed in a additional experiment (CRR), was used. The differences from the real intake values, obtained using C31[ratio ]C32 and C33[ratio ]C32 alkane pairs, decreased from 950 and 1260 g/day to 140 and 420 g/day, respectively, for Barrosã cows and from 750 and 1190 g/day to 290 and 90 g/day for Holstein–Friesian cows. The intake estimation using the Cr2O3/AIA procedure was not affected by correcting the CRC release rate, because the release rates of both MRR and the CRR were similar.

The results indicate that controlled-release capsules provide a uniform marker release in cattle, but also suggest that to obtain accurate estimates of intake, it is better to measure release rates within the context of particular experiments.

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.