Drosophila ananassae Doleschall is a cosmopolitan and domestic species. It occupies a unique status among Drosophila species due to certain peculiarities in its genetic behaviour and is of common occurrence in India. Quantitative genetics of sexual and non-sexual traits provided evidence for genetic control of these traits. D. ananassae exhibits high level of chromosomal polymorphism in its natural populations. Indian natural populations of D. ananassae show geographic differentiation of inversion polymorphism due to their adaptation to varying environments and natural selection operates to maintain three cosmopolitan inversions. Populations do not show divergence on temporal scale, an evidence for rigid polymorphism. D. ananassae populations show substantial degree of sub-structuring and exist as semi-isolated populations. Gene flow is low despite co-transportation with human goods. There is persistence of cosmopolitan inversions when populations are transferred to laboratory conditions, which suggests that heterotic buffering is associated with these inversions in D. ananassae. Populations collected from similar environmental conditions that initially show high degree of genetic similarity have diverged to different degrees in laboratory environment. This randomness could be due to genetic drift. Interracial hybridization does not lead to breakdown of heterosis associated with cosmopolitan inversions, which shows that there is lack of genetic co-adaptation in D. ananassae. Linkage disequilibrium between independent inversions in laboratory populations has often been observed, which is likely to be due to suppression of crossing-over and random genetic drift. No evidence for chromosomal interactions has been found in natural and laboratory populations of D. ananassae. This strengthens the previous suggestion that there is lack of genetic co-adaptation in D. ananassae.

To identify the disease-causing gene for a large multi-generational Chinese family affected by familial hypertrophic cardiomyopathy (FHCM), genome-wide screening was carried out in a Chinese family with FHCM using micro-satellite markers, and linkage analysis was performed using the MLINK program. The disease locus was mapped to 1q32 in this family. Screening for a mutation in the cardiac troponin T (cTnT) gene was performed by a PCR and sequencing was done with an ABI Prism 3700 sequencer. A novel C→G transition located in the ninth exon of the cTnT gene, leading to a predicted amino acid residue change from Ile to Met at codon 90, was identified in all individuals with hypertrophic cardiomyopathy (HCM). The results presented here strongly suggest that Ile90Met, a novel mutation in the cTnT gene, is causative agent of HCM in this family.

We have previously shown that laboratory populations of the olive fruitfly Bactrocera oleae come to equilibrium with allele frequencies at the 6-phosphogluconate dehydrogenase (6-PGD) locus markedly different from those of wild populations. In this study, we present new evidence from perturbation experiments in support of the notion that the locus is under selective pressure under laboratory conditions. Eleven populations were started with frequencies at the 6-PGD locus different from the laboratory equilibrium. Over 12 generations, the populations showed a return to the previous equilibrium, indicating a direct and powerful selection pressure on the naturally occurring allozymes of this locus. That is, a marked increase of the F allele followed by a compensatory decrease of allele I. Populations were set up to minimize the effects of associative overdominance, and we discuss the possible influence of this factor. Nucleotide sequence for the 6-PGD F and I alleles revealed two missense mutations at positions 501 and 730 leading to different amino acids among the two alleles.

Population genetics models show that, under certain conditions, the X chromosome is expected to be under more efficient selection than the autosomes. This could lead to ‘faster-X evolution’, if a large proportion of mutations are fixed by positive selection, as suggested by recent studies in Drosophila. We used a multispecies approach to test this: Muller's element D, an autosomal arm, is fused to the ancestral X chromosome in Drosophila pseudoobscura and its sister species, Drosophila affinis. We tested whether the same set of genes had higher rates of non-synonymous evolution when they were X-linked (in the D. pseudoobscura/D. affinis comparison) than when they were autosomal (in Drosophila melanogaster/Drosophila yakuba). Although not significant, our results suggest this may be the case, but only for genes under particularly strong positive selection/weak purifying selection. They also suggest that genes that have become X-linked have higher levels of codon bias and slower synonymous site evolution, consistent with more effective selection on codon usage at X-linked sites.

Obesity and osteoporosis affect millions of Americans. While phenotypically, obesity is negatively correlated with fracture risk, research on a genetic basis for this relationship is lacking. We used males and females from 16 LGXSM recombinant inbred (RI) mouse strains to investigate the genetically mediated relationship between obesity and osteoporosis-related traits. First, heritabilities were estimated for (1) bone morphology properties determined by microCT (femoral and radial diaphyseal bone cross-sectional area and moments of inertia, as well as proximal tibial trabecular bone volume, connectivity density, structure model index, trabecular number, trabecular thickness and trabecular separation), (2) mechanical properties determined by bending tests (femoral and radial rigidity, yield moment, ultimate moment, fracture displacement and post-yield displacement), and (3) effective material properties (femoral and radial modulus of elasticity and ultimate tensile strength). All femoral (H2=43–74%) and tibial traits (H2=31–56%) were heritable; as were 8 of 10 radial traits (H2=21–33%). Eighteen significant genetic correlations were discovered between obesity- and osteoporosis-related phenotypes. Genetic correlations indicate that gene effects associated with increased fat mass and leptin levels are also associated with larger, stronger femora. Gene effects associated with larger, stronger radii and with denser tibiae were also associated with increased fat mass but not with leptin levels. Furthermore, quantitative trait loci (QTLs) previously reported for obesity and leptin levels also had effects on bone morphology, mechanical and material properties. Our results support the use of the LG/J-by-SM/J mouse intercross populations as models for normal, complex genetic variation in obesity, bone properties and their interrelationship.

There are two types of 1-day field tests available for young Swedish Warmblood sport horses; one test for 3-year olds and one more advanced test for 4-year olds. Conformation, gaits and jumping ability are evaluated at both tests. Studies on various genetic parameters were based on about 20 000 tested horses. The data for 4-year olds consisted of 30 years of testing. The aims of the study were to estimate genetic parameters for results from different time periods, and to estimate heritabilities for, and genetic correlations between, traits scored in the two tests. The judgement of traits was shown to have been changed during the 30 years of testing, resulting in changes in higher heritabilities in, and stronger genetic correlations between, later time periods. In the first time period, records showed higher residual and lower genetic variances than in the subsequent time periods. Genetic correlations between traits recorded in the first and last time period deviated considerably from unity. Further studies are needed to investigate how to treat data from the early period in genetic evaluations. Heritabilities were moderate to high for conformation traits (0.24 to 0.58) at both types of tests, except for correctness of legs (0.08). The heritabilities for gait traits were also moderate to high (0.37 to 0.53). For jumping traits, the heritabilities ranged between 0.17 and 0.33. The highly positive genetic correlations (0.82 to 0.99) between corresponding traits tested at the simpler test for 3-year olds and at the ridden test of 4-year olds implied that it would be desirable to include the test results of 3-year olds into the genetic evaluation as breeding values for Swedish Warmbloods for many years has only been based on results from 4-year olds.

The foraging behaviour (grazing time and diet composition), live-weight (LW) changes and parasitic infection (faecal egg counts of gastrointestinal nematodes) of 12 beef cows, 84 ewes and 84 goats suckling their offspring, managed in mixed grazing on heathlands with 24% of improved pasture of perennial ryegrass-white clover, were studied during the years 2003 and 2006. The results showed that goats tended to graze for a longer time, and utilised significantly more heathland vegetation than cattle and sheep, including in their diet in an average of 0.39 herbaceous plants, 0.11 gorse and 0.51 heather over the grazing season, comparing with respective mean values of 0.85, 0.02 and 0.13 in cattle and sheep. Dietary overlap was higher between cattle and sheep (0.76) than between sheep and goats (0.53) or between cattle and goats (0.47). Despite the high performance of autumn-calving cows in spring, sheep had the best LW changes per livestock unit (LU) during the whole grazing season. Goats’ performance per LU was lower than in sheep but higher than in spring-calving cows. Regarding offspring production, lambs had higher LW gains per LU than calves and kids. Mean nematode eggs/g fresh faeces (epg) during the grazing season were higher in goats (91 epg) compared with sheep (34 epg) and cattle (14 epg), particularly from September to December. In conclusion, sheep performed best on these heathlands with improved pasture areas if the entire grazing season was considered, despite the good level of production in spring from autumn-calving cows. The results suggested the complementary use of goats in order to increase the effective utilisation of the available vegetation, achieving production levels similar to those from spring-calving cows. Therefore, mixed flocks of sheep and goats would be the most appropriate sustainable systems from the animal production and vegetation use points of view.

Five morphological fractions (leaf blade, leaf sheath, stem, husk and cob) of stover of five maize genotypes, namely waxy, conventional, fodder, sweet and high-oil maize, respectively, were used to test the effects of genotype and morphological fractions on chemical composition and in vitro fermentation characteristics. The waxy maize had a higher (P < 0.05) stem but lower (P < 0.05) leaf blade proportion and fodder maize had a higher (P < 0.05) leaf blade but lower (P < 0.05) leaf sheath proportion than other genotypes, respectively. Maize genotype had a significant effect (P < 0.001) on the chemical composition of stover parts except for organic matter (OM) concentration. Chemical composition of stover parts was affected (P < 0.001) by morphological fractions. The interaction effects between genotype and morphological fraction on the fiber content of stover parts were significant. Over 0.40 and 0.50 of phosphorus (P) and crude protein (CP) of whole-plant maize stover were averagely contributed by leaf blade. Leaf blade, stem and cob contributed over 0.75 of OM, CP, P and fiber in the whole plant. There were significant effects of genotype and morphological fraction on both in vitro gas production parameters and in vitro organic matter disappearance of maize stovers. The genotype and morphological fraction of maize stover and their interaction had significant effects on NH3-N and total volatile fatty acid concentration and the molar proportion of volatile fatty acid in the supernatant after 72 h of incubation except for valeric acid. The present data indicated that the genotype and morphological fraction of maize resulted in variation in the nutritive value of maize stover.

Red clover and fish oil (FO) are known to alter ruminal lipid biohydrogenation leading to an increase in the polyunsaturated fatty acid (PUFA) and conjugated linoleic acid (CLA) content of ruminant-derived foods, respectively. The potential to exploit these beneficial effects were examined using eight Hereford × Friesian steers fitted with rumen and duodenal cannulae. Treatments consisted of grass silage or red clover silage fed at 90% of ad libitum intake and FO supplementation at 0, 10, 20 or 30 g/kg diet dry matter (DM). The experiment was conducted with two animals per FO level and treatments formed extra-period Latin squares. Flows of fatty acids at the duodenum were assessed using ytterbium acetate and chromium ethylene diamine tetra-acetic acid as indigestible markers. Intakes of DM were higher (P < 0.001) for red clover silage than grass silage (5.98 v. 5.09 kg/day). There was a linear interaction effect (P = 0.004) to FO with a reduction in DM intake in steers fed red clover silage supplemented with 30 g FO/kg diet DM. Apparent ruminal biohydrogenation of C18:2n-6 and C18:3n-3 were lower (P < 0.001) for red clover silage than grass silage (0.83 and 0.79 v. 0.87 and 0.87, respectively), whilst FO increased the extent of biohydrogenation on both diets. Ruminal biohydrogenation of C20:5n-3 and C22:6n-3 was extensive on both silage diets, averaging 0.94 and 0.97, respectively. Inclusion of FO in the diet enhanced the flow of total CLA leaving the rumen with an average across silages of 0.22, 0.31, 0.41 and 0.44 g/day for 0, 10, 20 or 30 g FO/kg, respectively, with a linear interaction effect between the two silages (P = 0.03). FO also showed a dose-dependent increase in the flow of trans-C18:1 intermediates at the duodenum from 4.6 to 15.0 g/day on grass silage and from 9.4 to 22.5 g/day for red clover silage. Concentrations of trans-C18:1 with double bonds from Δ4–16 in duodenal digesta were all elevated in response to FO in both diets, with trans-11 being the predominant isomer. FO inhibited the complete biohydrogenation of dietary PUFA on both diets, whilst red clover increased the flow of C18:2n-6 and C18:3n-3 compared with grass silage. In conclusion, supplementing red clover silage-based diets with FO represents a novel nutritional strategy for enhancing the concentrations of beneficial fatty acids in ruminant milk and meat.

This experiment was carried out to determine the effects of the usage of dried brewing yeast in quail diets on laying performance, egg traits and blood parameters. A total of 240 Japanese quails (Coturnix coturnix japonica) aged 10 weeks were randomly allocated into one control group and three treatment groups. Each group was divided into five replicates as subgroups, comprising 12 quails each. Dried brewing yeast (Saccharomyces cerevisiae) was used at the levels of 1.5%, 3.0% and 4.5% in the diets of the first, second and third treatment groups, respectively. Soyabean meal was replaced with dried brewing yeast. The diets were formulated to be isocaloric and isonitrogenous. The experimental period lasted 18 weeks. Dietary treatments did not significantly affect body weight, daily feed intake, daily protein intake, egg production, egg weight, feed efficiency, mortality, egg shell thickness, egg albumen index, egg yolk index, egg Haugh unit, the percentages of egg shell, albumen and yolk, excreta moisture and small intestinal pH. Inclusion of 3% and 4.5% dried brewing yeast in diets reduced egg yolk cholesterol concentration as mg per yolk and mg per g yolk (P < 0.01). Blood serum cholesterol of groups fed diets with dried brewing yeast was significantly lower (P < 0.01) than that of the control group. Feeding diets containing 3.0% and 4.5% dried brewing yeast resulted in significant increases (P < 0.01) in blood serum levels of total protein, alanine aminotransferase at the end of the experiment. Blood serum levels of uric acid, triglyceride, aspartate aminotransferase and alkaline phosphatase were not affected by dietary dried brewing yeast. It is concluded that dried brewing yeast can be used up to 4.5% in the diets of laying quails without adverse effects on the measured parameters.

Weight of male and female Israeli Holstein calves and yearling gain were analyzed on 285 800 records from 105 935 animals from 458 herds recorded between 1994 and 2007. The difference between the sexes increased until around 400 days, at which point the difference between males and females was 110 kg. Yearling gain, defined as 365 × (weight − 35)/age + 35, was greatest for males at approximately 300 days and for females at 225 days. Yearling gain of male and female calves were highly correlated genetically; thus records from both sexes were combined into a joint genetic analysis. Heritability and repeatability were 0.33 and 0.73 in the analysis of both sexes, and similar in the single-sex analyses. Yearling gain is also highly correlated genetically with various measures of mature cow size. Yearling gain was positively correlated with milk, fat, protein production and somatic cell score, but negatively correlated with fertility and cow survival. Yearling gain was also positively correlated with both the sire and maternal grandsire effects on dystocia, but not with calf mortality. The genetic trend for yearling gain was 0.16 kg/year, while phenotypic trends for first and last weighings were both negative.

A Bayesian procedure was used to estimate linear reaction norms (i.e. individual G × E plots) on 297 518 litter size records of 121 104 sows, daughters of 2040 sires, recorded on 144 farms in North and Latin America, Europe, Asia and Australia. The method allowed for simultaneous estimation of all parameters involved. The analysis was carried out on three subsets, comprising (i) parity 1 records of 33 641 sows of line B, (ii) all parity records of 52 120 sows of line B and (iii) all parity records of 121 104 sows of lines A, B and A × B. Estimated heritabilities ranged from 0.09 to 0.10 (smallest to largest subset) for the intercept of the reaction norms, and were 0.15, 0.08 and 0.02 (ditto) for the slope. Estimated genetic correlations between intercept and slope were −0.09, +0.26 and +0.69 (ditto). The three subsets therefore showed a progressively lower genetic component to environmental sensitivity, and progressively less re-ranking of genotypes across the environmental (herd–year–season) range. In a genetic evaluation that does not include reaction norms in the statistical model, part of the G × E effect remains confounded with the additive genetic effect, which may lead to errors in the estimates of the additive genetic effect; the reaction norms model removes this confounding. The intercept estimates from the largest data subset show correlations with litter size estimated breeding values (EBV) from routine genetic evaluation (without reaction norms included) of 0.78 to 0.85 for sows with one to seven litter records, and 0.75 for sires. Hence, including reaction norms in genetic evaluation would increase the reliability of the EBV of young selection candidates without own performance or progeny data by considerably more than 100 × (1/0.75−1) = 33%. Reaction norm slope estimates turn out to be very demanding statistics; environmental sensitivity must therefore be classified as a ‘hard-to-measure’ trait.

One hundred and sixty pigs were used to evaluate dietary copper (Cu) and zinc (Zn) supplementation on performance, fecal mineral levels, body mineral status and carcass and meat quality. Diets differed in mineral form (MF) (Cu and Zn in the form of proteinate amino acid chelate (organic) or sulfate (inorganic)) and inclusion level (IL) (27 mg/kg of total Cu and 65 mg/kg of total Zn (‘low’) or 156 mg/kg of total Cu and 170 mg/kg of total Zn (‘high’)) according to a 2 × 2 factorial arrangement of treatments. Pigs were used from 25 to 107 kg body weight (BW) and fed their respective diets ad libitum. Blood and fecal samples were collected on days 14 and 77 of the experiment. Blood was analyzed for concentration of Cu and Zn, hemoglobin (Hb), Cu content of red blood cells (RBC Cu) and alkaline phosphatase (ALP) and feces for Cu and Zn concentration. Hot carcass weight (HCW) and backfat depth were measured at slaughter and indices of meat quality were assessed on a section of longissimus thoracis. Liver, kidney and bone samples were collected immediately after slaughter and liver and kidney were tested for Cu and Zn content, while bone was only tested for Zn. Over the entire experimental period (25 to 107 kg BW) no significant treatment differences in average daily gain (ADG) or average daily feed intake (ADFI) occurred; however, feed conversion ratio (FCR) was improved by the inclusion of proteinate amino acid chelate (P = 0.012). Copper and Zn concentrations in feces were in direct proportion to the IL in the diet. Blood mineral levels were within normal physiological ranges in all treatments and tissue Cu and Zn concentrations increased with dietary IL (P < 0.05). Results indicate that Cu and Zn fecal concentrations were reduced by approximately 6-fold for Cu and by 2.5-fold for Zn by feeding 27 mg/kg Cu and 65 mg/kg Zn, in either the proteinate amino acid chelate or the sulfate form, compared with a diet containing 156 mg/kg Cu and 170 mg/kg Zn. This decrease in total dietary Cu and Zn did not reduce performance or mineral status of pigs.

Even though extensive research has examined the role of nutrition on milk fat composition, there is less information on the impact of forages on milk fatty acid (FA) composition. In the current study, the effect of replacing grass silage (GS) with maize silage (MS) as part of a total mixed ration on animal performance and milk FA composition was examined using eight multiparous mid-lactation cows in a replicated 4 × 4 Latin square with 28-day experimental periods. Four treatments comprised the stepwise replacement of GS with MS (0, 160, 334 and 500 g/kg dry matter (DM)) in diets containing a 54 : 46 forage : concentrate ratio on a DM basis. Replacing GS with MS increased (P < 0.001) the DM intake, milk yield and milk protein content. Incremental replacement of GS with MS in the diet enhanced linearly (P < 0.001) the proportions of 6:0–14:0, decreased (P < 0.01) the 16:0 concentrations, but had no effect on the total milk fat saturated fatty acid content. Inclusion of MS altered the distribution of trans-18:1 isomers and enhanced (P < 0.05) total trans monounsaturated fatty acid and total conjugated linoleic acid content. Milk total n-3 polyunsaturated fatty acid (PUFA) content decreased with higher amounts of MS in the diet and n-6 PUFA concentration increased, leading to an elevated n-6 : n-3 PUFA ratio. Despite some beneficial changes associated with the replacement of GS with MS, the overall effects on milk FA composition would not be expected to substantially improve long-term human health. However, the role of forages on milk fat composition must also be balanced against the increases in total milk and protein yield on diets containing higher proportions of MS.

The aims of the study were to measure the mRNA expression of brain-derived neurotrophic factor (BDNF) in bovine oocytes and early embryos derived from in vitro fertilization (IVF), parthenogenetic activation (PA) and nuclear transfer (NT), and to investigate the effects of BDNF on the development of IVF and parthenogenetic embryos. Bovine oocytes matured in vitro for 22 h were in vitro fertilized or parthenogenetic activated. By reverse transcription-PCR and quantitative real-time PCR, we found that germinal vesicle (GV) oocytes, metaphase II (MII) oocytes, 4-cell and 8-cell embryos, morulae, and blastocysts were all shown to express mRNA for BDNF. The mRNA levels for BDNF gene were different in bovine oocytes and IVF embryos at different stages (P < 0.01), with the highest expression in MII oocytes and the lowest expression in 8-cell embryos. The mRNA for BDNF was highly expressed in the PA and IVF blastocysts compared to the NT blastocysts (P < 0.01). Supplementation of culture media with BDNF at the concentration of 40 μg/l caused a significant increase in the rates of in vitro-fertilized blastocyst formation (P < 0.05) and parthenogenetic blastocyst formation (P < 0.05). However, the rate of oocyte cleavage in BDNF groups was not significantly different from that in the BDNF-free control (P > 0.05) after IVF or PA. We have also investigated the effects of BDNF on the growth of granulosa cells, which were used for co-culture of bovine early embryos. The results revealed that supplementation of culture media with 20 μg/l BDNF promoted the growth of granulosa cells (P < 0.01). Taken together, these results provided evidence for the role of neurotrophins in promoting early embryonic development as well as in the growth of granulosa cells by the co-culture system, indicating that BDNF can directly or indirectly promote bovine early embryo development.

Information on 26 434 German Warmblood horses born between 1992 and 2001 was used for multivariate genetic analyses of radiographic health, conformation and performance traits to compare different modes of single- and multiple-trait selection of sires. Results of standardized radiological examinations of 5155 Hanoverian Warmblood horses, conformation evaluations from studbook inspections of 20 603 mares, and performance evaluations from mare performance tests and auction horse inspections of 16 098 horses were used for multivariate genetic analyses. Genetic parameters were estimated with restricted maximum likelihood (REML), and relative breeding values (RBV) were predicted with best linear unbiased prediction (BLUP) in multivariate linear animal models for four radiographic health traits, three conformation traits and five performance traits. Heritability estimates for osseous fragments in fetlock joints (OFF), osseous fragments in hock joints (OFH), deforming arthropathy in hock joints (DAH) and distinct radiographic findings in the navicular bones (DNB) ranged between 0.15 and 0.35 after transformation to the liability scale. Front limb conformation, hind limb conformation, withers height, walk, trot, canter, rideability and free jumping showed heritabilities between 0.09 and 0.49 and additive genetic correlations with OFF, OFH, DAH and DNB ranging between −0.53 and +0.52. Selection of sires was based on RBV or combinations of RBV, with selection for individual traits or traits from one of the three considered trait groups being considered as single-trait selection, and selection for traits from more than one trait group being considered as multiple-trait selection. The selection modes were compared by means of the expected selection response after one generation, calculated as the relative change in the prevalences of the radiographic findings or the mean conformation or performance scores in the offspring of the selected sires when compared with the offspring of all sires. The prevalences of OFF, OFH, DAH and DNB decreased by 30% to 57% after single-trait selection and 14% to 29% after multiple-trait selection, while mean conformation and performance scores increased by up to 4%. The results indicated that it is possible to simultaneously improve the radiographic health of the limbs, limb conformation, quality of gaits and rideability. However, genetic progress in free jumping ability and style could only be achieved by single- or multiple-trait selection with focus on jumping performance.

The aim of this study was to compare rumen pH and time-budget in eight mid-lactation goats receiving two diets in a cross-over design (low-concentrate diet (L): 30% and high-concentrate diet (H): 60% concentrate). Feeding H increased daily intake (4.3 ± 0.08% v. 4.7 ± 0.08% of body weight for L and H, respectively) and daily milk production (3.01 ± 0.130 v. 3.50 ± 0.130 kg/day of 3.5% fat-corrected milk for L and H, respectively). It decreased milk fat and inverted the fat-to-protein ratio (1.07 ± 0.054 v. 0.94 ± 0.054 for L and H, respectively). As suggested by the percentage of time spent with rumen pH below 6.0 (23.4 ± 6.60% v. 39.9 ± 5.88% for L and H, respectively), H was more acidogenic than L. When offered H instead of L, goats spent less time eating (298 ± 17.5 v. 265 ± 17.5 min for L and H, respectively) and ruminating (521 ± 21.0 v. 421 ± 21.0 min for L and H, respectively) but more time resting (352 ± 27.1 v. 459 ± 21.1 min for L and H, respectively) over a 24-h period. They also tended to spend more time drinking (20 ± 2.9 v. 25 ± 2.9 min for L and H, respectively; P = 0.08) when offered H rather than L. These differences in activities were mainly observed during the first hours following feeding. When offered H, goats adapted their feeding behaviour around the feedings, which allowed them to limit the physiological disturbances potentially inducible by H and to increase milk production, without experiencing too much acidosis.

Whether the rumen microbes are able to synthesize and/or degrade long-chain alkanes in anaerobic conditions remains a question to be answered before these hydrocarbons can be confidently used as duodenal flow or rumen transit markers. In this context, an experiment in vitro was carried out to establish whether within a rumen liquor fermentation system, n-alkanes can be derived from de-waxed structures of the plant or from non-alkane wax components (long-chain fatty alcohols, long-chain fatty acids and esters), or may be metabolized by bacteria to other components or to shorter-chain hydrocarbons. Ryegrass was labelled with 14C in growth chambers under controlled conditions in order to use it as a substrate. The labelled material obtained was separated in three fractions: labelled alkanes, labelled de-waxed plant and labelled wax components without the alkanes. These fractions were used for three different incubations in vitro, which objectives were as follows: 1. To check whether rumen bacteria can synthesize alkanes from carbon structures other than waxes (e.g. sugars). 2. To verify whether rumen bacteria can metabolize the n-alkanes to other compounds. 3. To check whether rumen bacteria can synthesize n-alkanes from other carbon compounds from waxes. The results showed that there was neither bacterial synthesis nor metabolism of the n-alkanes in in vitro conditions.