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Livestock genomics has gone through a paradigm shift since the advent of genome sequencing that includes Genome-Wide Association Studies (GWAS), Whole Genome Predictions (WGP) and Genomic Selection (GS). Beginning with a brief review of current progress and challenges in livestock GWAS, WGP and GS, opportunities for next generation methods are introduced that unravel the underlying systems genetics of complex traits and provide biologically meaningful and accurate predictions. Genome-Wide Epistasis Association (GWEA) and Weighted Interaction SNP Hub (WISH) network methods are introduced here to unravel complex trait genetics. These methods effectively address the problems of GWAS that have no ability to model and analyze genome-wide genetic interactions and thus do not capture any epistatic variance that could explain part of the missing heritability. Further, the Systems genomic BLUP (sgBLUP) prediction method is introduced in this paper as a next generation WGP or GS tool that can account for and differentiate SNPs with known biological roles in the phenotypic or disease outcomes and potentially increase the accuracy of prediction. It is emphasized that tools that link genetic variants to their functions, pathways and other biological roles will become even more important in the future. These tools include FunctSNP, Postgwas and NCBI2R which are briefly discussed. Genome-Wide Gene Expression (Transcriptomics) analyses using RNAseq technology are briefly discussed with some examples including results from our own pig experiments. In the last part of this review, systems genetics and systems biology approaches are introduced that involve joint modeling and analyses of multi-omics data types from genomics through transcriptomics (microarray and RNAseq), metabolomics to proteomics. It is shown using published studies that these systems approaches are valuable and powerful compared to stand-alone genomic methods in identifying key causal and highly predictive genetic variants for complex traits as well as in building up complex genetic regulatory networks. In all sections, some applications of next generation/-omics methods in livestock species (e.g. feed efficiency, growth, weight gain, fertility and disease resistance in cattle, pigs and sheep) are provided with references to relevant software and tools. In conclusion, this paper reviewed the current progress, lessons and challenges in livestock genomics and its ongoing transition to and opportunities for integrative systems genetics and systems biology in animal and veterinary sciences. Most of these integrative systems genetics and systems biology tools and methods presented here are equally applicable to plant and human genetics and systems biology.

Throughout human history, livestock producers have relied on a vibrant international exchange of genetic resources to achieve improvements in the quality and productivity of their animals. In recent years, however, some observers have argued that changes in the legal, technological, and economic environment now imply that international exchanges of animal genetic resources (AnGR) systematically benefit rich countries at the expense of poor countries. It is argued that international flows of AnGR are displacing the indigenous animal genetic resources of developing countries, and also that the genetic wealth of the developing world is being expropriated by rich countries. In reaction, there have been growing calls for limitations and/or barriers to the exchange of animal genetic resources. These discussions, however, seem to be based on limited information about the magnitude and direction of current trade flows in AnGR. This paper offers an analysis of AnGR trade flows from 1990 to 2005. The paper draws on national-level data from 150 countries that reported information to the United Nations Statistics Division. Three major trade categories were evaluated: live cattle and pigs for breeding, and cattle semen. Over the period studied, Europe and North America were the primary exporters of genetic resources for the species evaluated. OECD countries accounted for 98.7, 92.5, and 95% of cattle semen, live cattle, and swine exports in 2005, respectively. In evaluating the direction of trade between developed (North) and developing (South) countries, North–North trade had the largest magnitude, followed by North–South, South–South, and South–North. The data do not support the notion that Southern genetic resources are being used on a large scale in the North. We believe that importation from South to North is limited by the vast discrepancies in production efficiency and production systems between countries in the North and South. Given the low volume of South–North exchange, it seems doubtful that sufficient revenues could be acquired through a “benefit-sharing mechanism” to have any substantial impact on in situ or ex situ conservation efforts, or to generate benefits for poor livestock keepers in developing countries. We question whether global agreements or restrictions on trade will achieve the desired goal of conserving rare breeds and threatened genetic resources. We also doubt whether these agreements will succeed in improving the well-being of the poor. We suggest that resources instead be urgently employed for conservation and that more direct measures should be taken to aid poor farmers, ranchers, and herders in their efforts to conserve genetic resources.

This paper describes a choice experiment (CE) administered to explore farmer preferences for conservation agreements to conserve rare breeds among a sample of 174 respondents in Transylvania (Romania). The study site was chosen due to the prevalence of small-scale and extensive farm systems threatened by a changing policy environment that is increasing the scale and intensity of production units. Agreement attributes included length of conservation contract (5 or 10 years); scheme structure (community or individual managed conservation programme), and scheme support (application assistance or farm advisory support). A monetary attribute that reflects compensation for scheme participation allows the assessment of farmers’ willingness to accept (WTA) for different contracts. Results suggest 89% of respondents would be willing to farm with rare breeds; cattle and sheep being the most popular livestock option; 40% of farmers were reportedly farming with endangered breeds. However, only 8% were likely to qualify for funding support under current requirements. WTA estimates reveal minimum annual compensation values of €167 and €7 per year respectively, for bovine and ovine farmers to consider enrolling in a contract. These values are comparable to Romanian Rural Development Programme (RDP) support offered to farmers keeping rare breeds of €200 and €10 per year for bovine and ovine farmers respectively. Our estimates of scheme uptake, calculated with coefficient values derived from the CE, suggest rare breed conservation contracts are considered attractive by Romanian farmers. Analysis suggests meeting farmer preferences for non-monetary contractual factors will increase participation.

Numerous Red cattle breeds exist all throughout Europe. Some Red cattle breeds are only used locally in certain regions and are smaller in population size, whereas other Red cattle breeds are used in multiple countries in mainstream production environments. Conservation of local Red breeds is necessary to maintain genetic diversity. Collaboration between local and mainstream Red cattle breeds can increase the genetic potential of the local breed and thereby the success of survival. The aim of this paper was to explore possibilities to increase the genetic potential of local Red cattle breeds by collaboration with a mainstream Red cattle breed, while at the same time conserve the local Red cattle breeds. Three breeds were included in this study; the mainstream Red dairy cattle breed from Denmark, Finland and Sweden (RDC) and two local Red cattle breeds, German Red and White dual-purpose cattle (RDN), and Lithuanian Red (LIR). Each simulation included the RDC breeding program and one local Red breeding program. Simulated time was 30 years, in which the first 20 years were used to build up reference populations and the last 10 years were used to run a genomic selection scheme with varying levels of collaboration between the local and the mainstream breeding program in the different scenarios. The maximum percentage of breeding bulls selected for breeding to the cows in the local breeding program that could originate from the RDC breeding program differed between scenarios, and could be either 0, 20, 50 or 100%. Results show that the maximum rate of genetic gain in the local breeds was reached in the scenarios where maximum 20, 50 or 100% of the breeding bulls could originate from the RDC breeding program. The highest rate of inbreeding was found in the scenario where no RDC bulls were selected in the local breeding programs. However, even with very restricted selection, the breed proportion of the local breeds dropped significantly after ten years of genomic selection. To really conserve a local breed such as RDN or LIR, a different selection strategy is needed.

Genetic improvement programmes should incorporate emerging challenges about environmental concerns into breeding goals. The large volume of pig meat production implies important greenhouse gas (GHG) emissions despite its lower carbon footprint per animal in front of ruminant productions. The different breeding goals considered by swine industry depending on different purebred lines, or line crosses adapted to different market demands and production constraints, could mask the effect of incorporating GHG emissions into selection indexes for improving sow productivity traits in nucleus populations. This paper analysed this effect following a methodological approach consisting in augmenting existing selection indexes derived from profit functions. An index previously described in the literature including litter size at birth, piglet perinatal survival, piglet survival to weaning, age at first conception and weaning to conception interval, was employed. This index was expanded to include GHG emissions calculating the emission intensities per litter, assuming a finished pig market and different scenarios and financial costs of GHG emissions. Results indicated that the inclusion of GHG emissions diminished the economic weight of litter size and piglet survival vs. the age at first conception and the interval weaning to conception, but did not affect significantly the contributions of these traits in the selection indexes. The improvement of sow productivity traits diluted relevantly the GHG emissions per piglet produced, and so, per kg of pork produced. The approach used in this study, despite its limitations in front of bio-economic models, has shown to be a simple and flexible way to analyse the effect of incorporating GHG emissions into existing selection indexes.

The effect of vitamin E supplementation on the growth performance, carcass traits, meat quality, and immune response of male broiler chickens was studied using a meta-analysis. The database was consisted of 51 scientific papers published in peer-reviewed journals. The dependent variables for meta-analysis included final body weight, average daily gain, daily feed intake, feed conversion ratio, vitamin E concentration in the muscle, tissue polyunsaturated fatty acid concentration, lipid peroxidation value, post mortem pH, heterophil to lymphocyte ratio, and total immunoglobulins. Linear mixed models were used to analyze the data. Vitamin E supplementation did not influence growth performance, as the estimated slopes were not different from zero, with P-values equal to 0.92 for final body weight, 0.81 for average daily gain, 0.31 for daily feed intake, and 0.83 for feed conversion ratio. Dietary vitamin E supplementation increased the vitamin E content in the muscle (P = 0.001), did not change the polyunsaturated fatty acid concentration, and decreased the lipid peroxidation (P = 0.01). The immune response was improved, the heterophil to lymphocyte ratio was constant, and the total immunoglobulins were increased (P = 0.037) by dietary vitamin E supplementation. With regard to broiler chicken performance, there seemed to be no relationship between dietary vitamin E supplementation and growth performance. There is ample indication that meat quality and immune response could be improved by dietary vitamin E supplementation.

Horse conformation has been proposed as an indirect indicator of performance, since their genetic correlations are often positive and high. In Pura Raza Espanol (PRE) horses, the selection of conformation traits more related to functionality and performance allows a pre-selection of animals and contributes towards saving costs and increasing the genetic progress. The aim of this paper is to evaluate the predictability of 16 conformation traits (14 body measurements and 2 linear conformation traits) in adult PRE horses, focusing on the conformation traits of foals. The dataset included 155,716 records (82,408 young and 73,308 adult horses) with conformation traits from 142,244 different horses, aged between 1-36 years old. Animals between 1-3 years old were included in the ‘young’ group and older animals in the ‘adult’ group. A univariate General Linear Model procedure followed by a Tukey-post-hoc test were used to assess the statistical significance of non-genetic effects. Heritability values were estimated univariately. The fitted models included breeder, age and inbreeding (F) as covariates, and sex and coat colour as fixed effects. Coat colour and F were significant for 75% and 87.5% of the traits analysed, respectively; and the other effects analysed were significant for all the conformation traits. Heritability values ranged between 0.178±0.0063 and 0.795±0.0098 in young horses, and between 0.273±0.0038 and 0.894±0.0007 in adult horses. The genetic correlations of the conformation traits between young and adult horses were above 0.75 for 93.75% of the conformation traits analysed, which confirms the efficiency of pre-selection in young horses based on conformation features to predict their adult performance.

The aim of this paper is to develop a new specific algorithm (fat- and protein-corrected milk calculation) for dairy goat to be used in life-cycle assessment (LCA) studies. Though the contribution of goat milk to world milk production ranks third, the literature does not report any specific correction for goat's milk. Using the available bibliographic data, a multiple regression was performed that allowed obtaining the relationship between the energy content (EC) and the fat (FC) and protein content (PC) of dairy goat milk. The multiple regression resulting from the 3 variables analyzed through the data drawn from the literature was significant (R2= 0.99; p ≤ 0.001). The equation resulting from the correlation was used to develop algorithms for the calculation of fat- and protein-corrected milk (FPCM) at specific FC and PC. Since FC and PC are very different depending on the goat breed two different groups have been defined: i) goat breeds with FC in milk below 4% (FCB4), and ii) goat breeds with FC in milk above 4% (FCA4). The EC found for the FCB4 group (FC = 3.70 and PC = 3.27) was 728.11 kcal kg−1, while that of the FCA4 group (FC = 4.92 and PC = 3.61) was 860.69 kcal kg−1. After substituting the EC values obtained before, the resulting FPCM equations to calculate specific FC and PC by unit of mass (kg of milk = M), according to each group, are shown below: FCB4 group = FPCM (FC = 3.70, PC = 3.27) = M * [(0.12 * FC + 0.10 * PC + 0.23)]; FCA4 group = FPCM (FC = 4.92, PC = 3.61) = M * [(0.10 * FC + 0.08 * PC + 0.20)]. Finally, the variation between the FPCM values calculated using the specific equation obtained in this study for goats and those previously published (for sheep or modifications made from dairy cattle) was evaluated; in FCB4 group the differences varied between (-) 32% and (+) 14% and in FCA4 group between (-) 21% and (+) 35%. Values are overestimated if sheep's FPCM calculations are used (because sheep milk has higher fat content than goat milk) and underestimated if dairy cattle's FPCM calculations are used (because cow milk has lower fat content than goat milk). In conclusion, the results found in the present study show the need to use a specific FPCM formulation in the LCA equation for goat's milk. Unión Europea, Junta de Andalucía GOP21-GR-16-0016

In this paper, we examine preferences for flooring properties that enhance animal welfare in dairy cattle barns among a sample of Swedish dairy farmers. The findings reveal that respondents differ in their choice of flooring properties that improve farm animal welfare. The findings also show that they consider low-slip risk and the softness of floors to be the most important properties. Findings from a latent variable model revealed that floor packaging and installation, workability and animal welfare are important factors that explain the respondents’ preferences for different types of floors. The findings demonstrate that dairy farmers who prefer soft, low-slip and less abrasive floors are influenced by the way the floors are incorporated and installed into the building design, the ease with which other tasks can be performed after installing the flooring and the welfare that the specific flooring provides for the animals. The findings contribute relevant insights that are needed for the promotion and adoption of farm management practices that improve animal welfare.

Herd health slaughter checks regularly identify enzootic pneumonia-like (EP-like) lesions and pleuritis. The aim of this paper is to determine the associations between these lesions and post-trimming carcass weight. Data were collected on the presence/ absence and severity of EP-like lesions and presence/ absence of pleuritis from pigs at the abattoir. Linear mixed models identified a significant association between an increase in EP-like lesion severity and a decrease in post-trimming carcass weight (P=0.006) at the individual level. Each categorical increase in EP-like lesion severity (5 points step) was associated with a 0.37 kg reduction in post-trimming carcass weight. The presence of EP-like lesions in individual pigs, irrespective of severity (P=0.034) and the presence of pleuritis (P=0.038) were significantly associated with a reduction in post-trimming carcass weight of 1.26 kg and 1.25 kg respectively. The results confirm that the presence of these lesions at slaughter are associated with a significant decrease in production performance which can result in substantial economic implications for producers.

Farmers’ poor levels of knowledge are related to low rates of efficiency and productivity in milk production in Brazil due to problems of information diffusion and innovation. This paper set out to evaluate to what extent efficiency in production and the position of dairy farmers in the social network, formed by the Program for the Development of Dairy Farming (PDPL), affect the diffusion of technical information and technologies in the production chain. The data used in the study were made available by the PDPL technical staff and refer to 31 dairy farmers, located in municipalities in the Zona da Mata micro region of the state of Minas Gerais, who participated in the Program in 2016. Through Social Network Analysis, Data Envelopment Analysis and Agent-Based Modeling, a diffusion model was structured into which information on the technical efficiency of the dairy farmers was incorporated, as well as information about their relationship pattern. The efficiency analysis showed benefits when inefficient farmers sought best practices and the optimal production scale. Through the model created, it was found that the selection of technically efficient dairy farmers for the diffusion process is a good policy, but when the adoption pay-off is low and resources are scarce, selecting central farmers would be the more appropriate policy. Additionally, it was shown that the choice of the initial adopters, adoption and non-adoption pay-off values, and the relationship pattern all influence the diffusion process. The study, thus, suggests a new way of choosing policies to accelerate the diffusion of information and technology in typical dairy systems in Brazil and other countries.

Naturally hornless cattle are called polled. The possibility to introgress the allele responsible (P) for polledness in a cattle population that is more intensively selected for other traits is investigated in this paper. Gene introgression, generally carried out by several steps of backcrossing and selection, takes a long time and may lead to unacceptable genetic loss in other traits or inbreeding. The main objective of the current study was to evaluate the use of genomic selection to speed up the introgression of a target allele in a conventional dairy cattle breeding scheme with overlapping generations. A cattle population and a breeding program were simulated and run over a 12 year selection period. Assuming that the polled population was inferior for overall genetic merit , two selection strategies were evaluated: i) selection on conventional BLUP-EBV (CBLUP); ii) selection on genomic EBV (GEBV) obtained with the genomic relationship matrix used in BLUP (GBLUP). Both selection strategies were applied with (PSEL) and without (NOPSEL) selection for the single polled locus (P). The overall level of genetic merit, the P allele frequency and the inbreeding level (F) in the new born animals were monitored each year, as well as the average genetic gain per year of selection (ΔG). The overall genetic level of new born animals was higher for GBLUP compared to CBLUP, with an average ΔG/year of 8.34% (GBLUP) against 7.49% (CBLUP). The PSEL scenario reduced genetic gain, but P allele frequency increased from 0.130 to 0.415 (CBLUP) and from 0.128 to 0.440 (GBLUP) for PSEL, after 12 years of selection. No substantial changes in allele frequency were recorded for NOPSEL scenarios, both for CBLUP and GBLUP breeding schemes. The overall inbreeding rates for GBLUP were 0.28%/y (NOPSEL) and 0.30%/y (PSEL) and for CBLUP 0.52%/y (NOPSEL) and 0.44%/y (PSEL). In conclusion, application of GS to gene introgression helped to speed up the process of introgression of a gene while simultaneously increasing the genetic gain and reducing the inbreeding rate.

While genetic evaluation systems which combine performance records and pedigree data have been utilized in the beef industry for over four decades, the incorporation of genomic information into genetic evaluation, and the effective implementation of genomic tools within the industry is relatively novel. Genomic technologies have been effectively deployed in the dairy, swine, and poultry industries; however, the beef industry possesses unique challenges for technology transfer. In this paper, we discuss the current limitations of genomic technologies and hindrances to the transfer of these technologies to the beef industry, while also considering opportunities for improved genomic and epigenomic tools needed to surmount barriers to technology adoption.

[EN] The inclusion of genomic information on prediction of breeding values has been explored by the pig breeding industry as molecular techniques evolved. Except for a few successful cases, for example the HAL-1843 (R), the use of genomic information for pig breeding has been limited. The development of SNP chips with high density markers across the genome coupled with new statistical methods allowed genomic selection (GS) to become a common practice. GS application entailed important advantages for pig breeding as it increased the accuracy of the breeding values for selection candidates and offered an opportunity for the practice of new selection strategies. Nevertheless, the application of GS is not straightforward for every target trait and breeding scheme. Many efforts have been done to evaluate the new methods and strategies to efficiently implement GS in pig breeding. Several aspects of the population and breeding objectives must be considered before GS is applied. This paper reviews the current status and challenges faced by pig breeders in the implementation of GS and the future opportunities that may arise as molecular technologies advance. (C) 2014 Elsevier B.V. All rights reserved., This work was partially funded by the Ministerio de Economía y Competitividad, Spain (Project RTA2012-00054-C02-01).

Wolf, B. T., McLean, B. M. L., Davies, O. D., Griffith, J. B. (2014). Performance of purebred Welsh Mountain and cross bred ewes in a hill environment. Livestock Science, 165, 181-188 Paper submitted 9-8-13

The objective of this paper is to model variations in test-day milk yields of first lactations of Holstein cows by RR using B-spline functions and Bayesian inference in order to fit adequate and parsimonious models for the estimation of genetic parameters. They used 152,145 test day milk yield records from 7317 first lactations of Holstein cows. The model established in this study was additive, permanent environmental and residual random effects. In addition, contemporary group and linear and quadratic effects of the age of cow at calving were included as fixed effects. Authors modeled the average lactation curve of the population with a fourth-order orthogonal Legendre polynomial. They concluded that a cubic B-spline with seven random regression coefficients for both the additive genetic and permanent environment effects was to be the best according to residual mean square and residual variance estimates. Moreover they urged a lower order model (quadratic B-spline with seven random regression coefficients for both random effects) could be adopted because it yielded practically the same genetic parameter estimates with parsimony.

Monitoring animal production results in real time is a challenge. Existing management information systems (MIS) in pig production are typically based on static statements of selected key figures. The objective of this paper is to develop a dynamic monitoring system for litter size at herd and sow level, with weekly updates. For this purpose, a modified litter size model, based on an existing model found in the literature, is implemented using dynamic linear models (DLMs). The variance components are pre-estimated from the individual herd database using a maximum-likelihood technique in combination with an Expectation–Maximization (EM) algorithm applied on a larger dataset with observations from 15 herds. The model includes a set of parameters describing the parity-specific mean litter sizes (herd level), a time trend describing the genetic progress (herd level), and the individual sow effects (sow level). It provides reliable forecasting with known precision, on a weekly basis, for future production. Individual sow values, useful for the culling strategy, are also computed. In a second step, statistical control tools are applied. Shewhart Control Charts and V-masks are used to give warnings in case of impaired litter size results. The model is applied on data from 15 herds, each of them including a period ranging from 150 to 800 weeks. For each herd, the litter size profile, the litter size over time, the sow individual effect and sow economic value, are computed. Perspectives for further development of the model can take into account indices including conception rate, service rate, mortality rate etc. Such a model can be used as a basis for developing a new, dynamic, management tool.

Brazil has various species of domestic animals, which developed from breeds brought by the Portuguese settlers soon after the discovery of the country. After being submitted to a long process of natural selection, these breeds present characteristics adapted to specific Brazilian environmental conditions, and are known as “criollo”, “local” or naturalized breeds. From the beginning of the 20th century, some exotic breeds, selected in temperate regions, have begun to be imported, and, although more productive, they do not have adaptive traits, such as resistance to disease and parasites found in the naturalized breeds. Even so, they gradually replaced the native breeds, to such an extent that the latter are in danger of extinction. To avoid further loss of this important genetic material, in 1983 the National Research Center for Genetic Resources and Biotechnology (Cenargen) of the Brazilian Agricultural Research Corporation (Embrapa) decided to include conservation of animal genetic resources among its priorities. The conservation activities have been conducted under the Brazilian Genetic Resources Network — Renargen, and is carried out by various research centres of Embrapa, universities and State research institutions, as well as by private farmers, with a single coordinator at national level, Cenargen. The in situ conservation of cattle, horses, buffaloes, donkeys, goats, sheep and pigs is being carried out by Conservation Nuclei, located in the animal's original habitat. Ex situ conservation is centred at the Brazilian Animal Germplasm Bank (AGB), kept at Cenargen. This is responsible for the storage of semen and embryos of various breeds of domestic animals threatened with extinction. Presently the AGB has almost 60,000 doses of semen and more than 250 embryos, as well as over 7000 DNA samples. An important challenge for this program is to increase awareness within the different segments of society in terms of the importance of the conservation of animal genetic resources. The development and evolution of Renargen and its efforts to facilitate the conservation of genetic resources of livestock in Brazil are described in this paper.

The application of n -alkanes as faecal markers to estimate feed intake and apparent digestibility (DMD ap ) of equines and cattle was studied. Additionally, the effect of using different data on diet composition, known proportions of the diet components (DC1) and those estimated using the alkane markers (DC2), on the accuracy of intake and DMD ap estimates was evaluated. Six mature horses, divided in two groups of three animals (H1 and H2), and three adult non-lactating cows of Asturiana de los Valles breed ( C ) were housed in individual stalls. H1 and C groups were fed on a diet composed of Lolium perenne L . (70%) and heather (30%) and H2 received L. perenne (40%), heather (30%) and Ulex gallii Planchon (30%). The dietary component heather represented the field proportions of different plant species of heathland, namely Erica umbellata L., Erica cinerea L. and Calluna vulgaris L., at this experimental period. All animals received a daily dose of paper pellets containing C 24 , C 32 and C 36 n -alkanes as external markers with the purpose of using different n -alkane pairs of adjacent chain length for feed intake estimations. The results indicated that a period of 3 and 5 days was sufficient for these external markers to reach a steady concentration in faeces of cattle and equines, respectively. In contrast to the results obtained in cattle, the alkane faecal recovery in equines was unrelated to the carbon chain length. Diet composition only affected the faecal recovery of the alkanes C 24 ( P 31 ( P 32 ( P 36 ( P n -alkanes in the digesta. In equines, DMD ap estimates were not affected by the n -alkane (C 27 , C 29 , C 31 and C 33 ) used in the calculations, contrasting with the significant ( P ap estimates. Feed intake estimates were affected by the alkane pair used in the calculations in H1 ( P P C ( P P C . The differences from the known intake values were lower when using C 31 :C 32 alkane pair, overestimating intake in only an average of 4.5, 13.0 and 1.3% in H1, H2 and C , respectively, using DC1 or DC2. The results obtained in this study confirm the accuracy of the n -alkane markers to estimate simultaneously feed intake, apparent digestibility and diet composition of equines and cattle grazing these type vegetation communities.

The present study aimed to evaluate the reliability of the n -alkane technique for estimating herbage intake in beef cattle receiving two different feeding levels (low and high) and to test the effect of different faeces sampling procedures (total faeces samples or rectal grab samples at 8 h intervals) on the n -alkane faecal recoveries and hence on intake estimates. Two consecutive experiments were performed with 11 non-lactating beef cows of “Asturiana de los Valles” breed, fed with lucerne hay at two feeding levels: 1.0 or 1.7 kg DM/100 kg body weight (BW). Animals received a daily dose of paper pellets containing C 24 , C 32 and C 36 n -alkanes as external markers with the purpose of using different n -alkane pairs of adjacent chain length (C 23 /C 24 , C 25 /C 24 , C 31 /C 32 , C 33 /C 32 , C 35 /C 36 ) for intake calculations. A 5-day equilibrium period was sufficient for external marker concentrations and n -alkane pair ratios to reach steady state in faeces. There was no effect of different sampling times (every 8 h) on the faecal excretion of n -alkane pairs C 31 /C 32 and C 33 /C 32 . Grab samples obtained at the time of dosing (0830 h) gave the best estimate of n -alkane pair ratios in total faeces collection. There was a general trend of increasing n -alkane faecal recoveries with increased chain length, although n -alkanes C 30 , C 31 and C 33 showed lower faecal recoveries than expected. n -Alkane recoveries were in general lower at the low feeding level, where an increase in individual variability of natural n -alkane recoveries was observed. At both feeding levels, the n -alkane pairs C 23 /C 24 and C 35 /C 36 gave accurate estimates of the treatment average intake, although the natural n -alkane (C 23 or C 35 ) faecal recoveries showed high individual variability, which could be in part due to analytical bias caused by their extremely low concentration in the diet and faeces. However, the n -alkane pairs C 31 /C 32 and C 33 /C 32 gave the greatest deviations of intake estimates, due to the high discrepancy between the faecal recoveries of natural and dosed n -alkanes. These results demonstrate that in beef cattle, feeding level may have some influence on the relative faecal recoveries of the n -alkane pair used for intake calculations. This effect, together with the high individual variability of n -alkane recoveries, especially under low feeding level, may produce significant deviations of the individual intake estimates.