Measurement of dietary nutrient intake in free-ranging mammalian herbivores

Near-Infrared (NIR) Spectroscopy as an Alternative for Predicting n-Alkane Concentration in Excreta of Laying Hens: NIR-Generated Data for Dietary Composition Estimation

N-alkanes offer a promising approach for assessing the nutritional contribution of external sources to the diets of laying hens in free-range production systems. However, traditional laboratory methods, involving extraction, purification and gas chromatographic analysis, are both economically burdensome and time-consuming. Near-infrared spectroscopy (NIRS) is emerging as a viable alternative, with varying degrees of accuracy depending on the chemical nature and concentration of the component of interest. In our research, we focus on the accuracy of NIRS in predicting the concentrations of n-alkanes (C25-C33) in excreta under simulated free-range conditions with two different diets: one containing a commercial feed with minimal n-alkane content and another containing 1% alfalfa on top of the commercial feed. Spectra processing and calibration were tailored for each n-alkane, with NIRS performance influenced by diet type. Notably, plant predictions using NIR-generated data were consistent with laboratory results, despite a slight tendency toward overestimation (3.40% using the NIRS-generated C25-C29-C33 combination versus 2.80% using laboratory analysis). This indicates the potential of NIRS as an efficient tool to assess n-alkanes in excreta of laying hens and, consequently, the nutritional contribution of the free-range environment, providing rapid and cost-effective results.

Quantitative and Qualitative Evaluation of Plant Intake in Laying Hens: n-Alkanes as Predictive Fecal Markers for Dietary Composition Assessment

The shift in animal welfare standards towards free-range housing for laying hens in the EU has raised questions about changes in dietary composition. Accurate assessment of outdoor plant material intake is crucial for effective feeding strategies. This study introduces an approach using n-alkanes as markers to determine plant intake in laying hens, involving n-alkane recovery rate assessment, discriminant analysis and linear equation-solving for both qualitative and quantitative assessment, respectively, considering systematic n-alkane combinations. Two diets: a standard commercial diet and a diet incorporating 1% alfalfa were tested. Chemical analyses showed an altered n-alkane profile due to alfalfa inclusion, resulting a recovery rates ranging from 30-44% depending on the n-alkane type and diet. Statistical analysis revealed significant differences in recovery rates among the different alkanes for the same diets and between the diets for the same alkane, together with an interaction between n-alkane carbon chain length and initial concentration in the diet. The method accurately predicted plant inclusion, with a slight overestimation (2.80%) using the combination C25-C29-C33. Accurate qualitative classification of the animals based on fecal n-alkanes profiles was observed. The study successfully demonstrated the utility of n-alkanes for estimating dietary composition, providing a non-invasive approach for future free-range studies.

Effect of forage type on swallowed bolus mass and a method for counting swallows in dairy cattle

Dry matter intake (DMI) is a primary determinant of milk production in grazing dairy cows and an ability to measure the DMI of individual cows would allow herd managers to formulate supplementary rations that consider the amount of nutrients ingested from grass. The 2 related aims of this experiment were to define the mean number of swallowed boli and mass of the swallowed boli in Holstein-Friesian dairy cattle offered a variety of forages commonly fed in the dairy industry of southeastern Australia, and to evaluate 2 indirect methods for counting the number of swallows. Twelve ruminally-fistulated, lactating Holstein-Friesian cows were randomly assigned to 3 replicated 4 × 4 Latin square designs and offered 4 forages: fresh chicory (FC), fresh perennial ryegrass (RP), alfalfa hay (AH), and perennial ryegrass silage (RS). The experiment was conducted over 28 d with each of 4 periods consisting of 7 d with 3 d of measurement. Forage diets were offered to individual cows following the partial evacuation of the rumen. The first 20 min after forage was offered constituted the measurement period, during which all swallowed boli were manually captured by samplers who placed their hand through the ruminal fistula and over the cardia entrance of the rumen of each cow. Concurrently, microphones and video cameras were used for the indirect measurement of swallows. The average swallowed bolus mass overall was 17.4 g dry matter (DM) per bolus with the lowest mass observed in cows offered FC (8.9 g DM/bolus), followed by RP (14.9 g DM/bolus), compared with cows offered AH (23.6 g DM/bolus) and RS (22.3 g DM/bolus). The swallowing rate was greater in cows offered FC (78 swallows/20 min) than in cows offered RP, AH, and RS (62.3 swallows/20 min). The audio recording method showed greater concordance (Lin's concordance correlation coefficient = 0.90) with the physical capturing of the boli through the rumen, than the video recording method did (Lin's concordance correlation coefficient = 0.54). It is concluded that the mass of the swallowed boli is related to forage type and that using a microphone attached to the cow's forehead can provide an accurate measure of the number of swallows when verified against the actual number of swallows counted by manual interception of the boli at the rumen cardia.

Seasonal shifts in pronghorn antelope (Antilocapra americana) diets under a new lens: Examining diet composition using a molecular technique

Foraging is one of the most fundamental activities contributing to the maximization of an animal's fitness, and thus herbivores must optimize their diet selection and intake to meet their nutrient demands for survival, growth, and reproduction. Using plant DNA barcoding, we determined diet composition of five subpopulations of adult female pronghorn antelope (Antilocapra americana) grazing rangelands in southern and southeastern Idaho, USA. Fecal samples were collected for two years (2018-2019), and across metabolically-important adult female life history stages (late gestation, early lactation, breeding season). Plant DNA barcoding yielded 137 detected species within pronghorn diets across subpopulations and sampling periods with forbs being the most abundant. Pronghorn dietary functional group composition ranged from 52.2-60.3% from forbs followed by shrubs (22.6-28.2%), graminoids (8.7-15.7%), and legumes (5.5-9.6%). Dietary protein intake was also highest from forbs and ranged from 32.4-62.4% followed by graminoids (1.2-43.1%), shrubs (18.7-21.3%), and legumes (2.6-7.4%). We found significant intra- and interannual differences in the mean number of genera-based plant detections in pronghorn diets. Dietary protein intake of cultivated legumes (e.g., alfalfa [Medicago sativa] and sainfoin [Onobrychis viciifolia]) was lower than expected, ranging from <1.0-30.8%, suggesting that even within an agricultural-dominated landscape, factors other than plant nutritional composition contributed to pronghorn diets. Although the plant DNA barcoding technique exhibits limitations, it demonstrated potential for elucidating pronghorn dietary species richness, particularly for plants consumed in small proportions, as well as for observing temporal fluctuations in functional group composition and dietary protein intake explained through the interplay between environmental factors, plant chemical composition, and the animals' physiological needs.

Application of Fourier transform infrared spectroscopy (FTIR) techniques in the mid-IR (MIR) and near-IR (NIR) spectroscopy to determine n-alkane and long-chain alcohol contents in plant species and faecal samples

n-Alkanes and long-chain alcohols (LCOH) have been used as faecal markers to assess the feeding behaviour of both wild and domestic herbivore species. However, their chemical analysis is time-consuming and expensive, making it necessary to develop more expeditious methodologies to evaluate concentrations of these markers. This work aimed to evaluate the use of Fourier Transform Infrared Spectroscopy (FTIR) technology in the near infrared (NIR) and mid infrared (MIR) intervals, for the determination of n-alkane and LCOH concentrations of different plant species and faecal samples of domestic herbivores. Spectra of 33 feed samples, namely L. perenne, T. repens, U. gallii, short heathers (mixture of Erica spp. and Calluna vulgaris), improved pasture grasses (mixture of L. perenne and A. capillaris), heath grasses (mixture of P. longifolium and A. curtissii), improved pasture species (mixture of L. perenne, T. repens and A. capillaris) and herbaceous species (mixture of all herbaceous species found in the plot)) and 181 faecal samples (cattle and horses) were recorded. In order to develop calibrations for the prediction of n-alkanes and LCOH concentrations, partial least squares (PLS) regression was used. Regarding the models developed for plant species, the best results were observed for the calibrations using NIR. The best external validation coefficients of determination (R²v) obtained were 0.90 and 0.79 for LCOH and n-alkanes, respectively. For faecal samples, in the NIR interval, results indicate similar external validation predictions (R²v) for both animal species (0.64). On the contrary, in the MIR interval, differences between cattle (0.70) and horses (0.57) faecal samples in R²v were observed. Regarding the models created for both animal species faeces, LCOH (C₂₆-OH and C₃₀-OH concentrations ranging from 713.3 to 4451.9 mg/kg DM, respectively; R²v values ranging from 0.72 to 0.95) and n-alkanes (C31 and C33 concentrations ranging from 112.8 to 643.2 mg/kg DM, respectively; R²v values ranging from 0.19 to 0.90) present in higher concentrations tended to be those with better estimates. Results obtained suggest that the selection of the technique to be used may depend on the type of matrix, being the homogeneity of the matrices one of the most important factors for its success. In order to improve the accuracy and robustness of the models created for the estimation of the concentrations of these markers using these methodologies, the database (greater variability) used for the calibrations of these models must be increased.

Therapeutic potential of non-starch polysaccharides on type 2 diabetes: from hypoglycemic mechanism to clinical trials

Non-starch polysaccharides (NSPs) have been reported to exert therapeutic potential on managing type 2 diabetes mellitus (T2DM). Various mechanisms have been proposed; however, several studies have not considered the correlations between the anti-T2DM activity of NSPs and their molecular structure. Moreover, the current understanding of the role of NSPs in T2DM treatment is mainly based on in vitro and in vivo data, and more human clinical trials are required to verify the actual efficacy in treating T2DM. The related anti-T2DM mechanisms of NSPs, including regulating insulin action, promoting glucose metabolism and regulating postprandial blood glucose level, anti-inflammatory and regulating gut microbiota (GM), are reviewed. The structure-function relationships are summarized, and the relationships between NSPs structure and anti-T2DM activity from clinical trials are highlighted. The development of anti-T2DM medication or dietary supplements of NSPs could be promoted with an in-depth understanding of the multiple regulatory effects in the treatment/intervention of T2DM.

Different feeding strategies can affect growth performance and rumen functions in Gangba sheep as revealed by integrated transcriptome and microbiome analyses

Due to the harsh environment in the Tibetan Plateau, traditional grazing greatly limits the growth potential of local animals and causes severe ecosystem degradation. This is an urgent issue to be solved, which requires alternative strategies for grazing animals in the Tibetan alpine pastoral livestock systems. This study aimed to investigate the effects of different feeding strategies on growth performance and ruminal microbiota-host interactions in the local breed of sheep (Gangba sheep). Thirty 9-month old Gangba sheep (n = 10 per group) were assigned to natural grazing (G), semi-grazing with supplementation (T), and barn feeding (F) groups (supplementation of concentrate and oat hay) based on body weight. At the end of the experiment (75 d), all sheep were weighed, rumen fluid was obtained from six sheep per group, and ruminal epithelium was obtained from 3 sheep per group. The results showed that: (1) Compared with the G and T groups, the F group significantly increased dry matter intake, average daily gain, and feed conversion ratio of animals. Additionally, Gangba sheep in the F group had higher concentrations of ruminal short-chain volatile fatty acids (VFAs), especially propionate and butyrate (P <0.05) than sheep in the G and T groups. (2) The principal coordinates analysis indicated a significant difference in bacterial composition among different feed strategies. More specifically, the relative abundance of propionate (unidentified F082 and Succiniclasticum) and butyrate-producing (Eubacterium_coprostanoligenes_group) genera were also observed to be increased in the F group, in which unidentified F082 was identified as a differential biomarker among the three groups according to linear discriminant analysis effect size analysis. (3) The dynamics of the rumen epithelial transcriptome revealed that ECM-receptor interactions, focal adhesion, and PI3K-Akt signaling pathways, which are critical in mediating many aspects of cellular functions such as cell proliferation and motility, were upregulated in the F group. In conclusion, under harsh conditions in the Tibetan alpine meadow, barn feeding increased ruminal VFAs concentrations (especially propionate and butyrate), which stimulated gene expression related to cell proliferation in rumen epithelium, appearing to be superior to natural grazing and semi-grazing in gaining body weight of the local Gangba sheep.

The precautionary principle and dietary DNA metabarcoding: Commonly used abundance thresholds change ecological interpretation

Dietary DNA metabarcoding enables researchers to identify and characterize trophic interactions with a high degree of taxonomic precision. It is also sensitive to sources of bias and contamination in the field and laboratory. One of the earliest and most common strategies for dealing with such sensitivities has been to remove all low-abundance sequences and conduct ecological analyses based on the presence or absence of food taxa. Although this step is now often perceived to be necessary, evidence of its sufficiency is lacking and more attention to the risk of introducing other errors is needed. Using computer simulations, we demonstrate that common strategies to remove low-abundance sequences can erroneously eliminate true dietary sequences in ways that impact downstream inferences. Using real data from well-studied wildlife populations in Yellowstone National Park, we further show how these strategies can markedly alter the composition of dietary profiles in ways that scale-up to obscure ecological interpretations about dietary generalism, specialism, and composition. Although the practice of removing low-abundance sequences may continue to be a useful strategy to address research questions that focus on a subset of relatively abundant foods, its continued widespread use risks generating misleading perceptions about the structure of trophic networks. Researchers working with dietary DNA metabarcoding data-or similar data such as environmental DNA, microbiomes, or pathobiomes-should be aware of drawbacks and consider alternative bioinformatic, experimental, and statistical solutions.

Seasonal and agro-ecological associations with feed resource use and milk production of ranging dairy cows in the Southern Ethiopian Rift Valley

Inadequate feed quality and quantity are the major constraints to dairy cow productivity in the southern Ethiopian Rift Valley. Dairy cows thrives predominantly on high-fibre feeds, with a reduced capacity for microbial fermentation in the rumen. Although variations in free-ranging dairy cow rations of the Ethiopian Rift Valley are assumed to depend on season and altitude alias agro-ecological zone, their potential impact on milk production is undocumented. This study evaluated seasonal changes of ranging dairy cow rations and milk production at different altitude regions within the Southern Ethiopian Rift Valley. A cross-sectional field survey using a structured questionnaire was used to collect data from 430 households with distinctive agro-ecology using a structured questionnaire and observation from a total of 340 households. Eighteen major feed types used by dairy farms were identified in the area and categorized into five classes: grazing pasture, cultivated pasture, crop residues, crop aftermath, agro-industrial by-products, and non-conventional feeds. All farmers indicated the continuous use of natural pasture. The daily milk yield was higher during the rainy season than during the dry season. It was also highest in midlands, followed by the highlands and then the lowlands. A significant (P < 0.001) association was found between season and agro-ecological zone and season and milk yield. In the dry season, milk yield had the strongest positive association with access to crop aftermath. This association turned negative in the rainy season, when the use of hay and agro-industrial by-products was most positively associated with milk yield. The higher availability of hay in the midlands agreed with the higher milk production in this zone, especially during the rainy season. Therefore, ranging dairy cows in tropical regions might respond differently to dietary interventions not only because of seasonal changes, but also because of interactions with the agro-ecological zone.

What, how, and how much do herbivores eat? The Continuous Bite Monitoring method for assessing forage intake of grazing animals

Determining herbage intake is pivotal for studies on grazing ecology. Direct observation of animals allows describing the interactions of animals with the pastoral environment along the complex grazing process. The objectives of the study were to evaluate the reliability of the continuous bite monitoring (CBM) method in determining herbage intake in grazing sheep compared to the standard double-weighing technique method during 45-min feeding bouts; evaluate the degree of agreement between the two techniques; and to test the effect of different potential sources of variation on the reliability of the CBM. The CBM method has been used to describe the intake behavior of grazing herbivores. In this study, we evaluated a new approach to this method, that is, whether it is a good proxy for determining the intake of grazing animals. Three experiments with grazing sheep were carried out in which we tested for different sources of variations, such as the number of observers, level of detail of bite coding grid, forage species, forage allowance, sward surface height heterogeneity, experiment site, and animal weight, to determine the short-term intake rate (45 min). Observer (Pexp1  = 0.018, Pexp2  = 0.078, and Pexp3  = 0.006), sward surface height (Pexp2  < 0.001), total number of bites observed per grazing session (Pexp2  < 0.001 and Pexp3  < 0.001), and sward depletion (Pexp3  < 0.001) were found to affect the absolute error of intake estimation. The results showed a high correlation and agreement between the two methods in the three experiments, although intake was overestimation by CBM on experiments 2 and 3 (181.38 and 214.24 units, respectively). This outcome indicates the potential of CBM to determining forage intake with the benefit of a greater level of detail on foraging patterns and components of the diet. Furthermore, direct observation is not invasive nor disrupts natural animal behavior.

Understanding intake on pastures: how, why, and a way forward

An assessment of dietary intake is a critical component of animal nutrition. Consumption of feed resources is the basis upon which feeding strategies and grazing management are based. Yet, as far back as 1948, researchers have lauded the trials and tribulations of estimation of the phenomenon, especially when focused on grazing animals and pasture resources. The grazing environment presents a unique situation in which the feed resource is not provided to the animal but, rather, the animal operates as the mechanism of harvest. Therefore, tools for estimation must be developed, validated, and applied to the scenario. There are a plethora of methods currently in use for the estimation of intake, ranging from manual measurement of herbage disappearance to digital technologies and sensors, each of which come with its share of advantages and disadvantages. In order to more firmly grasp these concepts and provide a discussion on the future of this estimation, the Forages and Pastures Symposium at the 2020 ASAS-CSAS-WSASAS Annual Meeting was dedicated to this topic. This review summarizes the presentations in that symposium and offers further insight into where we have come from and where we are going in the estimation of intake for grazing livestock.

Production, milk iodine, and nutrient utilization in Jersey cows supplemented with the brown seaweed Ascophyllum nodosum (kelp meal) during the grazing season

Kelp meal (KM) is a supplement made from the brown seaweed Ascophyllum nodosum, known to bioaccumulate iodine (I) and to be the richest source of phlorotannins, which can inhibit ruminal proteolysis and microbial growth. The objective of this study was to investigate the effects of KM on production, milk I, concentrations of blood metabolites, apparent total-tract digestibility of nutrients, and CH4 emissions in grazing dairy cows. Eight multiparous Jersey cows averaging (mean ± SD) 175 ± 60 d in milk and 12 primiparous Jersey cows averaging 142 ± 47 d in milk at the beginning of the study were assigned to either 0 g/d of KM (control diet, CTRL) or 113 g/d of KM (brown seaweed diet, BSW) in a randomized complete block design. Diets were formulated to yield a 70:30 forage-to-concentrate ratio and consisted of (dry matter basis): 48% cool-season perennial herbage and 52% partial TMR (pTMR). Each experimental period (n = 3) lasted 28 d, with data and sample collection taking place during the last 7 d of each period. Cows had approximately 16.5 h of access to pasture daily. Herbage dry matter intake increased, and total dry matter intake tended to increase in cows fed BSW versus the CTRL diet. Milk yield and concentrations and yields of milk components were not affected by diets. Similarly, blood concentrations of cortisol, glucose, fatty acids, and thyroxine did not change with feeding CTRL or BSW. However, a diet × period interaction was observed for milk I concentration; cows offered the BSW diet had greater milk I concentration during periods 1, 2, and 3, but the largest difference between BSW and CTRL was observed in period 2 (579 vs. 111 µg/L, respectively). Except for period 2, the concentration of milk I in cows fed KM did not exceed the 500 µg/L threshold recommended for human consumption. Diet × period interactions were also found for serum triiodothyronine concentration, total-tract digestibilities of crude protein and acid detergent fiber, CH4 production, and urinary excretion of purine derivatives. Overall, the lack of KM effects on milk yield and concentrations and yields of milk components indicate that dairy producers should consider costs before making KM supplementation decisions during the grazing season. Future research is needed to evaluate the concentration of I in retail organic milk because of the high prevalence of KM supplementation in northeastern and midwestern US organic dairies and possibly in other regions of the country.

Choices between red clover and fescue in the diet can be reliably estimated in heifers post-weaning using n-alkanes

Measuring diet choice in grazing animals is challenging, complicating the assessment of feed efficiency in pasture-based systems. Furthermore, animals may modify their intake of a forage species depending on its nutritive value and on their own physiological status. Various fecal markers have been used to estimate feed intake in grazing animals. However, plant-wax markers such as n-alkanes (ALK) and long-chain alcohols may provide reliable estimates of both dietary choices and intakes. Still, their use in beef cattle has been relatively limited. The present study was designed to test the reliability of the ALK technique to estimate diet choices in beef heifers. Twenty-two Angus-cross heifers were evaluated at both post-weaning and yearling age. At each age, they were offered both red clover and fescue hay as cubes. Following 3-week acclimation periods, daily intake of each forage species was assessed daily for 10 days. During the final 5 days, fecal grab samples were collected twice daily. The ALK fecal concentrations were adjusted using recovery fractions compiled from literature. Diet composition was estimated using two statistical methods. Post-weaning, dietary choices were reliably estimated, with low residual error, regardless of the statistical approach adopted. The regression of observed on estimated red clover proportion ranged from 0.85±0.08 to 1.01±0.09 for fecal samples collected in the p.m. and for daily proportions once averaged, respectively. However, at yearling age, the estimates were less reliable. There was a tendency to overestimate the red clover proportion in diets of heifers preferring fescue, and vice versa. This was due to greater variability in ALK fecal concentrations in the yearling heifers. Overall, the ALK technique provided a reliable tool for estimating diet choice in animals fed a simple forage diet. Although further refinements in the application of this methodology are needed, plant-wax markers provide opportunities for evaluating diet composition in grazing systems in cattle.

Production, milk fatty acid profile, and nutrient utilization in grazing dairy cows supplemented with ground flaxseed

Flaxseed has been extensively used as a supplement for dairy cows because of its high concentrations of energy and the n-3 fatty acid (FA) cis-9,cis-12,cis-15 18:3. However, limited information is available regarding the effect of ground flaxseed on dry matter intake (DMI), ruminal fermentation, and nutrient utilization in grazing dairy cows. Twenty multiparous Jersey cows averaging (mean ± standard deviation) 111 ± 49 d in milk in the beginning of the study were used in a randomized complete block design to investigate the effects of supplementing herbage (i.e., grazed forage) with ground corn-soybean meal mix (control diet = CTRL) or ground flaxseed (flaxseed diet = FLX) on animal production, milk FA, ruminal metabolism, and nutrient digestibility. The study was conducted from June to September 2013, with data and sample collection taking place on wk 4, 8, 12, and 16. Cows were fed a diet formulated to yield a 60:40 forage-to-concentrate ratio consisting of (dry matter basis): 40% cool-season perennial herbage, 50% partial total mixed ration, and 10% of ground corn-soybean meal mix or 10% ground flaxseed. However, estimated herbage DMI averaged 5.59 kg/d or 34% of the total DMI. Significant treatment by week interactions were observed for milk and blood urea N, and several milk FA (e.g., trans-10 18:1). No significant differences between treatments were observed for herbage and total DMI, milk yield, feed efficiency, concentrations and yields of milk components, and urinary excretion of purine derivatives. Total-tract digestibility of organic matter decreased, whereas that of neutral detergent fiber increased with feeding FLX versus CTRL. No treatment effects were observed for ruminal concentrations of total volatile FA and NH3-N, and ruminal proportions of acetate and propionate. Ruminal butyrate tended to decrease, and the acetate-to-propionate ratio decreased in the FLX diet. Most saturated and unsaturated FA in milk fat were changed. Specifically, milk proportion of cis-9,cis-12,cis-15 18:3, Σn-3 FA, and Σ18C FA increased, whereas that of cis-9,cis-12 18:2, Σn-6 FA, Σ odd-chain FA, Σ<16C FA, and Σ16C FA decreased with feeding FLX versus the CTRL diet. In conclusion, feeding FLX did not change yields of milk and milk components, but increased milk n-3 FA. Therefore, costs and industry adoption of premiums for n-3-enriched milk will determine the adoption of ground flaxseed in pasture-based dairy farms.

Herbivore-Diet Analysis Based on Illumina MiSeq Sequencing: The Potential Use of an ITS2-Barcoding Approach to Establish Qualitative and Quantitative Predictions of Diet Composition of Mongolian Sheep

DNA-barcoding approaches to estimate the diet compositions of grazing animals have received significant attention, and particularly when combined with next-generation sequencing, these techniques have substantially improved in recent years. In this study, the identity and species composition of plant material ingested by Mongolian sheep were estimated through the use of 350 bp ITS2 gene sequences of the vegetation found in fecal samples. Four diets were formulated using varying amounts of eight plant species that are common in the grasslands of northern China. Sixteen Mongolian sheep were taken from pastures and randomly assigned to four groups, and each group received one of four diets. Each sheep was randomly assigned to one of 16 confinement pens and fed its respective diet for 12 consecutive days. Fecal samples were removed from each pen from days 7-12, preserved, and composited for each pen. All herbage species included in the daily diets were detected in each fecal sample, with the exception of Phragmites australis. Moreover, 12 additional different plant species were retrieved from feces of the experimental sheep. The obtained data provided preliminary support for the use of the ITS2 barcode to determine which plants were consumed. Moreover, the proportions of the herbage DNA sequences recovered from sheep feces and those of the herbage masses in the daily diets did not completely match. These results indicate that the non-Gramineae DNA sequences amplified with ITS2 primers (including those of Chenopodium album, Artemisia scoparia, Artemisia tanacetifolia, and Medicago sativa) far exceeded those of the Gramineae species (including Leymus chinensis and Puccinellia distans), which constitute the largest share of the experimental diets. A significant positive correlation (Spearman's ρ = 0.376, P = 0.003) between the actual herbage mass proportions in the experimental diets and the herbage-DNA-sequence proportions provided sufficiently favorable support for the further investigation of DNA barcoding for the quantification of plants in feces. A significant regression coefficient was found between the relative DNA-sequence proportions of L. chinensis ( R² = 0.82, P < 0.0001), P. distans ( R² = 0.64, P = 0.0017), and C. album ( R² = 0.98, P < 0.0001) and their respective herbage mass proportions. The quantitative relationship can be expressed by the linear-regression equations y = 0.90 x - 0.22, y = 0.98 x - 0.03, and y = 5.00 x - 0.25, respectively. Thus, these results demonstrate that dietary-DNA-barcoding methods exhibited potential in providing valuable quantitative information regarding food-item components. However, it should be noted that this explorative data needs to be further improved by using additional genes and by creating a sophisticated reference database, thus enhancing both quality and accuracy of the obtained results.

n-Alkane and long-chain alcohol recovery in moose (Alces alces), a browsing herbivore

Habitat management for herbivores often depends on an understanding of the food habits of animals. Plant cuticular waxes containing nearly indigestible complex mixture of n-alkanes and long-chain alcohols (LCOHs) have recently shown promise for diet analyses, but the accuracy of the technique depends strongly on the efficiency of recovery of the markers in feces. Fecal recovery of n-alkanes and LCOHs from 10 browse stems or leaves and two ensiled grass hays fed to moose (Alces alces (Linnaeus, 1758)) during in vivo digestion trials was investigated. n-Alkanes and LCOHs were extracted using a single-step accelerated solvent extraction technique and the recovery of these cuticular components was calculated from the feces of the animals. n-Alkane recoveries from feces averaged 0.82, ranging from a low of 0.58 (haylage) to a high of 0.95 (browse stems). LCOH recoveries averaged 0.92 across all forages, ranging from 0.80 (haylage) to a high of 1.13 (browse stems). n-Alkane and LCOH fecal recovery increased with increasing chain length, similar to findings in other studies. Although fecal recovery of n-alkanes and LCOHs were variable, we conclude that they are inversely related to forage digestibility, are consistent within forage classes, and are therefore predictable markers for use in assessing herbivore diets.

The use of n–alkanes and other plant–wax compounds as markers for studying the feeding and nutrition of large mammalian herbivores

In the study of the feeding behaviour and nutrition of free-ranging mammalian herbivores, determining what the animals are eating, its quality and quantity can be difficult to accomplish. The measurement processes themselves may disturb the animals’ normal foraging behaviours which can be a major problem in rangeland, forest and other semi-natural environments. Furthermore, animals are likely to select mixtures of plants and their components which differ from the available vegetation. Quantitative measures of diet composition, digestibility, faecal output and intake in individual grazing or browsing animals have depended on the use of faecal markers. These are materials measurable in faeces that originate from the diet (internal markers), or are absent from the diet, but administered by oral dosing (external markers). The ‘ideal’ faecal marker needs complete recovery in faeces, simple and accurate quantitative measurement, inertness in having no effect on the animal or its diet, and similar physical characteristics (in terms of particle size and density) to the digestive tract contents. No individual material or chemical entity has been found which fulfils all of the ‘ideal’ marker attributes. For example, lignin, indigestible acid-detergent fibre (IADF) and ‘chromogen’, have been used as internal markers, but since they are not discrete compounds, analytical methods are empirical., resulting in inconsistent faecal recoveries.

Virtually all higher plants have an outer surface layer of wax, which is usually a complex mixture of aliphatic lipid compounds whose composition differs between plant types, and different parts of the same plant. Plant waxes can be analysed as discrete compounds, are relatively inert, and because the patterns of individual compounds tend to differ between plant species, they offer the potential of enabling measurement of the contributions of specific plant species to the diet. Leaves and floral parts tend to have the highest concentrations; roots have very low levels. The main classes of plant waxes are straight and branched chain alkanes, alkenes, long–chain fatty acids and esters, long–chain fatty alcohols; long–chain fatty aldehydes and ketones and b–diketones. Analysis is usually carried out by a stepwise process of solvent extraction, purification and gas chromatography (GC). Straight–chain alkanes (n–alkanes) have been the most commonly used marker to date, being present as mixtures with chain lengths ranging from 21 to 37 carbon atoms. Over 90% of n–alkanes have odd–numbered carbon chains, with C29, C31and C33alkanes being dominant in most pasture species. Recovery in faeces of plant waxes is high but not complete, and is related to chain length, the longer the chain, the higher the recovery. Correction factors have been measured in a number of herbivore species.

The first application of plant-wax n-alkanes as faecal markers was to determine herbage digestibility in ruminants. Subsequently it was realised that dosed synthetic alkanes could be used to determine faecal output, and hence dosed and herbage alkanes could be concurrently used to estimate intake. This offered substantial advantages over other methods. Furthermore, differences between plant species and parts in their patterns of individual alkanes can be exploited to enable quantitative determination of diet composition from the patterns found in faeces. Since differences in the relative faecal recoveries of individual markers could modify the faecal marker pattern, recovery corrections may be necessary. This approach was first used for measuring the composition of simple dietary mixtures and the intake of dietary supplements to be determined. The use of long-chain fatty alcohols and fatty acids as additional markers offers the potential for more complex diets to be evaluated. The fact that plant-wax alkanes remain attached to particulate dietary residues throughout the ruminant gut, means that they are also good markers for determining the rate of passage of material along the digestive tract

Estimates of digestibility and faecal output obtained from respective natural and dosed n-alkanes will be biased, unless corrections are made to account for incomplete faecal recoveries. However, intake estimates will be unbiased if the faecal recoveries of the two markers are the same. Studies in sheep, cattle and goats have shown plant C33and dosed C32alkanes to have very similar faecal recoveries and thus give unbiased estimates of herbage intake. The alkane method for estimating intake offers advantages over other techniques. It gives individual-animal intakes and can be used where animals are receiving feed supplements. Also, GC analysis allows both plant and dosed markers to be determined at the same time, which limits analytical time, error and bias. Since the ratio of the concentrations in faeces is used, it is not necessary to obtain absolute faecal concentrations.

Alkenes and branched-chain alkanes have been investigated as additional markers for diet composition estimation since they can be quantified in the same GC analysis asn-alkanes. Although alkenes, which tend to be associated with floral plant parts, have low recoveries (25-40%), they can be useful diet composition markers since their recoveries are little affected by chain length. Faecal recoveries of the branched-chain alkanes, fromAgrostis capillarisherbage, were slightly lower (60-65%) than the respectiven-alkanes (C30and C32) of equivalent carbon number (85-90%). These alkanes are rare in forage species, and their practical usefulness as markers for quantitative composition estimation has yet to be tested.

Long-chain fatty alcohols have been shown to be effective diet composition markers. In most plants fatty alcohol concentrations are higher than those of hydrocarbons, and there can be profound differences in composition between species. They may be of particular value for diets containing plants with low alkane concentrations. Faecal recoveries in sheep, liken-alkanes, increase progressively with chain length from about 60% to 90%. It has been shown experimentally that the use of alcohols, together withn-alkanes, is likely to give a better estimate of diet composition in a given situation than n-alkanes alone.

The very long-chain fatty acids of plant cuticular wax (C20-C34), originally suggested as digestibility markers, may also have potential as diet composition markers. Liken-alkanes and long-chain fatty alcohols, the faecal recoveries of plant-wax fatty acids in sheep increase with carbon chain length. Comparisons withn-alkanes and fatty alcohols suggested that the fatty acids were inferior as diet composition markers. This may have been due to the fact that the fatty acid extracts analysed by GC were relatively impure, containing a number of unidentified compounds. The reliability of plant-wax fatty acids as markers may be improved with more effective analytical procedures.

There are a number of ways of calculating the diet composition from marker patterns in the faeces and potential dietary components. A simple approach is to determine a solution from a matrix of simultaneous equations; the number of dietary components must equal the number of markers used. Because, for simple dietary mixtures, there may be more available markers than dietary components, difficulties may arise in making the best choice of marker. Least-squares optimisation methods allow the number of markers to exceed the number of diet components, and thus (in theory) make better use of available information.

Since the concept of using faecal marker patterns for making quantitative diet composition estimates is relatively new, the associated mathematical and statistical procedures used to date have been rather crude and simplistic. There is potential to make more effective use of the marker data by using more sophisticated computational approaches. These include a range of multivariate techniques, including: a) Principal component and discriminant analysis; b) The weighting of the contribution of different markers, since with the leastsquares optimisation procedure, markers with the highest overall concentrations contribute most to the composition estimate, even though some markers with low concentrations may have large relative differences between dietary components. It would logical to weight markers in favour of those having the greatest relative variation across dietary components, and those providing the least compositional information could be weighted against; c) Statistical procedures are needed to evaluate the quality of diet composition estimates. The minimisation procedures described earlier take no account of any within-component variation in marker composition, and the effect of such variation on the quality of resultant diet composition estimate is not known. Attempts are being made to develop statistical procedures which will provide details of confidence intervals of compositional estimates resulting from particular plant species mixtures of known within- and between-species variability in marker composition.

For reliable estimation of digestibility, intake and diet composition, the feed sample must be representative, with respect to its plant wax marker concentration, of the material ingested by the animals under investigation, not necessarily all of the material present. Since marker concentrations can differ for different plant parts and plant species, care must be taken in sampling the vegetation for analysis. Although oesophageal-fistulated animals have been used to collect samples of ingested vegetation, hand-plucked grass samples have been found to be adequate for uniform grass swards,. In heterogeneous vegetation environments, especially when browse species are present, herbivores are likely to be highly selective. It is thus wise to make preliminary observations of animals’ ingestive behaviours, so appropriate parts of the dietary plants are sampled.

The use of plant waxes, initially with alkanes, as markers in the study of the diets of domestic ruminants is finding increasing use in other herbivores, both domesticated and wild (moose, fallow deer, mountain hares, pigs, rabbits, horses, donkeys, giraffes). Such methodologies have been applied in non-mammalian herbivores, including birds (pigeons, and ostriches) and reptiles (tortoises). Synthetic alkanes have been used as markers to estimate digestibility and intake in fish. Although tests have not yet been carried out, plant wax marker methods may even be applicable to non-vertebrate herbivores, such as caterpillars, slugs and snails. Expansion of the technique to include plant wax compounds other than alkanes will broaden the spectrum of animals and systems which can and could be studied. Alkanes can be used to estimate the botanical composition of plant mixtures, including mixed root mats, and since these compounds can remain in soil for a considerable period, they may also be used to describe the vegetation history of an area by analysis of soil strata. There may be potential for this approach to be extended into archaeological and forensic studies. Insects and spiders contain hydrocarbons (mainly branched-chain alkanes) in their cuticular wax, and preliminary tests have indicated that these compounds are recoverable in the faeces of bats and insect-eating birds; thus they could be used to determine the insect species composition of the diets of insectivores. Analysis of these waxes is relatively simple, and although good GC equipment is required, there is scope for laboratories which do not posses the equipment to make the initial extractions and purification (simple but laborious), with the final GC analysis undertaken by a collaborating laboratory. Thus there are many uses of plant and animal waxes as markers, and potential applications are probably limited only by our imagination.

The ability of the n-alkane technique to estimate intake and diet choice of sheep

This study assessed the efficacy of the n-alkane technique to estimate intake and diet composition in animals given single foods or a choice of two. In the first experiment intakes of pelleted ryegrass and lucerne, given either alone or as a choice, were measured in lambs housed indoors in individual pens. Each of the three feeding treatments was given to 12 lambs at two degrees of maturity (0·30 and 0·45 of estimated mature sizes). The 12 lambs were constituted as three replicates of the two sexes of each of two breeds. The measured intakes were compared with those estimated using the n-alkanes C31and C33, found naturally in the foods, and C32, which was given as a dose. On the choice treatment diet composition was estimated using a non-negative least squares procedure and data on C31and C33alone. The agreement between actual and predicted intake was good:R2of 0·938 for log-linear regression with a residual standard deviation of 0·0845. Intake of lucerne when offered alone was slightly yet significantly over-predicted. The proportion of ryegrass in the diet was also accurately predicted (R2of 0·950 and residual s.d. of 0·0398). Using the data on C27and C29, in addition to that on C31and C33, gave a poorer agreement with the observed diet compositions. The low and similar levels of C27in the two foods meant that this n-alkane provided little extra information that could be used to estimate diet composition. In a second experiment faecal samples were collected every 4 hours over a 24-h period in six lambs on ad libitum, and in six lambs on a restricted quantity, of pelleted ryegrass. There was no significant diurnal variation in the ratios of either C31or C33to C32on either ad libitum or restricted feeding. The time of faecal collection within a day should not therefore affect the reliability of the predictions. The study confirmed the value of using n-alkanes in methods to determine the intake of forages by sheep, and that the time of faecal collection within the day does not affect the reliability of these predictions. The results also confirm the utility of the n-alkane method for estimating diet choice, at least with two-component mixtures.

Use of n-alkanes for determination of Kikuyu grass (Pennisetum clandestinum) intake in free-range broilers

N-alkanes, long-chained saturated hydrocarbons occurring in plant cuticles, were used for estimating grass intake in fast-growing, free-range broilers. A total of 1440 as hatched mixed sex Cobb 500 broilers were equally divided between one of four experimental treatments in a 2 by 2 factorial arrangement involving conventional (barn) or free-range (barn and range access) production systems and diets (crude protein: 21%, metabolisable energy: 13 MJ/K) with or without in-feed antibiotic (Zinc Bacitracin: Albac® G 150 antibiotic feed premix, Pfizer Australia Pty Ltd, Sydney, NSW, Australia). Day-old chicks were randomly allocated to 48 pens (12 replicates/treatment) with 30 birds in each pen. Chicks were assigned to treatment diets on Day 1 while free-range access was available to birds from Day 21 onwards. Alkane concentrations in litter were measured and compared with alkane profiles of the intake components (grass, diet pellets and woodchip). Correction for incomplete recovery followed by estimation using a non-negative least square procedure resulted in calculation of total grass intake from the range area. Kikuyu grass consumption was estimated to be 13.5–14.7% of total ‘as-fed’ intake, equating to 6.34–6.78 g of grass per bird per hour of range access in this study. Taking into account grass consumption, this resulted in a significant increase in feed intake by 8.7–8.9% (P < 0.01) and feed conversion ratio from 2.30 to 2.54 points (P < 0.01). It can be concluded that broilers reared under free-range conditions eat a substantial quantity of grass. However, the nutrient profile of grass is not complementary to the formulated ration and its consumption is likely to lead to an array of nutritional changes for the bird, thus affecting performance.

Estimation of herbage intake and digestibility of grazing sheep in Zhenglan Banner of Inner Mongolia by using n-alkanes

To reveal the seasonal dynamics of herbage intake, diet composition and digestibility and clarify the relationship of those with herbage nutrient and botanical composition of grazing sheep in Zhenglan Banner of Inner Mongolia, the n-alkane technique was used to test in sheep grazed during June, August and December. The results showed that the sheep mainly ate Fringed sagebrush, Stipa krylovii and Carex in proportions of 33.5, 17.9 and 21.2%, respectively, in spring. In summer, the sheep consumed cleistogenes, Potentilla tanacetifolia, Thyme, etc; the intake of Fringed sagebrush, Carex and Stipa declined. In winter, Fringed sagebrush accounted for 50.1% of herbage intake, and the intakes of Cleistogenes and Stipa krylovii increased to 15.3 and 18.4%, respectively. Herbage intake by the sheep in spring was 1.8 kg DM/d, and digestibility was 71.4%. Herbage intake and digestibility decreased slightly to 1.7 kg DM/d and 68.4% during the summer, respectively and decreased significantly to 1.2 kg DM/d and 36.4% in winter. There were significant correlations between diet composition and CP content in winter, diet composition and botanical composition in summer. A highly positive correlation between herbage intake and digestibility was observed in grazing sheep.

Integrating spot short-term measurements of carbon emissions and backward dietary energy partition calculations to estimate intake in lactating dairy cows fed ad libitum or restricted

The objective of this study was to use spot short-term measurements of CH4 (QCH4) and CO2 (QCO2) integrated with backward dietary energy partition calculations to estimate dry matter intake (DMI) in lactating dairy cows. Twelve multiparous cows averaging 173±37d in milk and 4 primiparous cows averaging 179±27d in milk were blocked by days in milk, parity, and DMI (as a percentage of body weight) and, within each block, randomly assigned to 1 of 2 treatments: ad libitum intake (AL) or restricted intake (RI=90% DMI) according to a crossover design. Each experimental period lasted 22d with 14d for treatments adaptation and 8d for data and sample collection. Diets contained (dry matter basis): 40% corn silage, 12% grass-legume haylage, and 48% concentrate. Spot short-term gas measurements were taken in 5-min sampling periods from 15 cows (1 cow refused sampling) using a portable, automated, open-circuit gas quantification system (GreenFeed, C-Lock Inc., Rapid City, SD) with intervals of 12h between the 2daily samples. Sampling points were advanced 2h from a day to the next to yield 16 gas samples per cow over 8d to account for diurnal variation in QCH4 and QCO2. The following equations were used sequentially to estimate DMI: (1) heat production (MJ/d)=(4.96 + 16.07 ÷ respiratory quotient) × QCO2; respiratory quotient=0.95; (2) metabolizable energy intake (MJ/d)=(heat production + milk energy) ± tissue energy balance; (3) digestible energy (DE) intake (MJ/d)=metabolizable energy + CH4 energy + urinary energy; (4) gross energy (GE) intake (MJ/d)=DE + [(DE ÷ in vitro true dry matter digestibility) - DE]; and (5) DMI (kg/d)=GE intake estimated ÷ diet GE concentration. Data were analyzed using the MIXED procedure of SAS (SAS Institute Inc., Cary, NC) and Fit Model procedure in JMP (α=0.05; SAS Institute Inc.). Cows significantly differed in DMI measured (23.8 vs. 22.4kg/d for AL and RI, respectively). Dry matter intake estimated using QCH4 and QCO2 coupled with dietary backward energy partition calculations (Equations 1 to 5 above) was highest in cows fed for AL (22.5 vs. 20.2kg/d). The resulting R(2) were 0.28 between DMI measured and DMI estimated by gaseous measurements, and 0.36 between DMI measured and DMI predicted by the National Research Council model (2001). Results showed that spot short-term measurements of QCH4 and QCO2 coupled with dietary backward estimations of energy partition underestimated DMI by 7.8%. However, the approach proposed herein was able to significantly discriminate differences in DMI between cows fed for AL or RI.

Influence of Restricted Grazing Time Systems on Productive Performance and Fatty Acid Composition of Longissimus dorsi in Growing Lambs

Fifty 3-month-old male Tan lambs (similar in body weight) were divided into 5 groups to investigate the effects of different restricted pasture grazing times and indoor supplementation on the productive performances and fatty acid composition of the intramuscular fat in growing lambs. The lambs grazed for different periods of time (12 h/d, 8 h/d, 4 h/d, 2 h/d, and 0 h) and received various amounts of supplementary feedings during the 120-day trial. Pasture dry matter intake (DMI), total DMI, average daily gains and the live body weights of the lambs were measured during the experiment. The animals were slaughtered at the end of the study, their carcass traits were measured, and their longissimus dorsi muscles were sampled to analyze the intramuscular fat (IMF) content and fatty acid profiles. The results indicated that the different durations of grazing and supplementary feedings affected the animal performances and the composition of fatty acids. Grazing for 8 h/d or 2 h/d with the corresponding supplementary concentrate resulted in lambs with higher body weights, carcass weights and IMF contents. Lambs with longer grazing times and less concentrate accumulated more healthy fatty acids such as conjugated linoleic acid and n-3 polyunsaturated fatty acid and had higher n-3/n-6 ratios. Overall, a grazing allowance of 8 h/d and the corresponding concentrate was recommended to maintain a high quantity and quality of lamb meat.

Continuous bite monitoring: a method to assess the foraging dynamics of herbivores in natural grazing conditions

Accurate estimates of bite mass and variations in the short-term intake rate of grazing herbivores has been historically considered as a fundamental methodological difficulty, a difficulty that increases with the complexity of the feeding environment. Improving these methodologies will help understand foraging behaviours in natural grazing conditions, where habitat structure and interactions among different forages influence feeding decisions and patterns. During the past 30 years, we have been developing the ‘continuous bite-monitoring’ method, an observational method that allows continuous assessment of foraging behaviours, including bite mass, instantaneous intake rate and food selection, in simple to complex feeding environments. The centrepiece of the method is a ‘bite-coding grid’ where bites are categorised by structural attributes of the forage to reflect differences in bite masses. Over the years, we have been using this method with goats, sheep, llamas and cattle across a range of different habitats. After reviewing the development of the method, we detail its planning and execution in the field. We illustrate the method with a study from southern Brazilian native Pampa grassland, showing how changes in the forages consumed by heifers strongly affect short-term intake rate during meals. Finally, we emphasise the importance of studying animals grazing in their natural environments to first identify the relevant processes that can later be tested in controlled experiments.

Prediction of diet quality for sheep from faecal characteristics: comparison of near-infrared spectroscopy and conventional chemistry predictive models

This study evaluated the ability of equations developed from the analysis of faecal material by conventional chemistry (F.CHEM), and by near-infrared spectroscopy (F.NIRS), to predict intake and digestibility of forages fed with or without supplements. In vivo datasets were obtained using 30 sheep and 25 diets to provide 124 diet–faecal pairs, with each sheep fed four or five of the diets. The diets were five forages fed alone or with urea, molasses, cottonseed meal or sorghum grain supplements. Ninety-nine diet–faecal pairs were selected at random, but ensuring that all diets were represented and both the F.CHEM and F.NIRS prediction equations were developed from this dataset. The remaining 25 diet–faecal pairs were used as a validation dataset. Regressions for F.CHEM were developed by stepwise regression, and F.NIRS prediction equations were developed by partial least-squares regression. Prediction equations based solely on faecal analyte concentrations (F.CHEMc) had poor predictive ability, and models incorporating faecal constituent excretion rates (F.CHEMe) were the best at predicting feed constituent intakes. These models had slightly lower standard errors of prediction (SEP) for organic matter (OM) intake and digestible OM intake compared with the F.NIRS models that did not include faecal excretion rates. However, F.NIRS models had lower SEP for protein intake and OM digestibility. Good agreement between the F.CHEMe and F.NIRS methods was evident (according to the 95% limits-of-agreement test), and both predicted the reference values precisely and with small bias. Equations derived from a dataset that included representatives of all diets used in the experiment gave much better prediction of diet characteristics than those developed from a dataset constructed entirely at random. Equations for F.NIRS developed in this way successfully predicted the characteristics of diets that included forages fed alone and with the type of supplements used in tropical Australia.

The trials and tribulations of estimating the pasture intake of grazing animals

The present paper reviews estimation methods for measuring pasture intake of individual grazing animals, in particular, the use of indigestible plant markers. Natural alkanes and alcohols function essentially as an internal marker and thus accommodate differences in forage digestibility among individuals and those arising from interactions between supplement and forage. An estimate of diet composition partitions total intake into its component plant species. Estimates of diet composition require correction for incomplete faecal marker recovery, where relative recoveries (i.e. the recovery of the alkanes relative to each other) suffice. If estimates of whole-diet digestibility are also wanted, actual faecal alkane recoveries must be used. Using known labelled supplement intakes as a means of estimating the intake of all other diet components avoids the need to dose animals separately with synthetic alkanes. The results, problems and possible workarounds for a commercial system under development to estimate individual animal pasture intakes using known labelled-supplement intakes are outlined. A prototype bin system was trialled and, despite many initial technological problems, it showed enough promise for Sapien Technology to continue to develop the system with Proway Livestock.

Using n-alkanes to estimate diet composition of herbivores: a novel mathematical approach

N-alkanes are long-chain saturated hydrocarbons occurring in plant cuticles that can be used as chemical markers for estimating the diet composition of herbivores. An important constraint of using n-alkanes to estimate diet composition with currently employed mathematical procedures is that the number of markers must be equal or larger than the number of diet components. This is a considerable limitation when dealing with free-ranging herbivores feeding on complex plant communities. We present a novel approach for the estimation of diet composition using n-alkanes which applies equally to cases where the number of markers is lower, equal or greater than the number of plant species in the diet. The model uses linear programming to estimate the minimum and maximum proportions of each plant in the diet, and avoids the need for grouping species in order to reduce the number of estimated dietary components. We illustrate the model with two data sets of n-alkane content of plants and faeces obtained from a sheep grazing experiment conducted in Australia and a red deer study in Portugal. Our results are consistent with previous studies on those data sets and provide additional information on the proportions of individual species in the diet. Results show that sheep included in the diet high proportions of white clover (from 0.25 to 0.37), and relatively high proportions of grasses (e.g. brome from 0.14 to 0.26) but tended to avoid Lotus spp. (always less than 0.04 of the diet). For red deer we found high proportions of legumes (e.g. Trifolium angustifolium and Vicia sativa reaching maximum proportions of 0.42 and 0.30 of the diet, respectively) with grasses being less important and Cistus ladanifer, a browse, also having relevance (from 0.21 to 0.42 of the diet).