Bite Area Research Articles

The effects of stem density of tropical swards and age of grazing cattle on their foraging behaviour

AbstractThe effects of stem density of tropical swards and age of cattle on their foraging behaviour were evaluated using artificial microswards, consisting of leaves of 20 cm in height and high tensile‐resisting stems of 25 cm in height of Panicum maximum. The treatments consisted of a factorial combination of four stem densities of swards (0, 100, 200 and 400 stems m−2) and two ages of cattle (1‐ and 3‐year‐old steers). There was a significant interaction between stem density of sward and age of cattle for bite area (BA), bite mass (BM) and instantaneous intake rate (IIR). Stem density had a significant negative effect on these variables describing ingestive behaviour which was particularly strong for older steers. In leaf‐only swards, mature cattle achieved a much greater BA (106·5 vs. 57·9 cm2), BM (0·88 vs. 0·47 g DM) and IIR (46·9 vs. 17·2 g DM min−1) than did young cattle. However, these variables were very similar across ages of cattle at the highest stem density of sward. These results show the importance of the high tensile‐resisting stems as deterrents of the grazing process in tropical pastures, particularly in older cattle.

Foraging mechanics and their outcomes for cattle grazing reproductive tropical swards

For grazing animals an important determinant of animal performance is the rate of nutrient intake (RNI) which depends on diet quality and instantaneous intake rate (IIR). In turn, diet quality and IIR are the outcome of the interaction between the morphology and behaviour of the animal and the structure of the sward. Using artificial microswards of Panicum maximum we evaluated the effect of four levels of the tensile resistance of stems in tropical swards on the grazing behaviour of cattle of two age classes (1- and 3-year-old steers) faced with a stem barrier either in a vertical (experiment 1, E1) or horizontal plane (experiment 2, E2). The animals did not select against low tensile resistance stems (LTRS) but did avoid high tensile resistance stems (HTRS) which resulted in a significant difference ( P < 0.001) between diet DM (dry matter) digestibility and forage DM digestibility in swards with HTRS. IIR decreased ( P < 0.001) on average 62% in E1 and 67% in E2 as stem tensile resistance increased, 144% and 177% in E1 and E2, respectively. This led to a reduction ( P < 0.001) in digestible DM IIR in both young and mature cattle respectively of 56% and 68% in E1, and 45% and 79% in E2, as stem tensile resistance increased. The decline in IIR was due to an increase in time per bite and a reduction in bite dimensions that were the result of different mechanisms in the two experiments: when leaves were taller than the stems (E1) the decrease in bite area was associated with an asymptotic increase ( P < 0.001) in bite force in mature animals, and a maintenance ( P = 0.456) of bite force in young animals, suggesting that maximum bite force regulated bite area in E1. This was not the case in E2 because both bite area and bite force decreased ( P < 0.05) with the increase in stem tensile resistance suggesting that the animals were not able to gather enough plant material with the tongue in order for bite force to regulate bite area. We conclude that bite force and tongue force regulate selectivity and bite dimensions, which are the ultimate determinants of the RNI; IIR is the primary determinant of the RNI with diet quality being of lesser importance; and HTRS act as deterrents to achieving maximum IIR in tropical swards, particularly in mature cattle.

Cross-shelf variation in the role of parrotfishes on the Great Barrier Reef

Herbivorous fishes are a key functional group on coral reefs. These fishes are central to the capacity of reefs to resist phase shifts and regenerate after disturbance. Despite this importance few studies have quantified the direct impact of these fishes on coral reefs. In this study the roles of parrotfishes, a ubiquitous group of herbivorous fishes, were examined on reefs in the northern Great Barrier Reef. The distribution of 24 species of parrotfish was quantified on three reefs in each of three cross-shelf regions. Functional roles (grazing, erosion, coral predation and sediment reworking) were calculated as the product of fish density, bite area or volume, bite rate, and the proportion of bites taken from various substrata. Inner-shelf reefs supported high densities but low biomass of parrotfishes, with high rates of grazing and sediment reworking. In contrast, outer-shelf reefs were characterised by low densities and high biomass of parrotfish, with high rates of erosion and coral predation. Mid-shelf reefs displayed moderate levels of all roles examined. The majority of this variation in functional roles was attributable to just two species. Despite being rare, Bolbometopon muricatum, the largest parrotfish species, accounted for 87.5% of the erosion and 99.5% of the coral predation on outer-shelf reefs. B. muricatum displayed little evidence of selectivity of feeding, with most substrata being consumed in proportion to their availability. In contrast, the high density of Scarus rivulatus accounted for over 70% of the total grazing and sediment reworking on inner-shelf reefs. This marked variation in the roles of parrotfishes across the continental shelf suggests that each shelf system is shaped by fundamentally different processes.

Effects of ruminal fill on short‐term herbage intake rate and grazing dynamics of beef heifers

AbstractThe impact of manipulating ruminal fill (RF) on intake rate of herbage and grazing dynamics was measured with three rumen‐cannulated beef heifers grazing Bermudagrass pastures individually. The treatments compared were removal of proportions of rumen contents of 0 (treatment RF0), 0·33 (treatment RF33), 0·66 (treatment RF66) and 1·00 (treatment RF100). Treatments were randomly applied in a 3 × 4 Youden‐square design. The rumens were emptied before and after planned grazing sessions (30 min) to set up the treatments, and to estimate intake rate and bite mass, respectively. Measurements were made of bite rate, bites per feeding station, feeding stations per minute, intake per feeding station, time per feeding station, eating and searching step rates and times. Apparent bite area and area grazed per feeding station were calculated. Ruminal fill affected short‐term intake rate and changed grazing dynamics. As RF increased, step rates, searching times, bite mass, apparent bite area, bites per feeding station, area grazed per feeding station, time per feeding station and intake per feeding station decreased (P &lt; 0·01) while step times, eating step rates and bite depth increased (P &lt; 0·01). The results of the present study indicate that RF is an important factor governing the intake characteristics and behaviour of grazing beef heifers.

The effect of the density and physical properties of grass stems on the foraging behaviour and instantaneous intake rate by cattle grazing an artificial reproductive tropical sward

AbstractIn reproductive swards, stems appear to act as vertical or horizontal barriers to bite formation, influencing instantaneous intake rate (IIR). The hypothesis was tested that the stems’ barrier effect is determined by the physical properties and density of stems. Artificial microswards, consisting of 20‐cm leaves and 15‐cm stems of Panicum maximum, were offered to three steers (362 kg) in a factorial combination of three stem densities (0, 100 and 400 stems m−2) and two levels of stem tensile resistance [low (LTRS) and high tensile‐resisting stems (HTRS)]. LTRS were not a barrier to defoliation and did not affect bite depth and bite mass. HTRS acted as both a horizontal barrier and a vertical barrier depressing bite depth (13·4, 13·6 and 5·1 cm for 0, 100 and 400 stems m−2, respectively), bite area (89·3, 50·8 and 47·6 cm2 for 0, 100 and 400 stems m−2, respectively), bite mass (0·51, 0·29 and 0·11 g for 0, 100 and 400 stems m−2, respectively) and IIR (23·8, 10·5 and 3·6 g sec−2 for 0, 100 and 400 stems m−2, respectively). The results confirmed the importance of the density and physical properties of stems as determinants of the stems’ barrier effect on bite dimensions and IIR.

A video and acoustic methodology to map bite placement at the patch scale

Bite placement plays an important role in determining the mean weight of bites removed from a patch, and hence intake rate. This paper describes a video and acoustic methodology to map the sequential placement of bites on the sward surface. The methodology was evaluated for dairy heifers grazing small (0.34 m 2) patches of alfalfa ( Medicago sativa L.) to three levels of depletion (6, 18 and 30 bites). Grazing was recorded by a single video camera positioned 0.9 m in front of the animal and on average 1.67 m above the ground. Acoustic monitoring enabled the precise timing of biting jaw movements (bite or chew-bite). For each bite, a single video frame showing the position of the animal's head in the sward canopy was selected at the point in time corresponding to bite severance. Custom image-processing software was used to extract the image (apparent) coordinates of the tip of the muzzle, which was then converted geometrically to world (true) coordinates on the sward surface. A fixed displacement of 8 cm was applied to the world coordinates in order to determine the bite centre. The pattern of grazing impact across the sward surface was predicted by assuming a radius of impact around each bite centre. This pattern was compared with the measured status (grazed or un-grazed) of the herbage beneath each cell of a grid placed over the patch after grazing. Bite placement on the sward surface, as defined by the bite-centre coordinates, followed a progressing, side-to-side pathway. The median distance between the centres of consecutive bites was 12.1 cm, and was significantly less than expected by random bite placement. The orientation of consecutive bite pairs differed significantly from random, consistent with the side-to-side pathway of bite placement. Nevertheless, based on nearest neighbour analysis, the overall pattern of bite spacing on the surface of the sward did not differ significantly from random. These results suggest that the observed declining trend in mean effective bite area with increasing depletion ( P = 0.06) derived from inefficient exploitation of the sward surface. The assumption of a radius of impact of 6 cm revealed a broad correspondence between the measured and predicted patterns of grazing impact across the sward surface. Discrepancies most likely reflected sweeping actions of the tongue during bite formation, lateral head movements during bite severance and simplifying assumptions required by the single-camera approach. The results indicate that the methodology is potentially useful for investigating the rules governing bite placement in the horizontal plane.

EFFECT OF DEGREE OF COMPRESSION ON TEXTURE

ABSTRACTi

Bite dimensions and grazing movements by sheep and cattle grazing homogeneous perennial ryegrass swards

Pairs of ewes or heifers were allowed to graze for short periods from previously prepared ‘homogeneous’ areas of ryegrass, in order to study their bite dimensions and movement patterns and to investigate the role of different species in initiating spatial heterogeneity. Apparent bite area was calculated from number of bites and total bitten area when ewes or heifers took 10–15 bites from an 80 cm×80 cm area in a homogeneous Lolium perenne sward. Apparent bite depth was calculated from sward surface height (SSH) within and adjacent to bitten areas. Apparent bite mass was calculated from grazed stratum bulk density. Incisor arcade breadth was measured. Animals also grazed 20 m×40 m plots for 45 min. Position and activity were recorded and distance travelled calculated. Number of bites and steps, number and duration of grazing bouts, feeding station dimensions and horizontal head sweep were recorded. Bites per bout, per feeding station and per m forward movement, bite rate, inter-bout interval, and distance travelled, speed of movement, number of steps, step length and step rate within and between bouts were calculated. Distribution of grazing bout and inter-bout durations and the animals’ foraging paths were tested for randomness. Apparent bite area for heifers was 2.2 times that for ewes and incisor arcade breadth 1.8 times that for ewes. Apparent bite depths were similar at 0.35 of SSH. SSH distribution within bitten areas was non-normal and differed between animal species. Heifers’ bite mass was 2.1 times that for ewes. Heifers had longer grazing bouts, more feeding stations per bout, moved farther per bout but had similar movement speed while grazing. Distance between feeding stations was similar between species but heifers’ feeding station residence time was twice as long. Heifers’ biting rate was lower but they took more bites per bout, per feeding station and per metre of forward movement. Mean head sweep distance was greater for heifers. Both species moved a similar distance between grazing bouts but ewes moved more slowly with more, shorter steps. For both species, grazing bout and inter-bout durations were not randomly distributed. At a 1 m 2 scale for both species and a 5 m 2 scale for heifers, movement was non-random with a strong propensity to walk in a straight line but at a 5 m 2 scale sheep movement was uniformly distributed on the circle.

Challenges to prevent dengue among German travelers to endemic areas

Nine-year long surveillance for dengue virus infection among Germans returning from a travel to dengue endemic areas by Teichman et al identified at least seventy-one patients with different manifestations of dengue. Their recommendation about a pre travel advice on different aspects of dengue is very appropriate. Nevertheless prospective briefings of travelers against dengue virus infections would be comprehensive only through their appreciation of the fundamental properties of the vector the Aedes aegypti. A. aegypti popularly known as the “yellow fever mosquito” has been responsible for the global endemicity and epidemics of yellow fever virus as well as dengue fever virus. A. aegypti is an early morning or late afternoon feeder but would also bite at night under artificial illumination. Human blood is preferred over other animals and ankles as the favorite bite area. A. aegypti can resist desiccation for up to 1 year; eggs hatch when flooded by deoxygenated water. Larval habitats are artificial containers; larvae feed on the aquatic life that develops in artificial containers. Larvae die at temperatures below 10°C. A. aegypti flies only a few hundred yards from its breeding sites. Unfortunately such fundamental about the so-called “yellow fever” mosquito have not been addressed all the seriously by the practitioners of medicine and public health personnel. (excerpt)

Prospective study of centipede bites in Australia.

There are limited reports of definite bites by centipedes with expert identification, which are required for attribution of particular clinical effects to different species. To describe the clinical effects of centipede bites in Australia. Prospective study of calls regarding centipede exposures to a state poison information center, from December 2000 to March 2002. Information collected included demographics, details of the exposure, local effects, systemic effects, and treatment. Collected centipedes were identified by an expert. All subjects were followed until clinical effects had resolved. Of 48 centipede exposures, 3 were centipede ingestions with no adverse effects and one was a contact reaction to the centipede that resulted in erythema and delayed itchiness. Of 44 definite centipede bites, the centipedes obtained and formally identified in 14 cases were from the genera Scolopendra (5), Cormocephalus (6), and Ethmostigmus (3). Of these 14 bites, 13 occurred distally (hands or feet). Pain occurred in all 14 cases and was severe in 7 patients. Redness/red mark occurred in 53%, swelling/raised area in 43%, and itchiness in 14%. No systemic effects were reported. Ethmostigmus spp. and Scolopendra spp. caused more severe effects. Of the bites, 57% occurred indoors and 50% at night. Treatment consisted of supportive measures including ice packs and simple analgesia, and 4 patients reported pain relief after immersing the bite area in hot water. Similar clinical effects were reported in the other 30 definite centipede bites. Australian centipede bites cause minor effects with moderate to severe pain, associated with localized swelling and erythema in bites by the genera Ethmostigmus and Scolopendra. Hot water immersion may potentially be beneficial for centipede bites. The genus Scolopendra occurs worldwide and the results may have international applicability.

The role of incisors in selective grazing by cattle and horses

To clarify the role of the incisors in selective grazing by cattle and horses, experiments were conducted in July 1999, using three Holstein cattle and three thoroughbred horses to investigate bite weight and bite force using hand-constructed swards with 15 loadcells spaced 6×12 cm apart. Leaves of perennial ryegrass (Lolium perenne: PRG) were mixed with leaves of tall fescue (Festuca arundinacea: TF) or reproductive culms of reed canarygrass (Phalaris arundinacea: RCG).There was little difference between cattle and horses in bite rate, but DM intake rate of horses was almost twice that of cattle in the PRG/TF mixture. In the PRG/RCG mixture, both animals tended to graze only leaves of PRG. Total bite force was 3270–3280 N/min in cattle and 5350–6350 N/min in horses in the PRG/TF mixture. Means of maximum values of one bite force (not total force per bite) were 88±5·5 N in cattle and 141±11·0 N in horses. These values corresponded to 1·6±0·10% of body weight in cattle and 2·2±0·16% in horses, after converting Newton force into kilogram force. Bite area was higher in horses than in cattle. Both cattle and horses did not discriminate between leaves of PRG and TF. In the PRG/RCG mixture, horses prehended both leaves and culms in 33% of total clumps grazed, compared with only 5% in cattle. Many culms escaped from the mouth at the moment of prehension. In mixtures of soft leaves and stiff stems, the lack of upper incisors in cattle may have the advantage over horses. The term ‘comb-out strategy’ is proposed for this selective foraging by cattle. DM intake per bite force was highest in TF leaves (7·5 mg DM/N) grazed by horses and similar (3·7–4·6 mg DM/N) in PRG leaves grazed by both cattle and horses.

Influence of sward height on bite dimensions of horses

AbstractThe management of pastures used by horses poses various problems: swards are often grazed down rapidly, patches of bare ground and refused areas develop. In order to gain a better understanding of the plant-animal interaction behind this problem the influence of sward height on bite dimensions (bite depth, weight, volume, area) of horses was investigated. Perennial ryegrass (Lolium perenne) microswards were grown on artificial substrate to four different heights (3, 8, 15, 19 cm) but the same plant density. Biomass and bulk density for each sward height was determined. Eight horses (predominantly Thoroughbred ×) were allowed to take six bites of each grass height. Bite depth, weight, volume and bite area were calculated.Bite depth, weight, volume and area were not fixed, but increased with sward height (P&lt; 005). For all sward heights, the horses removed between 51% and 68% of the initial grass length. The horses adjusted their bite dimensions to sward height but did not maximize food intake per bite. The response to sward height might be explained by a preference for easily digested food or the trade-off between energy intake and the cost for food processing.This experiment suggests that grass height has a major influence on bite dimensions of horses. However there may be more complex factors influencing ingestive behaviour of horses (e.g. age, dietary experience and social behaviour) that have to be considered when horses are grazing pasture.

Grazing and pasture management for biodiversity benefit

The primary role of grazing animals in grassland biodiversity management is mainte- nance and enhancement of sward structural heterogeneity, and thus botanical and faunal diversity, by selective defoliation due to dietary choices, treading, nutrient cycling and propagule dispersal. Most research on dietary choices uses model systems that require considerable extrapolation to more com- plex communities. Grazing animals' diets are constrained by temporal and spatial changes in sward structure, plant defence mechanisms, herbage availability, plant phenology and animal physiological state. Potentially, these could be exploited to manipulate choice in diverse communities. Dietary choice differs between animal species, driven by factors such as body size, digestive physiology and dental anatomy. There is anecdotal evidence for breed differences but little experimentation, with ge- netic effects often confounded with background experience. There is information about landscape- scale breed and background effects but little about parameters such as bite and feeding station areas that allow reconstruction of the development of small-scale sward patchiness. An experiment at five European sites is examining breed effects on grazing behaviour, structural, floral and faunal diversity, animal production and economic impacts. In another project, calves are being reared by their own mothers or by cows of another breed allowing genetic effects on grazing behaviour to be separated from effects of early experience. 'Designer animals' may be needed to deliver desired grazing behav- iour and biodiversity outcomes, either by breeding or by the use of training and previous experience to manipulate choices. Application of research results requires consideration of conservation goals, whether at landscape, habitat, plant community or plant species level. There is a need to replace stocking rate prescriptions with sward-based methods and to integrate biodiversity goals into inten- sive systems. Major gaps in our knowledge of grazing behaviour and its impact on biodiversity re- main, necessitating greater integration of plant ecophysiology, plant community ecology and animal behavioural ecology research. grazing / biodiversity / pasture management / dietary choices / animal type

The imprints created by cattle grazing short sequences of bites on continuous alfalfa swards

Grazing by cattle on the scale of a single feeding station was studied to determine the patterns of defoliation and bite dimensions in short bite sequences. The sward was a continuous and homogeneous expanse of alfalfa without any imposed patchiness of structure. Treatments were bite sequences of 3, 6, 9 and 12 bites, with the forelegs of the observed animal stationary. Four 18-month-old heifers were used and the treatments were conducted over two grazing cycles. The bite scale defoliation imprints (non-contiguous grazed areas separated by undefoliated vegetation) were marked with white spray paint and photographed for shape and area measurements. The mean pre-grazing plant heights for all lengths of bite sequence were 24.8±0.6 cm (cycle 1) and 20.9±0.7 cm (cycle 2), and the mean grazed (residual) plant heights within the defoliation imprints were 14.4±0.6 cm (cycle 1) and 12.9±0.7 cm (cycle 2). One or more separate defoliation imprints was/were obtained for each length of bite sequence. Each imprint was created by one bite or a number of bites in touching or overlapping locations, and contained few undefoliated plant elements. The bite sequences created a variety of defoliation imprints with irregular, often lobed or fingered shapes, which were clearly related to the number of bites removed. The maximum dimension of the grazed imprint tended to be perpendicular to the orientation of the animal, and increased from 46 and 40 cm in cycles 1 and 2, respectively, after three bites to 76 and 85 cm in cycles 1 and 2, respectively, after 12 bites. The overall mean effective bite areas were 101±6.2 and 115±7.5 cm 2 per bite in cycles 1 and 2, respectively. The mean effective bite area tended to decline with bite number in cycle 1 only, but the effect was not significant in the overall model. In the absence of a discrete, imposed feeding station structure, bite placement may result in depletion without depression. Care should be taken in applying patch depletion curves to continuous swards when these are derived from discrete-patch studies in which patch dimensions constrain bite placement.

Effect of liveweight and pasture height on cattle bite dimensions during progressive defoliation

Five experiments each with a different forage species (wheat, oats, forage sorghum, millet, and lucerne) were performed to determine the effects of cattle liveweight and pasture height, created by progressive defoliation, on bite dimensions and bite weight. In each experiment, 3 levels of liveweight and 3 levels of initial sward heights were used. Sward height had a positive effect on bite depth and bite area, although the effect on bite weight differed among forage species. In general, the effect of liveweight on bite dimensions was not significant. It is concluded that bite area and bite weight are determined principally by pasture structure (e.g. height and bulk density) rather than by mouth dimensions. According to our results, when forage intake or ingestive behaviour are to be explained, pasture measurements should describe successive horizons equal to 50% of pasture height to reflect the bite depth measured in cattle. Also, the results indicate that lighter animals could get a nutritional advantage since they may achieve a relative high bite weight per kg liveweight.

The influence of grass height on bite dimensions of horses

The management and maintenance of swards grazed by horses is known to be a difficult task. In a short period of time (2 to 3 weeks) pastures used for horse grazing develop patches of bare ground, short grass and areas which horses refuse to graze because of faecal contamination. Bite depth and bite area are important in determining the effects of grazing on the vegetation. The dimensions of the bite have been investigated in cattle (Ungar et al., 1999), sheep and goats (Concha, 2000), but not horses. The interaction of the horse with the pasture surface is poorly understood but important to improve management and maintenance of areas grazed by horses. The study reported examines the influence of grass height on bite dimensions, i.e. bite depth, bite volume and bite area of the horse at grazing.

Bite dimensions for cattle grazing herbage at low levels of depletion

The processes that occur during the depletion of a single feeding station by grazing cattle are important to our understanding of intake at larger spatial scales. Factorial experiments were conducted in which feeding stations of different sizes were grazed individually by cattle to various levels of depletion, defined as the number of bites removed. Feeding stations in Experiment 1 (alfalfa) measured 0·11, 0·24 and 0·45 m2, and the numbers of bites removed for depletion levels 1–3 were 35, 70 and 104 m−2 respectively. Feeding stations in Experiment 2 (oats) measured 0·11 and 0·24 m2, and the numbers of bites were 45, 95 and 140 m−2 offered. In both experiments a fourth depletion level (not included in the analysis of variance) determined the maximum voluntary depletion, and exceeded 250 bites m−2 offered. Initial sward height was 20 cm. Bite dimensions were derived from the frequency distribution of residual herbage heights. Treatments were replicated over six and four animals of approximately 500 kg live weight in Experiments 1 and 2 respectively.The mean residual herbage height and the frequency distribution of residual heights indicated that bites were removed predominantly from the top grazing horizon at depletion levels 1–3, with a mean effective bite depth of 8·6 cm. Nevertheless, at the same depletion levels, the mean effective bite area declined from 148 to 87 cm2 in Experiment 1 (alfalfa, Medicago sativa L.) and from 86 to 58 cm2 in Experiment 2 (oats, Avena sativa L.). Feeding station size did not significantly affect mean effective bite area in either experiment.Simulation was used to examine the implications of various overlap rules (from completely random to highly systematic) for within‐grazing‐horizon placement of a circular bite of constant potential area. These rules shaped the relationship between mean effective bite area and number of bites removed per unit sward area offered. Bite placement in which permissible overlap became progressively more lenient as the grazing horizon was depleted, and, with acceptable estimates of potential bite area, yielded results that were similar, though not identical, to those measured. These results can help understanding of the factors that determine the intake gain function at a single feeding station.

Bite horizons and dimensions for cattle grazing herbage to high levels of depletion

A simple model of depletion by a grazing ruminant was tested at high depletion levels and for different sizes of feeding station. The model divides an initially uniform sward profile into grazing horizons, dependent on bite depth, and assumes a constant within‐horizon bite area.Two grazing experiments were conducted using cattle. Uniform areas of oats and alfalfa herbage were grazed individually to a high level of depletion (≈150 bites m–2). Feeding station areas were 0·16, 0·30 and 0·53 m2. Initial sward heights were 10 and 20 cm in oats and 20 cm in alfalfa. Size of area did not significantly affect the observed number of bites removed per square metre, the mean residual herbage height or mass, or the proportion of each grazing horizon depleted, derived from the frequency distribution of residual heights. The mean residual height for all treatment combinations could be explained by assuming a ‘take half’ rule for mean bite depth, and allowing for the derived proportion of the area of each grazing horizon depleted.A simple bite placement simulator was used to generate, for a single grazing horizon and for a given maximum potential area of a bite, the expected relationship among mean effective area of a bite, the proportion of the area of the horizon grazed and the number of bites removed per unit area. The simulator mimics a loosely systematic grazing style. The observed bite numbers and the derived proportions of grazing horizon depleted can be reconciled if the within‐horizon mean effective bite area is not constant but declines as predicted by the bite placement simulator. The implications for the shape of the gain function within a feeding station are discussed.

Analysis of Salivary DNA Evidence from a Bite Mark on a Body Submerged in Water

A female body was recovered after approximately 5.5 h in a river with slow-moving current. On the victim's right breast, a patterned injury was discovered and determined to be from human adult teeth. Evidence was collected according to established techniques including recovery of saliva from the bite mark area despite the body being found submerged in water. DNA analysis by PCR using polymorphic STR markers revealed a DNA profile of mixed origin. In addition to the victim's DNA profile, a genotype contribution from the perpetrator was identified as a minor component. The DNA typing results from the bite mark correlated with the DNA typing results obtained from other biological trace evidence identified from the victim's genital samples. The bite mark and the DNA evidence were used to screen suspects and played an important role in obtaining resolution of this case. Consequently, it is advisable that investigators routinely swab for salivary DNA in bite mark cases, even when the amount is thought to be minimal.

ELISA for the detection of venoms from four medically important snakes of India

A double antibody sandwich enzyme linked immunosorbent assay (ELISA) was developed to detect Echis carinatus venom in various organs (brain, heart, lungs, liver, spleen and kidneys) as well as tissue at the site of injection of mice, at various time intervals (1, 6, 12, 18, 24 h and 12 h intervals up to 72 h) after death. The assay could detect E. carinatus venom levels up to 2.5 ng/ml of tissue homogenate and the venom was detected up to 72 h after death. A highly sensitive and species-specific avidin–biotin microtitre ELISA was also developed to detect venoms of four medically important Indian snakes ( Bungarus caeruleus, Naja naja, E. carinatus and Daboia russelli russelli) in autopsy specimens of human victims of snake bite. The assay could detect venom levels as low as 100 pg/ml of tissue homogenate. Venoms were detected in brain, heart, lungs, liver, spleen, kidneys, tissue at the bite area and postmortem blood. In all 12 human victim cadavers tested the culprit species were identified. As observed in mice, tissue at the site of bite area showed the highest concentration of venom and the brain showed the least. Moderate amounts of venoms were found in liver, spleen, kidneys, heart and lungs. Development of a simple, rapid and species-specific diagnostic kit based on this ELISA technique useful to clinicians is discussed.