Animal health and greenhouse gas intensity: the paradox of periparturient parasitism.

Here we provide the first known direct measurements of pathogen challenge impacts on greenhouse gas production, yield and intensity. Twin-rearing ewes were ad libitum fed pelleted lucerne from day -32 to 36 (day 0 is parturition), and repeatedly infected with 10,000 Teladorsagia circumcincta infective larvae (n=16), or sham-dosed with water (n=16). A third group of 16 ewes were fed at 80% of uninfected ewes' feed intake during lactation. Methane emissions were measured in respiration chambers (day 30-36) whilst total tract apparent nutrient digestibility around day 28 informed calculated manure methane and nitrous oxide emissions estimates. Periparturient parasitism reduced feed intake (-9%) and litter weight gain (-7%) and doubled maternal body weight loss. Parasitism reduced daily enteric methane production by 10%, did not affect the methane yield per unit of dry matter intake but increased the yield per unit of digestible organic matter intake by 14%. Parasitism did not affect the daily calculated manure methane and nitrous oxide production, but increased the manure methane and nitrous oxide yields per unit of dry matter intake by 16% and 4%, respectively, and per unit of digestible organic matter intake by 46% and 31%, respectively. Accounting for increased lucerne input for delayed weaning and maternal body weight loss compensation, parasitism increased the calculated greenhouse gas intensity per kg of lamb weight gain for enteric methane (+11%), manure methane (+32%) and nitrous oxide (+30%). Supplemented with the global warming potential associated with production of pelleted lucerne, we demonstrated that parasitism increased calculated global warming potential per kg of lamb weight gain by 16%, which was similar to the measured impact of parasitism on the feed conversion ratio. Thus, arising from a pathogen-induced feed efficiency reduction and modified greenhouse gas emissions, we demonstrated that ovine periparturient parasitism increases greenhouse gas intensity. This implies that ewe worm control can not only improve production efficiency but also reduce the environmental footprint of sheep production systems.

The use of conditioned place preference to determine broiler preferences for quantitative or qualitative dietary restriction.

1. Calcium propionate (CAP) may improve the welfare of feed restricted broiler breeders by improving their satiety when included within the feed ration. However, the evidence for this is mixed. 2. This study used a closed economy conditioned place preference (CPP) task and aimed to identify whether broilers (as a model for broiler breeders) preferred an environment associated with quantitative food restriction (QFR) or an environment associated with a diet quality-adjusted by the inclusion of CAP. Birds taught to associate different environments with QFR and ad libitum (AL) access to feed were used to validate the methodology. 3. The two treatment groups were (1) QFR/AL (n = 12) in which birds alternated every 2 d between QFR and ad libitum access to food, and (2) QFR/CAP (n = 12) in which birds alternated every 2 d between QFR and QFR + calcium propionate (increased from 3-9% over the study period). Birds were taught to associate one diet option with vertical stripes and the other with horizontal black and white stripes. Each bird was tested twice for a CPP (once per diet). 4. QFR/AL birds showed a significant preference for the pen associated with ad libitum access to feed, but only when tested hungry (i.e. fed QFR on day of testing). QFR/CAP birds did not show a preference under either hunger state. 5. Reasons for the failure of QFR/CAP birds to show a preference are unclear but could include a lack of preference or failure to learn the task. 6. The existence of state-dependent effects indicates that care is needed in the design of future CPP studies and that the effect of calcium propionate and level of hunger on ability to learn a CPP needs further investigation.

The effects of acute versus chronic health challenges on the behavior of beef cattle.

The changes in behavior associated with a (subclinical) acute and a chronic health challenge were investigated to assess their potential value for the development of an early disease detection system in beef cattle. The hypothesis was that acute challenges would lead to acute but transient changes in behavior, whereas the converse would be the case during chronic challenges, with changes taking longer to develop, but being more persistent. For this purpose, Holstein-Friesian beef bulls were challenged either with a repeated lipopolysaccharide (LPS) intravenous bolus given at 3 increasing doses over the course of 5 d, or with a single dose of the abomasal parasite Ostertagia ostertagi, acting as models of acute and chronic challenge respectively. A third unchallenged group acted as controls. Fecal and blood samples were taken regularly and analyzed for fecal egg counts (FEC), pepsinogen concentration and LPS antibodies. A sensor was fitted to the front leg of each bull to record activity and posture. Video recordings were taken to monitor drinking and feeding behavior. Antibodies to LPS were detected only after the third LPS challenge. Fecal egg counts were detected 3 wk post infection, and pepsinogen increased roughly at the same time in parasitized bulls. Body weight of parasitized animals was reduced relative to controls after 17 d post infection (P < 0.001), whereas there was no difference in performance between the LPS and control animals (P > 0.05). Effects of LPS on behavior lasted only for a few hours, presenting themselves as reduction in activity approximately 10 h after the first challenge (P = 0.057). The clearest behavioral changes due to parasitism were on posture. Parasitized animals had less frequent (P = 0.003), but longer lying episodes (P = 0.038) than controls. Once established, these changes persisted for 30 d post infection. However, there was no treatment effect on overall activity, measured by the number of steps taken or on total lying time (P > 0.05). Frequency of feeding and drinking episodes and their duration were not affected by health challenge (P > 0.05); however there was an increase in average duration of feeding (P = 0.013) for the parasitized animals. Even though the parasite challenge had significant effects on several aspects of behavior, these may be considered too subtle to be useful indicators of disease; however when used with other measurements, they may prove helpful for the early detection of disease in beef cattle.

Genetic parameters of feeding behavior traits and their relationship with live performance traits in modern broiler lines.

Current selection goals in broiler breeding focus on the improvement of live performance traits, such as feed intake, BW, and feed conversion ratio (FCR). The use of electronic feeders allows measurement of feed intake of individuals housed in groups as well as the identification of different feeding behaviors. Feed intake can thus be split into underlying feeding behavior traits, allowing the estimation of genetic correlations and assessment of the genetic consequences of selecting for performance traits on feeding behavior traits. To investigate the genetic relationships between performance traits and feeding behavior, data of visits to feeders by birds from 4 lines of broilers that differed in selection focus on growth and FCR were analyzed. Visits were recorded electronically and grouped into meals using an existing model for estimating meal criteria. Mean individual feeding behavior traits were then calculated across the entire test period (2 to 5 wk of age). Records were available for between 14,000 and 18,000 birds/line. Analyzed feeding behavior traits were meals per day, meal size, visits per meal, meal duration, nonfeeding time in meal, time feeding per day, proportion of meal spent feeding, feeding rate, and ADFI. Analyzed performance traits were 35-d BW, total feed intake over the entire test period, and FCR. All feeding behavior traits showed moderate to high heritabilities (0.24 to 0.57) but low genetic correlations with performance traits (-0.20 to 0.18), except for ADFI, which was moderately correlated with total intake on test (0.57) and highly correlated with FCR (0.91). The low genetic correlations indicate that the difference in selection intensity among lines for these performance traits has had limited effect on feeding behavior. Different feeding strategies that would result in favorable breeding values for FCR were identified, adding opportunities for further improvements in feed efficiency within and across environments.

Short-term feeding behaviour has a similar structure in broilers, turkeys and ducks.

1. This study is the first to quantitatively compare the structure of feeding behaviour of broilers, ducks and turkeys as recorded by electronic feeders. It tests the hypothesis that this structure is so similar that the same models would be suitable to group the feeding behaviour of these species into meals. 2. Visits to electronic feeders were recorded from 3470 broilers, 3314 turkeys and 480 ducks. The frequency distributions of the length of short intervals between visits to feeders varied between species as a result of differences in the number of visits within a feeding bout, the frequency of re-visits to the same feeder and probably in the likelihood of birds drinking within meals. 3. The lengths of longer day-time intervals between visits to feeders were all log-normally distributed. Disaggregation of these intervals by feeding strategy (meal frequency) showed that the probability of birds starting to feed increased with time since feeding last in all species, which is consistent with the satiety concept. 4. Two methods, one based on fitting a truncated log-normal, function, the other on observed changes in the probability of birds starting to feed with time since last feeding, gave very similar meal criteria estimates. These ranged from 1050 to 1200 s in broilers, 1650 to 1725 s in ducks and 1250 to 1320 s in turkeys. 5. There were large between-species differences in the average number of daily meals, intake per meal, and feeding rate. Despite this variation, the overall structure of feeding behaviour of broilers, ducks and turkeys was so similar that the same models were suitable for application in all three species. This would allow for standardised analyses of feeding behaviour of different avian species kept in different husbandry systems.

Efficiency of energy utilisation and voluntary feed intake in ruminants.

Energy requirements of animals are most readily expressed in terms of net energy (NE), while the energy yield of feed is, at least initially, expressed in terms of metabolisable energy (ME). Energy evaluation systems 'translate' NE requirements into ME requirements (ME systems) or assign NE values to feeds (NE systems). Efficiency of ME utilisation is higher for maintenance than for production and the NE yield of a feed varies, therefore, with ME intake. In addition, energetic efficiency for maintenance and production is thought to be different for lactating and non-lactating animals and to be affected by diet quality. As a result, there are currently many national energy evaluation systems that are complex, differ in their approach and are, as a result, difficult to compare. As ruminants in most production systems are fed ad libitum, this is also the most appropriate intake level at which to estimate energetic efficiency. Analyses of older as well as more recent data suggest that ad libitum feeding (i) abolishes the effects of diet quality on energetic efficiency (almost) completely, (ii) abolishes the differences between lactating and non-lactating animals (almost) entirely and (iii) results in overall energetic efficiencies that are always close to 0.6. The paper argues that there is now sufficient information to develop an international energy evaluation system for ad libitum fed ruminants. Such a system should (i) unify ME and NE systems, (ii) avoid the systematic bias and large errors that can be associated with current systems (iii) be simpler than current systems and (iv) have as a starting point a constant efficiency of ME utilisation, with a value of around 0.6. The remarkably constant efficiency of ME utilisation in ad libitum fed ruminants could be the result of energetic efficiency as well as feed intake regulation being affected by the same variables or of a direct role of energetic efficiency in feed intake regulation. Models to predict intake on the basis of the latter hypothesis are already available for non-reproducing ruminants but remain to be developed for reproducing animals.

Effects of maternal protein nutrition and subsequent grazing on chicory (Cichorium intybus) on parasitism and performance of lambs.

Forty-eight 4- to 5-yr-old Blackface x Bluefaced Leicester (Mule) ewes and their 24-d-old twin lambs were used to assess the effects of maternal protein nutrition and subsequent grazing on chicory (Cichorium intybus) on performance and parasitism. The experiment consisted of 2 grazing periods: safe pasture period and experimental pasture period. During an adaptation period of 66 d, ewes were infected through oral dosing with Teladorsagia circumcincta infective larvae (3 d per wk) and were supplemented with protein (HP) or not (LP) for the last 45 d of this period. At the end of this period, ewes and their lambs were turned out onto a parasitologically safe pasture; all ewes continued to be dosed with parasite (once a week), and HP ewes received protein supplementation for the first 35 d. Ewes and lambs grazed the safe pasture for an additional 43 d after termination of protein supplementation and of oral dosing with parasites. Ewes and their lambs were then moved onto newly established experimental pastures sown with chicory or grass/clover (Lolium perenne/Trifolium repens). During the safe pasture period, HP ewes had decreased fecal egg counts (FEC) compared with LP ewes, whereas HP lambs had temporarily less (P < 0.05) FEC, decreased (P < 0.001) plasma pepsinogen concentrations, and grew faster (P = 0.028) than LP lambs. Lambs grazing chicory had consistently less (P < 0.001) FEC and grew faster (P = 0.013) than lambs grazing grass/clover but had greater (P < 0.001) concentrations of pepsinogen. Pasture larvae counts were decreased (P = 0.07) for the chicory compared with the grass/clover plots. There were no interactions (P > 0.10) between maternal nutrition and grazed forage type on performance or parasitological measurements. Our results suggest that increased maternal protein nutrition and subsequent grazing of chicory independently improve lamb performance and reduce lamb parasitism.

The structure of feeding behavior in commercial broiler lines selected for different growth rates.

Selection for increased growth rate in livestock is accompanied by increased requirements for food resources. It has been suggested that more intensively selected birds, such as broilers, have altered food intake control mechanisms and may be constantly hungry, due to the high demands of fast growth rates. If this is the case, it would be a major welfare issue. We investigated the hypothesis that more intensive selection for growth in some lines of broilers has altered feeding behavior by analyzing short-term feeding behavior bouts in relation to the roles of hunger and satiety mechanisms in the control of food intake. Using 4 genetic lines, resulting from different levels of selection for growth rate, meal pattern analysis was performed and the bouting of short-term feeding behavior was estimated. All lines showed bouted feeding behavior, although differences in meal size, number of meals, and meal duration were evident across lines. In all lines, the probability of birds starting a new meal was low immediately after finishing the previous meal and increased with time, as expected for feeding behavior governed by hunger and satiety mechanisms. Normal feeding behavior was, therefore, not affected by the intensity of selection. Feeding rate increased with growth rate, suggesting that this may be a consequence of selection. However the other characteristics of feeding behavior, such as meal duration, did not change consistently with higher growth rate. Due to differences between lines in bird size, the number and weight of birds per pen also differed between the lines. The differences in feeding behavior between lines were greatly diminished when weight of birds per square meter was taken into account but were still statistically significant. Overall, it is apparent that even when growth rate and body size have been substantially altered by genetic selection, the underlying normal controls of feeding behavior are conserved in broiler birds.

Toward a new practical energy evaluation system for dairy cows.

Energy evaluation systems translate an animal's net energy (NE) requirements into feed metabolisable energy requirements (MER). The Feed into Milk (FiM) project (Agnew RE, Yan T, France J, Kebreab E and Thomas C 2004. Energy requirement and supply. In Feed into Milk. A new applied feeding system for dairy cows (ed. C Thomas), pp. 11-20. Nottingham University Press, Nottingham, UK) proposed a new system to predict MER of dairy cows that is, in contrast to previous energy evaluation systems for cattle, independent of feed quality. The FiM system shares this characteristic with an energy evaluation system for ad libitum-fed cattle proposed in 1994 by Tolkamp and Ketelaars (T&K). The FiM system requires nine parameters to translate requirements for NE into MER for dairy cows, while the T&K system for cattle requires only two for the same purpose. This paper analyses the contribution of each of the parameters to the final MER predictions, the differences in MER prediction between the two systems and the underlying causes of these differences. The systems differ considerably in their estimates of the NE that is required for maintenance and in their (implicit) assumptions about the partial efficiency of ME utilisation for lactation. The T&K system is based on a constant partial efficiency of ME utilisation, but in the FiM system this efficiency changes with milk yield (MY) and shows a sharp discontinuity that is at odds with the underlying biology. These are the two main causes of the differences in MER predictions. Nevertheless, over a range of MYs between 10 and 40 kg, and for cows maintaining, gaining or losing weight, the MER predictions of the two systems are very similar with maximum differences of up to ±2% only. FiM predictions of MER are systematically higher than T&K predictions for cows with very low and very high MY. It is concluded that the FiM system could reduce parameter requirements with negligible effects on MER predictions. The combination of a very high maintenance NE parameter and a curvilinear model with two subsequent corrections leads to internal inconsistencies in the FiM system. The T&K system is much simpler but it might benefit from including more recent information for the estimation of its parameters.

Changes in food intake and circulating leptin due to gastrointestinal parasitism in lambs of two breeds.

A reduction in food intake is a prominent feature of many infectious diseases. However, the underlying mechanisms of parasite-induced anorexia in sheep are poorly understood. Here, we tested the hypotheses (a) that the degree of parasite-induced anorexia in lambs is influenced by their growth potential and (b) that nematode infection results in elevated plasma leptin concentration in lambs. The hypotheses were tested with Suffolk x Greyface (S) and Scottish Black-face (B) lambs that are known to differ in their growth potential (S lambs are of greater growth potential than B lambs). During a primary parasite infection, 24 out of 48 lambs per breed were trickle-infected with 7,000 infective Teladorsagia circumcincta larvae per day, 3 d/wk, for a period of 12 wk (experiment I). The lambs were then dewormed, and after a 2-wk interval, half of the 24 lambs per breed that were previously infected were reinfected for another 12 wk with the same parasite and dose as used in the primary infection (experiment II). In both experiments, infected lambs were fed grass pellets for ad libitum intake, whereas noninfected lambs were fed grass pellets for either ad libitum or restricted intakes. The S lambs were more susceptible than B lambs to nematode infection, as judged from the differences in fecal egg counts (P = 0.007). Parasitized lambs of the more susceptible breed (S) showed anorexia [i.e., a decrease in intake of 13% compared with uninfected controls (P = 0.01)], whereas no significant reduction in food intake was observed in lambs of the more resistant breed (B). Reexposure to nematode infection of previously infected animals tended to result in renewed anorexia in S lambs but not in B lambs (P = 0.08) in a similar extent as during primary infection. Plasma leptin concentrations did not differ between ad libitum-fed infected and control lambs but were greater in infected than in noninfected lambs at a similar level of food intake during both the primary (P = 0.02) and the secondary parasitic infection (P = 0.004) in both breeds. The results show that leptin may be involved in the response of lambs to infection but that it is unlikely that leptin alone is responsible for the parasite-induced anorexia in lambs.

Changes in feeding behavior as possible indicators for the automatic monitoring of health disorders in dairy cows.

Changes in short-term feeding behavior of dairy cows that occur with the onset of the health disorders ketosis, acute locomotory problems, and chronic lameness were investigated using data collected during previous experiments. The objective of the study was to describe and quantify those changes and to test their suitability as early indicators of disease. Feed intake, feeding time, and number of daily feeder visits were recorded with computerized feeders. Ketosis in 8 cows was characterized by rapid daily decreases in feed intake [-10.4 kg of fresh matter (FM)], feeding time (-45.5 min), and feeding rate (-25.3 g of FM/min) during an average of 3.6 d before diagnosis by farm staff. Acute locomotion disorders in 14 cows showed smaller daily decreases in feed intake (-1.57 kg of FM) and feeding time (-19.1 min), and a daily increase in feeding rate (+21.6 g of FM/min) during an average of 7.7 d from onset to diagnosis. The effects of chronic lameness on short-term feeding behavior were assessed by analyzing changes during the 30 d before and 30 d after all cows were checked for foot lesions and trimmed, and cows were classified as either lame (n = 81) or not lame (n = 62). During the 30 d before trimming, cows classified as lame showed significant changes in daily feeding time, number of daily visits, and feeding rate, but nonlame cows did not. In lame cows, the observed daily changes (slope) for the 30 d before and the 30 d after trimming were -0.75 and +0.32 min/d for daily feeding time, -0.35 and +0.31 for daily number of visits, and +0.77 and -0.35 g/min for feeding rate, respectively. These changes in feeding behavior were not different among cows consuming low or high forage rations. Daily feeding time was the feeding characteristic that changed most consistently in relation to the studied disorders. A simple algorithm was used to identify cows whose daily feeding time was lower than the previous 7-d rolling average minus 2.5 standard deviations. The algorithm resulted in detection of more than 80% of cows with acute disorders at least 1 d before diagnosis by farm staff. Short-term feeding behavior showed very characteristic changes with the onset of disorders, which suggests that a system that monitors short-term feeding behavior can assist in the early identification of sick cows.

Body fatness affects feed intake of sheep at a given body weight.

In a 1-yr experiment, nutritional treatments were used to produce different combinations of BW and BCS in lambs. The experiment served to quantify the effects of BW and BCS on ADFI by sheep. Ewe lambs (n = 78) were assigned to treatment groups that had ad libitum access to one feed at a time. Three feeds were used: a medium-quality chopped hay (L), a pelleted feed based on oat feed (M), and a pelleted feed based on barley (H). Three groups received only one of these feeds throughout. Two groups first received H and then were switched to M when they reached a BW of 45 or 65 kg. Two groups first received L and then were switched to M or H after reaching a BW of 45 kg. Three groups first received H or M but were switched to L after reaching a BW of 45, 65, or 95 kg. Daily feed intake, BW, and BCS were recorded, and ME content of the feeds was estimated in a separate digestibility experiment. The lambs consuming M ate more (P < 0.001) feed than lambs consuming H, but this had no significant effects on ME intake or gain in BW or BCS. Animals that had had access to L were lean for their BW when switched to H or M and showed compensatory intake and gain. Animals switched from M or H to L all lost BCS; BW change depended on the BW at the switch. The treatments produced different combinations of BW and BCS for animals with access to the same feed. The ADFI of a given feed varied systematically with BCS for animals of a given BW. The model ADFI = a x BW x [1 - (b x BCS)] gave a reasonable description of the data in all treatments. A model using BW, BCS, and their interaction gave a slightly better fit but explained little more of the variation in ADFI than the simpler model. The implications of the collected data are that BW alone is an insufficient descriptor of the animal to correctly predict feed intake and that intake predictions can be improved by taking BCS into account.

Control of energy balance in relation to energy intake and energy expenditure in animals and man: an ecological perspective.

In this paper, we consider the control of energy balance in animals and man. We argue that patterns of mammalian feeding have evolved to control energy balance in uncertain environments. It is, therefore, expected that, under sedentary conditions in which the diet is rich in nutrients and abundantly available, animals and man will overeat. This suggests that no physiological defects are needed to induce overweight and ultimately obesity in man. Several considerations arise from these observations. The time period over which energy balance is controlled is far longer than allowed by most experiments. Physiological models of energy balance control often treat excess energy intake as a defect of regulation; ecological models view the same behaviour as part of normal energy balance control in environments where resources are uncertain. We apply these considerations to common patterns of human and animal feeding. We believe that the ecological perspective gives a more accurate explanation for the functionality of excess fat and the need to defend nutrient balance and avoid gross imbalances, as well as explaining hyperphagia in the face of plenty. By emphasising the common features of energy balance control in different mammalian species, the importance of changes in behaviour to accommodate changes in the environment becomes apparent. This also opens up possibilities for the control of body weight and the treatment of obesity in man.

Effects of qualitative feed restriction during rearing on the performance of broiler breeders during rearing and lay.

To prevent health and fertility problems associated with excessive weight gain, broiler breeders are severely feed restricted during rearing, which may affect welfare. We compared the effects of an experimental ad libitum feeding regimen based on qualitative restriction of food intake with conventional quantitative food restriction on the performance of female broiler breeders during rearing and lay. During rearing up to 20 wk of age, control birds were fed restricted amounts of standard broiler breeder mash once daily. Experimental birds had ad libitum access to the same standard mash mixed with 400 g of oat hulls/kg of feed and increasing concentrations of Ca propionate, an appetite suppressant. Mean total mash intake during rearing was 8.12 kg and did not differ between treatments. Both control and experimental birds showed an almost linear growth curve, treatment mean body weights were always within 100 g of the target weight line, and treatments did not differ for body weight uniformity. Groups were subjected to the same quantitative feed restriction from during lay. Feeding regimen during rearing did not affect number of eggs produced, egg weight, or egg quality up to 46 wk of age. We concluded that it may not be necessary to subject chicks to severe quantitative feed restriction to achieve desirable growth curves and body weight uniformity during rearing. Qualitative restriction of feed intake can achieve desirable growth curves in ad libitum fed chicks during rearing, and such a feeding regimen does not have negative effects on hen performance during lay.

The evolution of the control of food intake.

The ultimate goal of an organism is to maximise its inclusive fitness, and an important sub-goal must be the optimisation of the lifetime pattern of food intake, in order to meet the nutrient demands of survival, growth and reproduction. The conventional assumption that fitness is maximised by maximising daily food intake, subject to physical and physiological constraints, has been challenged recently. Instead, it can be argued that fitness is maximised by balancing benefits and costs over the organism's lifetime. The fitness benefits of food intake are a function of its contribution to survival, growth (including necessary body reserves) and reproduction. Against these benefits must be set costs. These costs include not only extrinsic foraging costs and risks, such as those due to predation, but also intrinsic costs associated with food intake, such as obesity and oxidative metabolism that may reduce vitality and lifespan. We argue that the aggregate of benefits and costs form the fitness function of food intake and present examples of such an approach to predicting optimal food intake.

The relationship between meal composition and long-term diet choice.

When animals are offered a choice of feeds that are nutritionally complementary, they are able to select a consistent combination of these feeds over long periods of time. Analysis of how such consistent diet choice is achieved, in terms of short-term feeding behavior, may further our knowledge of how animals regulate nutrient intake. Previous work, on meal pattern analysis and on nutrient synchronization, led us to hypothesize that animals may select a consistent diet within a meal. In three experiments cows were offered a choice between high- (H) and low- (L) protein feeds and short-term feeding behavior data were collected using computerized feeders. Feeding behavior was first analyzed in terms of visit characteristics. A greater average daily intake of H, relative to L, was more closely related to the ratio of H visits to L visits than to differences in the intake per visit to feeders supplying H or L. Individual meal criteria were estimated using a mixed-distribution model, and visits were clustered into meals. Cows typically had approximately six meals per day. The observed frequency distribution of meal composition, in terms of the proportion of visits to H feeders, was determined. Subsequently, the observed visits were randomly reclustered into bouts consisting of the same number of visits as were observed in meals, and the frequency distribution of random bout composition was calculated. If frequency distributions of meals and random bouts coincide, then this is evidence that cows do not regulate diet choice within a meal. Comparison of the frequency distributions of meals and random bouts provided no evidence that cows attempted to achieve their long-term average diet composition within a meal. We also investigated whether cows tried to achieve a consistent diet choice within a meal by adjusting their intake per visit, depending on the feed type visited and the proportion of visits to H feeders in a meal. There was no evidence that this occurred. In conclusion, our analyses have shown that cows did not attempt to select within a meal a consistent diet in terms of protein to energy ratio. Indeed, our data and the literature suggest that the timeframe over which the intake of energy and protein is regulated must be greater than a meal in a number of animal species.

The use of mixed distribution models to determine bout criteria for analysis of animal behaviour.

Feeding behaviour consists of feeding events, separated by non-feeding intervals. Feeding events are often clustered into bouts, which may be called meals. Grouping feeding events into meals requires the determination of a bout or meal criterion, that is, the longest interval accepted as part of a meal. Tolkamp & Kyriazakis (1999a) proposed a three-Gaussian model to estimate meal criteria. The three Gaussians each described the frequency distribution of the log(e)-transformed lengths of a population of intervals. These populations were thought to be: (1) short intervals within meals; (2) intervals within meals during which animals drink; (3) intervals between meals. This model predicted that the probability of an animal starting a meal would first increase, and then decrease with time since the last meal. This contrasts with expectations based on the satiety concept, which predicts that the probability of an animal starting a meal will increase with time since the last meal. This discrepancy is related to the symmetrical nature of the Gaussian distribution. Alternatively, the two-parameter Weibull distribution can take a skewed form and perhaps is more suitable to describe the different populations of intervals. In this study, models consisting of combinations of Gaussian and Weibull distributions were examined for their suitability to describe the observed feeding behaviour of cows. Weibulls did not improve the description of the populations of within-meal intervals, compared to Gaussians. However, the Weibull distribution was found to describe the between-meal population of intervals statistically better than the Gaussian. Additionally, this inclusion of a Weibull, as opposed to a Gaussian, resulted in predictions that were in better agreement with the satiety concept over the entire range of interval lengths observed. A model based on Gaussians to describe the within-meal populations of intervals and a Weibull to describe the population of between-meal intervals is, therefore, proposed. This model leads to biologically more satisfactory estimates of bout criteria than previous models and is likely to be applicable both across species and behaviours.

Theoretical developments in the study and prediction of food intake.

The purpose of the present paper is to review recent theoretical developments in food intake modelling applied to animal science and ecology. The models are divided into those that have been developed for intensive agricultural systems, and those which consider more extensive systems and natural systems. For the most part the present paper discusses models that predict the food intake of herbivores. The mechanisms of each model are discussed, along with a brief mention of the experimental support for the most popular models. We include a discussion of models that approach the study of food intake behaviour from an evolutionary perspective, and suggest that lifetime models are especially useful when food intake carries an intrinsic cost. These long timescale evolutionary models contrast with the more common food intake models, whose timescale is usually much shorter. We conclude that the 'eating to requirements' model highlights an important food intake mechanism that provides an accurate predictive tool for intensive agricultural systems. The mechanisms of food intake regulation in extensive systems are less certain, and closer links between the ideas of animal science and ecology will be helpful for improving our understanding of food intake regulation.

The biologically relevant unit for the analysis of short-term feeding behavior of dairy cows.

To determine whether visits or meals are the most biologically relevant unit of short-term feeding behavior, we analyzed 209,025 records of visits to feeders by 37 cows. Two feeds were used that differed in protein content. Cows were divided into control groups for the low and high protein feeds and a choice group that had access to both. Daily number of visits and intake per visit were very variable. Cows fed low protein feed had lowest daily intakes, but single-visit characteristics were poorly correlated with daily intake. The probability of cows ending a visit did not change greatly with visit length. Log-normal models were used to estimate individual meal criteria (44.7+/-2.1 min), and visits were grouped into meals. Meal duration (36.9+/-1.3 min) and daily number of meals (6.1+/-0.1) were not affected by treatment. Feeding rate and intake per meal were lowest for cows fed low protein feed. Meal size decreased systematically during the day. The probability of cows ending and starting a meal increased with meal length and interval between meals, as predicted by the satiety concept. Meals are, therefore, a biologically relevant unit of short-term feeding behavior and visits are not.