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PubMed1999

Evaluation of the importance of the digestibility of neutral detergent fiber from forage: effects on dry matter intake and milk yield of dairy cows.

Effects of the digestibility of neutral detergent fiber (NDF) from forage on performance of dairy cows were evaluated statistically using treatment means for 13 sets of forage comparisons reported in the literature. All comparisons reported significant differences in NDF digestibilities of forages in situ or in vitro. Treatment means were blocked by study or by additional factorial treatment within a study to remove variation among experiments. The statistical model included random effect of block, fixed factorial effect of NDF digestibility (high or low), and dietary NDF concentration as a covariate. Enhanced NDF digestibility of forage significantly increased dry matter intake (DMI) and milk yield. A one-unit increase in NDF digestibility in vitro or in situ was associated with a 0.17-kg increase in DMI and a 0.25-kg increase in 4% fat-corrected milk. Differences in NDF digestibility between treatments were greater when measured in vitro or in situ than when measured in vivo. Digestibility of NDF in vitro or in situ might be a better indicator of DMI than NDF digestibility in vivo because forages with high in vitro or in situ NDF digestibilities might have shorter rumen retention times, allowing greater DMI at the expense of NDF digestibility in vivo. Digestibility of NDF is an important parameter of forage quality.

Animals↗
PubMed1999

The implications of condensed tannins on the nutritive value of temperate forages fed to ruminants.

New methodology for measuring forage condensed tannin (CT) content is described and the effects of CT upon forage feeding and nutritive value for ruminant animals are reviewed. CT react with forage proteins in a pH-reversible manner, with reactivity determined by the concentration, structure and molecular mass of the CT. Increasing concentrations of CT in Lotus corniculatus and Lotus pedunculatus reduce the rates of solubilization and degradation of fraction 1 leaf protein in the rumen and increase duodenal non-NH3 N flow. Action of medium concentrations of total CT in Lotus corniculatus (30-40 g/kg DM) increased the absorption of essential amino acids from the small intestine and increased wool growth, milk secretion and reproductive rate in grazing sheep without affecting voluntary feed intake, thus improving the efficiency of food conversion. High concentrations of CT in Lotus pedunculatus (75-100 g/kg DM) depressed voluntary feed intake and rumen carbohydrate digestion and depressed rates of body and wool growth in grazing sheep. The minimum concentration of CT to prevent rumen frothy bloat in cattle is defined as 5 g/kg DM and sheep grazing CT-containing legumes were shown to better tolerate internal parasite infections than sheep grazing non CT-containing forages. It was concluded that defined concentrations of forage CT can be used to increase the efficiencies of protein digestion and animal productivity in forage-fed ruminants and to develop more ecologically sustainable systems of controlling some diseases under grazing.

Amino Acids, Essential↗
PubMed2002

Relationship of milk yield and quality to preweaning gain of calves from Angus, Brahman and reciprocal-cross cows on different forage systems.

Interactions of the regression of preweaning ADG on dam milk yield and quality with breed group and forage environment were evaluated in a two-phase study. Phase I consisted of milk yield and quality and calf gain records from 1989 to 1991 for purebred Angus (n = 64) and Brahman (n = 62) cows mated to sires of both breeds. Phase II consisted of milk yield and quality and calf gain records from 1991 to 1997 for Angus (n = 94), Brahman (n = 85), Angus x Brahman (n = 86) and Brahman x Angus (n = 93) mated to Polled Hereford sires. In Phase I, forage environments included common bermudagrass and endophyte-infected tall fescue. In Phase II, forage environments included common bermudagrass and endophyte-infected tall fescue (1991 to 1995) and a rotational system of both forages (1995 to 1997) in which each forage was grazed during its appropriate growing season, usually June through October for bermudagrass and November through May for tall fescue. Milk yield was estimated monthly six times during lactation from spring through fall and converted to a 24-h basis. Milk fat, milk protein, and somatic cell count were analyzed by a commercial laboratory. In Phase I, the relation of preweaning ADG to milk yield, milk fat yield, and protein yield was greater (P < 0.05) in Brahman cows on bermudagrass than Angus on bermudagrass. The regression of preweaning ADG on milk yield in Phase I was greater (P < 0.05) for cows on tall fescue than cows which grazed bermudagrass. In Phase II, the relation of preweaning ADG to milk yield, milk fat yield, and milk protein yield was greater or tended to be greater (P < 0.01, P < 0.11, P < 0.01, respectively) in purebred cows compared to reciprocal-cross cows. The regression of preweaning ADG on milk yield and milk protein yield was greater (P < 0.05) on tall fescue than bermudagrass in Phase II. These results suggest that the influence of milk yield and quality on calf growth may differ among breed types and production system, and the efficacy of genetic improvements in milk traits may depend on the breed type and forage environment.

Animal Feed↗
PubMed2002

[Dynamics of forage supplement and nutrition requirements of grazing sheep in alpine grasslands].

The dynamics of forage supply and nutrition requirements of sheep were monitored for a whole year under alpine grassland conditions in Sunan County, Gansu Province. The digestion and metabolism of grazed sheep were determined in different seasons. The results showed that the DE(9.76 MJ), CP(21.53%) and the ratio of crude protein to digestible energy (22.06 g.MJ-1) of forage were the highest in Spring, while the herbage dry matter yield and dry matter intake (60.51 +/- 3.42 g.W0.75kg-1.d-1) by grazed sheep were the lowest. Supplementary DM especially in energy should be provided. The ratio of crude protein to digestible energy was 17.62 g.MJ-1 in Summer, and was somewhat higher. The nitrogen utility of the forage would be improved, if energy feed was supplemented. Both the quality and quantity of forage produced in grasslands in Autumn could meet the sheep requirement. Whereas during Winter, neither forage yield nor nutritive value was sufficient for sheep, and the contents of the DE and CP of forage were the lowest in the year, which were 4.30 MJ and 4.63%, respectively. The nitrogen metabolism of sheep was negative. Therefore, DM, especially DE and CP, should be supplemented. To improve the conditions, it was necessary to develop seasonal animal husbandry, and combine the subsystems into coupling systems.

Agriculture↗
PubMed1987

Time horizons in rats foraging for food in temporally separated patches.

An important tenet of optimal foraging theory is that foragers compare prey densities in alternative patches to determine an optimal distribution of foraging behavior over time. A critical question is over what time period (time horizon) this integration of information and behavior occurs. Recent research has indicated that rats do not compare food density in a depleting patch with that in a rich patch delayed by an hour or more (Timberlake, 1984). In the present research we attempted to specify over what time period a future rich patch would affect current foraging. The effect of future food was measured by early entry into the rich patch (anticipation) and by a decrease in food obtained in the depleting patch (suppression). The rats showed anticipation of a rich patch up to an hour distant, but suppressed current feeding only if the rich patch was 16 min distant or less. The suppression effect appeared mediated by competition for expression between anticipatory entries into the rich patch and continued foraging in the depleting patch. These results suggest that optimal foraging is based on a variety of specific mechanisms rather than a general optimizing algorithm with a single time horizon.

Animals↗
PubMed1997

Effects of adult mortality risks on parasitoid foraging tactics

When searching on Scots pines, females of the aphid parasitoid Pauesia silvestris responded to differences in mortality risks, host distribution and host quality by changing foraging tactics. They foraged more successfully (i.e. they laid more eggs per unit time) on the pine aphid Cinara pini than on Cinara pineaTherefore, the former species was considered to be of higher quality. However, P. silvestris suffered from a high mortality (19.5%) from ant aggression when foraging for C. piniwhile mortality was zero on pines with C. pineaAll females that were killed were foraging on the bark, while females searching on needles were safe from ant attacks. When searching for C. pineaP. silvestris spent significantly more time on needles if the aphid colonies were ant-attended. On pines with C. piniin contrast, females spent more time on bark in ant-attended colonies. The high adult mortality risk on bark was counterbalanced by a significantly higher foraging success in ant-attended colonies.

Journal Article↗
PubMed1997

Feather pecking in domestic chicks: its relation to dustbathing and foraging

Feather pecking is a serious problem in poultry housing, as it may lead to feather damage, injuries and even mortality. We tested predictions of the two prevalent hypotheses claiming that feather pecking is related to dustbathing and foraging, respectively. Forty-two groups of 30 laying hen chicks, Gallus gallus domesticuswere reared in pens with a slatted floor. Access to sand as a dustbathing substrate and straw as a foraging substrate was varied between groups. The rate of feather pecking was measured in early development up to week 7. The provision of a sand area did not prevent the chicks from developing high rates of feather pecking that caused injuries. Chicks that had access to sand from day 10 showed higher rates of feather pecking than chicks that had access to sand from day 1. The provision of straw to chicks that had developed high rates of feather pecking led to a decrease in this behaviour. Chicks that could use both sand and straw from day 1 on did not show high rates of feather pecking, and no injuries were observed in these groups. There was no significant difference in dustbathing activity between housing conditions characterized by high or low rates of feather pecking. On the other hand, foraging activity was inversely related to the rate of feather pecking, and the occurrence of feather pecking could be delayed from week 4 to week 7 by postponing procedures that led to changes in foraging behaviour. In conclusion, the results show that the presence of an appropriate substrate for dustbathing does not prevent domestic chicks from developing feather pecking. On the other hand, housing conditions that promote foraging behaviour are effective in reducing and preventing feather pecking.Copyright 1997 The Association for the Study of Animal Behaviour1997The Association for the Study of Animal Behaviour

Journal Article↗
PubMed1997

Balancing foraging and reproduction in the male harbour seal, an aquatically mating pinniped

Aquatically mating male harbour seals, Phoca vitulinamust balance the competing demands of foraging and reproduction while at sea during the breeding season. Time-depth recorders (TDRs) were attached to 31 adult male harbour seals to investigate changes in diving behaviour at Sable Island, Nova Scotia, during the 1992-1994 breeding seasons. Male seals were captured, fitted with TDRs and weighed at the beginning of the season in late May, then recaptured for TDR removal and reweighing at the end of June. Males made deep dives (to maximum depths >20 m) more frequently early in the breeding season, then switched to shallow (</=20 m) diving later during the mating period. Deep dives (38.8&plusmn;2.2 m; 4.6&plusmn;0.1 min) were fairly uniform in shape, appearing flat-bottomed with rapid rates of descent and ascent and long bottom time, but shallow dives (10.5&plusmn;0.5 m; 3.0&plusmn;0.1 min) were more variable in shape. Rates of mass loss varied inversely with time spent in deep dives, indicating that deep diving behaviour reflects foraging activity. Males lost mass while making shallow dives associated with mating behaviour later in the breeding season. Deep diving occurred more frequently during daylight hours. Shallow dives were predominant at twilight and at night when females are likely to be departing and returning to the island from foraging trips in late lactation. At Sable Island, males may maximize their encounter rates with oestrous females by ceasing to make offshore foraging trips, and increasing the time spent patrolling home ranges and displaying in shallow water near the breeding colony in late lactation. Relatively larger males may have a competitive advantage since they can afford to spend less time making foraging trips away from the concentration of females and more time displaying in shallow water near the shore.1997The Association for the Study of Animal Behaviour

Journal Article↗
PubMed1998

Effects of pollen quality and genotype on the dance of foraging honey bees.

Animals assess the quality and quantity of food and choose among different foods based on these assessments. We explored whether there was genetic variation for assessment of pollen quality by foraging honey bees, Apis mellifera. Honey bees derived from two genotypic strains foraged for pollen of varying quality from a petri dish placed inside an outdoor flight cage. The strains were the result of a colony-level, two-way selection on amount of stored pollen. We used the forager's round dance to quantify the assessments of pollen quality by individually marked worker bees. The dance rate (number of 180 degrees turns per minute) and the probability of dancing were each greater when bees foraged for pure pollen compared with a lower-quality mixture of pollen and alpha-cellulose (1:1 by volume). Bees from the high-pollen genotypic strain had a higher dance rate than those from the low-pollen strain, suggesting different assessments. Bees from the low-pollen strain, however, had a higher probability of dancing than did bees from the high-pollen strain. Dance duration was not affected by a bee's strain or by the quality of pollen. We conclude that the dance rate may be used to quantify a forager's subjective evaluation of pollen quality and that this evaluation has a genetic component. Our results also suggest that the dance may function at the colony level to recruit bees to more profitable pollen sources. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1998

Foraging behaviour and sexual segregation in bighorn sheep.

Like many sexually dimorphic ungulates, bighorn sheep, Ovis canadensis, form sexually segregated groups. Nursery groups include females, lambs and subadult males, while adult males form bachelor groups. Previous hypotheses to account for sexual segregation in ungulates have suggested sexual differences in energy requirements, predation risk and social preferences. I tested the hypothesis that differing nutritional demands, due to sexual dimorphism in body size, would lead to different movement patterns and time budgets. If ruminating/foraging schedules differed according to body size, males and females could not synchronize their activities and therefore would segregate by sex. To test this hypothesis, I observed a population of marked bighorns. I recorded the time males and females spent lying, grazing or walking during 8-14 h of focal-animal observations. Initial and final location of groups and steps taken per minute foraging were also noted. Females spent more time foraging and walking and had longer foraging and walking bouts than adult males, but did not differ in numbers of steps taken while foraging. Males spent more time lying than females. Subadult males switched between nursery and bachelor groups and changed their foraging behaviour depending on the type of group they were in. The distance moved was on average almost four times greater for female than for male groups. I suggest that sexual difference in time budgets and movement patterns make it difficult for males and females to stay in the same group and therefore lead to sexual segregation. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1998

Foraging site displacement in common crane flocks.

Optimal foraging theory predicts that an individual should resort to intraspecific kleptoparasitism when this foraging strategy helps to maximize its intake rate. Thus aggressor and victim should be foraging at lower and higher rates, respectively, than the flock average (intake rate maximization). Independent of the maximization principle, moreover, an aggressor should attack when its intake rate falls below a threshold critical for survival, and select a victim foraging at an intake rate high enough to ensure survival (starvation risk minimization). We tested both hypotheses using 324 aggressive displacements from feeding sites observed in flocks of common cranes, Grus grus, foraging on cereal fields. Aggressors attacked cranes feeding at higher rates than average birds. The immediate consequences of a successful attack were an increase in intake rate for the aggressor and a decrease for the victim. The intake rate of the aggressor prior to the attack was lower than both the mean intake rate of the flock and the minimum intake rate necessary to cover basic metabolic needs. After displacing its victim, the intake rate of the aggressor was higher than before the attack and also higher than the average intake rate of the flock. The intake rate of the aggressor after the attack was not higher than the mean intake rate of the flock, however, when the time spent on the attack was included. We conclude that cranes used a kleptoparasitic strategy to recover from temporary reductions in feeding rate. This was particularly the case below the threshold of intake necessary for survival. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1999

Context-dependent, risk-sensitive foraging preferences in wild rufous hummingbirds.

We tested the risk-sensitive foraging preferences of wild rufous hummingbirds, Selasphorus rufus, with three types of artificial flowers. All three flower types provided the same mean volume of 30 µl of sucrose, but differed in terms of variability of the reward: constant, low variance and high variance. In trinary comparisons, subjects preferred the low-variance reward over the constant reward, and the constant reward over the high-variance reward; a result not predicted by risk-sensitive foraging theory. However, when tested with traditional binary comparisons, hummingbirds showed conventional risk-averse behaviour and selected the constant reward over the low- or high-variance rewards. This reversal of preference represents a context-dependent foraging preference. The utility of selecting intermediate levels of risk and the source of the preference reversal are discussed relative to risk-sensitive foraging theory and the effects of local context on foraging choices. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1999

Competitive foraging in the social spider Stegodyphus dumicola.

Reproductive skew models have greatly enhanced the study of sociality but are applicable only to societies where the aim of the members of the group is to reproduce. In 'foraging societies', where the aim of the members of the group is to grow, quite different parameters will govern the form that the societies take. We examined factors that influence the structure of foraging groups in the social spider Stegodyphus dumicola (Eresidae). In particular, we examined food distribution and consumption within groups, and how this related to predictions derived from two models. One model indicates that colonies in which individuals compete for resources via interference competition are more likely to survive than those in which individuals divide resources using scramble competition. The second model predicts the proportions of hunters, cheaters and scavengers expected in foraging groups. We found that food was not distributed evenly among group members, and that spiders that fed primarily on the head and thorax of the prey during the middle of a feeding event gained the most body mass. Spiders even lost mass if they fed only in the last hour of a foraging event. Large spiders had a competitive advantage (via interference competition) in obtaining preferred positions, and could ingest food faster than small spiders. Distributing food among colony members in this manner could cause large size differences between colony members, as predicted by the models. The implications of competitive foraging for sociality are discussed. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed2000

Mechanisms of dispersed central-place foraging in polydomous colonies of the Argentine ant.

Many species of ants occupy multiple nests, a condition known as polydomy. Because of their decentralized structure, polydomous colonies may be removed from some of the constraints associated with classic central-place foraging. We used laboratory and field experiments to assess the mechanisms involved in dispersed central-place foraging in polydomous colonies of the Argentine ant Linepithema humile, a widespread invasive species. Both in the laboratory and in the field, Argentine ants established new nests at sites located near food. Laboratory colonies of L. humile redistributed workers, brood and resources among nests in response to the spatial heterogeneity of food resources. In addition, laboratory colonies formed recruitment trails between nests in the context of foraging, providing a mechanism for the transport of material between nests. This highly flexible system of allocating nests, workers and brood throughout a colony's foraging area potentially increases foraging efficiency and competitive ability. The importance of polydomy as a determinant of competitive ability is underscored by its prevalence among ecologically dominant ants, including most, if not all, highly invasive species. Copyright 2000 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed2000

Optimal Bayesian foraging policies and prey population dynamics-some comments on Rodriguez-Girones and Vasquez.

In this paper we show the density-dependent harvest rates of optimal Bayesian foragers exploiting prey occurring with clumped spatial distribution. Rodríguez-Gironés and Vásquez (1997) recently treated the issue, but they used a patch-leaving rule (current value assessment rule) that is not optimal for the case described here. An optimal Bayesian forager exploiting prey whose distribution follows the negative binomial distribution should leave a patch when the potential (and not instantaneous) gain rate in that patch equals the best long-term gain rate in the environment (potential value assessment rule). It follows that the instantaneous gain rate at which the patches are abandoned is an increasing function of the time spent searching in the patch. It also follows that the proportion of prey harvested in a patch is an increasing sigmoidal function of the number of prey initially present. In this paper we vary several parameters of the model to evaluate the effects on the forager's intake rate, the proportion of prey harvested per patch, and the prey's average mortality rate in the environment. In each case, we study an intake rate maximizing forager's optimal response to the parameter changes. For the potential value assessment rule we find that at a higher average prey density in the environment, a lower proportion of the prey is taken in a patch with a given initial prey density. The proportion of prey taken in a patch of a given prey density also decreases when the variance of the prey density distribution is increased and if the travel time between patches is reduced. We also evaluate the effect of using predation minimization, rather than rate maximization, as the currency. Then a higher proportion of the prey is taken for each given initial prey density. This is related to the assumption that traveling between patches is the most risky activity. Compared to the optimal potential value assessment rule, the current value assessment rule performs worse, in terms of long-term intake rate achieved. The difference in performance is amplified when prey density is high or highly aggregated. These results pertain to the foraging patch spatial scale and may have consequences for the spatial distribution of prey in the environment.

Animals↗
PubMed1995

A mathematical framework for optimal foraging of herbivores.

The aim of this paper is to study a model of optimal foraging of herbivores (with special reference to ungulates) assuming that food distribution is arbitrary. Usually the analysis of foraging of herbivores in the framework of optimal foraging theory is based on the assumption of a patchy food distribution. We relax this assumption and we construct more realistic models. The main constraint of our model is the total amount of food which the animal may eat and the currency is the total foraging time. We represent total foraging time as a variational expression depending on food eaten and the length of the path. We prove that there exists a threshold lambda for food acquisition. More explicitly, it exists a positive real number lambda such that, at any point x of the path, the animal either eats till the density of food is decreased to the value lambda or, if the density of food at x is less than lambda, there it does not eat. We discuss the results and emphasize some biologically important relationships among model parameters and variables. Finally,we try to give a sound biological interpretation of our results.

Animals↗
PubMed2001

Satiation differentially affects performance in a learning assay by nurse and forager honey bees.

When not satiated prior to training, there were no differences between foragers and nurse honey bees in the acquisition of an appetitively based conditioned response in an olfactory associative learning assay, but when satiated foragers showed faster acquisition than did nurses. Satiation-related differences between foragers and nurses were more a function of behavioral state than age, because satiated precocious foragers also showed faster acquisition rates than did satiated nurse bees, despite their similar ages. Tests of sucrose responsiveness and retention of conditioned responses indicate that the observed performance differences between nurses and foragers were more likely due to differential sensitivity of sensory and motor processes related to satiation rather than differences in cognitive ability.

Aging↗
PubMed2006

Modification of leech behavior following foraging for artificial blood.

In this study we examined whether the foraging for artificial blood affected the behavioral responsiveness of leeches to electrical stimulation of the body wall. After foraging for artificial blood, electrical stimulation of the posterior end of the leech significantly increased the percentage of stimulation trials that elicited locomotory activity--swimming and crawling--compared to the behaviors elicited when leeches did not forage or foraged for normal saline. On the other hand, shortening always dominated the behavioral profile of the leech to anterior stimulation even after foraging for artificial blood. In intact anterior end-isolated nerve cord preparations, we also found that application of artificial blood to the intact anterior end was sufficient to modify motor responsiveness to DP nerve stimulation. Full strength artificial blood had an overall negative effect on the likelihood of DP nerve stimulation initiating swimming and on the average length of elicited swim episodes compared to when pond water surrounded the anterior end. Application of a 10% solution of artificial blood to the anterior end led to an increase in the likelihood of DP nerve stimulation eliciting swimming.

Action Potentials↗