Articles 101-110

A glutenfree diet for callitrichids and marmosets in Emmen-zoo, the Netherlands

C. Berndt1, R. Spijker2 and G. Wind2

1Noorder Dierenpark Emmen, The Netherlands;
2Students Nutrition and Dietethics ( Hanzehogeschool Groningen, the Netherlands

Callithrichids living in zoos are prone to developing several symptoms that belong to the “Wasting Marmoset Syndrome”. Research has been done, but the cause of the Syndrome is not completely known and opinions about this differ. Possible causes that are mentioned are a lack of energy, incorrect nutrition, infections and stress. In the Noorder Dierenpark in Emmen, Holland, it is believed that an intolerance for gluten might be one of the causes. The symptoms of the “Wasting Marmoset Syndrome” are similar to the symptoms of gluten intolerance (coeliac disease) in people. These symptoms are: intestinal problems, a swollen abdomen, chronic stinking diarrhoea, stomach-ache, anaemia, fatigue, listlessness, weight loss, osteoporosis, enamel deviation, and in children, growth retardation. Coeliac disease is a condition in which the lining of the small intestine is damaged by gluten. Gluten is a protein found in wheat, rye, oats and barley. In people who are sensitive to gluten, gluten damages the mucous membrane of the small intestine. The damage which occurs considerably impairs the absorption of nutrients from the small intestine, causing several problems. When a patient follows a strictly gluten-free diet the intestinal villi can restore and after a few weeks the symptoms will decrease. However, it takes 1 to 2 years for the mucous membrane to fully recover. The disease cannot be cured, which is why the patient has to follow the diet strictly during his whole life. Considering the possibility that some of the Callitrichids might suffer from coeliac disease, they probably cannot be cured either. The only possibility is that the mucous membrane of the small intestine of the Callithrichids fully recovers, providing that the damage of the intestinal villi was not too progressive. A monkey who is thought to have “Wasting Marmoset Syndrome” probably cannot be saved, (whether or not it is coeliac disease), because the damage of the intestinal villi already is too far ahead. It may be advisable to give the remaining Callithrichids of a group from which one monkey died from “W.M.S.” a gluten-free diet, even though they do not have any symptoms of the disease yet, since coeliac disease is thought to be hereditary. By providing the rest of the group with a gluten-free diet these animals have a chance to recover from damage in the lining of the small intestine; it is just preventive and a gluten-free diet is not harmful anyway. A six-month pilot project was conducted at Edinburgh Zoo in 1998, regarding the influence of wheat on the health of Callithrichids. The research found that a gluten-free diet had a positive influence on the health. This was one reason for the Noorder Dierenpark to introduce a gluten-free diet for the Callithrichids in January 1999. We also observed positive effects: the incidence of diarrhoea, hunger, wasting, and other symptoms described earlierd are greatly reduced. This is not an illogical result when you keep in mind that cereals don’t grow in the natural habitat of these animals.

Handfeeding of young parrots – techniques, diets and recommendations

Petra Wolf

Institute of Animal Nutrition, School of Veterinary Medicine Hannover, Bischofsholer Damm 15, D-30173 Hannover

In recent years handrearing of pet birds has become a standard procedure for breeding valuable pet birds (e.g. African greys). In this case nestlings are fed with a special powdered complete diet mixed with water (i.e. 1st to 4th day of life: 1 part diet diluted with 6 parts water; 5th to 8th day of life: 1 part diet diluted with 4 parts of water; from the 9th day of life: 1 part of water : 2 parts of diet). This prepared solution is administered directly by a syringe into the crop during the first few days of life or afterwards into the beak by a teaspoon. The labled ingredients of commercial handrearing diets comprise only a few nutrient contents (e.g. crude protein or crude fat), whereas data on amino acids or minerals are frequently absent. Therefore this investigation will evaluate the energy and nutrient contents in commercial handrearing diets (n=11) in order to assess the suitability for rearing young pet birds.

nutrient contents1) of handrearing diets2) necessary nutrient contents3) for Nutrients x ± s min. max. budgerigars lovebirds
crude protein 14.4 ± 1.82 12.4 17.8 9.54 8.90
Lysine 0.735 ± 0.110 0.491 0.880 0.329 0.316
Met + cys4) 0.462 ± 0.184 0.234 0.695 0.469 0.368
Arginine 0.729 ± 0.143 0.591 1.140 0.484 0.430
Calcium 0.616 ± 0.243 0.349 1.145 0.276 0.271
Phosphorus 0.312 ± 0.121 0.175 0.518 0.156 0.160
Magnesium 0.086 ± 0.024 0.053 0.128 0.011 0.012
Sodium 0.133 ± 0.095 0.049 0.356 0.028 0.036
Potassium 0.346 ± 0.119 0.236 0.552 0.069 0.072
1) g/MJ ME
2) MJ ME/kg dry matter: Æ 15.2 ± 1.16 (min.: 13.0; max. 16.8); crude fat: 7.38 ± 1.10 g/MJ ME; starch: 29.5 ± 3.16 g/MJ ME; sugar: 2.48 ± 2.47 g/MJ ME;
3) derived from growth rates of youngs as well as the body composition (KAMPHUES et al. 1996);
4) methionine + cystine

A comparison of the analysed nutrient contents and the factorially derived necessary nutrient contents in handrearing diets for budgerigars and lovebirds shows sufficient crude protein, lysine and arginine contents. On the other hand some of the products showed a lack of the sulphureous containing amino acids methionine and cystine (feather growth ¯).
All minerals met the requirements of the youngs, but some mineral concentrations were higher than needed (i.g. high calcium contents ® possible interactions with copper or zinc; high sodium contents among a limited water intake). Furthermore some of the handrearing diets contain an excessivly high content of vitamin A (up to 47,000 IE/kg diet). In general the results verify, that on the one hand the requirements of sulphureous amino acids for feather growth in nestlings are frequently underestimated and that on the other hand the calcium requirements (mineralisation of skeleton) is often overestimated. However, the primarily problem of handrearing in pet birds is most likely not caused by insufficient energy and nutrient contents of the diets, but to the consistency of the suspended diets within the gastrointestinal tract (e.g. stasis of the crop content).

KAMPHUES, J., N. RABEHL and P. WOLF (1996): Derivation of necessary nutrient concentrations related to energy content in diets for growing pet birds (canaries, budgerigars, lovebirds). Proc. of the European Society of Veterinary and Comparative Nutrition, Veldhoven, 12.9.1996, 29-30

Experimental data on feeding extruded diets in parrots

Petra Wolf, Sabine Graubohm and Josef Kamphues

Institute of Animal Nutrition, School of Veterinary Medicine Hannover, Bischofsholer Damm 15, D-30173 Hannover

The feeding of pelleted/extruded diets to parrots has been a controversial subject. Some bird fanciers dislike the use of these diets because of body weight losses of their parrots during conversion from existing seed mixtures to formulated diets. Also, a reduced time for feed intake is linked with behaviour disorders (feather biting/picking) due to boredom, and a reduced attrition of the beak. In spite of those reservations pelleted/extruded diets allow the composition of a well-balanced diet that meets the nutritional requirement of the parrot at each stage of life. A pelleted or extruded diet also prevents the selection of individual ingredients within the offered feed (i.e. the choice of seeds like sunflower seeds, that are characterized by a high fat and energy content increasing the risk of obesity).
Another positive aspect of feeding a pelleted diet is the improved hygienic quality due to the commonly used ingredients (mostly based on cereals). In feeding trials with amazons, grey parrots and cockatoos, the parameters mentioned above were tested. The comparison of the chemical composition shows great differences between formulated diets and commercial seed mixtures based on fatty seeds like sunflower seeds, safflower, hemp, pumkins, peanuts etc. (see Table 1).
Compared to seed mixtures the pelleted/extruded diets are characterized by lower crude protein, fat, fiber and energy contents, but higher amounts of carbohydrates (diets are based on maize, wheat and oat especially). In particular, the calcium content of 10.9 g/kg dry matter (on average) indicates a high calcium supply. The calcium:phosphorus ratio was well-balanced. Sodium contents point to a supply, even if amounts of 1-2 g sodium/kg dry matter are not recommended.

Table 1: Chemical composition of pelleted/extruded diets compared to seed mixtures data per kg dry matter pelleted/extruded diets (n=16) seed mixtures (n=10)* crude protein (g) 196 ± 38.7 243 ± 63.6
crude fat (g) 81.6 ± 24.9 383 ± 125
crude fiber (g) 32.0 ± 14.0 38.2 ± 25.1
carbohydrates (g) 566 ± 56.4 284 ± 30.9
energy (MJ ME) 15.8 ± 0.60 21.4 ± 3.51
calcium (g) 10.9 ± 4.10 1.79 ± 1.24
phosphorus (g) 5.68 ± 1.26 9.08 ± 3.59
sodium (g) 3.21 ± 1.90 0.54 ± 0.24 *related to the ‘kernels’, that means the real intake after dehusking/shelling of the seeds

Conversion of parrots from usual seed mixtures to unknown mixed diets was done within a short time and without any problems (i.e. refusal of the diet combined with body weight losses). Offering seed mixtures ad libitum a typical rhythm of feed intake could be observed (higher ingestion activities in the early morning and in the afternoon), whereas formulated diets were ingested continuously during the whole day. The time spent for feed intake (measured in minutes/g feed) did not differ significantly between pelleted/extruded diets and seed mixtures. When mixed diets were fed, digestibility of organic matter varied between 76 and 84% (in comparison: 78% ingesting fatty seeds and 87% fed seeds rich in carbohydrates). In general the results do not support the reservations held against formulated diets, but for a final determination long term studies over several year are required.

Feed composition and digestive capacity in parrots

Josef Kamphues, Petra Wolf, Karen Heisler and Markus Frömbling

Institute of Animal Nutrition, School of Veterinary Medicine Hannover, Bischofsholer Damm 15, D-30173 Hannover

Nutrition in many species of parrots is traditionally based on seeds, feeds offered as mixtures (the composition depends on species) and supplemented by fruits, vegetables and plants, Byproducts of animal origin (food like cheese etc.) are also used. The aim of several investigations on parrot nutrition performed during the last 10 years, was the characterization of different ingredients by commonly used parameters of feed science. Of special interest is the proportion of husk and kernel in seeds, and the content of crude nutrients (including starch and sugar) in the part of feed that is actually ingested, i.e. the kernel. The protein quality (content of amino acids), the mineral and vitamin contents as well as the palatability of various ingredients (for example in choice trials) were tested. Historical data published on the composition of seeds in toto (including their husks or shells) can often result in an incorrect determination of the nutritive value of the part of the seed really ingested. Of importance in formulation complete diets for different species of parrots is the observation that some of preferred seeds and ingredients fed traditionally to parrots have characteristic patterns of amino acids (for example: peanuts and hemp contain high levels of arginine). The mineral content of seeds used in parrot feeding are characterized generally by low calcium concentrations (in kernels of starchy seeds: < 0.7 g Ca/kg dry matter [DM]; of fatty seeds: 0.9-3.6 g Ca/kg DM) and high phosphorus levels (in starchy seeds: 1.5-6.4 g P/kg DM, in fatty ones: 7-16 g P/kg DM), whereas the sodium content is low in general (0.1–0.6 g/kg DM).

Further studies were done to characterize the supply of granivorous pet birds with b-carotene, tocopherols, thiamine, riboflavin and vitamin B-6 in more detail. Evidently, b-carotene and riboflavin requirements of pet birds cannot be met by exclusive feeding seeds. Under certain feeding conditions (e.g. when only few species of seeds are offered or birds develop a selective feeding behaviour) vitamin E and B-6 may be in short supply (without supplementation of the seed mixture). Only the relative high activity of analyzed seeds for thiamine is expected to meet the animals’ demand.

In recent studies the effect of crude fibre in the diet on digestibility of organic matter was tested in different species of pet birds (in comparison to hens). Digestibility of organic matter of identical diets clearly revealed species-specific effects (digestibility for love birds > cockatiels > budgerigars > canaries > hens > amazons). There may be differences in the enzyme concentration within the intestinal contents or the species differences could be based on anatomical conditions (size and proportion of the hindgut) and potential differences in intestinal microflora. Of special interest is the adaptation in enzyme secretion when the dietary fat or carbohydrate intake is changed, as was demonstrated in canaries and budgerigars.

An overview of captive Aceros and Buceros hornbill diets in some Dutch- and US Facilities

SG. Foeken1, Vries1, T.R. Huisman1*

1 Van Hall Institute, P.O. Box 1528, 9801 BV Leeuwarden, The Netherlands.* Contact person:

Hornbills are very popular and spectacular exhibit animals in collections of zoos and aviculturists. In recent years the birds have been identified as a group in need of good husbandry guidelines and a priority for captive breeding, because of their threats in the wild. Unfortunately, captive reproductive success is not very high. Diet could be a key factor in developing successful programs (Dierenfeld et al,. 1991) and it would be useful to determine nutrient requirements in order to compose or evaluate (current) hornbill diets. However, as with most zoo species, actual requirements have not been previously determined.
To obtain more insight in the current status of captive Aceros and Buceros hornbills nutrition, a survey was conducted among several Dutch and US facilities which keep these species. Ten facilities were visited and in each facility an interview concerning the hornbill diets took place. The nutritional composition of 12 diets was calculated using Zootrition software (Wildlife Conservation Society, 2001), and compared with available literature concerning nutrition of frugivores as well as results from the study on nitrogen requirements by Foeken and de Vries (2001).
Preliminary results of the analysis show a considerable spread in ingredients used and nutritional composition (i.e. different types of offered domesticated fruits and vegetables, meat and commercial diets, protein levels, Ca, Ca/P ratio and iron levels). All data obtained will be presented as an overview of captive Aceros and Buceros hornbill diets in some Dutch- and US facilities.

Foeken, S.G., and de Vries, M. (2001). Nitrogen requirements for maintenance of captive Aceros- and Buceros hornbills. BSc thesis, Van Hall Institute, Leeuwarden.
Dierenfeld, E.S., Conklin, N.L., Sheppard, C.D. and Grajal, A. (1991). Of Hoatzins and Hornbills: Duplicating natural diets. Proc. 9th Ann Conf. Dr. Scholl Conf.Nutrition Captive Wild Animals, Chicago.

KEY-NOTE LECTURE Allometry and ecology of feeding behavior and digestive capacity of herbivores: a review Revisited

P.J. Van Soest

Cornell University, Ithaca, NY 14853.

Herbivores have evolved in response to plant composition and morphology. Plants in turn have evolved defenses as well as exploitation of the animal presence. Plants offer food to herbivores and in return have obtained seed dispersal and altered chemical composition to favour animals. However, plants have also evolved protection through resistant structures fiber, lignin and secondary compounds that limit digestion. These resistant substances are at the expense of photosynthesis. Herbivores in return have developed means of coping with less digestible food. One of these is increased body size which promotes greater digestive capacity. Animal gut capacity forms a linear function (power one) relationship with body weight, while energy requirements are related to metabolic size (power three-quarter of body weight). The interaction of these two power relationships favour digestive capacity to increase at the one-quarter power of body weight. Thus small animals are less efficient utilisers of slower digesting fibre. The indigestible fibre must pass through the digestive tract or else be avoided by selective feeding. Monocots (grasses) are more difficult to selectively feed upon than dicotyledonous species because of morphology. Selective passage occurs in rabbits and lemmings. Intraspecific comparative digestive trials are often confused by failure to measure the fibre and lignin content of uneaten food. Avoidance of the more lignified structures by small herbivores allows higher digestibility and longer retention times. Ruminating animals with foregut fermentation are more efficient in extracting energy from fibre relative to non ruminants of the same size. Rumination allows a smaller animal to achieve the digestive capacity of larger non ruminant herbivores.
Plant fibre varies widely in nutritive quality, decreasing with plant maturity and warm climates. Geographic variation creates a difficulty for zoo nutritionists because local sources of feed may not match the adaptations of specialised animals from foreign habitats. Pelleting fibrous feeds forces the animal to consume the lignified matter and effectively limits selective feeding. This can be a problem for small selectors. Grinding also eliminates the “scratch factor” needed by larger bulk and roughage eaters, and compromises the rumination process in ruminants.

Van Soest, P.J. 1994 Nutritional Ecology of the Ruminant. 2nd edition, Cornell University Press, Ithaca, NY. pp. 476
Van Soest, P.J. 1996 Allometry and ecology of feeding behavior and digestive capacity in herbivores: A review. Zoo Biology 15:455-479.
Van Soest, P.J., E.S. Dierenfeld and N.L. Conklin. 1995. Digestive strategies and limitations of ruminants. In: Ruminant physiology: Digestion, metabolism, growth and reproduction.
Proceedings of the Eighth International Symposium on Ruminant Physiology. Eds. W.v. Engelhardt, S. Leonhard-Marek, G. Breves and D. Giesecke. Ferdinand Enke Verlag Stuttgart. pp.581-600.

Body size limitations in ruminants, or why buffalo defecate pies not pellets

M. Clauss1, M. Lechner-Doll2, W.J. Streich2, R. Frey2, G.E. Rössner3

1Institute of Animal Physiology, Physiological Chemistry and Animal Nutrition, Veterinaerstr. 13, 80539 Munich, Germany
2Institute of Zoo Biology and Wildlife Research (IZW) Berlin, Germany
3Palaeontology Munich, Dept. of Geo- and Environmental Sciences, Germany

While the lower body size limit of ruminants has been explained convincingly, the upper body size range attainable for ruminants still poses a theoretical problem. In this contribution, we focus attention on the morphophysiological consequences of ruminant foregut fermentation. Ruminant forestomachs were designed to delay ingesta passage; as a side effect they limit food intake. Therefore, with increasing body size their relative capacity has to increase in order to compensate for this intake limitation. It seems that the foregut fermenting ungulates did not evolve species in which the intake-limiting effect of the foregut could be reduced, e.g. by special bypass structures, and hence this digestive model imposed an intrinsic body size limit. This limit will be lower the more the natural diet enhances the ingesta retention and hence the intake-limiting effect. Therefore, due to the mechanical characteristics of grass, grazing ruminants cannot become as big as the largest browsing ruminant, and our model precisely predicts the observed difference in maximum body weight attained by grazing and browsing ruminants.
Ruminants are not absent from the very large body size classes because their digestive physiology offers no particular advantage, but because their digestive physiology itself intrinsically imposes a body size limit. We suggest that the decreasing ability for colonic water absorption in large grazing ruminants and the largest extant foregut fermenter, the hippopotamus, are an indication of this limit, and are the outcome of the competition of organs for the avaiable space within the abdominal cavity. Our hypotheses are supported by the fossil record on extinct ruminant/tylopod species that did not surpass extant species in maximum body size.

Browse silage: the solution for browsers in wintertime?

J. Nijboer1, M. Clauss2, J.J.L. Nobel3

1Veterianary Department Rotterdam zoo, the Netherlands,
2 Institute of Animal Physiology, Physiological Chemistry and Animal Nutrition, University of Munich
3 Animal Department Rotterdam zoo, the Netherlands

According to Hofmann (2000), ruminants can be divided into concentrate selectors/browsers, intermediate types and grass/roughages eaters. The group of browsers consists of fruit eaters, animals with a high amount of herbaceaous dicots in their diet, and tree and shrub eating animals. Several diseases in browsing ruminants are linked to nutrition like gastrointestinal disorders, rumen acidosis and phytobezoars. There is also a difference in the physiology between grazers and browsers (Hummel and Clauss, 2001).
Giraffes, kudus, bongos, dikdik’s and duikers belong to the group of concentrate selectors or browsers which are often found in zoos. They are mostly fed a diet which consists of ‘browser pellets’ as well as alfalfa and some greens and fruits. However, browse should be a major part of their diet in order to prevent acidosis (Hummel and Clauss, 2001 ). If available in summertime, browse often consists of willow or poplar. Especially in temperate climates, it is difficult to feed fresh browse during wintertime to browsers. If a zoo intends to feed browse in wintertime, it should be harvested in autumn and properly stored until winter. This presentation will summarize the ways browse can be stored – fresh, frozen and dried.
Another option is to produce silage. Silaging is an anaerobic process. Anaerobic bacteria ferment the browse, and lactic acid is set free. At a pH of 4.2, the silaging process stops and the browse is ready to be fed. In Zurich (Hatt and Clauss, 2002), willow, hazel and maple are processed in a chafcutter and stored under anaerobic conditions in plastic containers. The product is fed in wintertime to rhinoceros. Analyses showed no significant alteration in composition before and after silaging.
At Rotterdam Zoo, in autumn 2001, willow branches and leaves were bailed by a bailing machine under high pressure and automatically double wrapped in plastic. The 70 bails of willow and 15 of poplar weighed between 45 and 50 kg. The dimensions of the bails were 100 x 50 x 35 cm. The silage was fed to the browsers in the wintertime. All the browsers (okapi, giraffe, kudu, tuffed deer and bongo) preferred the silage browse rather browse which had been frozen. In the future, it is planned that browse silage will be an important part of the diet in both winter- and summertime.
The process and conditioning of the silaging as well as the palatability of willow browse and other browse species will be discussed in detail. More research concerning the digestion of browse silage is in preparation.

Hummel J., Clauss M. 2001. Browsers. Workshop on designing diets for browsing ruminants. EAZA conference Prague.
Hatt J.M., Clauss M. 2001. Browse silage in zoo animal nutrition. Feeding enrichment of browsers during winter. Abstract Book Second European Zoo Nutrition Conference.
Winchester, UK Hofmann R.R. 2000. Zoo Animal Nutrition (J.Nijboer et al. ed.): 163-182. publisher Filander Verlag

Irregular patterns for low amounts of dietary tannins in captive roe deer (Capreolus capreolus): Implications for the validity of preference trials

M. Clauss 1, K. Lason2, M. Lechner-Doll2, J. Fickel2, J. Gehrke2

1Institute of Animal Physiology, Physiol. Chemistry and Animal Nutrition, Munich, Germany
2Institute of Zoo Biology and Wildlife Research (IZW) Berlin, Germany

Recently, it was demonstrated that captive roe deer actively select for a low amount of dietary tannins in preference trials (1). However, the periods of these trials comprised mostly 5-8 days only. Other ruminants, e.g. goats, have been shown to develop a food aversion to dietary tannins after only a few days (2). We intended to replicate the results with roe deer in longer trials, and with different types of tannins. Three groups of adult and two groups of growing roe deer were submitted to series of longterm preference trials in which different combinations of a regular pelleted feed and the same feed with the addition of 3 or 6 % of tannic acid or quebracho were tested. Food consumption of each group was determined by weighing offered components and leftovers the next day. We could not elucidate a consistent preference pattern for the roe deer groups used in this study. One group consistently preferred the highest available tannin concentration, whereas the other groups mostly preferred the tannin-free feed, but included tannins in differing amounts. There seemed to be a general pattern that tannin consumption peaked after 5-10 days but declined afterwards again.
The most important implication of these findings is that - at least where tannins are concerned - results of short-term preference trials might be misleading. If the trials would have been terminated after 5-10 days, most groups would have shown a continuous increase in tannin consumption. Similarly, one group showed a distinct tannin rejection during the first 5 days and increased their consumption afterwards. Obviously, long-term diet choice needs to be considered when designing preference trials. If results from preference trials are to be used in a conclusive way, the scope, and possibly the reasons, for immense individual differences need to be further elucidated.

(1) Verheyden-Tixier H, Duncan P (2000) J Chem Ecol 26: 351-358
(2) Provenza et al. (1991) Am Nat 136: 810-828

Grazing, ruminating and resting in Bos taurus, when herbage availability is limiting.

E.J. Finegan, J.L. Atkinson, J.G. Buchanan-Smith, J.P. Cant

Department of Animal and Poultry Science, University of Guelph, Ontario, Canada

In intensively managed, temperate pastures herbage availability may become limiting when sward height, sward bulk, or a combination of sward height and bulk, drop below certain critical values. For a grazing ruminant there are three major time-consuming, daily maintenance activities: grazing to apprehend and ingest herbage, ruminating to facilitate herbage digestion, and rest/sleep. Other important maintenance activities, drinking, urination, and defaecation, represent a very small daily time investment.
When herbage availability becomes limiting, and there is insufficient time in the day (24 hours) to ingest adequate food, to ruminate the ingested food and to sleep, the time spent on one or more of these activities must be reduced. Time spent sleeping by cattle at pasture is rarely observed to drop below four hours a day, with approximately 0.5 hours of rapid eye movement (REM) or paradoxical sleep, and 3.5 hours of non-REM or slow wave sleep (Ruckebusch et al., 1975). Time spent ruminating is affected both by the quality, defined as neutral detergent fibre (NDF %DM), and quantity of the herbage consumed (Bae et al., 1983). So when the grazing animal cannot eat enough in the time available, the time spent grazing and consequently the time spent ruminating are reduced. It is also suggested by certain recently published data (Gibb et al., 1999) that the time spent ruminating each kg NDF consumed may also be reduced, thus leaving more time for grazing.
Using a basic model which describes daily maintenance activities in grazing beef cattle (Finegan et al., 2001), two scenarios of response to time constraint (where daily time spent grazing, ruminating and sleeping would need to exceed 24 hours to achieve adequate feed intake) have been investigated. For scenario 1, predicted grazing and ruminating time in excess of 24 hours was deleted in proportion to predicted total grazing and ruminating times. For scenario 2, the time spent ruminating each kg NDF was reduced by 15% (based on an evaluation of data from Gibb et al., 1999), prior to proportional deletion of any grazing and ruminating time still in excess of 24 hours. The predicted total daily dry matter intake (DMI), recalculated after reducing daily maintenance activities to 24 hours, was 3.1, 4.2, and 5.3 % higher (for cattle of 200, 400 and 800 kg live weight) when ruminating time /kg NDF was reduced (scenario 2).
Little is known about the circumstances under which grazing cattle may reduce ruminating time /kg NDF. Such a reduction in ruminating time might be expected to be associated with some reduction in feed digestibility, if the increased quantity of feed ingested moves more quickly through the digestive tract (Van Soest, 1994). It is also not known whether the increased DMI would more than compensate for any decrease in digestibility. It is possible that a strategy of reduced rumination to allow time for increased DMI would be advantageous to the grazing animal if the quality of herbage on offer was good, but not if it was poor and difficult to digest.

Bae D.H. et al., 1983. J Dairy Sci 66: 2137-2141.
Finegan E.J. et al., 2001. Proc AZA NAG 4th Conf Zoo Wildlife Nutr 86-90.
Gibb M.J. et al., 1999. Appl Anim Behav Sci 63: 269-287.
Ruckebusch Y. et al., 1975. Sleep 1974. 2nd Europ Congr Sleep Res 273-276.
Van Soest P.J., 1994. Nutritional Ecology of the Ruminant.