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I Kyriazakis

Publications and source records attributed to I Kyriazakis.

At least 55 records · Page 3Linked to original sources
PubMed1999

Diet selection and animal state: an integrative framework.

In the present paper we deal with the problems of explaining and predicting diet selection of animals under controlled conditions, i.e. conditions that can be described and in which any influences of the environment can be either controlled or at least monitored. Diet selection is considered within an integrative framework of feeding behaviour that views both food intake and diet selection as an outcome of the animal's internal state and knowledge of the feeding environment. Three questions that arise from the framework are considered: (1) how do animals learn about foods available to them as a choice? (2) what changes in internal state affect diet selection? (3) how much time is needed for a change in the animal's internal state to be detected and for it to react to this change through a modification of its diet selection? It is proposed that animals have developed behavioural mechanisms that allow them to recognize foods on the basis of their nutritional as well as other properties. The rate at which animals learn about foods depends largely on the extent of the animal's deficiency and on the extent of the post-ingestive consequences induced by the foods. There is little evidence that animals modify their diet selection in response to short-term systemic fluctuation of their internal environment. On the other hand, long-term changes in the internal state of the animal lead to consequent long-term changes in diet selection. The time needed for a change in diet selection to be observed depends on the deviation created in the animal's internal state, either as a result of a physiological change or as a consequence of feeding. Thus, a more appropriate question to consider is not 'what time period matters to the animal?' but 'how much change or deviation in the internal state is the animal prepared to accept?'

Animals↗
PubMed1998

Satiety splits feeding behaviour into bouts

Animal behaviour is frequently displayed in bouts. Bout analysis aims at finding a bout criterion, i.e. that time between events that separates intervals within, from intervals between, bouts. Methods used for quantitative bout analysis are log-supervivorship and log-frequency analysis. Both models assume that the probability of the start of an event (or a bout) is independent of the time since the last event (or bout) and that, therefore, events as well as bouts occur according to Poisson processes, i.e. purely at random. The frequencies of intervals within, as well as between, bouts are then distributed as negative exponentials. These models are also widely applied in feeding behaviour analysis, where bouts can be meals. However, the satiety concept predicts that after terminating a meal, the animal's feeding motivation will be low. The probability of the animal initiating the next meal is expected to increase with time since the last meal and, therefore, meals will not likely be randomly distributed. A negative exponential is then not the most appropriate model to describe the frequency distribution of intervals between meals. Results of an experiment in which feeding behaviour of 16 cows was recorded continuously for 30 days were used to test the suitability of existing bout analysis techniques. It is concluded that these techniques are inadequate for the description of the observed interval distributions. A new model is proposed that takes account of the observed "shortage" of short intervals between meals. In contrast to existing models, that describe log-transformed frequency distributions of interval lengths, the proposed model describes frequency distributions of log-transformed interval lengths. Compared with existing models, this log-normal model is in better agreement with the biological phenomenon of satiety, it gave a better fit to the observed interval distribution and led to a more meaningful meal criterion.Copyright 1998 Academic Press Limited

Journal Article↗
PubMed1998

Towards a functional explanation for the occurrence of anorexia during parasitic infections.

The development and occurrence of anorexia, the voluntary reduction in food intake during parasitic infections in animals, is somewhat paradoxical and contrary to conventional wisdom and expectation. We take the view that its occurrence is an evolved, costly behavioural adaptation which serves a function. Five such functional and general hypotheses to account for it are developed: (1) anorexia is induced by the parasite for its own benefit; (2) food intake decreases to starve parasites; (3) the negative effect on the host's energetic efficiency during parasitic diseases has a direct effect on food consumption; (4) food intake decreases for the purpose of promoting an effective immune response in the host; and (5) anorexia allows the host to become more selective in its diet, and thus select foods that either minimize the risk of infection or are high in antiparasitic compounds. Only hypotheses (4) and (5) survive the comparison for consistency with the physiological, metabolic and behavioural alterations that occur during the development of parasitic infections, and with the rule of generality (i.e. account for its occurrence in both protozoan and helminth infections). Both surviving hypotheses will need further experimental testing for their support or rejection, and such experiments are proposed. Also, the advantages and consequences of viewing anorexia during parasitic infections within a functional framework are discussed. These arise from the recognition that anorexia is a disease-coping strategy, part of the mechanism of recognition of parasite invasion by the immune system, which leads to a modification of the host's feeding behaviour. Copyright 1998 The Association for the Study of Animal Behaviour

Journal Article↗
PubMed1998

Conditioned flavour aversions in sheep: the relationship between the dose rate of a secondary plant compound and the acquisition and persistence of aversions.

Within the overall objective of whether ruminants are able to form conditioned aversions (CFA) toward a food flavour associated with the administration of an aversive stimulus which occurs naturally in food plants (oxalic acid, OA), two specific objectives were tested: (1) whether the rate and degree of formation of CFA are dependent on the dose rate of OA administered and (2) whether the persistence of formed CFA depends on the previous dose rate of OA. Sheep were conditioned to associate the specific flavour of one of two novel foods with either the oral administration of OA or equivalent placebos. Four dose rates of OA were tested (0.06, 0.12, 0.18 and 0.24 g/kg sheep live weight per d), with twelve sheep per dose. Each conditioning period lasted for 8 d and was repeated four times. At the end of each conditioning period the preference for the two flavours was measured in short-term, 20 min preference tests. The persistence of the CFA was measured at 0, 7, 21 and 49 d after the completion of the conditioning phase with long-term, 3 h preference tests. The results of the experiment indicated that: (1) the rate and degree of formation of CFA were dependent on the rate of administration of OA; (2) sheep required repeated exposures to the lower dose rates of OA in order to develop CFA and these CFA did not persist in the absence of continual reinforcement; (3) CFA to the higher dose rates of OA were developed after as little as one exposure and persisted over a period of at least 7 weeks. These findings are consistent with the expectation that ruminants should be able to select a diet which minimizes the risk of consumption of potentially harmful foods, whilst at the same time maintaining a degree of flexibility in their feeding behaviour.

Administration, Oral↗
PubMed1998

Feed intake relative to stage of lactation for dairy cows consuming total mixed diets with a high or low ratio of concentrate to forage.

This experiment examined the effect of feed quality on the relationship between intake and stage of lactation in dairy cows. Two total mixed diets composed of grass silage and concentrate were formulated. The high concentrate total mixed diet was designed to meet energy requirements, and the low concentrate total mixed diet was designed to limit intake. Twenty-four Holstein-Friesian cows were offered the total mixed diets in a full 2 x 2 change-over design with control treatments. The changeover was at 153 d in milk (DIM). For the statistical analyses, two periods of 13 wk, one period before and one period after the changeover, were used. Dry matter intake (DMI), milk yield, body weight, and body condition score were significantly greater for cows fed the high concentrate total mixed diet than for cows fed the low concentrate total mixed diet. Significant interactions between total mixed diet and period were observed for DMI and milk yield. However, no significant residual effects of changing from one total mixed diet to the other were observed. The interactions were due to substantially different slopes of DMI and milk yield relative to DIM for cows fed the two different total mixed diets. For cows fed the low concentrate total mixed diet, there was no effect of stage of lactation on DMI; the slope was 0. For cows fed the high concentrate total mixed diet, there was a significant decline in DMI as lactation progressed.

Animal Feed↗
PubMed1998

Diet choice by dairy cows. 1. Selection of feed protein content during the first half of lactation.

Effects of weeks in milk and milk yield on diet choice were recorded during the first half of lactation. Low and high protein feeds were used, and both consisted of 30% concentrate and 70% grass silage (fresh matter basis). Both feeds contained similar amounts of energy, but the crude protein contents were 131 and 185 g/kg of dry matter (DM), respectively, for the low and high protein feeds. In a nutrient flow experiment with three cannulated lactating cows, the metabolizable protein yields of the low and high protein feeds were 75 and 114 g/kg of DM, respectively. Thirty-seven cows were divided into control groups for the low and high protein feeds, and a choice group had access to both the low and the high protein feeds. Intake of DM and milk yield by cows in the control group fed the high protein feed were higher than those by cows in the control group fed the low protein feed, but these measurements did not differ from those of cows in the choice group. Cows in the choice group consumed a mean of 683 g of high protein feed/kg of total intake, which differed from what would be considered random intake (500 g/kg total intake). Diet choice did not systematically change during the experiment and was not correlated with weeks in milk, milk yield, or milk protein output. We concluded that diet selection differed significantly from what would be considered random, which allowed cows in the choice group to perform well. However, diet choice did not reflect the estimated metabolizable protein requirements of the cows.

Ammonia↗
PubMed1998

Diet choice by dairy cows. 2. Selection for metabolizable protein or for ruminally degradable protein?

Diet choice, expressed as grams of high protein feed selected per kilogram of intake, was measured for lactating cows with ad libitum access to two feeds. First, cows were given a choice between a low protein feed and a high protein feed for 9 wk while feeds were alternated between feeders. The proportion of feed chosen from a feeder depended on the feed it contained, which showed that cows selected for feed characteristics. Diet choice was then measured over six periods during which cows had access to either a low protein feed and a high protein feed or to these feeds plus added urea. Diet choice was lower when urea was added, suggesting a substantial effect of the content of ruminally degradable protein (RDP) in feeds on diet selection. All feeds had equal RDP contents in Experiment 3 when early and late lactating cows had access first to two feeds with a low and high yield of metabolizable protein and then to two feeds with a low and medium yield of metabolizable protein. Diet choice did not differ from what was considered to be random and was not affected by milk yield or stage of lactation. No evidence suggests that cows selected for metabolizable protein when both feeds contained adequate RDP.

Animal Feed↗
PubMed1998

Effects of feed composition and stage of lactation on the short-term feeding behavior of dairy cows.

Twenty Holstein-Friesian cows were assigned to one of four feeding groups throughout lactation in a full change-over experiment using two total mixed diets. The low concentrate total mixed diet contained 100 g of concentrate/kg of fresh matter, and the high concentrate total mixed diet contained 300 g of concentrate/kg of fresh matter. The remainder of the total mixed diet was grass silage. The two changeover groups switched total mixed diets at 153 d of lactation; the other two treatment groups remained on their assigned diets throughout lactation. For analysis of short-term feeding behavior, four periods of 3 wk each were identified. The midpoints of these periods were -102, -18, 18, and 102 d from the changeover. The concentrate content of the total mixed diet significantly affected dry matter intake and all short-term feeding behavior variables. Cows that consumed the high concentrate total mixed diet had fewer but longer visits to the feeders and ate more feed per visit than did cows consuming the low concentrate total mixed diet. With one exception, no significant effect of stage of lactation was detected for any of the short-term feeding behavior variables. Despite a highly significant decline in dry matter intake as lactation progressed for cows consuming the high concentrate total mixed diet, there were no interactions between total mixed diet and stage of lactation for any of the short-term feeding behavior variables. Large differences in feeding behavior were detected between cows consuming the same total mixed diet. These last two findings suggest that the use of short-term feeding behavior variables to predict daily intake is unlikely to be successful.

Animal Feed↗
PubMed1997

Food intake and diet selection in sheep: the effect of manipulating the rates of digestion of carbohydrates and protein of the foods offered as a choice.

An experiment was designed to investigate whether the degree of synchrony between the rates of digestion of carbohydrates and N of foods offered as a choice would have an effect, through their consequences, on the short- and long-term diet selection of sheep. Four foods (RL, RH, SL and SH) with the same high metabolizable energy, and similar high metabolizable protein contents were made into pellets. Foods RL and RH were based on a rapidly fermentable carbohydrate source and foods SL and SH on a slowly fermentable carbohydrate source; within each source one food (RL or SL) had a low, and the other (RH or SH) a high, rumen-degradable protein (RDP) content. The foods within a carbohydrate source were offered either singly or as a choice (RL/RH or SL/SH) to eleven rumen-fistulated mature sheep. The design was two 3 x 3 Latin squares (replicated once) with 5-week periods; squares consisted of two single foods and their respective choice. Weeks 1, 3 and 5 were considered to be controls, and weeks 2 and 4 used for rumen infusions of either urea or fructose infused over 4 h (10.00-14.00 hours). Food intake (FI) and diet selections (DS) were recorded daily and every 2 h (08.00-16.00 hours) on days 2-5 of each week; rumen pH and NH3 concentrations were also measured during these time intervals of day 5. As expected, feeding treatment affected significantly the rumen measurements: rumen NH3 concentrations were higher on foods RH and SH, and rumen pH lowest on RL. Daily FI was lowest on treatments SL, and choice SL/SH. The mean daily proportion of the low-RDP food in the selected diet was lower when the carbohydrate source was rapidly (choice RL/RH) rather than slowly fermentable (choice SL/SH); this was consistent with the experimental hypothesis. Short-term infusions affected further rumen variables (in the expected directions), irrespective of feeding treatment. However, DS over the 4h infusion period were unaffected; these short-term DS were consistent with the ones selected over the longer term (daily). The results suggest that the long-term (daily) diet selection of sheep may be affected by the degree of synchrony of energy and protein to the rumen. The fact that diet selections were not altered further by short-term manipulations of these supplies might reflect inadequacies of the methodology (infusions) adopted here.

Ammonia↗
PubMed1996

The pathophysiology and development of immunity during long-term subclinical infection with Trichostrongylus colubriformis of sheep receiving different nutritional treatments.

The objective of this study was to investigate the relationship between protein nutrition, the pathophysiology, and acquisition and expression of immunity in long-term subclinical intestinal parasitism in sheep. Growing sheep were either uninfected controls or parasitised for 27 weeks with a daily dose of 2500 larvae of Trichostrongylus colubriformis, whilst they were given access to: (1) a low protein food, (2) a high protein food, or (3) a choice between the two foods, where they were allowed to select their diet. Blood samples were taken weekly for determination of serum albumin, total protein, Ca, P, urea and fructosamine concentrations. At the end of the study all sheep received a single (secondary) challenge infection (30,000 T. colubriformis L3) after treatment with anthelmintic to assess their immune status. The concentrations of sheep-mast cell proteinases (SMCP) in intestinal tissue, the number of circulating eosinophils and the total worm numbers recovered from the intestinal tract were used to investigate the effects of previous nutrition on the acquisition and expression of immunity. From the biochemical variables measured over 27 weeks, only serum fructosamine was affected by the interaction between feeding treatment and parasitism: fructosamine concentrations declined only in the parasitised animals on the low protein food during Weeks 6-15 of infection. This casts doubt on the usefulness of plasma fructosamine levels as an indicator of gastrointestinal parasitism, due to its being influenced by the nutritional environment. Total protein, albumin, calcium and phosphorus concentrations in the serum were affected by parasitism, but independently of feeding treatment. During the period of secondary challenge eosinophil numbers and SMCP concentrations were higher in the parasitised animals, reflecting the animals immune responsiveness. The numbers of worms recovered from the intestine of previously parasitised sheep were low; all three indicators of the development of acquired immunity were unaffected by previous nutritional treatment of the sheep. The results do not support the view that the pathophysiology of long term subclinical intestinal parasitism and the expression of acquired immunity induced by a trickle infection could be affected by the feeding treatment of the sheep (protein nutrition).

Animal Nutritional Physiological Phenomena↗
PubMed1996

Long-term subclinical infection with Trichostrongylus colubriformis: effects on food intake, diet selection and performance of growing lambs.

Growing lambs (mean liveweight 22.4 kg) were used to test for the effects of long-term subclinical infection with Trichostrongylus colubriformis (2500 larvae per day) on the voluntary food intake (VFI), diet selection and performance of sheep given a choice between two foods of different protein content (low versus high). Sheep were either uninfected controls or parasitised for 27 weeks (Group 27P). Additional sheep were infected for either 9 or 18 weeks (before and after the development of complete resistance to parasites, as assessed by faecal egg counts) and then treated with anthelmintic to remove the parasites (Groups 9P and 18P). Group 18P remained uninfected after anthelmintic treatment whereas Group 9P was infected again for the last 9 weeks after a 9 week worm-free period. The VFI declined or remained static from Week 5 up to Week 11/12 of continuous infection, for the 27P and 18P groups. For 9P sheep, VFI recovered within a few days after the anthelmintic administration and was unaffected during re-infection over the last 9 weeks of the experiment. Diet selection changed in such a pattern that the proportion of the high protein food (prop H) in the selected diet started to increase from Week 6 of the infection. The prop H selected remained higher over the interval 10-18 weeks of the continuous infection for 27P and 18P groups than the uninfected controls. There were no significant differences in diet selection among any of the groups beyond Week 18 of the experiment. The infection caused a growth check from Week 7 to approximately Week 12/14 of dosing; these was no evidence of compensatory growth following the development of resistance or recovery. The results are consistent with the view that sheep given a choice between two appropriate foods will modify their diet selection in order to moderate the adverse effects of subclinical nematode infection. The performance and diet selection of all sheep beyond Week 18 of infection suggest that no obvious nutritional penalties are incurred with the continuation of the infection once the animals have become resistant to parasites.

Animals↗
PubMed1996

The effects of physical form of feed, carbohydrate source, and inclusion of sodium bicarbonate on the diet selections of sheep.

We proposed an hypothesis that ruminants attempt to select a diet that promotes high levels of feed intake by maintaining optimal ruminal conditions. Three tests of the hypothesis considered whether the diet selection of sheep given either a choice of two high energy density (ED) feeds or a choice between a high and a low ED feed is affected by 1) sodium bicarbonate inclusion (NaHCO3; 1, 2, and 4% [wt/wt]) in the high [ED] feed); 2) dietary carbohydrate source (barley-based, B and sugar beet/ barley, S) of the high ED feed; or 3) physical form (alfalfa: pelleted, ALFP and long chop, ALFL) of the low ED feed. To conduct these, 42 lambs were used in seven 6 x 6 Latin squares, which were either foods ALFL and ALFP offered alone and paired with feed B or S and their NaHCO3 derivatives as a choice, or foods B and S offered alone and paired with their NaHCO3 derivatives as a choice. Each Latin square period lasted for 3 wk. For the choices between a NaHCO3-supplemented high ED feed and either a high or a low ED one, the inclusion of NaHCO3 increased feed intake. Its level of inclusion had a marked effect on the proportion of unsupplemented high ED feed selected (P < .05) but not on the proportion of low ED feed (alfalfa) selected. More alfalfa was selected when the high ED feed was based on barley (B) rather than sugar beet/barley (S) (P < .05). The physical form of the alfalfa affected diet selection because its selection was greater (P < .001) when ALFP (pelleted) was offered in the feed choice rather than ALFL (long-chop). The significant effects of NaHCO3 level, dietary carbohydrate, and physical form on the diet selection and feed intake of the sheep are consistent with the proposed experimental hypothesis.

Animal Feed↗
PubMed1995

The voluntary feed intake of pigs given feeds based on wheat bran, dried citrus pulp and grass meal, in relation to measurements of feed bulk.

Two experiments were carried out to investigate the capacities of pigs for bulky feeds. In Expt 1 fifteen pigs were offered, from 12 to 25 kg live weight, ad lib. access to one of five feeds which were made by progressively diluting a high-quality feed with wheat bran. Intake initially increased, and then declined, as the proportion of wheat bran was increased. The pigs became better able to accommodate to the more bulky feeds over time. In Expt 2 thirty-six pigs, initially of 12 kg live weight, were used. The feeds were the same high-quality basal feed as in Expt 1 and three others made almost entirely of either wheat bran, dried grass or dried citrus pulp, respectively. The equal-parts mixtures of each of these three bulky feeds with the basal feed were also made to give three series of feeds each comprising the basal, the mixture and the bulky feed. The three feeds in each series were given ad lib. to twelve pigs in a design of two replicated Latin squares with three time-periods. Within each series, and across periods, the intakes of the feeds that were limiting intake were directly proportional to live weight and so a scaled intake, expressed as g/kg live weight per d, was calculated. Across the six limiting feeds, scaled intakes in the final 5 d of each period, when the pigs were in equilibrium with their feeds, were directly proportional to the reciprocal of the water-holding capacities (WHC) of the feeds, as measured by a centrifugation method. There were large effects of feed changes on intake, in the short term, with previous experience of a bulky feed leading to higher intakes of another bulky feed. The intake of the basal feed was not affected by the feed given previously. It was concluded that: (a) the time of adaptation to bulky feeds needs to be considered when attempting to measure, or predict, the rates of intake on different bulky feeds and, (b) the WHC of the feeds could be an appropriate measurement of 'bulk' responsible for limiting their intake, and could be used to predict the maximum feed intake capacity of pigs on different bulky feeds.

Adaptation, Physiological↗
PubMed1995

Diet selection in sheep: the role of the rumen environment in the selection of a diet from two feeds that differ in their energy density.

The effect of the energy density (ED) of feeds offered as a choice on the diet selection of sheep, and the relationship between the rumen environment and the diet selected from feeds of different ED were investigated in two experiments. In the first experiment two feeds, L and H, and their mixture M (3:1 w/w) were formulated. All feeds had similar calculated metabolizable protein:metabolizable energy (ME) ratios, but differed in ED (7.4, 8.1 and 10.1 MJ ME/kg fresh feed for L, M and H respectively). The feeds were offered ad lib. either singly or in paired choices (L/M, L/H and M/H; n6 per treatment) to growing sheep. Although the rate of live-weight (Lwt) gain on feed H was higher than on feeds L or M, and the daily rate of feed intake lower, the sheep on feed choices did not consume only feed H. Instead they selected a mixture of both feeds offered, such that the total amount of H consumed per kg fresh feed was similar on choices L/H and M/H. The rate of Lwt gain of sheep on choices L/H and M/H was not different from that achieved on feed H alone. In the second experiment the choice L/H was offered to fistulated sheep (10 months of age, mean Lwt 57.5 kg) in an 8 x 8 Latin square, with 7 d periods. Treatments were infusions into the rumen (total volume 1 litre) over 4 h on days 1-4 of each period of acid (HCl; Acid 1, 400; Acid 2, 300 and Acid 3, 200 mmol/l), alkali (NaOH; Alk 1, 316; Alk 2, 212 and Alk 3, 109 mmol/l) and control (NaCl; Con 1, 315 and Con 2, 209 mmol/l). Infusate osmolalities (mOs/kg) were 795 (Acid 1), 585 (Acid 2, Alk 1 and Con 1), 390 (Acid 3, Alk 2 and Con 2) and 200 (Alk 3). Infusion treatment significantly affected the diet selection of the sheep (P < 0.05) according to the osmolality of infusate, but not according to rumen pH. During infusions intake of feed H tended to decline with increasing treatment osmolality, whereas intake of L remained constant. The effects on diet selection and feed intake were of a short duration with no carry-over effects.(ABSTRACT TRUNCATED AT 400 WORDS)

Animal Feed↗
PubMed1995

Do breeds of pig differ in the efficiency with which they use a limiting protein supply?

An experiment was designed to test the prediction that two genetically-very-different kinds of pigs would retain the same amounts of protein in their bodies when given the same allowances of the same feed for the same period of time, when these allowances were limiting for both. An allowance of 33.957 kg of a feed with 12.76 MJ metabolizable energy (ME) and 189 g crude protein (N x 6.25)/kg feed was given to Large White x Landrace (LW x) and Chinese Meishan (CM) female pigs over three different periods of time: (1) ad lib. (AL) with the time taken by individual pigs to consume the allowance being a variable, (2) over a period of 7 weeks (H) and (3) over a period of 9 weeks (L). In addition, in a fourth treatment, pigs of both breeds received the same allowance but supplemented with starch also over a period of 7 weeks (HS). The performance of the pigs on treatment AL was affected by pig breed, with CM pigs gaining protein at a slower, and lipid at a faster, rate than LW x pigs. On treatments L, H and HS the average amounts of protein retained were 2.693 and 2.655 kg for the LW x (n 15) and CM (n 15) pigs respectively (SED 0.106 kg). There was a statistical indication that the LW x pigs may have been more efficient on L, and less efficient on HS, than the CM pigs but we have been unable to propose any biological reason for such an effect, if it was in fact a real one. Thus, the efficiency with which ideal protein was utilized was close to being constant, and apparently at its maximum, for the two breeds. However, although CM pigs had the same protein gain, and the same live weights, on the same feed allowances as the LW x pigs, they gained significantly more lipid. This was attributed in part to their digesting their feed better and in part to their having a lower energy requirement for maintenance through a lower level of physical activity. Given that these two very different kinds of pigs use limiting protein with the same efficiency, it is suggested that it is safe to make the assumption in models of pig growth that the material efficiency of using limiting protein is constant across genotypes of pig.

Animal Feed↗