Level Of Feeding Motivation Research Articles

Size-dependent predation on juvenile herring (Clupea harengusL.) by Northeast Arctic cod (Gadus morhuaL.) in the Barents Sea

Stomach samples from Northeast Arctic cod (Gadus morhua L.) in the Barents Sea were analysed to study size-dependent predation on juvenile Norwegian spring-spawning herring (Clupea harengus L.). The relationship between prey and predator body lengths was examined by regression analysis, separately for the first and second halves of the year. The slopes of the relationships were similar for both halves of the year. The effects of feeding motivation of individual cod and the occurrence of capelin (Mallotus villosus Müller, 1776) were included in the regression. In the first half of the year, cod <34 cm did not eat herring if capelin was present. For larger cod the body size of herring consumed increased with the level of feeding motivation, and was highest for cod with capelin in the environment. Feeding motivation and occurrence of capelin had no effect in the second half of the year. Cod <25 cm rarely consumed herring. In general, the age of herring eaten increased with cod size. The youngest age group of herring was consumed by cod of size 25-75 cm from the moment they entered the Barents Sea in the autumn and throughout the winter. The age-dependent spatial distribution of herring in the cod stomachs conformed to the general geographical distribution of different age groups of juvenile herring in the Barents Sea.

Size-dependent predation on juvenile herring ( Clupea harengus L.) by Northeast Arctic cod ( Gadus morhua L.) in the Barents Sea

Stomach samples from Northeast Arctic cod (Gadus morhua L.) in the Barents Sea were analysed to study size-dependent predation on juvenile Norwegian spring-spawning herring (Clupea harengus L.). The relationship between prey and predator body lengths was examined by regression analysis, separately for the first and second halves of the year. The slopes of the relationships were similar for both halves of the year. The effects of feeding motivation of individual cod and the occurrence of capelin (Mallotus villosus Müller, 1776) were included in the regression. In the first half of the year, cod <34 cm did not eat herring if capelin was present. For larger cod the body size of herring consumed increased with the level of feeding motivation, and was highest for cod with capelin in the environment. Feeding motivation and occurrence of capelin had no effect in the second half of the year. Cod <25 cm rarely consumed herring. In general, the age of herring eaten increased with cod size. The youngest age group of herring was consumed by cod of size 25-75 cm from the moment they entered the Barents Sea in the autumn and throughout the winter. The age-dependent spatial distribution of herring in the cod stomachs conformed to the general geographical distribution of different age groups of juvenile herring in the Barents Sea.

Effects of parasitic status and level of feeding motivation on the diet selected by sheep grazing grass/clover swards

An experiment was carried out to determine the effects of parasitic status and level of feeding motivation on the diet selected by sheep grazing perennial ryegrass/white clover swards. Twenty-four female Scottish Blackface weaned lambs were divided into four treatment groups each of six animals. Pre-grazing treatments were imposed to create two levels of feeding motivation, low (fed ad libitum) and high (0·60 of ad libitum diet) and two parasitic states, parasitized (daily dose of 2500 L3Ostertagia circumcincta) and non-parasitized. Each treatment group was placed in one of four 0·35 ha field plots and allowed to graze a mixed grass/clover sward. Mean clover height was manipulated pre-grazing by cutting so that it was less than the mean grass height. This maximized the probability that clover in the diet of sheep was due to selection. No fertilizer was added to the sward in order to ensure that the nitrogen content of the clover was higher than that of the grass. Each treatment group was rotated around the four plots on a daily basis for 2 weeks. Sheep with a high feeding motivation strongly and significantly selected clover and had a higher proportion of clover in their diet compared with sheep with low feeding motivation. Parasitic status had no significant effect on the diet selection of sheep; but the level of parasitic burden within parasitized sheep was positively correlated with the proportion of clover in the diet. Parasitized sheep spent less time grazing each day and had lower daily herbage intakes compared with non-parasitized sheep. This was a result of a reduction in the duration of feeding bouts and not a reduced number of bouts per day. Sheep with the higher feeding motivation had a greater number of feeding bouts per day and this resulted in those animals having a greater daily herbage intake. Level of feeding motivation had greater effects on the diet selection of sheep than parasitic status. Sheep with a high feeding motivation are able to select strongly for clover in their diet when there is low overall clover availability and are capable of dramatically affecting the species composition of a sward. This has implications to the maintenance of a desired grass/clover ratio in grazed swards.

Trade-offs between sward nitrogen intake and faecal avoidance in sheep foraging decisions: the effect of parasitic status and level of feeding motivation

The deposition of dung on pasture may create a trade-off between the benefit of increased nutrient intake due to the leaching of nutrients and the risk of parasitism due to migration of helminth parasite larvae (Sykes, 1987), from the faeces to the sward. Physiological state can affect herbivore foraging decisions in relation to this trade-off. Our objectives were to determine whether such a trade-off exists in a grazing situation for sheep and whether level of feeding motivation and parasitic status affect the grazing behaviour of sheep faced with this trade-off.Texel x Greyface lambs were presented pairs of swards (36 x 21cm) which varied in nitrogen content (high=N+; low=N-) and level of contamination with faeces from sheep infected with Ostertagia circumcincta (Ost.) (20g faeces per sward=F+; no faeces=F-) and allowed to graze for short periods (60 bites or ten minutes). We defined ‘taking the trade-off’ as taking more bites from an N+F+ sward compared to an N-F- sward, when presented together as a choice.

The use of a second-order schedule to assess the effect of food bulk on the feeding motivation of growing pigs

AbstractIt has been suggested that feeding motivation, and hence the incidence of certain abnormal behaviours, may be reduced by the gastro-intestinal distension which results from the ad libitum provision offoods with a high water-holding-capacity (WHO. Therefore, the aim of this experiment was to test the hypothesis that feeding motivation is inversely proportional to the WHC of meals which supply the same level of nutrients. Eight male pigs (initial body weight 54·0 (s.d. 5·76) kg) were offered a series of four foods which possessed increasing WHC due to a linearly increasing inclusion of dried citrus-pulp (2·18, 3·52, 5·60 and 6·92 g water per g dry food for LB, MLB, MHB and HB), but all with similar ratios of digestible energy (DE) to crude protein and minerals. The experimental treatments were allocated in two 4X4 Latin squares with blocks of 6 days separated by a 4-day change-over period. On each day the pigs were given food twice (09.00 h and 16.00 h) to provide the same level of scaled DE across the meals of each treatment. The resulting level offeeding motivation was measured in two successive tests at 30-min intervals before, and eight successive tests at 30-min intervals after, the ingestion of the first meal using a second-order operant conditioning schedule; a methodology which requires pigs to press a paddle to obtain a feeding-related stimuli (CS). It was found that the number ofCS earned pre-feeding was not affected by treatment (17·2, 17·2, 17·6 and 17·5 (s.e.d. 1·58) CS per test for LB, MLB, MHB and HB; P &gt; 0·05), whereas, the number of CS earned post feeding was significantly affected by treatment (16·6, 15·5, 14·6 and 13·8 (s.e.d. 1·15) CS per test for LB, MLB, MHB and HB; P &lt; 0·001). Within each treatment, the number ofCS earned did not alter significantly across any of the time-periods post feeding. As the number of CS earned has been shown to be a reliable indicator of feeding motivation, the results from this experiment support the hypothesis that feeding motivation is inversely proportional to the WHC of iso-energetic meals.

The effects of foods of different water-holding-capacity on the level of feeding motivation in growing pigs.

Pigs exhibit a range of abnormal behaviours (e.g. stereotypies or tail-biting) which may, at least in part, be linked to feeding regimes which produce high levels of feeding motivation. Therefore, a welfare dilemma exists because the quantitative food restriction of sows and boars remains an essential husbandry practice to reduce excessive weight-gain and maintain breeding efficiency. However, it has recently been proposed that underlying levels of feeding motivation may be reduced through the ingestion of foods of high bulk (e.g. Brouns et al .,1994). These foods may serve to reduce feeding motivation through gastro-intestinal distension rather than by increased nutrient supply. Therefore, the aim of this experiment was to investigate whether iso-energetic foods with different bulk characteristics (water-holding-capacity - WHC) affect the level of feeding motivation, and if so, the duration of their effect.

An investigation into the potential use of a second order schedule of operant reinforcement for measuring feeding motivation in the pig

The measurement of feeding motivation is of central importance in the study of the factors which control feeding behaviour. Current behavioural models describing the control of feeding behaviour define feeding motivation as a temporary and reversible brain state induced by both internal and external stimuli which result in the tendency to perform feeding behaviour (for a review see Lawrence et al., 1993). One of the most sensitive methodologies to measure feeding motivation is operant conditioning where an individual is trained to perform an operant response (behavioural work) to obtain food reinforcement. An index of feeding motivation can then be obtained by varying the quantity of behavioural work required to obtain each unit of food reinforcement and observing the subsequent operant responding. However, this methodology is flawed because it requires a feed restricted animal to regularly ingest food during the test which results in feedback, affecting the underlying level of feeding motivation. A possible solution to this problem is the use of a second order schedule of food reinforcement which assesses an animal's feeding motivation without allowing it to ingest food. During a second order schedule an individual is required to express an operant response for the repeated presentation of a conditioned stimulus (CS) which has previously been associated with the delivery and ingestion of food, with the schedule terminating with food reinforcement. Using this schedule the quantity of behavioural work required per unit food reinforcement could be gradually increased such that a measure of feeding motivation could be obtained in the period prior to the terminal food reinforcement. Therefore, the aim of this study was to investigate whether the CS presented within a second order schedule had reinforcing properties which were linked to the level of feeding motivation. The experiment formed a part of a larger study which had the ultimate objective of developing a methodology to measure feeding motivation without allowing an individual to ingest food.

Further quantification of pigs needs for food using operant conditioning

The study of motivational states underlying behaviour is seen as critical to understanding the implications of restricted husbandry conditions on animal welfare. Yet the measurement of the strength of motivation remains a perennial problem in welfare studies. Previous work at Edinburgh using operant conditioning identified an apparently high level of feeding motivation throughout the day in pigs fed [ARC, 1981] recommended levels for sows and boars [Lawrence et al. 1988]. Pigs trained to press a panel consistently 10 times for a food reward (fixed ratio or FR responding) maintained high levels of panel pressing across the day when offered 0.6 of their ad libitum intake approximating to ARC (1981) recommended feeding levels. However, as the level of operant responding required was not great, it is arguable to what extend these results demonstrate a strong need for food by pigs on restricted feeding. The present paper reports on an experiment to test more accutely the strength of feeding motivation in relation to food restriction by comparing responding on FR with that on a progressive ratio (PR) where the animal has to work progressively harder for successive rewards. It was hoped that PR. reputedly a sensitive measure of motivation, would indicate with greater certainty restrict fed pigs need for food.

Blood glucose levels and food intake in the domestic chicken.

Synopsis Hyperglycemia was produced in female Brown Leghorn fowls by oral or intravenous injection of glucose solutions, at high and low levels of feeding motivation. A significant effect on food intake during a subsequent 15‐min test period was found only for the oral/low‐motivation condition. This may have been due to the osmotic effect of the solution on the gut rather than a true lowering of feeding motivation. It is unlikely that feeding motivation is directly related to blood glucose levels.