Abstract

Keywords

broiler breeders, controlled feeding, behavior

Introduction

There exist a general antagonism between growth rate and reproduction in domestic animals.

Breeds selected for high growth rate allocate nutrients preferably in body mass development. This has detrimental effects egg production, fertility and livability. Therefore it is necessary to control the development of body weight development of broiler breeders through reduced feed intake. The common practice is a single meal allocation in the morning using a balanced diet. The control of feed intake below the level of ad libitum feeding has been reported to cause welfare problems. It was assumed that the birds would suffer from “chronic hunger” or deprivation of satiation” (Pledl, 2008). Since there exist no valid physiological criteria for hunger as a subjective experience in chickens the most important indicators of suffering are abnormal behaviours. There are many publications showing changes in feeding behavior, locomotor activity, preening, feather pecking and increase of stereotyped behaviors when the feed allocation was regulated below the level the birds would eat under ad libitum conditions. It has been assumed that stereotyped behavior is the result of reduced time spent feeding under controlled feeding conditions. The physiological satiation mechanisms may become active in a later phase only (see for review Bessei, 2014). After completion of the daily ration the motivation of feed pecking persists and may be deviated towards non-feed objects, such as feeder, drinker, walls or feathers of pen mates. Eventually this pecking activity appears as stereotyped behavior. Stereotyped behavior is assumed as indicator of an inadequate feeding behavior. Although there is no consistent interrelationship between stereotyped behavior and hunger throughout the experimental work reported in the literature (Bessei, 2014), the development of this abnormal behavior should be avoided. There are reports showing that feed pecking after completion of the meal can be diverted towards the litter. Litter pecking and litter scratching are considered to express foraging behavior, which is the adequate response to the bird`s situation. Indeed the distribution of whole grains in the litter has been used in layers to stimulate litter pecking and reduce feather pecking in laying hens. The present study was carried out to use coarse Ca particles to direct the pecking activity towards the litter. In order to be effective the distribution of the particles in the litter should be carried out before the feed provided in the feeders is completely eaten.

Materials and methods

A total of 11,556 broiler parent stocks were used, 10,700 females and 856 males.

The birds were housed in two windowless houses of 812 m² (80,4 x 10, 1 m) each. Stocking density was 8 birds/m² usable space. Approximately two thirds of the pens were littered with wood shavings and one third was covered with wooden slats. The littered area was located at both side walls. Nests were situated in the central part of the slatted area. Feed was supplied through 3 chain feeder lines, which we are located in the deep litter area. Feeder space was 17.6 cm per hen. The males were fed separately on suspended round feeders, one feeder for 8 males each. Feed was provided in a single meal per day at 5:00h. Water was supplied through nipple drinkers, 7.8 birds per nipple. The drinker lines where positioned in front of the nest entrances on the slatted area. Fresh air was supplied through an underpressure ventilation system with a capacity of 8 m³ per kg live weight. Light duration was 14.5 hours, from 2:30h to 17:00h. There was the dim and dusk phase of 15 minutes at the beginning and the end of the light period.

A conventional parent stock diet was fed throughout the experiment. The daily feed allocation was 120 g per bird and increased up to 170 g at the end of the of the observation period. 2 g/bird and day of a coarse calcium carbonate was scattered in the litter areas. This treatment was carried out by hand about 1 to 1.5 hours after feeding.

Behavioural observations

Two video cameras were installed in each pen, one at the entrance and one in the middle. The viewing range comprised the whole width of the pen including the litter area with the feeders and the slatted area with the drinkers. The area for the behavioural observations was defined by a frame over the video screen, which contained the width (4,35 m) of the pens and a depth of about two meters. Because of different positions of the cameras at the different locations, it was not possible to exactly determine the same size of area on each position. Therefore the number of birds in the region of interest was determined in the first step of observation, and the behavioural data were expressed as percentage of the birds in the defined area. The following behaviours were recorded by instant scan sampling with a 10 minutes interval:

feeding (pecking in the feeder), drinking (pecking at the drinker nipples), preening (pulling the beak through own feathers), scratching/litter pecking (scratching and litter pecking usually occur in repeated sequencies), walking (locomotor activity including transitions from the litter area to the slatted floor or on the feeders), stereotyped object or spot pecking (repeated and uniform pecking at feeders, drinkers and other objects).

Behavioural recording took place from February to June 2014. At the beginning of the experiment the birds were the 25 weeks old. In the first step of observations, scans of the entire lighting period were made of one camera position from 2h to 17h in 10 minutes intervals. These results were used to determine the time pattern of the behaviours over the light period and to select regions of interest for the full evaluation of all camera positions. The following periods over the time of day were determined: 4h to 8h and 15h. Three scans per hour were carried out within the selected time. The observation started when the birds were 25 weeks of age and were repeated in four weeks intervals, from March until June 2014.

Data analysis

The number of birds within the observation area was used as a basis of determination of the percentage of birds showing the above defined behaviours. The results were aggregated as mean values per hour and plotted over time of observation. The overall means of the behaviours in response to the treatments (with and without distribution of calcium particles) were calculated. Since only one replicate (pen) per treatment was available, the effect could not be tested statistically.

Discussion

Feeding behaviour in chickens represents a large part of the total behavioural budget. Under ad libitum feeding laying hens spend about 40% of the light period food pecking. The feeding activity under ad libitum feeding follows a biphasic pattern with one maximum in the morning and another in the afternoon. When feed is supplied below the ad libitum level, the pattern of feeding behaviour is determined by the time of feeding and the level of feed restriction. The intensity of feed intake increases with the severity of feed restriction, and feeding activity is concentrated on the time of feed supply.

The total time spent feeding is reduced concurrently with the level of feed restriction. The intensity of feed intake after feed deprivation or under different levels of feed restriction has been used as an indicator for the strength of feeding motivation or hunger in chickens (Wood-Gush and Gower, 1968). The reduction of time spent feeding is considered the cause of stereotyped pecking activity. The birds in the present study, however, showed little pecking in the feeder, in the litter or stereotyped pecking during the first hours of the light period, though hunger is supposed to be greatest at that time. This is in agreement with findings of Puterflam et al. (2006). In contrast to our expectation the birds where very quiet and approached the feeder only a short time before the feeder chain was operated. The increase in walking and pecking in the feeder prior to feeding was probably initiated by acoustic and visual stimuli related to the preparation of feeding, e.g. opening of doors and appearance of the stock personnel.

Very high feeding activities (90%) occurred for a short period only after the arrival of feed. The hourly averages were 40% to 35% in the two hours following feeding.

These values are lower than those reported by Puterflam et al. (2006) in feed restricted broiler parent stocks (54.5%) but similar to the ad libitum fed birds of the same authors (42.5%). This shows that supply of fresh feed also stimulates the feeding activity in ad libitum fed birds. The overall daily means of time spent pecking in the feeder varied from 20 to 22%. This is within the range of feeding activity of parent stocks reported by Puterflam et al. (2006) (17.4%) and Hocking et al. (1997) (30%). The percentage of birds pecking in the empty feeder was 6.5% and 3.5 to 13.9% respectively as reported by Puterflam et al. (2006) and Pledl (2008). The differentiation of feed pecking and pecking in the empty feeder is difficult under practical conditions. It is not possible to exactly determine the time when there is no feed left. Feed consumption is getting more difficult when the feed level declines. There remain some feed particles in between and underneath the elements of the feeder chain which are difficult to acquire. It has also to be considered, that under even under ad libitum feeding a considerable part of pecking activity in the feeder is not connected with feed intake (Bareham, 1972; Masic et al., 1974). Therefore pecking in the empty feeder cannot generally be assumed as abnormal behavior. Therefore the data on feed pecking and pecking in the empty feeder reported in the literature has to be considered with care. There is spillage of feed into the litter, in particular when the feed is presented as mash. In the present study there was increasing litter pecking as pecking in the feeder decreased (figure 1). This suggests a gradual transition from feeding of the trough towards feeding of the litter and litter pecking and scratching as explorative behavior. Similar results have been reported by Savory and Maros (1993) and de Jong et al. (2005).

In the present study the pattern of pecking in the feeder occurred at a low frequency in the time, when there is no feed left in the feeder, e.g. evening and in the morning before feeding. Nevertheless the pattern of this pecking activity did obviously not differ from the normal feed or litter pecking and could clearly be differentiated from stereotyped pecking. The latter, which has been described as abnormal behavior in response to feed restriction, was found very rarely in the present study. This may be due to the fact that feed was provided as mash and the feeders were located in the litter area. There is more feed spillage with mash than with pelleted feed, and the spilled feed redirects the pecking activity towards the litter as soon as the feeder is emptied. Litter pecking, in contrast to stereotyped pecking, is considered a natural expression of foraging behavior. Therefore redirection of the pecking activity from the feed to the litter has been recommended as a means to reduce stereotyped pecking in chickens (Nicol et al., 2001).

In some studies on feed restriction of broiler breeders the authors recorded stereotyped walking (pacing) (Savory and Maros, 1993). Increased walking was observed immediately before the delivery of feed. This behavior showed no stereotypic pattern. In line with our observations, Kostal et al. (1992) reported increased non-stereotypic walking behavior prior to feeding in broiler breeders. There was a tendency of increased walking activity in the group which received Ca particles in the present study. This indicates that the treatment increased foraging behavior in general. Restricted feeding has been reported as risk factor for feather pecking. Feather pecking occurred in the present study at a very low level in the afternoon. The low incidence of this damaging behavior may be attributed to the high level of foraging behavior. Occupation with litter has proved to attenuate feather pecking in many studies (van Krimpen et al., 2009; Kjaer and Bessei, 2013).

The distribution of Ca particles in the litter showed only a short time effect on litter pecking, which is not reflected in the mean values of the hour of application in figure 1. However, there was obviously a long lasting effect and the litter pecking and scratching. This behaviour was clearly higher at 9h am and 15h pm in the treatment group than in the control (figure 4). This shows that it is possible to redirect the pecking activity through strategic feeding. This measure may show more pronounced effects when the birds are fed pelleted diets and the feeders are located on the slatted area where the birds are not able to retrieve spilled feed. Other behaviours were not influenced by the treatment.