The development of egg-laying behaviour and nest-site selection in a strain of white laying hens

Since World War II livestock husbandry has been highly intensificated. This trend was most obvious in the poultry industry. Laying hens used to be housed outdoors in free-range systems, but nowadays these systems have almost entirely been replaced by the battery-cage. In the early sixties scientists and the general public started to express much concern for the well-being of hens kept for egg-production in battery cages. In reaction to this concern for the well-being of farm animals, several research programs were started. One of them concentrated on the objective assessment of welfare. Moreover, investigations to improve existing systems and to develop alternative floor-systems were started (chapter 1). However, a problem common to all floor-systems is the reluctancy of a various percentage of hens to use the laying nests provided. This has considerable economic implications, such as loss of eggs , dirty eggs and time consuming eggcollection. Acceptation of alternatives will be promoted if such a problem is solved. The general aim of the present study was to trace factors that cause floor-laying.Chapter 2 reviews some literature on the physiology and the normal nesting behaviour of domestic hens. It is concluded that irregularities during, for example, the hormonal control of ovulation may easily lead to abnormalities in egg-production and nesting behaviour and thus to flooreggs, as well. In chapter 7 these parameters were used in order to find out to what extent floor-laying is caused by physiological irregularities (see below).Chapter 3 presents a description of the rearing and experimental housing conditions and of the hens used in this study. Furthermore, it provides a definition of the behavioural elements scored.In chapter 4 the development of egg-laying behaviour and nest-site choice is described in seven flocks of hens housed in small floor-pens (2 x 2 square meter). Special interest is directed towards social dominance and the effect of the presence of a cock on the hen's nest-site choice.In the weeks before the hens came into lay they frequently examined the nests, whereas nest-entries only occurred some days before or in the hours preceding the first oviposition. It was postulated that the early examinations serve the selection of a suitable nest-site.In order to study perseverence in nest-box choice, two parameters were used: a perseverence index defined as the number of the same choices on successive oviposition days divided by the total number of choices and a frequency index, defined as the number of the same choices divided by the total number of choices. Hens were judged to persevere in their choice if both measures reached values larger than 0.7.Only one of the 13 observed hens persevered in nest-box choice within clutches; she nearly always chose the same box on subsequent days, but started another egg-laying sequence in another nest-box. The other hens frequently changed nest-boxes. Consistency in nest-choice increased, if three boxes along one side of the pen were regarded as one nest; four of the 13 hens nearly always used the same side of the pen. Four other birds did choose the same side of the pen on successive oviposition days, but started another egg-laying sequence on the other side of the pen. One hen used nest-boxes on one side of the pen more frequently, although not on subsequent oviposition days. The remaining four hens did not show any consistency in their nest-choice behaviour. It was concluded that individual hens involved different factors in their nest-site choice.Furthermore, individual hens were consistent in using either the floor or a nest-box as a nesting site. No relationship was found between social status and nest-box choice, nor between social status and using the floor or a nest-box for laying. Some evidence was provided that the presence of a cock could reduce the percentage of floor-eggs in a pen provided with rollaway boxes.Chapter 5 presents the results of an experiment designed to investigate the effect of rearranging the sites of four different nest-boxes on the nest-examination duration in the weeks before and during the egg-laying period. Two types of examinations were distinguished: inspections and glances. Moreover, the development of inspections and glances in the weeks before laying is described and compared (experiment 1). Finally, in the first and in a second experiment the nest-examination pattern in the weeks before laying and its relationship with the final nest-choice is studied.In the first experiment sixteen white laying hens were placed in 8 round floor-pens (1.5 m Ø); two hens per pen. Each pen was provided with four different nest-boxes; nest-floors were covered with astroturf, wood- shavings, buckwheat husks or a wire basket. In the weeks before laying the hens were exposed to an exploration test in their home pen. During the first two weeks of the experiment the positions of the nests never changed. Subsequently the positions of the nests in four of the 8 pens were changed 3-4 times a week (=experimental group). In the other four pens nests were always in the same position (=control group). Exposing hens to an exploration test was continued in the egg-laying period.No differences were present in the total time spent in inspections and glances in the period before the rearrangement of the nests between control and experimental hens. However, as a result of changing the positions of the nests regularly, experimental hens spent more time in nest-inspections than did control hens. Likewise, the inspection duration increased in the experimental group if days without a change were followed by days with a change and, vice versa, decreased if days with a change were followed by days without a change. From these results it was concluded that inspections during the weeks before laying serve the acquisition of information.The total time spent in glancing at the nests remained unaffected by the treatment. Moreover, glances and inspections followed a different temporal pattern over time. In the course of time (in the weeks before laying) the glance duration decreased, whereas the time spent in inspections showed an increase. Apparently glances and inspections do not represent the same type of exploration. Glancing at the nests was regarded to be a passive form of exploration, which is initially elicited by a change in the environment. Nest-inspections were regarded as an active form of exploration during which information is gathered from the nests, which may be used for the final selection of a nesting-site.Moving the nests to new places during the laying period did not result in an increase in the inspection duration. Obviously nest-inspections during this period do not serve the same function as those during the weeks before laying. Inspections in the hours before oviposition were supposed to represent intention movements to enter a nest-box. In the hours before oviposition glances were almost never performed.To study the relation between nest-examinations in the weeks before laying and later nest-preference a correlation coefficient was computed between nest-preference in the weeks before and during laying. In none of the hens a significant coefficient was found. Apparently the final nestchoice could not be predicted by the amount of attention paid to the nest boxes during the period considered.In the second experiment the nest-examination pattern and its relation to later nest-preference is studied in five hens that had been observed until the day of first oviposition. Experimental conditions were the same as described for experiment 1, however, nest-boxes were always in the same position. The results revealed that one day before the day of first oviposition all hens showed the tendency to spent most time in inspecting the nest they preferred for the oviposition of the first series of eggs. Apparently the final nest-choice was established one day before the day of first oviposition.Chapter 6 presents the results of two experiments designed to reduce the percentage of floor-eggs. The effect of the properties of the nests (factor 1) and the moment the hens got access to the nests (factor 2) on the percentage of floor-eggs is investigated. Moreover, in experiment 1 the interrelationship between these two factors is examined. In both experiments the effect of the treatments are described over time. The effectiveness of a treatment was judged according to the percentage of floor-eggs laid during the whole 6-week egg-laying period and during the 6th week of the egg-laying period.In the first experiment twenty-four flocks of white laying hens were housed at an age of 16 weeks in small floor-pens. Two types of nests were used (litter and roll-away nests); the nests were opened at two different moments (on the day the first egg appeared in a f1ock=late, or on the day the flocks were housed in the pens = early). A main effect was present of the properties of the nests: more floor-eggs were found in pens provided with roll-away nests than in pens provided with litter nests, indicating that litter was preferred over a wire basket. Furthermore, a significant interaction was present between the two factors under study; opening rollaway boxes late resulted in fewer floor-eggs than opening these boxes early, whereas no differences were found between opening litter nests early and late. It was concluded that the extent to which early experience with nests affects the incidence of floor-laying depends upon the type of nestbox used.In order to reduce the percentage of floor-eggs even more as compared to opening roll-away nests late, the influence of converting litter nests into roll-away nests at about 15 and 35 % of lay on the percentage of floor-eggs was studied (experiment 2). For this purpose sixteen flocks of white laying hens were housed in floor-pens at an age of 16 weeks. In 8 pens litter nests were converted into roll-away nests at an average laying percentage of 17.7 % (group LT1) and in the remaining 8 at an average laying percentage of 38.6 % (group LT2). More floor-eggs were found in group LT1 than in group LT2 , not only if the total period after the nestchange is considered, but also during the last egg-laying week.A comparison of the results within and between both experiments showed that replacing the litter with a wire basket at 17.7 % of lay resulted in more floor-eggs during the 6th egg-laying week than opening roll-away nests at the start of the egg-laying period. Obviously the latter treatment did not reduce the incidence of floor-laying further. In contrast, it appeared to have a negative effect. In the week immediately following the nestchange the percentage of floor-eggs in group LT1 significantly increased. From this it was concluded that if hens have only been able to inspect nests visually in the weeks before laying, they are less likely to start using roll-away nests later on.Changing litter nests into roll-away nests at about 38.6 % of lay resulted in a comparable percentage of floor-eggs as opening roll-away nests late, if the 6th egg-laying week is considered. Thus the first mentioned treatment did not reduce floor-laying further as compared with opening roll-away nests late.Replacing the litter with a wire basket at 38.6 % of lay (LT2) resulted, as expected, in fewer floor-eggs during the 6th egg-laying week as compared with changing the nests at 17.7 % of lay (LT1). Postponing the moment of the nest-change allowed a larger number of hens to start using the litter nests. Probably these hens were trained in the use of a nest-box and continued in doing so, even after the replacement of wood-shavings with a wire basket.As had become evident in chapter 4, some hens always used the floor for laying, while other hens, kept under the same circumstances always used a nest-box. Chapter 7 concentrates on the question which factors may cause individual differences in site use. Two possibilities that might explain such differences are considered. First, in order to detect whether floorlaying is caused by physiological irregularities, egg-laying records of floor-and nest-layers are described and compared. The following parameters were used: daily egg-production per hen, egg-shell quality, lag duration and consistency in site use. No differences were found with respect to each of these measures between floor-and nest-layers. It was concluded that physiological irregularities are uncommon in this laying strain. Therefore this factor was not supposed to account for the differences in site use between individual hens.Second, to find out whether floor-and nest-layers react differently to environmental stimuli or whether floor-layers simply prefer the floor for laying, the pre-laying behaviour of five floor-and five nest-layers is described and compared. The results indicated that floor-layers performed more behaviour indicative of frustration due to the nesting situation than the nest-layers. Furthermore, floor-layers spent like nest-layers some time in inspecting and entering nest-boxes during egg-laying sessions. Therefore the results did not support the view that floor-layers simply prefer the floor for laying. It is more likely that the nesting tendency in these hens is frustrated by particular properties of the (roll-away) nests or perhaps by the inability to move away from the flock.In chapter 8 the development of nesting behaviour, the selection of a nest and factors that appeared to affect floor-laying are discussed in some detail. It was concluded that the selection of a nest is a process which starts in the weeks before laying. In order to reduce floor-laying it is recommended to take all factors, that affect the hen's nest-site choice, into account.Furthermore recommendations to reduce the percentage of floor-eggs are derived from the results obtained in this and other studies concerning nest-site choice in domestic hens and their practical significance is discussed