Effects of nest box arrangement on behavior, physiology and mortality for layer breeders in natural mating colony cages

Abstract: Due to the increasing consumer concern for animal welfare and growing labor costs. A production practice that has been widely adopted by many commercial farms in China is the use of natural mating colony cage systems for parent-stock (PS) layer breeders. Although the hens in this type of colony cage can express their natural mating behavior and have broader activity space compared with that of the conventional artificial insemination cages, the environment of the colony cages is still relatively barren and invariant. Environmental enrichment devices, such as nest boxes are absent. Behavioral problems, such as feather pecking and cloacal cannibalism are serious in the system, which subsequently reduce the fertility rate of layer breeders and cause severe health, welfare and economic problems. 2160 beak-trimmed Hy-Line brown parent-stock layer breeders were used in the present study to investigate the application of nest boxes in natural mating colony cages for layer breeders and the effect of nest provisions on feather pecking behaviors and physiological stress, which aimed at providing data support for the development and optimization of such breeding cage systems, and improving the health and welfare level of layer breeders. Each experimental cage accommodated 90 layers and 10 roosters, providing each bird 57 600 cm2 floor areas. Three different types of nest boxes were provided before onset of lay, Nest1 (length × width × height, 90 cm ×40 cm × 60 cm), Nest2 (45 cm ×40 cm × 60 cm), Nest3 (70 cm × 52 cm × 60 cm). Each treatment was replicated in 6 cages along the length of the house at the fourth tier. The number of eggs laid in the nest and on the floor, nesting behaviors and pecking behaviors were observed. Blood samples were collected and basal plasma concentrations of corticosterone, thyroxine (T4) and triiodothyronine (T3), 5-HT were measured. The results showed that: 1) Through a sufficient time to accustom to the nests, the nest boxes applied were well used by the hens. The ratio of nest eggs were 80.5%±7.8%, 67.4%±8.1% and 87.3%±7.6% respectively for Nest1, Nest2, Nest3 at 32 weeks of hen age. The ratio of nest eggs, the number of hens, nest visits, and sitting events in Nest1 and Nest3 were significantly higher than that of Nest2 (P<0.05). There were no significant difference in the duration of nest visits of laid hens in the nests, (51.3±11.7), (49.8±11.3) and (53.5±11.3) for Nest1, Nest2, Nest3 respectively; 2) The control groups (P=0.003) and Nest1 (P=0.035) showed more aggressive pecks given than the Nest3. For aggressive pecks received, the control groups were higher than the Nest1 (P=0.015). For severe feather pecks given, control groups were significantly higher than Nest1 (P<0.001) and Nest3 (P<0.001), Nest2 were significantly higher than Nest3 (P=0.030). The gentle feather pecks given of control groups were significantly more frequent than Nest1 (P=0.015), Nest2 (P=0.002), Nest3 (P=0.024). It was noticed that less gentle feather pecks received was shown in Nest 3 compared with control groups (P=0.012); 3) No significant differences were found in the concentration of triiodothyronine, thyroxine, and 5-HT between control groups and treatment groups. The exception was the significantly higher concentration of corticosterone of birds in control groups compared with treatment groups (P<0.05). Overall mortality for control groups and Nest2 were significantly higher than that of Nest1 and Nest3 (P<0.05). Mortality from cannibalism and vent pecking was significantly higher (P<0.05) in control groups than treatment groups (P<0.05). Overall, the results indicated that the colony nests, such as Nest1 and Nest3 could satisfy the nesting requirements of layers during the laying period. The provision of nest boxes in the colony cage system could be regarded as environmental enrichment device, which not only satisfied the expression of natural nesting behavior of laying hens, but also reduced feather pecking behaviors, fearfulness and physiological stress. Nest boxes can provide a supernumerary profit of constructing microenvironments that may be perceived as more safe, thus stimulating the performance of comfort behaviors and ultimately increase welfare.