Effects Of Cage Systems And Stress On The Performance And Welfare Of Laying Hens

In Part 1, in order to investigate cage systems on the performance and health in laying hens, we recommended characteristics of several cage systems by comparing indices of physiological parameters, production, egg quality and behaviors of laying hens. In Part 2, high temperature and corticosterone (CORT) were administered to mimic a stress response, and investigated the effects of stress on performance, physiology, follicular development and levels of relative genes mRNA expression in follicular theca of laying hens to study the stress on the mechanism of production in laying hens.In Part 1, a total of 924 Hy-Line Brown layers (24-36 wk) with similar body weight (BW) were assigned to conventional cages (CC, n=6, 384 hens), furnished cages 1 (FC1, n=6, 384 hens) and furnished cages 2 (FC2, n=6, 288 hens). In 37-59 wk, layers were assigned to CC (n=6, 192 hens), FC1 (n=6, 252 hens), FC2 (n=6, 288 hens) and modified cages (MC, n=6, 192 hens). Productions (24-59 wk) and behaviors (24 wk) were measured in the experiment 1. Appearance (n=72) parameters were evaluated at wk 60. Blood was drawn from wing vein using a heparinized syringe after 12 hours fasting. Plasma was obtained after centrifugation and was stored at -20°C for further analysis. Liver was sampled immediately after hens were killed and was cooled down in liquid nitrogen and stored at -80°C until analysis. Liver, heart, thymus, spleen and intestines were weighed, intestines were measured for length. Layers, aged 33-36 week, experienced high temperature in summer. Performance, behaviors, egg quality and rectal temperature were measured in trial 2. Plasma was obtained after centrifugation and was stored at -20°C for further analysis at wk 36. Layers, aged 56-59 week, experienced low temperature in winter. Performance, behaviors, and egg quality were measured in trial 3. Plasma was obtained after centrifugation and was stored at -20°C for further analysis at wk 59. Hens aged wk 26, were exposed to fear for 2 d in trial 4. The hens were assigned to fear treatment group and control group. After hens were set in fear section for 10 min, blood sample was withdrawn from fear treatment group and control group.The results showed that cage systems had no significant effects on the Ca-P metabolism. Production of hens in FC1 and FC2 was not better, whereas feed conversion decreased during wk 24 to 59, which was probably related to the increase of activity of hens housed in FC1 and FC2. Compared with hens in CC, behaviors and appearances of hens in FC1 and FC2 were improved significantly, time performing pecking and standing decreasing, comfortable behaviors increasing, and back feather coverage and feet was intact. Hens in FC1 were less fearful. High temperature had significant effects on production of hens in CC. The level of CK and NEFA decreased significantly and the frequency of panting and sitting of hens in FC1 decreased at high temperature, whereas time performing walking increased, which likely was due to lower density. Hens in FC2 had higher energy utilization, and in FC1 and FC2 had better behaviors in winter.In Part 2, 48 hens with similar BW and egg production, aged 26 wk, were divided into 2 groups at random: CORT (hypodermic of abdomen on 7:00 and 19:00, 2mg/Kg·BW·Day) and control group (corn oil, hypodermic of abdomen on 7:00 and 19:00, 2mg/Kg·BW·Day). Egg production, egg weight and feed intake were recorded every day. After 7 days CORT exposure, 10 eggs were sampled for the egg quality. Hens of each treatment were divided into fasting groups and feeding groups, access to water. 8 hens were weighed for each groups, blood was drawn from a wing vein using a heparinized syringe and was stored at -20°C for further analysis after centrifugation. After hens were killed, preponderant follicle theca was sampled, cooled down in liquid nitrogen immediately and stored at -80°C until analysis. The abdominal fat, preponderant follicles and small yellow follicles (SYF) were harvested and weighed, and the numbers of follicles were recorded. Another 48 hens with similar BW and egg production, aged 65 wk, were divided into CORT group (15mg/kg food) and control group (no CORT). After 7 days treatment, 8 hens (fasting 12 h) of each treatment were sampled as above. 48 hens with similar BW and egg production, aged 26 wk, were divided into 2 groups at random in trial 2: heat stress (30.5±0.1℃) and control group (23±0.1℃). After 7 days treatment, 8 hens of each treatment were fasted for 12h and sampled as above in trial 1.The results showed that CORT treated hens (26 wk) had lower body weight, egg production, egg weight, albumen height and haugh unit, higher egg shape index. Yolk index increased significantly in CORT treated 65-wk hens. Feed intake, production, egg weight, yolk weight and shell thickness decreased significantly after exposure to heat stress. The results implied that heat stress had significant effects on the composition and quality of eggs, whereas CORT had only significant effects on egg composition. Hens (26-wk) exposured to CORT had low plasma TG, E2 and VLDL concentration, high level of LH, FSH and cholesterol. Plasma CORT concentration increased significantly of 65-wk hens in CORT group. There were no statistical effects on plasma parameters in hen exposure to heat stress, suggesting that heat stress had little effects on the neuroendocrine and metabolism. The level of E2 in fasting hens (26-wk) and the expression of CYP19A1 mRNA decreased significantly in CORT treatment group, which indicated that synthesis and secretion of E2 were affected by CORT administration, and the expression of CYP19A1 in follicle theca was related to atresia of follicles. The concentration of insulin in fasting hens increased, whereas the expression of INSR mRNA decreased significantly in CORT treatment group, which indicated that CORT administration caused insulin resistance in hens. CORT treated hens had higher liver index, and those in fasting group had lower ovarian and follicle weight, and had less follicles. Heat stress caused body weight, ovarian weight, follicle weight and the number of follicles decreased significantly, too. These meant that CORT administration and heat stress can affect follicular development and induce ocarian atrophy of laying hens, and the effect of CORT administration on young hens was greater than that on old hens. Heat stress had no statistical effects on expression of relative genes in follicle theca. Above all, heat stress and CORT inducing stress had different mechanism of decreasing production. Heat stress caused the production to decrease mainly by directly affecting ovary, whereas CORT likely by affecting the hypothalamic-pituitary-gonadal axis.