investigating behavior changes of laying hens molted by high dietary zinc

introduction the commercial egg industry commonly uses induced molt procedures to rejuvenate flocks for a second or third laying cycle. molting may be induced by feed withdrawal for up to 10 days (7), water withdrawal for 2 days (19), or both, along with a reduction of day length (14). such programs cause concern about animal welfare because it is thought that they may be harmful to hens (28). given the concerns for potential bird stress, various methods of nutrient restriction that would avoid long term feed withdrawal have been investigated (20, 24). one of the alternative methods for molt induction is high-dietary zn (4). materials and methods in this study, a total of 30 hy-line w-36 leghorn hens (at 50 wk old) (1400 ± 150 g), were randomly assigned to 5 replicate. ten cages (3 hens in each cage) on both the upper and lower tiers were considered to observe behavior patterns. data recording of predetermined behavioral patterns were carried out using five camera digital video recorder multiplexer system. behavior recording began at 9:00 h each day and ended at 11:00 h and a second observation starting at 16:00 p.m and ended at 18:00 p.m. total of ten cages (containing 3 hens/ cage (30 hens total)) were used to collect 5 behaviors (feeding, drinking, nonnutritive pecking, preening and aggression pecking) and one posture (sitting). the following ethogram was adopted from webster (27) feeding defined as pecking behavior directed toward the feed trough or toward a neighboring feed trough. drinking was defined as the appearance of ingesting water from the nipple at the near of the cage. nonnutritive pecking was defined as non aggressive pecking at anything other than feed, which included cage pecking, feather pecking, bill pecking and air pecking. preening behavior involved the manipulation of the plumage with the beak. aggressive was the sum of pecks that occurred within a cage or between neighboring cages. sitting was defined as a crouched posture with shanks or breast in contact with the cage floor. results and discussion percentage of observation of all behaviors except for non-nutritive pecking was significantly affected by high dietary zinc (p<0/05). the highest and lowest percentages of eating behavior were observed on d 1 and 8 and the lowest drinking behavior was in d 4 and the highest percentage of non -nutritive pecking was observed on d 5 and 8 (p<0/05). in this study the eating behavior decreased, non nutritive pecking increased, which was consistent with reports by webster (27) and dunkely et al (13). they observed that the reduction of feeder-related activities by feed-withdrawal hens was accompanied by an increase in non nutritive pecking. increase in drinking behavior probably was due to the increased feed consumption. this is supported by woodward et al (29) who observed that fully fed hens drank nearly twice as much as feed withdrawal hens. on the basis of our results and the results of other studies (29) it appears that birds receiving high level of zn had the lowest feed intake, they tended to drink less, because it was observed that feed withdrawal hens were not eating, they tended to drink less. aggressive behavior was not observed on d 3, 4 and 8 and the highest percentage of aggressive pecking was observed on first day. the minimum and maximum percentage of preening behavior have been occured on d 3 and 6, respectively and the highest and lowest sitting percentage has been observed on d 4 and 1 (p<0/05). preening behavior is generally suppressed when hens are involved in other activities such as feeding. dunkley et al. (13) observed that the feed withdrawal hens spent more time preening until the last few days of the most period, where as the fully fed hens did not. their findings are in accordance with the results of this experiment that hens spent less time at the feeder, they spent more time involved in preening activity. reduce aggressive behavior on days 3 and 4, was probably due to the reduced eating and drinking behavior, so probably reduced competition for food and water can be attributed to aggressive behavior and this dcrease on day 8 is probably the result of an increase of preening behavior. given that eating behavior has been decreased by the fifth day the bird has a chance to be in a sitting position. conclusions use of high zinc molt diet method could be effective to reduce aggressive behavior and increase preening behavior of laying hens during force molting.