Preference and behavioral responses to synbiotic supplementation via drinking water in laying hens under social stress.

Synbiotics (SYN) have the potential to enhance animal health, but their efficacy depends on both biological impact and voluntary intake, particularly under stress, when hydration and gut support are critical. This study presents the first investigation of SYN supplementation delivered exclusively through drinking water in laying hens, evaluating both preference and behavioral responses, particularly feather pecking, during a period of social stress induced by repeated mixing of unfamiliar birds. A total of 226 White Leghorn hens (37 weeks old) were housed in enriched floor pens with simultaneous access to color-coded SYN-enriched and plain water containers. Following a 2-week associative learning phase and 1-week washout, hens entered a 6-week preference testing period encompassing pre-stress, stress, and post-stress phases. Water consumption was measured at the group level, while individual jug visits were tracked using RFID technology. Feather pecking was measured (10 min/day) and feather damage assessed according to severity. Hens showed a clear preference for SYN-enriched water, consuming significantly more than plain water (p < 0.0001). While overall intake remained stable, SYN consumption fluctuated across stress phases, with the strongest preference pre-stress and a modest decline during stress. Although hens with higher rates of severe feather pecking (SFP) visited SYN-enriched water more frequently than hens with lower rates (p = 0.0288), suggesting a potential coping mechanism, overall, SFP rates remained stable across all phases. Notably, the level of SFP observed during the pre-stress phase was already sufficient to cause progressive plumage deterioration, which continued throughout the study. The proportion of birds with severe feather damage rose from 39.4% to 53.5%, while those with intact plumage dropped from 37.6% to 19.9% over time. Thus, SYN supplementation via drinking water is feasible and preferred by laying hens, even under stress. These findings highlight the potential of nutraceuticals delivered through drinking water to influence hen behavior; however, the progressive plumage deterioration despite stable SFP rates suggests that SYN supplementation alone may be insufficient, underscoring the need for integrated management strategies.