Does smothering occur in rearing?

Recent research indicates that smothering accounts for up to 16% of mortality in adult laying hens in Australian commercial free-range egg farms (Hemsworth et al., 2022). In addition, UK data indicates that piling (a precursor to smothering where hens press tightly together into dense packs) has implications not only for the risk of mortality due to smothering, but also may negatively impact egg production (Armstrong et al., 2023). Smothering research to date has been focused on identifying risk factors in adult flocks, but there is little available information on the incidence of, and possible risk factors for, smothering during rearing. This study aimed to investigate the incidence of smothering during rearing utilizing a limited data set collected within the research conducted by Hemsworth et al., (2022).

Surveys on management practices and flock behaviour were completed by rearing managers in relation to 50 pullet flocks across Victoria (n=21) and Queensland (n=29). The flocks were either Hy-line Brown (n=42), ISA Brown (n=7) or mixed (ISA Brown and Lohmann, n=1) and were housed indoors in either aviary (n= 17), jumpstart (n= 26) or floor rearing (n = 7) systems from day-old chicks. The surveys were completed by flock managers when the flocks were 16-17 weeks old.

Smothering-related mortality was reported in 44% of the flocks in the study, occurring between 3 to 15 weeks of age. Smothering occurred in 71% (n = 12) of aviary flocks, 35% (n = 8) of jumpstart flocks and 14% (n = 1) of floor-reared flocks. Reported locations for smothering were next to gates or partitions (36%, n = 4), at either the front or the back of the shed (27%, n =3), against walls (9%, n =1), in the system (18%, n =2), or near cooling pads or exhaust fans (9%, n =1). Preliminary analyses on some management practices were conducted using t-tests comparing the mean set temperature (temperature setting for the climate control) and lux (at the time of the survey) of flocks that smothered compared to those that did not. There was no significant difference in shed temperature between flocks with smothering compared to flocks with no smothering. However, in flocks where smothering occurred, the lux at the time of the survey was significantly lower (x̄Smother = 14.1 ± 2.1 lux, x̄No smother = 41.3 ± 4.2 lux, p < 0.001). Manipulation of lux is a common management practice to reduce problem behaviours (Janczak and Riber, 2015), and thus this association may simply reflect a management strategy to reduce smothering in problematic flocks.

These results are based on a limited data set and thus it is not possible to determine causal factors or risk factors; however, it does clearly indicate that smothering and piling occur during rearing as early as 3 weeks of age. Since early life experiences are known to influence the behaviour of the adult laying hen, there is a need to conduct further research into piling and smothering behaviours during rearing as these behaviours, which are known to be problematic in adult flocks, may actually develop during rearing.