Effects of Body-Mounted Inertial Measurement Unit (IMU) Backpacks on Space Use and Behaviors of Laying Hens in a Perchery System

Round 1

Reviewer 1 Report

Effects of body-mounted inertial measurement unit backpacks on spatial allocation use and behaviors of laying hens in a perchery system

This paper presents a well-done study of the impact of backpack mounted devices for monitoring animal behavior and space use on the behavior of laying hens. The study found brief changes in space use patterns by the hens, but this returned to baseline normal patterns of space use within about two weeks of placement of the devices. There was no significant changes in the behavior of the animals. Overall the findings of the study support the minimally invasive nature of using body mounted devices to monitor animal health and well-being in production systems.

I suggest the paper for publication after some revisions and clarifications throughout the manuscript. The language in places is unclear. The methods could use more detail in places. The statistics are appropriate, but the number of analyses conducted on space use by day makes the results section very dense. In turn this makes finding the main point of the findings rather difficult for the reader.

I have outlined specific revisions below.

Line 43 – “Well-being conditions” delete conditions

Line 43- “and their preferences” delete their

Line 46 – Change “transferring” to “converting”

Line 47 – “which are characterized as…” change as to by

Line 48 – “complex environment” change environment to environments

Line 48- “Many efforts have been conducted…” change to “Many techniques are available”

Line 54 – “…but the potential impact is not explicitly assessed yet.” Change to “but this assumption has rarely been tested.”

Line 62 – “While such impacts occur in species that dominate walking and flying of wild birds and are therefore may apply to laying hens…” – I can’t tell what this sentence means, please clarify. Also break this sentence, which continues into line 65, into two for readability.

Materials and Methods

The methods in general need to be clarified in a number of places. Also there are a lot of time periods being aggregated and analyzed together in different ways/at different time scales throughout the methods, which in places is difficult to follow. Providing some justification for why these time scales vary might help clarify what and why different methods are used.

Line 90-92: Need more details about the hens and the perchery system –

                -How old are the hens? This is listed later in the methods but probably belongs here

                -Where were they sourced from?

- Is the perchery layout used comparable to what is used in production systems in China or was this a unique lay out for the study?

- How many hens per enclosure?

Line 106 – Feed and water were ad libitum – change to “Food and water were offered ad libitum”

Line 130 – (65 weeks of bird age) – This information should be earlier in the methods

Line 135-136 – It’s not clear to me whether spatial allocation is a mutually exclusive behavior from the other categories (a hen scored as “nest box perch” cannot also be scored as “preening”), so this subsection is difficult to understand. Since space use is a question of interest, recording the behavior and the location of the behavior seems more standard? I also find it hard to believe the hens never preened while settling in to roost? In either case the behavioral sub groupings are confusing and this needs to be clarified

Line 139 – “….while other relevant behaviors were rarely found and exclusive in this study.”  I am not sure what the “and exclusive” part of this sentence means here, can you rephrase?

Also can you provide a % estimate of how often other behaviors were observed? E.g. “Other behaviors were observed in <5% of videos and therefore not recorded during data collection”

Line 144 – Here and throughout – the phrase “spatial allocation” is not quite the right term, please consider changing to “space use”

Line 161 – “Six hens were random selected..” – Are these six hens across all cages? Within each cage? Please clarify

Line 164 – Why are the date groupings different between space use and behavioral data?

Line 165 – I’m not sure I understand the comment about preening here – all behaviors were scored continuously over the 20 min observation period (per line 161). Do you mean continuous data sampling as here it sounds as if the frequency (count) of each behavior was recorded during the 20 minute observation sessions but continuous sampling (total time engaged in) preening was recorded at the same time as the counts?  Consider rephrasing:

                We recorded each instance of pecking and aerial ascent/descent, and each bout of preening. We also recorded the total time engaged in preening bouts, and total time spent walking per 20 minute observation session. This was converted to percent of total observation period for analysis.

Line 178 – For the Kruskal-Wallis test, was this comparison done on total counts of these behaviors aggregated to the day level? Or were these converted to a rate (frequency per unit time)?

Line 179 – “differences in in” – delete one of the “in”

Were no analyses done on total locomotion and total preening times? Those aren’t described here

Results

Spatial allocation use

Is there a justification for providing the information for comparisons between every observation day? This section is very dense and somewhat confusing to read. I would suggest significantly simplifying how this is presented for readability.

Figure 2 and Figure 3 – These are both well done, please fix the legends in figure 3 – the labels read p_low and can no doubt be changed to “Perch – Low” or something to that effect

Table 2,3 – These are useful, I know it says in the body of the text that ED scores closer to one mean the distance is more similar, but this would be useful to have in the figure captions to aid interpretation of the values in the table

Figure 4 – This is very hard to read, poorly reproducible in gray scale, and generally very noisy data. I don’t think you really need to present a figure for every behavior for every time frame, at all times of day, the reader will likely get overwhelmed and not gain meaningful information from looking at this. I would suggest dropping the lines for each day and combining the 1-3 panels into a single graph with the mean value indicated by lines of different solid or dashed lines for each grouping of days (e.g. Figure A is Feeder Use with three lines showing means of days -6 to -1, 1 to 4, 13 to 15)

Line 248 – You don’t need to explain what color the line is on the graph in the text, this information can be moved to the figure caption

Line 257 – After the intensely detailed results from the space use data at different day groupings and throughout the day, the very condensed results of behaviors presented here is somewhat startling? The space use presentation could be significantly streamlined.

Line 268 – “…were able to habituate to wearing” – add “them” after “wearing”

Line 269 – “…can be recovered” – rephrase – “returned to baseline”

Line 297 – “…suggesting a decrease in appetite due to discomfort” – This is a minor phrasing issue, but I would not expect a decrease in appetite due to discomfort so much as a decrease in feeding behaviors due to increased time spent preening or perched and inactive after the backpack was mounted.  Unless the backpack was physically painful to the birds, it would be behavioral discomfort and unfamiliarity with the sensation of the device changing their behaviors, not an appetite issue.

Line 307 – “…due to the change in their appearances…” – This isn’t incorrect but I don’t think its entirely accurate either – the hens don’t care about how they look but the restricted motion or perceived change in their mobility may lead to isolating more while they adjust to the device.

Line 315 – Rephrase the last sentence “During the lights-off period, the hens slept mainly on upper perches, rarely roosting on low perches.”

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Line 142 (Table 1): 'grain' must be feed

Figure 3: I think that you swapped the charts. The left must be the lights-off (night) with almost no birds on the lower perches

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Dear Authors,

It’s fantastic to see applied studies providing clear information on the application of inertial measurement unit backpack to the evidence of comfort behavior and locomotion behavior of laying hens,. This manuscript is already written to a very high standard, which is also appreciated by this reviewer. I do have only a two suggestions, mainly to make it easier to read and understand.

1. It would have been beneficial and refreshing for the article to insert a photo of the IMU bacpack and its attachment to the birds, even though it was well described in section 2.2.

2. L. 345-349 These are conclusions, so they should be moved to conclusions at the end of the article or at all delete. Note that some of the statements presented are not based on your research (e.g. species, husbandry system, weight of device etc.).

Author Response

Please see the attachment.

Author Response File: Author Response.docx