• Dogs that developed a GDV during the course of the study: 98
• Dogs that did not develop a GDV during the course of the study: 1539

Nb. This study was derived from a larger prospective cohort study carried out by the authors. 1991 dogs initially enrolled on this study; however, for inclusion in the current study, dogs needed to be 6 months or older, and owners needed to have provided vital status information (undefined in the paper) and have completed the detailed questionnaire initially sent out to owners.

Dogs were recruited through breed clubs and dog shows. At the start of the study, owners were asked about the presence of GDV in the medical history of the dog or any of its first-degree relatives. The dog was physically assessed for body condition and temperament, and conformational measurements taken.

Within thirty days of recruitment, owners were provided with a detailed questionnaire to complete that provided data on the dog’s GDV history (if positive, the dog was excluded), breeding, medical history, reproductive status, personality and temperament, and dietary factors.

Owners were instructed to notify the researchers if any of the following outcomes occurred:

• The dog developed a GDV (if so, the researcher confirmed this with the veterinarian who treated the dog)
• The dog died of another cause
• The ownership of the dog was transferred to another person

Owners were contacted in 1997, 1998, and 1999 to find out if, over the duration of the study, their dog had developed a GDV and if so, whether the dog died or survived.

This was the methodology for the original prospective cohort study by the authors (referred to above). Dogs from that study were included only if:

• The initial questionnaire had been fully completed
• There was at least one follow up set of data for that dog
• 7% of the owners in this study fulfilled both criterion for inclusion (n = 1660)
• 4% of these owners were excluded because their dog was less than 6 months old at the point of completing the initial questionnaire, leaving 1637 (82.2% of the original sample) available for analysis in this study.

Of these dogs, the median duration during which the dogs were followed up was 2.4 years (Max: 4.8 months; minimum: no stated). The reasons for loss to follow – up (other than death) are not stated. 182 dogs died during this period: 29 died due to the GDV episode, 24 died for unknown reasons. 55 are reported to have died from other medical problems. 74 dogs are not accounted for in the figures reported.

Of relevance to this PICO, the authors’ asked owners about the height from which they fed their dog. From this, they derived two specific aspects to assess for risk:

1. Was the food bowl raised?

• Yes / No

2. What was the height of the food bowl?

• Not raised / raised ≤ 1 foot / raised > 1 foot

In analysing and presenting the data, the authors split the data according to the size of the dog:

1. Large breed dogs
2. Giant breed dogs

Large breeds (n = 889):

• The relative risk posed by feeding from a raised feeder was 2.17 (95% confidence interval: 1.27 – 3.71; P = 0.01).
• 4% of the cases of GDV could be attributed to the dog being fed from a raised feeding bowl.
• The incidence (± 95% confidence interval) of GDV per 1000 dog years was 18 (12 – 24), for dogs fed from the floor (n = 625).
• The incidence (± 95% confidence interval) of GDV per 1000 dog years was 40 (24 – 56) for dogs fed from a raised feeder (n = 264).

Giant breeds (n = 742):

• The relative risk posed by feeding from a raised feeder was 1.99 (95% confidence interval: 1.00 – 3.95; P = 0.05).
• 8% of the cases of GDV could be attributed to the dog being fed from a raised feeding bowl.
• The incidence (± 95% confidence interval) of GDV per 1000 dog years was 17 (7 – 27) for dogs fed from the floor (n = 341).
• The incidence (± 95% confidence interval) of GDV per 1000 dog years was 34 (22 – 46 for dogs fed from a raised feeder (n = 401).

However, there was an interaction between the height of the feeder that increased the risk and the size (giant versus large breeds) of the dog. If the dog was fed from a raised bowl, the actual height (≤ 1 foot high versus > 1 foot high) of the bowl significantly affected relative risk:

• Large breeds: Dogs that were fed from a bowl ≤ 1 foot high (n = 105) were 3.06 times (95% confidence interval: 1.60 – 5.87, P = 0002) more likely than dogs that were not fed from a raised bowl (n = 625) to experience a GDV.
• The incidence (± 95% confidence interval) of GDV per 1000 dog years was 56 (26 – 86) for dogs fed from a bowl ≤ 1 foot high.
• Dogs that were fed from a bowl > 1 foot high (n = 144) were no more likely to experience a GDV than dogs not fed from a raised bowl (n = 625).
• The incidence (± 95% confidence interval) of GDV per 1000 dog years was 29 (- 11 – 47) for dogs fed from a bowl > than 1 foot high.

Giant breed dogs:

• Dogs that were fed from a bowl ≤ 1 foot high (n = 60) were no more likely to experience a GDV than dogs not fed from a raised bowl (n = 341).
• The incidence (± 95% confidence interval) of GDV per 1000 dog years was 15 (- 6 – 36) for dogs fed from a bowl ≤ less than 1 foot high.
• Dogs that were fed from a bowl > 1 foot high (n = 324) were 2.29 times (95% confidence interval: 1.15 – 4.58, P = 0.02) more likely than dogs that were not fed from a raised bowl (n = 341) to experience a GDV.
• The incidence (± 95% confidence interval) of GDV per 1000 dog years was 39 (25 – 53) for dogs fed from a bowl > 1 foot high.

The authors do not examine interactions between:

• Speed of eating and the height of the feed bowl
• Morphometric measurements (particularly height of the dog) and speed of eating

The total number of dogs lost to follow up is not reported. The authors exclude dogs from the original study that were lost to follow up before at least one follow up questionnaire was completed. However, this is not the same as saying these dogs were not lost to follow up as, for example, if the study was still in operation, why were further questionnaires not completed by these owners? The authors do not report how many dogs recruited to the study, remained with the study until the study ended. Instead they report only median duration of follow up; this is meaningless to assess the number of dogs that remained with the study from recruitment to study end, as the dogs were signed up to the study at different time points. If the dogs that developed GDV and the dogs that didn’t develop a GDV differentially dropped out prematurely, this could introduce a ‘loss to follow up bias’. We know that, by the nature of the recruitment process for the subset of dogs included in this study, that already 13.3% of dogs had been excluded due to lack of follow up data (no follow up questionnaires completed). Therefore, it seems likely that total losses to follow up before the study ended would be higher (and possibly considerably so) but the authors fail to give us the information needed to assess this.

There is not attempt by the authors to assess whether participant drop out before the study ended was random or whether particular risk factors or characteristics were associated with an increased risk of drop out. Furthermore, there are a lot of dogs lost to death that remain unaccounted for in the authors’ reporting.

The survey was potentially available to English speaking dog owners with access to the internet in any country worldwide.

• Control group (dogs without a GDV): 1437 respondents
• Gastric dilation-volvulus group (GDV): 1114 respondents

The questionnaire was divided into three sections:

1. Demographic information (year of birth, breed, sex, neuter status, and purpose of the dog; country and postcode of respondent). Whether the dog had ever had a GDV that required surgical intervention. This latter question was used to divide dogs into the control group and the GDV group. However, the authors then also included within the GDV group dogs that did not have surgery, or died / were euthanised without surgery but were considered to have a GDV (whether confirmed or presumed).
2. GDV group: a series of 44 questions divided into 4 categories:
   1. Dog specific factors
   2. Management factors
   3. Environmental factors
   4. Personality factors
3. Control group: The same questions were asked of the control group dog owners as were asked of the GDV group, with the exception that they were not asked any questions about the GDV episode (as the dogs had not experienced a GDV). They were asked one additional question (had the dog had a prophylactic gastroplexy?). These changes reduced the total number of questions asked to 32.

Of relevance to this PICO, the authors’ asked owners whether the dog was fed from a raised bowl.

The incidents of GDV were retrospective so owners may have already taken measures to alter their height from which their dog was fed post-surgery, on the basis of veterinary recommendation or lay research. The authors do not outline whether owners were asked to complete the form on the basis of the height the dog was fed from at the time (or preceding) the GDV or, present time, or not directed as to a time frame to use.

There was no attempt to match control and GDV cases across other dimensions that may have been relevant (e.g. breed, size, and / or age).

The population of dogs studied is not constrained to types of dogs at high risk of GDV (large and giant breed dogs). Therefore, if any risk factors identified co-vary with the size of the dog, this would represent a confounding variable in interpreting the data that limits any conclusions that may be drawn.