Table 2.

Quality assessment of the included studies

	Jones et al. [3]	Mathew et al. [46]	Mathew et al. [32]	Hubens et al. [44]	Le Moine et al. [49]	Wu et al. [48]	Watson et al. [36]	Canis et al. [45]	Lee et al. [57]	Lee et al. [53]	Paik et al. [29]	Hopkins et al. [11]	Hofstetter et al. [30]	Tsivian et al. [43]	Gutt et al. [51]	Ishida et al. [52]	Tomita et al. [33]	Wilkinson et al. [41]	Brundell et al. [50]	Zayyan et al. [42]
I	√	√	√	√	√	√	√	√	√	√	√	√	√	√	√	√	√	√	√	√
II	√	√	√	√	√	√	√	√	√	√	√	√	√	√	√	√	√	√	√	√
III	√−	√−	√−	√−	√−	√−	√−	√−	√−	√−	√−	√−	√−	√−	√−	√−	√−	√−	√−	√−
IV	√	√	√	√	√	√	√	√	√	√	√	√	√	√	√	√	√	√	√	√
V	√	√	–	–	–	√	√	√	–	–	√	√	–	–	–	–	√	–	√	–
VI	–	√	–	–	–	–	–	–	–	–	–	–	√	–	–	–	–	–	–	–
TS	7	8	6	6	6	7	7	7	6	6	7	7	7	6	6	6	7	6	7	6
G	A	A	B	B	B	A	A	A	B	B	A	A	A	B	B	B	A	B	A	B

√: complete data; – : not stated; √−: incomplete data. I (score of 2): peer-reviewed publication; II (score of 2): Random allocation of treatment and control; III (score of 2): animal species (inbred line, age-matched, MHC (mismatch); IV (score of 1): sample size calculation (sample size of both control and experimental groups must be clarified); V (score of 1): compliance with animal welfare regulation; and VI (score of 1): statement of potential conflict of interest (source of funds must be clarified). Study quality was stratified into four ranks according to their scores: A (a score of 7–9); B (a score of 5–6); C (a score of 3–4); D (a score of 0–2)

TS total score, G grade