Figure 1
Diagram of knowledge gaps in literature reviews regarding EE for dairy calves. For this review, we used physical enrichment as defined by Mandel et al. (2016) and Veissier et al. (2024).
Table 1
Population and outcome search term strings used for the final search in the systematic review
| Acronym | Search string |
|---|---|
| Population | (calf OR calves OR heifers) AND (dairy OR milking) |
| Intervention and comparison | (“environmental enrichment” OR “space allowance” OR (indoor AND outdoor) OR substrate OR floor OR “wood shavings” OR sand OR accessories OR furnished OR objects OR brush OR ball OR rope OR “dry teat”) |
| Outcome | (behavio* OR play OR explor* OR lying OR intake OR growth OR “body weight” OR “weight gain” OR mortality OR health OR diarrhoea OR respiratory) |
Figure 2
Flowchart following preferred reporting items for Systematic Review and Meta-Analyses guidelines (Page et al., 2021) showing the process used to identify and screen articles for eligibility and inclusion in this systematic review.
Table 2
Summary of the direction of evidence for the effects of physical enrichment type on dairy calves reported in studies (n = 64) included in this systematic review
| Outcomes | Physical enrichment type | |||
|---|---|---|---|---|
| Space allowance | Outdoor access | Flooring type | Enrichment objects | |
| Behaviour | ↑ 12 · ↔ 4 | ↑ 4 · ↔ 3 | ↑ 14 · ↓ 0 · ↔ 1 | ↑ 19 · ↓ 0 · ↔ 0 |
| Growth | ↑ 2 · ↓ 0 · ↔ 4 | ↑ 3 · ↓ 4 · ↔ 6 | ↑ 3 · ↓ 3 · ↔ 7 | ↑ 2 · ↓ 0 · ↔ 7 |
| Intake | ↑ 0 · ↓ 0 · ↔ 5 | ↑ 1 · ↓ 3 · ↔ 5 | ↑ 3 · ↓ 3 · ↔ 2 | ↑ 1 · ↓ 0 · ↔ 5 |
| Health | ↑ 0 · ↓ 0 · ↔ 3 | ↑ 7 · ↓ 1 · ↔ 2 | ↑ 3 · ↓ 2 · ↔ 4 | ↑ 0 · ↓ 1 · ↔ 5 |
| Physiology | ↑ 5 · ↓ 2 · ↔ 1 | ↑ 1 · ↓ 0 · ↔ 2 | ↑ 4 · ↓ 2 · ↔ 3 | ↑ 0 · ↓ 0 · ↔ 2 |
↑ improvement or increase associated with enrichment; ↓ reduction associated with enrichment; ↔ no statistically significant effect. Values represent the number of studies reporting each outcome direction.
Figure 3
Heatmap showing the strength of evidence from studies included in this systematic review (n = 64) evaluating different physical enrichment types for dairy calves.
Figure 4
Representation of different space allowances (m2 per calf) and social housing evaluated in 18 studies included in this systematic review. Each group size evaluated is represented by a symbol.
Figure 5
Illustration of different flooring types used for dairy calves in 20 studies included in this systematic review. Note that all studies evaluated at least two flooring types.
Figure 6
Graphical illustration of the enrichment objects used for enriching dairy calves’ enclosure over 19 studies included in this systematic review.