Table 5.
Univariate meta-regression results showing significant (P < 0.05) and marginally significant (0.05 ≤ P < 0.10) covariates investigated as potential sources of study heterogeneity for total milk yield. The explained results for each of the covariates included in the meta-analysis are presented for daily production.
| No. of studies 1 (trials) 2 | Covariate (trials) | Estimate 3 | 95% CI 4 | P-value | I 2 (%) | Adj-R2 (%) |
|---|---|---|---|---|---|---|
| Total milk yield 3 (9) | Null model | −796.10 | −1,765.62, −173.41 | 0.095 | 99.9 | NA |
| Publicarion year (9) | 233.83 | −0.52, −468.18 | 0.050 | 99.9 | 0 | |
| Continent | – | – | 0.019 | 99.9 | 0 | |
| South America (9) | Reference | |||||
| Europe (9) | 1,905.75 | 413.93, 3,397.57 | 0.019 | |||
| Sample size (9) | −2,563.72 | 0.04, 0.36 | 0.022 | 99.9 | 0 | |
| Cattle group (9) | - | - | 0.019 | 99.9 | 0 | |
| Zebu (9) | Reference | |||||
| Europe (9) | 1,905.75 | −3,397.57, −413.93 | 0.019 | – | – | |
| Clustering (9) | - | - | 0.019 | 99.9 | 0 | |
| No (9) | Reference | |||||
| Yes (9) | 1,905.75 | 413.93, 3,397.57 | 0.019 |
I 2 between-study residual variation; Adj-R2 percentage of the residual variation.
1 Number of studies included in the meta-regression.
2 Number of trials included in the meta-regression.
3 Standard mean difference of the effect size.
4 These values represent 95% confidence intervals (CI) for the effect size.