A meta-analysis of the genetic contribution to greenhouse gas emission in sheep.

The objective of this study was to use a random-effects model of meta-analysis to merge various heritability estimates of different gas emission traits (methane yield [METY], methane production [METP], carbon dioxide production [CO 2 ], the sum of carbon dioxide and methane production [METP + CO 2 ], METP METP + CO 2 $$ \frac{\mathrm{METP}}{\mathrm{METP}+{\mathrm{CO}}_2} $$ ratio, and oxygen consumption [O 2 ]) and their genetic association with growth and partial efficiency traits in sheep. A total of 53 genetic correlations and 47 heritability estimates from 13 scientific articles were used in the meta-analysis. The included papers were published between 2010 and 2022. To measure heterogeneity, Chi-square (Q) test was performed, and the I 2 statistic was determined. The average heritability estimates for the studied traits were low to moderate and ranged from 0.137 (for METY) to 0.250 (for METP + CO 2 ). The heterogeneity test of heritability estimates indicated that heritability estimates for METY, O 2 consumption, and METP METP + CO 2 $$ \frac{\mathrm{METP}}{\mathrm{METP}+{\mathrm{CO}}_2} $$ had low Q values and non-significant heterogeneity (p > 0.10). However, the average heritability estimates for other traits experienced significant heterogeneities (p < 0.10). The genetic correlation estimate between METP with O 2 was -0.597 (p < 0.05), but its genetic correlations with other gas traits ranged from 0.593 (with METP + CO 2 ) to 0.653 (CO 2 ; p < 0.05). Also, mean estimates of genetic correlation between METP with live weight (LW), feed intake (FI), and residual feed intake (RFI) were 0.719, 0.598, and 0.408, respectively. The genetic correlations of CO 2 with performance traits varied from 0.641 (with RFI) to 0.833 (with FI; p < 0.05). This meta-analysis showed gas emission traits in sheep are under low-to-moderate genetic control. The average genetic parameter estimates obtained in this study could be considered in the genetic selection programmes for sheep, especially when there is no access to accurate phenotypic records or genetic parameter estimates for gas emission traits.