Breeding for reduced methane emission and feed-efficient Holstein cows: An international response

摘要

Selecting for lower methane (CH_4) emitting animalsis one of the best approaches to reduce CH_4 given thatgenetic progress is permanent and cumulative over generations.As genetic selection requires a large number ofanimals with records and few countries actively recordCH_4, combining data from different countries couldhelp to expedite accurate genetic parameters for CH_4traits and build a future genomic reference population.Additionally, if we want to include CH_4 in the breedinggoal, it is important to know the genetic correlationsof CH_4 traits with other economically important traits.Therefore, the aim of this study was first to estimategenetic parameters of 7 suggested methane traits, aswell as genetic correlations between methane traits andproduction, maintenance, and efficiency traits using amulticountry database. The second aim was to estimategenetic correlations within parities and stages oflactation for CH_4. The third aim was to evaluate theexpected response of economically important traits byincluding CH_4 traits in the breeding goal. A total of15,320 methane production (MeP, g/d) records from2,990 cows belonging to 4 countries (Canada, Australia,Switzerland, and Denmark) were analyzed. Records ondry matter intake (DMI), body weight (BW), bodycondition score, and milk yield (MY) were also available.Additional traits such as methane yield (MeY;g/kg DMI), methane intensity (MeI; g/kg energy-correctedmilk), a genetic standardized methane production,and 3 definitions of residual methane production(g/d), residual feed intake, metabolic BW (MBW),BW change, and energy-corrected milk were calculated.The estimated heritability of MeP was 0.21, whereasheritability estimates for MeY and MeI were 0.30 and0.38, and for the residual methane traits heritabilityranged from 0.13 to 0.16. Genetic correlations betweendifferent methane traits were moderate to high (0.41to 0.97). Genetic correlations between MeP and economicallyimportant traits ranged from 0.29 (MY) to0.65 (BW and MBW), being 0.41 for DMI. Selectionindex calculations showed that residual methane hadthe most potential for inclusion in the breeding goalwhen compared with MeP, MeY, and MeI, as residualmethane allows for selection of low methane emittinganimals without compromising other economically importanttraits. Inclusion of residual feed intake in thebreeding goal could further reduce methane, as the correlationwith residual methane is moderate and elicitsa favorable correlated response. Adding a negative economicvalue for methane could facilitate a substantialreduction in methane emissions while maintaining anincrease in milk production.