Methane emission intensities by Holstein and Holstein x Jersey crossbreed lactating cows in two Brazilian grazing systems

Abstract Text: The aim of this study was the evaluation of methane emissions from pure Holstein and ½Jersey½Holstein high producing lactating cows grazing two different forages. The study was conducted at EMBRAPA's (Brazilian Agricultural Research Corporation) experimental station located in São Carlos city, in the Southeast region of Brazil. Treatments were a combination of two factors: two breeds (Holstein - HOL and ½Jersey½Holstein - JH) and two grazing systems (extensively grazed pastures with low stocking rate, ELS, or irrigated pastures under intensive management and high stocking rate, IHS). A total of 24 dairy cows were used (2 breeds x 2 grazing systems x 3 animals per paddock x 2 replicates), grouped according to age, stage of lactation and level of milk production. Cows were kept on pasture and supplemented with minerals and concentrates in accordance with milk yield (1 kg of concentrate/3 kg of milk produced). IHS pasture was rotationally managed and both IHS and ELS were managed under variable stocking rates ("put-and-take"). Forage production and animal performance variables were measured to determine environmental, technical and economic assessments. Methane emission evaluation took place in May 2013 using the SF6 tracer technique. Each animal received two permeation tubes (average load of 1431.0±76.2 mg of SF6 with an average emission rate of 1.74±0.18 mg/d) five days before collection. Samples were collected every 24 hours for five consecutive days. Gases were measured on a Shimadzu GC 2014. Data were analyzed using the MIXED procedure of SAS and averages were compared using Tukey’s test with significant differences at P<0.05. No interactions were observed between breed and grazing system. Crossbred JH presented lower (P<0.05) methane emission intensity than pure Holstein (11.26±1.11 vs. 14.62±1.11 gCH4/L milk) regardless of grazing system. Crossbreed ½Jersey½Holstein cows emitted less (P<0.05) methane per day than pure Holstein (275.1±20.8 vs. 337.2±20.8 gCH4/day) and produced the same amount of milk (25.11±1.11 vs.23.76±1.11 L/day). Efficiency of milk production can be a mitigation strategy when less methane is emitted per liter of milk..

Keywords: dairy cows; emission intensity; methane emission