Methane emissions of multiparous dairy cows of two contrasting breeds at different lactation stages in a low input pastoral system.

JORGE-SMEDING E.; LOZA C.; RICO DE.; ORCASBERRO M. S; GERE J. I.; ASTIGARRAGA L.; ALVAREZ OXILEY A.

Colonia

Conferencia; III Conferencia de Gases de Efecto Invernadero en Sistemas Agropecuarios de Latinoamérica (GALA 2017); 2017

INIA

Introduction: Major studies on enteric methane emissions (ME) have been focused on dietary effects in confinement systems of the Northern hemisphere, but there are few reported studies evaluating the association between breed and ME. Objective: the aim of this work was to evaluate the effect of the breed (Holstein, HF; Normande, N) and lactation stage (111 and 222 days in milk, LS) on fat and protein corrected milk yield (FPCM), ME, methane intensity per unit of FPCM (imFPCM) or milk solids (imS) and methane yield relative to MEI (Yem). Materials and methods: The experiment was carried out at the Bernardo Rossengurtt Research Station of the Faculty of Agronomy, Udelar, Uruguay (32°22?S, 54°26?W) during Winter (W) and Spring (S) 2016. Ten multiparous cows of each breed calved in autumn were evaluated in grazing conditions over the entire lactation. In W the diet consisted of rice bran (5.0 kg/cow.d), sorghum silage (20 kg FM/cow.d) and one grazing session of Avena bizantina. In S the cows grazed a Festuca arundinacea and Trifolium repens pasture twice a day and 3.0 kg/cow.d of rice bran was offered in the milking parlor. ME were estimated by the SF6 tracer technique (Johnson et al., 1994; modified by Gere & Graton, 2010). Individual milk yield was recorded daily and milk samples stored with preservative at 4 °C for composition analyses. MEI was estimated by the NRC system (NRC, 2001). Results and discussion: HF cows produced more FPCM (17.9 vs. 12.8 kg/d; P=0.0348) with the same fat content (P=0.0796) and lower protein content (P=0.0480) than N as previously reported (Delaby et al., 2009). Consequently, N cows produced lesser amounts of solids than HF (0.932 vs. 1.269 kg/d; P=0.0405) due to their lower milk production in concordance with Reiche (2015). The LS only affected protein content (2.87 vs 3.33 %; P=0.0133). There was no evidence of breed effect in MEI, nevertheless there was a tendency of increased MEI in spring (129.8 vs. 152.9 MJ/cow.d, P= 0.658), perhaps due to the higher pasture allowance during this season. Both breeds had similar ME (391 vs. 472 g/cow.d, P= 0.1637), probably due to high intra race variability. In disagreement with other studies on ME between contrasting dairy breeds (Münger & Kreuzer, 2006), imFPCM and imS were not genetically affected. On the other hand, ME were greater in the advanced LS (P=0.0052) while imFPCM did not change with LS. Finally, Yem was not affected by the breed, while it increased with LS. This result could be associated with the energy partioning dynamic between milk production and repletion process; in fact, there was no evidence of differences in terms of FPCM yield between LS despite MEI tended to be greater in the advanced LS. Conclusions: Despite lower FPCM and solids yield in N cows, imFPCM, imS and Yem were not different between breeds. Further research should investigate breed differences in beef production and their effects on whole system im and efficiency.