Effect of pasture height on intake, milk yield and methane emissions of grazing dairy cows.

LOZA C.; GERE J. I.; ORCASBERRO M. S; JULIARENA P.; ALVAREZ OXILEY A.; ASTIGARRAGA L.

Colonia

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

INIA

Introduction: Ruminants have been questioned for their contribution to climate change due to enteric methane (CH4) emission (Gerber et al., 2013). National research has shown that an increase in concentrate supply without efficient use of pastures does not contribute to reduce Carbon Footprint (Lizarralde et al., 2014). For Uruguay, with predominant pasture based dairy systems, it is important to adjust management practices that lead to an increase in milk production and therefore, a reduction of Carbon Footprint. Hypothesis: At the same forage allowance, a low available pre-grazing herbage mass would be associated with an increase in methane emissions per liter of milk. Objective: The aim of the present study was to quantify the effect of pasture height at the same herbage allowance on daily methane emission and fat and protein corrected milk yield (kg/cow/day) of grazing dairy cows. Materials and methods: The experiment was carried out in ?Estación Experimental Bernardo Rosengurtt?, Experimental Station of the Faculty of Agronomy of the Universidad de la República in Cerro Largo, Uruguay (32°22´S, 54°26´W) during November 2015 (spring), on a Dactylis glomerata and Medicago sativa based pasture. Treatments consisted of two contrasting pre-grazing herbage heights (HHH: high herbage height and LHH: low herbage height). Swards were strip-grazed at a daily herbage allowance of 30 kg DM/cow/day (above 5 cm). A 2×2 Replicated Latin Square design was implemented, with eight multiparous Holstein-Friesian dairy cows in mid lactation (four animals per treatment) in two measurement periods. Daily individual herbage intake (DMI) was estimated using chromic oxide (Cr2O3) and herbage organic matter digestibility was estimated by faecal index (N and ADF in the faeces). Methane emission was determined using the sulfur hexafluoride (SF6) tracer technique reported by Johnson et al., (1994), adapted by Gere y Gratton (2010). Individual milk yield and milk composition were measured daily. Results and Discussion: Pre-grazing herbage height tended to differ (47 vs 34 cm, P = 0.0621) while herbage mass above 5 cm (1846 vs 1392 kg DM/ha, P = 0.0499) differed significantly. However DMI did not show differences among treatments (18.3 kg/a/d; P = 0.5101). Fat and protein corrected milk yield (20.6 kg FPCM/cow/day), daily methane emission (363 g CH4/cow/day), methane emissions corrected per FPCM (18.3 g CH4/kg LCGP/d) and methane yield as gross energy intake (Ym = 6.7%) did not differ between treatments as was expected, based on previous research (Astigarraga and Peyraud, 1995; Peyraud et al., 1996; Delagarde et al., 2000). Conclusion: In the current study, herbage height in the LHH sward was higher than attempted, which may explain the lack of difference in daily intake so as to on milk production and methane yield as energy expenditure at grazing might have been similar.