Methane and carbon dioxide production of lactating Holsteins with different crude protein feeding strategies

MaryGrace Erickson¹, Dante M. Pizarro¹, Geoffrey I. Zanton², and Michel A. Wattiaux¹

¹University of Wisconsin—Madison, Madison, WI, USA

²USDA Agricultural Research Service, US Dairy Forage Research Center, Madison, WI, USA

ABSTRACT: 

Although ruminal production of greenhouse gases (GHG) has been well-studied in relation to carbohydrate nutrition, limited research has studied the potential mediating effects of level of crude protein (CP) on ruminal carbohydrate fermentation and subsequent GHG emissions. Additionally, it is unclear how time-varying dietary composition affects GHG production. Our objective was to quantify the methane (CH₄) and carbon dioxide (CO₂) production of 8 non-cannulated, multiparous mid- to late-lactation Holsteins (M = 133, SD = 12 days in milk) during a 2x2 factorial study of CP level (LP, 13.9%; HP, 15.4%) and feeding pattern (O = CP oscillating at 48 hr interval, S = static). Cows were housed in tie stalls and fed total-mixed rations with a 60:40 forage-to-concentrate ratio. Each O feeding pattern consisted of one lower and one higher CP diet (O-HP 13.9-16.9%; O-LP 12.2-15.5%) alternated at 48 hr intervals such that the average diet composition over time equaled that of the corresponding S diet (S-HP; S-LP respectively). Diets were formulated by linearly exchanging soy hulls and ground corn with solvent soybean meal, maintaining a constant NDF:starch ratio (1.18) and constant ratio of rumen-degradable to crude protein (0.61). Treatments (n = 4) were arranged in a replicated Latin Rectangle design across four 28-d periods. On d 25-28 of each period, we recorded feed intake and milk production and took samples of orts and milk to calculate dry matter intake (DMI) and production. From day 14-21 of each period, we sampled gas production 3x/day with a GreenFeed unit (C-Lock, Rapid City, SD) during balanced intervals (-2.5)-(-0.5), 1-3, 4-6, 6.5-8.5, and 11-13 hr relative to 1x daily morning feeding. We fit linear mixed models with fixed effects of CP level, feeding pattern, and period, and a random intercept for cow and computed model-implied means and standard errors (SEM). Neither CP level, feeding pattern, nor their interaction influenced DMI (26.3 ± 0.8 kg/d; p = 0.401-0.935) or affected production of milk (36.7 ± 1.3 kg/d; p = 0.335-0.745) or fat-protein-corrected milk (FPCM; 36.6 ± 1.3 kg/d; p = 0.353-0.910). We observed no significant effects of CP level, feeding pattern, or their interaction on CH₄ production (474 ± 24 g/d; p = 0.461-0.892), intensity (13.1 ± 0.6 g/kg FPCM; p = 0.500-0.943), and yield (18.0 ± 0.7 g/kg DMI; p = 0.280-0.917). HP tended to increase CO₂ production (p = 0.070), feeding pattern had no effect (p = 0.123) and CP level tended to interact with feeding pattern (p = 0.084), with O-HP driving the interaction (O-HP = 15,597, S-HP = 14,890, O-LP = 14,827, S-LP = 14,870 g/d; SEM = 410.). Neither CP level, feeding pattern, nor their interaction affected CO₂ intensity (418 ± 16 g/kg FPCM; p = 0.226-0.870). HP increased CO₂ yield (P = 0.022) although neither feeding pattern (p = 0.474) nor the interaction (p = 0.927) influenced CO₂ yield (O-HP = 595, S-HP = 586, O-LP = 565, S-LP = 557 g/kg DMI; SEM = 16).  Neither CP level, feeding pattern, nor their interaction affected the ratio of CH₄:CO₂ in daily emissions (0.095 ± 0.004 L/L; p = 0.309-0.950) or affected oxygen consumption (10,362 ± 296 g/d; p = 0.102-0.646). Neither experimental factor nor their interaction influenced the respiratory quotient (1.05 ± 0.01; p = 0.263-0.865), which suggested positive energy balance. Overall, results showed minimal effects of CP level and feeding pattern on GHG emissions. Tendencies for greater CO₂ production and yield in cows fed O-HP relative to other treatments require further investigation of ruminal and post-absorptive metabolism. 

Contact Information: Michel Wattiaux, University of Wisconsin—Madison, 1675 Observatory Dr., Madison, WI, 53706, Phone: 954-555-1212, Email: wattiaux@wisc.edu

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