Carbohydrate-rich supplements can improve nitrogen use efficiency and mitigate nitrogenous gas emissions from the excreta of dairy cows grazing temperate grass

Abstract

Temperate pasture species constitute a source of protein for dairy cattle. On the other hand, from an environmental perspective, their high N content can increase N excretion and nitrogenous gas emissions by livestock. This work explores the effect of energy supplementation on N use efficiency (NUE) and nitrogenous gas emissions from the excreta of dairy cows grazing a pasture of oat and ryegrass. The study was divided into two experiments: an evaluation of NUE in grazing dairy cows, and an evaluation of N-NH3 and N-N2O volatilizations from dairy cow excreta. In the first experiment, 12 lactating Holstein × Jersey F1 cows were allocated to a double 3 × 3 Latin square (three experimental periods of 17 days each) and subjected to three treatments: cows without supplementation (WS), cows supplemented at 4.2 kg DM of corn silage (CS) per day, and cows supplemented at 3.6 kg DM of ground corn (GC) per day. In the second experiment, samples of excreta were collected from the cows distributed among the treatments. Aliquots of dung and urine of each treatment plus one blank (control – no excreta) were allotted to a randomized block design to evaluate N-NH3 and N-N2O volatilization. Measurements were performed until day 25 for N-NH3 and until day 94 for N-N2O. Dietary N content in the supplemented cows was reduced by 20% (P < 0.001) compared with WS cows, regardless of the supplement. Corn silage cows had lower N intake (P < 0.001) than WS and GC cows (366 v. 426 g/day, respectively). Ground corn supplementation allowed cows to partition more N towards milk protein compared with the average milk protein of WS cows or those supplemented with corn silage (117 v. 108 g/day, respectively; P < 0.01). Thus, even though they were in different forms, both supplements were able to increase (P < 0.01) NUE from 27% in WS cows to 32% in supplemented cows. Supplementation was also effective in reducing N excretion (761 v. 694 g/kg of Nintake; P < 0.001), N-NH3 emission (478 v. 374 g/kg of Nmilk; P < 0.01) and N-N2O emission (11 v. 8 g/kg of Nmilk; P < 0.001). Corn silage and ground corn can be strategically used as feed supplements to improve NUE, and they have the potential to mitigate N-NH3 and N-N2O emissions from the excreta of dairy cows grazing high-protein pastures.

Potential to reduce greenhouse gas emissions through different dairy cattle systems in subtropical regions

“…Ireland [9], different scenarios in Australia [51,52] and Uruguay [11], which ranged from 0.98 to 1.16 kg CO 2 e (kg ECM) -1 . When local emission factors for N 2 O emissions from urine and dung [37] and those from Table 4 were taking into account, the C footprint for scenarios including pasture, without accounting for sequestered CO 2 -C from perennial pasture-0.91 kg CO 2 e (kg ECM) -1 -was lower than the range of values described above. However, these values were still greater than high-performance confinement systems in UK and USA [53] or grass based dairy systems in Ireland [9,53] and New Zealand [8,54], which ranged from 0.52 to 0.89 kg CO 2 e (kg ECM) -1 .…”

“…Primary sources were direct and indirect N 2 O-N emissions from organic and synthetic fertilizers and crop/pasture residues, CO 2 -C emissions from lime and urea applications, as well as fuel combustion. The direct N 2 O-N emission factor (kg (kg N input) -1 ) is based on a local study performed previously [37].…”

“…Using IPCC emission factors [38], manure emissions increased as TMR intake went down (Fig 2A and 2B). However, using local emission factors for estimating N 2 O-N emissions [37], manure emissions decreased as TMR intake went down (Fig 2C and 2D). Regardless of emission factors used (Tables 3 or 4), emissions from feed production decreased to a small extent as the proportion of TMR intake decreased.…”

“…(a) N 2 O emission factors for urine and dung from IPCC [38], feed production emission factors from Table 3 without accounting for sequestered CO 2 -C from perennial pasture, production of electricity = 0.73 kg CO 2 e kWh -1 [41]. (b) N 2 O emission factors for urine and dung from IPCC [38], feed production emission factors from Table 3 without accounting for sequestered CO 2 -C from perennial pasture, production of electricity = 0.205 kg CO 2 e kWh -1 [46]; (c) N 2 O emission factors for urine and dung from local data [37], feed production EF from Table 4 without accounting for sequestered CO 2 -C from perennial pasture, production of electricity = 0.205 kg CO 2 e kWh -1 [46]. (d) N 2 O emission factors for urine and dung from local data [37], feed production emission factors from Table 4 accounting for sequestered CO 2 -C from perennial pasture, production of electricity = 0.205 kg CO 2 e kWh -1 [46].…”

“…The lower C footprint in scenarios with access to pasture, when local emission factors [37] were used for N 2 O emissions from urine and dung and for feed production (Table 4), may also be partially attributed to the small negative effect of pasture on ECM production. Nevertheless, local emission factors for urine and dung had a great impact on scenarios including pastures compared to ad libitum TMR intake.…”