Nitrogen use efficiency and carbon footprint by beef cattle limit-fed co-product feedstuffs

Abstract Text:

In terms of energy density, the cost of importing hay is often not justified in years where adverse conditions limit local hay production. Co-product feedstuffs could represent an alternative to feeding hay in these conditions. While the primary objective of our work was to determine if co-product feedstuffs could be used to meet the energy demands for cows, also of interest was the nitrogen use efficiency of such a system, as well as the potential environmental impacts. Eight ruminally-fistulated cows (671 ± 32.0 kg BW) were stratified by BW and allocated randomly to 1 of 4 treatments in a 2-period study: 1) limit-fed soybean hulls (LSH), 2) limit-fed distillers’ dried grains with solubles (LDG), 3) a limit-fed mixture of soybean hulls and distillers’ dried grains with solubles (MIX), or 4) ad libitum mixed-grass hay (HAY; 10.6% CP, 71% NDF). Limit-fed diets were formulated to meet the ME requirements of an 11-mo post-partum mature beef cow. Diet amounts were increased over a 14-d period. Cows were then moved to indoor 3 × 4.3 m concrete pens fitted with rubber mats for a 14-d adaptation and 5-d total fecal collection period. Carbon footprint and emissions were predicted according to an IPCC (2006) model for cows housed on pasture. Excretion of total N, as well as percentage excreted in feces and urine, was not different (P ≥ 0.31) among treatments. Concentration of ammonia-N in the urine was greater (P = 0.02), and concentration of urea-N tended to be greater (P = 0.07) from LDG than from other treatments. Both ammonia-N and urea-N, when expressed as a percentage of the total urinary N, were greater (P ≤ 0.04) from LDG than other treatments. Predicted enteric CH₄, CH₄ from manure, direct loss of N₂O, as well as N₂O from volatilization and leaching were not different (P ≥ 0.12) among treatments. Contribution of feedstuffs to total CO₂ load tended to be greatest (P = 0.07) from LDG and least from HAY, with MIX intermediate to LDG and LSH and LSH intermediate to MIX and HAY. However, total carbon footprint (kg CO₂eq/d) was not different (P= 0.55) among treatments. Based on this information, co-product feedstuffs may be used in lieu of hay to meet the energy requirements of cows without adverse effects on total N excretion or environmental impact.

Keywords: limit feeding, co-product feedstuffs, carbon footprint