# Effects of Substituting Dietary Corn with Grain Byproducts on Fattening Hu Sheep: Growth Performance, Rumen Fermentation, Energy-Nitrogen Metabolism and Greenhouse Gas Emissions

## TL;DR

Replacing corn with grain byproducts in sheep diets slightly lowers costs but increases methane emissions, while fermentation of byproducts improves performance and reduces emissions.

## Contribution

Bacterial-enzymatic fermentation of grain byproducts is proposed as a strategy to enhance cost-effectiveness and reduce greenhouse gas emissions in sheep diets.

## Key findings

- Replacing corn with unfermented byproducts increased methane emissions and reduced nitrogen retention in Hu sheep.
- Fermented byproducts improved economic returns, nitrogen metabolism, and reduced methane emissions compared to unfermented byproducts.
- Fermentation lowered the abundance of methane-producing microbes and improved rumen fermentation parameters.

## Abstract

Replacing corn with grain byproducts in fattening Hu sheep diets numerically reduced formula cost and nitrogen utilization while increasing methane emissions, but did not significantly alter growth performance. Consequently, it failed to improve overall economic returns compared to the control diet. Based on this, bacterial-enzymatic fermentation treatment of the byproducts would lower the relative abundance of methanogens and greenhouse gas emissions, and improve finishing economic returns. Thus, bacterial-enzymatic fermentation presents a potential strategy for achieving cost-effective corn substitution.

Grain byproducts can serve as cost-effective alternatives to corn, but may lead to reduced production performance and increased greenhouse gas emissions. This study aimed to investigate the effects of replacing corn with the grain byproducts (wheat bran, sprayed corn bran) subjected to bacterial-enzymatic fermentation treatment or not in Hu sheep, mainly focusing on production performance, energy-nitrogen metabolism, rumen fermentation and greenhouse gas emissions. A total of fifty-four 6-month-old Hu sheep were divided into three groups, with 6 pens per group and 3 sheep per pen, and then randomly allocated to one of the three dietary groups for 60 days, i.e., a control group (CON), a group (RC) that corn was partially (~42%) replaced with grain byproducts, and a group (BF) that corn was partially replaced by fermented grain byproducts. Compared with the CON group, the RC group showed numerically lower rumen total volatile fatty acid (TVFA) concentration and its propionate proportion, nitrogen retention content (NR; −10.22%) and its retention ratio (NR/NI decreased by 4.27 percentage points, absolute reduction from 24.30% to 20.04%), corresponding to a relative decrease of 17.6%.) as well as a numerically reduced net profit (−2.18%) with a decreased feed price (−¥0.16/kg TMR). Meanwhile, the RC group showed a significant increase in the relative abundance of Methanobrevibacter (p < 0.05), accompanied by numerically higher daily methane emissions (+6.14%) and emission intensity (+4.08%), although these methane-related differences did not reach statistical significance (p > 0.05). Compared to the RC group, the BF group resulted in a numerical increase in feed price (+¥0.03/kg TMR), net profit (+27.93%), TVFA concentration, propionate proportion, NR (+28.17%), NR/NI (an increase of 5.38 percentage points), the relative abundance of Prevotella, Shuttleworthia and Succinivibrio as well as the decrease of fecal nitrogen (FN; −12.29%), daily methane emissions (−8.75%), emission intensity (−5.83%) and the relative abundance of Methanobrevibacter. In summary, replacing dietary corn by 42% with wheat bran and sprayed corn bran numerically reduced formula cost and nitrogen utilization, while increasing methane emissions and methanogens abundance, without significantly affecting growth performance. This combination led to no improvement in economic returns for fattening Hu sheep. Bacterial-enzymatic fermentation treatment of these byproducts could mitigate these drawbacks, being superior energy-nitrogen metabolism and lower greenhouse gas emissions intensity, presenting a potential strategy for cost reduction and efficiency enhancement. Further research with larger sample sizes is warranted to confirm these findings and support broader application.