Potential of feeding microwave-treated forage hays to improve sheep intake, digestion, nitrogen partitioning, and metabolism.

Microwave (MW) treatment has been suggested to improve forage hays' nutritive value and sheep growth performance. However, the extent to which the MW-treated forage hay affects apparent digestibility and nitrogen partitioning is not documented. This study examined the potential to use the MW as a novel thermal treatment to improve forage hay intake, digestibility, and nitrogen utilisation of sheep. A total of 24 merino rams (18 months of age, 42 ± 2.0 kg initial body weight) were randomly divided into four dietary treatments: Control lucerne hay (CLH), MW-treated lucerne hay (MLH), Control wheat hay (CWH), and MW-treated wheat hay (MWH). The study had 14 days adaption and 7 7-day sample collection period, with 6 sheep replicates/treatment. Feed, faeces, urine, and blood plasma samples were collected. Higher dry matter (DM) intake was observed in MLH vs. CLH (P < 0.001). The DM and organic matter digestibility both increased by 8% in MLH compared to CLH (P <0.001). The digestibility of neutral detergent fibre (NDF), acid detergent fibre (ADF), and nitrogen increased by 12%, 9%, and 10%, respectively in MLH compared to CLH (P < 0.001). The MLH-feed sheep showed higher nitrogen retention (P = 0.037) and microbial nitrogen synthesis (P = 0.047) compared to CLH-fed sheep. A limited effect was observed in CWH vs. MWH, with only ADF digestibility (P = 0.023) and plasma glucose (P < 0.05) being higher in sheep fed with MWH. Electron microscope images showed clear cell microstructure destruction (P <0.001) due to MW treatment in lucerne hay but there was no difference observed in wheat hay. The result provided first-hand comprehensive data to quantify MW treatment's effect on hay quality and sheep performance, with potential mechanisms explained underpinning the observed changes.