Energy partition and nitrogen utilization lambs fed Willow (Salix alba) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Animal Science at Massey University, Manawatu, New Zealand
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2025
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Massey University
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Abstract
Willow (Salix spp.) has gained attention in recent years for its potential to enhance livestock nutrition and mitigate environmental impacts, particularly in the context of reducing methane (CH4) emissions from ruminants. This study investigated energy metabolism and nitrogen (N) utilization of Romney lambs under two treatments: summer pasture and willow + summer pasture. All lambs were placed in metabolic crates for three days where feed intake, faecal excretion, live weight changes were measured, and feed, faecal, and urine samples were analysed for nutrient composition. The contents of dry matter (DM), organic matter (OM), crude protein (CP), fat and lignin in willow were higher than those in summer pasture (366.8 g/kg willow vs. 357.5 g/kg pasture; 918.0 vs. 905.8 g/kg DM; 133.6 for 100g/kg DM; 44.8 vs. 34.8g/kg DM; 91.2 vs. 50.8 g/kg DM; respectively), while the ash, neutral detergent fibre (NDF) and acid detergent fibre (ADF) contents were lower than those of summer pastures (82 vs. 94.2 g/kg DM; 303.2 vs. 562.6 g/kg DM; 223.7 vs. 324.4 g/kg DM; respectively). The apparent digestibility of willow (DM: 63.7%; OM: 65.1%; CP: 50.8%; fat: 61.6%; NDF: 51.6%) was higher than that of summer pasture (DM:57%; OM: 59.1%; CP: 50.2%; fat; 54.5%; NDF: 51.2%). It was found that the use of willow as a supplementary feed in summer resulted in improved apparent digestibility, energy utilization and N balance in lambs. Willow supplemented lambs had lower urine N loss. However, willow supplementation did not reduce the live weight loss of lambs, which may be related to the insufficient proportion of willow in the mixed diet, the inadequate adaptation of rumen fermentation to willow and the detoxification process caused by secondary compounds in willow. Although willow supplementation led to an increase in faecal N, and an increase in estimated CH4 emissions in the predicted model, willow reduced the proportion of energy loss in the faeces, urine, and methane. Willow is a potential feed that provides a higher metabolizable energy (ME) intake and apparent digestibility during the summer months, reducing energy loss and improving energy utilization and N balance in lambs.