Effect of age and dietary crude protein level on nitrogen excretion in dairy heifers

The aim of this study was to examine the effect age and dietary crude protein (CP) level on nitrogen (N) excretion in dairy heifers develop simple models predict N farm based nutrient intake parameters. Thirty-six Danish Holstein were divided into 4 groups; 8, 12, 16, 20 months old (M8, M12, M16, M20), respectively, with 9 animals per group. Heifers within groups blocked 3 according pregnancy stage randomly assigned treatments a × Latin square design. consisted diets total CP concentrations 9.8, 12.2, 14.6, 17.0%, which highest (i.e. 17.0%) provided M8 M12 heifers, lowest 14.6%) M16 M20 heifers. experiment periods, each period lasting for 2 weeks first 11 days used as adaptation last sampling recording. Feed water recorded daily, feces (n = 6, pooled) urine samples 2, collected analyzed chemical composition. Fecal output increased level, probably due increase dry matter (DMI) observed when increasing level. Urinary diet, greatest older Thus, urinary appeared be strongly correlated seemed age. A 12.2% sufficient all maintain adequate rumen microbial digestion, underpinning potential reducing by manipulation. However, short experimental cannot state whether fulfills requirement growth during whole rearing Furthermore, prediction equation established feces: (g/d) 0.054 + 6.52 DMI considered reliable proxy replacement application farm.