The accuracy with which several laboratory-based measurements predict the metabolizable energy (ME) value of whole-crop wheat (WCW) was determined. Twenty-six WCW forages differing in variety (cv. Slepjner, Hussar and Cadenza), maturity at harvest (milk, cheese and dough stages) and treatment applied (urea-treated, untreated or acid-based additive treated) were harvested in 2 years and conserved anaerobically in 200·1 barrels. The forages were then scanned using near infrared reflectance spectroscopy (NIRS) and analysed for chemical composition, in vitro rumen fluid-pepsin digestibility, in vitro neutral detergent-cellulase plus gamannase digestibility, in vitro fermentation gas production and in situ rumen degradability. ME was calculated using measured energy losses in faeces and urine and predicted energy losses as methane. The relationships between ME and the laboratory-based measurements were determined by regression. Gross energy was consistently the best predictor of ME (R2 = 0.53 and 0.86 in years 1 and 2 respectively). However the autocorrelation involved, militates against the prediction of ME from gross energy. None of the chemical constituents or biological techniques gave a good, robust prediction of ME. However, an NIRS calibration developed using the WCW samples was highly correlated (R2 = 0.68) with ME. This work therefore suggests that traditional laboratory-based, food evaluation techniques are unsuitable for predicting the ME content of WCW but that NIRS holds promise.

To measure the effect of partially replacing grass silage with urea-treated whole-crop wheat (WCW) four multiparous Holstein/Friesian lactating cows fitted with cannulas in the rumen and proximal duodenum were offered four diets in a Latin-square experiment. Grass silage (GS) was produced from the primary growth of a perennial ryegrass sward. Spring wheat (cv. Axona) was harvested at 603 g dry matter (DM) per kg and preserved with 20 (WCW-20) or 40 (WCW-40) kg urea per t DM. The diets were 6 kg DM of a dairy concentrate daily with one of four forages offered ad libitum The forage treatments were GS alone, a 2: 1 DM ratio of GS with WCW-40 (2: 1 40), or a 1: 2 DM ratio of GS with WCW-20 (1: 2 20) or WCW-40 (1: 2 40). Each period lasted 4 weeks with rumen and duodenal samples being taken on 2 days in the last week. Concentrations of milk fat and protein were increased by WCW inclusion. The digestibility in the rumen of DM, organic matter (OM) neutral-detergent fibre (NDF), acid-detergent fibre and starch fell with increasing WCW-40 inclusion in the diet. Flow of starch and non-ammonia nitrogen to the duodenum increased with WCW inclusion. It was estimated that the amounts of OM, starch, NDF and nitrogen digested post ruminally increased with WCW. With WCW there were increases in the rumen in the ratio of acetic acid plus n-butyric acid to propionic acid and in ammonia concentrations. The level of urea inclusion had no significant effects on rumen digestion. It is concluded that the large reduction in the contribution of the rumen to total OM digestion when WCW partially replaces grass silage may have implications for calculations of metabolizable protein supplies to animals given such diets. Possible means to improve food utilization include processing of the wheat grains and inclusion of readily fermentable carbohydrates in the diet to facilitate the utilization of the rumen ammonia.