Frothy bloat is a serious digestive disorder in cattle (Bos taurus L.) grazing winter wheat (Triticum aestivum L.) forage in the southern Great Plains of the USA. Wheat plant metabolism is one of the factors involved in bloat. We determined diurnal and seasonal patterns of total phenolic accumulation and foam strength (a measure of bloat potential) in forage of winter wheat cv. Cutter in response to nitrogen (N) fertilisation when grown at Vernon, Texas, during two growing seasons (November–March) in 2006–07 and 2007–08. The diurnal pattern of phenolic accumulation followed the diurnal pattern of solar radiation, with lower values in the morning and the evening, and maximum values around midday. The range of phenolic concentrations measured was 1.9–6.6 mg/g dry matter (tannic acid equivalent). The diurnal pattern of foam strength was opposite to that of phenolic accumulation and ranged from 15.5 to 21.8 min/cm. Nitrogen fertilisation (33, 67, and 134 kg/ha) had inconsistent effects on diurnal patterns of phenolic accumulation and foam strength. With increased N fertilisation rate, concentrations of total, soluble, and insoluble protein fractions increased, whereas soluble carbohydrate concentrations declined. Phenolic concentrations were higher in January–February 2007 and November–December 2007 than in other months and declined in March of each growing season. Foam strength was higher in late autumn than spring in both growing seasons. The results suggest that diurnal patterns of phenolic accumulation in wheat forage respond to diurnal pattern of solar radiation and are inversely correlated with diurnal patterns of foam strength. Breeding wheat cultivars with enhanced phenolic content in forage may be one approach to reduce bloat incidence in grazing cattle.
Cross-pollination in wheat Triticum aestivum L. and its wild relative Aegilops biuncialis Vis.