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The effect of treatment temperature, treatment time and glucose addition on digestibility of starch of barley grain and pea grain were studied in situ in non-lactating dairy cows, and the relationship between rumen degradation of starch (RDS) and protein was also determined. Ground barley and peas were heat-treated at 100, 125 and 150 °C for 5, 15 and 30 min with and without addition of glucose. Samples were incubated in the rumen for 4, 8 and 16 h using the in situ method, and rumen degradation of starch was measured. The total tract indigestible starch fraction (ISF) was measured on the 16 h rumen residues using the mobile nylon bag method. Heat treatment at 100 and 125 °C significantly decreased RDS of both barley and peas, and the RDS was higher after treatment at 150 °C than at 125 °C. Treatment time had a significant effect on RDS, but only at 100 °C in both feeds. The lowest RDS of barley after 8 h rumen incubation occurred at 125 °C and treatment for 30 min, which decreased RDS 34% units compared to untreated barley. For peas, the lowest RDS after 8 h rumen incubation was observed after treatment at 125 °C for 5 min, causing a reduction of 21% units compared to untreated peas. The ISF was significantly higher in untreated peas than in untreated barley (9% versus 0.1%). Heat treatment had no effect on the ISF in barley, while in peas the ISF was significantly increased after treatment at 100 and 125 °C, but decreased at 150 °C. Addition of glucose before treatment reduced RDS significantly in both feeds at two of three incubation times. Correlation evaluation showed that in both feeds RDS mimicked rumen degradation of protein after treatment at 100 and 125 °C, but not after treatment at 150 °C. Glucose addition increased the relationship between RDS and RDP in both feeds. |
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