ESTIMATION OF THE PROTEIN VALUE OF FINELY OR COARSELY MILLED LUPIN SEEDS

Samples of Lupinus albus cv Lublanc were ground to pass either through a 1.0, a 1.5-mm (fine) or a 5-mm (coarse) screen and particle sizes were measured. The effect of milling the seeds and of particle size on in situ nitrogen (N) degradability (Dg) was measured by the nylon bag technique using fistulated non-lactating Holstein cows. Animals were fed a ration of 30% soybean meal and Italian rye-grass hay. To estimate rumen degradation of N, nylon bags were placed in the rumen for 2, 4, 8, 16, 24 and 48 h. The effective DgN was calculated assuming a rumen outflow rate of 0.06/h. To evaluate feed-indigestible N, bags were left in the rumen for 16 h, placed in a pepsin bath for 2 h and then introduced into the duodenum for subsequently recovery in the feces. The PDI contents of the samples tested were calculated using DgN and fermentable organic matter (French PDI system). The in vitro N solubility of the same samples was also measured. Significant correlations were found between N solubility and the in situ rumen degradability of N (2 h), and between N solubility and the coefficient a of degradability kinetics in situ. The effective DgN values for coarse and fine samples of lupin seeds were: 62.5, 93.0 and 94.9% respectively. The mean value for whole tract digestion of N was always high (99.8%). Grinding the lupin coarsely decreased ruminal DgN, with a corresponding increase in the amounts digested in the intestine; intestinal disappearance of N for coarse and fine samples of lupin was 37.3, 6.8 and 4.9%. The PDIN and PDIE contents (g/kg DM) for lupin ground finely enough to pass through a 1-mm screen were 232 and 91 respectively; milling the lupin to pass through 1.5 or 5.0-mm screen increased these values by 1.7 and 25.4% for PDIN and by 7.8 and 140.6% for PDIE. The differences in values obtained from coarse and fine lupin samples were also confirmed when the effects of substrate particle size were tested.