Variation of digestibility and intake by sheep of lucerne (Medicago sativa L.) hays cut at sunrise or sunset

An experiment was carried out in 2006 in the Ebro Valley of Spain to test the differences in chemical composition, ruminal degradation, in vivo digestibility and intake between lucerne hays cut at sunrise (AM) or at sunset (PM). Measurements were carried out at 0.50 flowering during spring, summer and autumn growth cycles. PM hays showed higher contents of soluble carbohydrates, starch and total non-structural carbohydrates than AM hays. No significant differences between times of cutting were found for crude protein, neutral detergent fibre, acid detergent fibre or acid detergent lignin. Effective degradability of dry matter (DM) was higher in autumn PM hay (0.57 +/- 0.008) than AM hay (0.47 +/- 0.008). No differences between times of cutting were found for hays cut in spring or summer. Effective degradability of nitrogen was significantly higher in summer and autumn PM hays than in AM hays. However, degradability did not differ significantly between times of cutting for the hays cut in spring. Differences in organic matter digestibility averaged 0.02 +/- 0.008 in spring and 0.05 +/- 0.008 in autumn, but no differences were found between cutting times for lucerne hays in summer. For DM intake, differences between PM and AM hays were significant in spring (57 +/- 2.0 v. 46 +/- 2.0 g/kg BW0.75, respectively) and summer (60 +/- 2.0 v. 52 +/- 2.0 g/kg BW0.75, respectively), but not significant in autumn (55 +/- 2.0 v. 51 +/- 2.0 g/kg BW0.75, respectively). Finally, digestible organic matter intake in sheep was higher for PM (34 +/- 1.3, 36 +/- 1.3 and 32 +/- 1.3 g/kg BW0.75) than for AM hays (27 +/- 1.3, 30 +/- 1.3 and 27 +/- 1.3 g/kg BW0.75) in spring, summer and autumn, respectively. In conclusion, cutting lucerne at sunset could be a simple management strategy for improving the feed value of hays.