Ruminal degradation of maize starch is affected by sowing date

Abstract

Context Delaying sowing date of maize allows producers to achieve stabilised yield. Delays in the sowing date generate changes in the grain structure, which may affect the ruminal degradability of the maize starch. Aims The objective of this study was to evaluate the effects of maize sowing date on ruminal starch degradability, and how it is related with grain physical characteristics and source:sink ratio during the grain-filling period. Methods To study the effects of maize sowing date on grain physical characteristics and on starch in situ effective degradability (ED; 6%/h passage rate from the rumen), eight treatments were defined on the basis of eight different sowing dates in Argentina of a commercial semi-dentate maize hybrid (Dekalb 7210 VT3P), as follows: Treatment 1 (13 October), Treatments 2, 3, and 4 (4, 17 and 26 November respectively), Treatments 5, 6 and 7 (3, 15 and 28 December, respectively) and Treatment 8 (5 January). For each sowing date, three plots of maize were sown in a complete randomised-block design and harvested at grain physiological maturity. Key results Starch ED of ground (2.0-mm) grains ranged from 631 to 801 g/kg and showed a ‘J’-shape response, being lower for the sowing dates from 17 November to 3 December and highest on the sowing date of 5 January. Grain density increased until the sowing date of 17 November, and then decreased. Grain vitreousness and hardness were initially not affected, but started to decline after the sowing date of 17 November. Grain test weight was not affected until the sowing date of 15 December, when it started to decline. The source:sink ratio during the grain-filling period decreased as the sowing date was delayed. Effective starch degradability was negatively correlated with the physical characteristics evaluated and the source:sink ratio. Conclusions Delaying sowing date affected the maize source:sink ratio during the grain-filling period; this was associated with changes in grain physical characteristics and with an increase in ruminal starch degradability. Implications Delaying sowing date increases dry matter (DM) and starch effective degradability, and therefore could affect cattle weight gain and feed conversion efficiency.