Ruminal degradation of maize starch is affected by sowing date

Abstract

Context. Delaying sowing date of maize allows producers to achieve stabilized 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 based on eight different sowing date in Argentina of a commercial semi-dentate maize hybrid (Dekalb 7210 VT3P), as follows: 1 (October 13th), 2, 3, and 4 (November 4th, 17th and 26th, respectively), 5, 6 and 7 (December 3rd, 15th and 28th, respectively) and 8 (January 5th). For each sowing date, three plots of maize were sown in a complete randomized 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 (P < 0.01), being lower for the sowing dates from November 17th to December 3rd and highest on the sowing date of January 5th. Grain density increased until the sowing date of November 17th and then decreased. Grain vitreousness and hardness were initially not affected but started to decline after the sowing date of November 17th (P < 0.001). Grain test weight was not affected until the sowing date of December 15th, when it started to decline. The source/sink ratio during the grain filling period decreased as the sowing date was delayed (R2 = 0.97; P < 0.0001). Effective starch degradability was negatively correlated with the physical characteristics evaluated and the source/sink ratio (P < 0.05).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.