Effect of Maturity at Harvest on Yield, Chemical Composition, and In Situ Degradability for Annual Cereals used for Swathgrazing.

Rosser, C.L., Górka, P., Beattie, A.D., Block, H.C., McKinnon, C.M., Lardner, H.A., and Penner, G.B. (2013). "Effect of Maturity at Harvest on Yield, Chemical Composition, and In Situ Degradability for Annual Cereals used for Swathgrazing.", Journal of Animal Science, 91(8), pp. 3815-3826. doi : 10.2527/jas.2012-5677  Access to full text

Abstract

The objective of this study was to determine how harvest maturity of whole-crop cereals commonly used in swathgrazing systems in western Canada affects yield, chemical composition, and in situ digestibility. We hypothesized that the increase in yield with advancing maturity would not offset the decline in digestibility and thus, the yield of effectively degradable DM (EDDM) would decline with advanced stages of maturity. Four replicate plots of barley (Hordeum vulgare L.; cv. CDC Cowboy), millet (Panicum milliaceum; cv. Red Proso), oat (Avena sativa L., spp.; CDC Weaver) and wheat (Triticum aestivum L.; cv. 07FOR21) were grown, with a subsection in each replicate harvested at 4 different maturities; head elongation, late milk, hard dough, and fully mature. At each stage of maturity, the wet and DM yields, and chemical composition (DM, OM, NDF, crude fat and non-fiber carbohydrates; NFC) were determined. Whole-crop samples were ground (2-mm screen), weighed into nylon bags (pore size of 53 ± 10 µm), and duplicate incubation runs were conducted by crop type. For each incubation run, nylon bags were randomly allocated (randomized by field replication, stage of maturity, and incubation time) to 1 of 7 heifers (32 bags/heifer during each run). Degradation rates were determined using a first-order kinetic model, and data were analyzed with stage of maturity as a fixed effect and plot as a random effect. The yields DM, OM, and NFC increased linearly for barley and oat (P < 0.001) and increased quadratically for millet and wheat (P ≤ 0.025). Neutral detergent fiber yield increased linearly for barley (P = 0.005) and quadratically for millet, oat and wheat (P = 0.044). There were no changes in CP yield observed for barley, millet or oat with advancing maturity, but there was a linear increase observed for wheat (P = 0.002). The NFC concentration increased linearly for barley, millet, and oat (P < 0.001), and quadratically for wheat (P < 0.001) while the EDDM concentration decreased quadratically for millet, oat, and wheat (P = 0.003). The degradation rate of NDF decreased linearly with advancing maturity (P ≤ 0.014) for millet, oat and wheat, but was not affected for barley (P = 0.13). The yield EDDM increased linearly for barley and oat (P < 0.001) and increased quadratically for millet and wheat (P ≤ 0.025). These findings suggest that harvesting whole-crop annual cereals at the hard dough and mature stages may maximize the yield of EDDM.

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