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Fiber digestion kinetics of summer annual grasses with or without brown midrib genotype.

G. Ferreira

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06-24-2020

Abstract:

371
Fiber digestion kinetics of summer annual grasses with or without brown midrib genotype.
G. Ferreira*1, A. I. Silva-Reis1,2, A. A. Pereyra1,3, C. L. Teets1. 1Department of Dairy Science, Virginia Tech Blacksburg, VA, 2Facultad de Ciencias Agrarias, Universidad Nacional del Nordeste Corrientes, Corrientes, Argentina, 3Facultad de Agronom�a y Veterinaria, Universidad Nacional de R�o Cuarto R�o Cuarto, C�rdoba, Argentina.

The objective of this study was to determine fiber digestion kinetics of summer annual grasses containing (BMR) or not (CONV) the brown midrib genotype. Four varieties (2 CONV and 2 BMR) of corn (CN), sorghum (SG), and pearl millet (PM) were planted in 1 m � 3 m plots (3 plots/variety). All plots were planted and harvested on 5/30/19 and 9/18/19, respectively. Samples of leaf-blades, stems, and whole plants were collected, dried, and ground to pass a 2-mm screen, and 0.25 g was put into Ankom F57 porous bags previously rinsed with acetone to perform in situ digestibility in 3 cows. All samples from 1 of the 3 replicates per species and variety were incubated within the same cow, so cow was considered a blocking factor. All bags were placed simultaneously into the rumen and incubated for 0, 3, 6, 9, 12, 18, 24, 48, 96, and 240 h. In situ disappearance parameters were determined using Proc NLIN of SAS according to the model ISNDFD = B � [1-e(-k � T)], where B is the potentially digestible NDF, and k is the fractional digestion rate of B. Kinetic parameters were contrasted using a mixed model that included the effects of cow (random), species (fixed), genotype (fixed), species � genotype (fixed), and the residual error. For the whole plants, fraction B was 82.1, 73.5, and 70.6% for CN, PM and SG, respectively (P < 0.01) and 71.2 and 79.5% for CONV and BMR, respectively (P < 0.01). The fractional digestion rate did not differ among species (2.85%/h; P = 0.85) but was greater for BMR than for CONV (3.19 vs. 2.51%/h). For the blades, fraction B was 87.2, 82.7, and 82.2% for PM, CN and SG, respectively (P < 0.01) and 81.1 and 86.9% for CONV and BMR, respectively (P < 0.01). The fractional digestion rate was 3.59, 3.06, and 2.99%/h for PM, SG, and CN, respectively (P < 0.04) and 3.56 and 2.87%/h for BMR and CONV, respectively (P < 0.01). For the stems, fraction B (62.4%) did not differ among species (P = 0.12) and genotypes (P = 0.24), and k (2.08%/h) did not differ among species (P = 0.59) and genotypes (P = 0.08). In conclusion, when comparing species, BMR varieties do not necessarily have greater fiber digestibility than CONV varieties.

Keywords: summer annuals, fiber digestibility, brown midrib (BMR).