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Switchgrass (Panicum virgatum) harvested using two different strategies in lactating dairy cow rations.

B. Lemay



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Switchgrass (Panicum virgatum) harvested using two different strategies in lactating dairy cow rations.
B. Lemay*1, R. Nagle1, A. J. Carpenter1, T. J. DeVries1, P. H. Luimes1, M. Thimmanagari2, J. DeBruyn2, A. Heeg2. 1University of Guelph Guelph, ON, Canada, 2OMAFRA Ontario, Canada.

Switchgrass (Panicum virgatum) is a native tall grass that has been researched as a novel species in the biomass industry and as a promising crop for livestock feed. Two harvesting strategies are employed for switchgrass hay: switchgrass is 1) cut and baled in the fall, or 2) left to over-winter in the field, and cut and baled in the spring. This study aimed to compare switchgrass harvested by either of these 2 methods to use of wheat straw in lactating dairy cow rations. Holstein cows (n = 12, DIM = 158 � 48.4; parity = 1.6 � 0.67) were exposed to each of 3 treatments in a 3 � 3 LSD with 14-d periods (10d of adaptation and 4d of sampling). Treatments consisted of TMR containing equal amounts of: 1) wheat straw (CON), 2) spring-baled switchgrass (SSG), or 3) fall-baled switchgrass (FSG) at 0.5% inclusion, on a DM basis. Milk samples were collected twice daily at each milking, and feed and blood samples were collected before the morning feeding. Feed refusal samples were taken and subjected to particle size analysis to determine feed sorting. All statistical analyses were conducted using a repeated measures mixed-effect linear regression model with the fixed effect of treatment and random effects of cow and day. Analysis of feed samples indicated no differences between treatments for NDF, ADF, CP, or TDN (P ≥ 0.60). DMI was consistent between treatments (SSG = 23.5, FSG = 24.8, CON = 24.1 kg/d; SE = 1.35; P ≥ 0.63), as was milk yield (FSG = 27.6, SSG = 28.0, CON = 27.8.7 kg/d; SE = 1.37; P ≥ 0.93). Milk fat was greater (SE = 0.015; P = 0.01) for cows fed a TMR containing CON (4.5%) vs. SSG (4.2%), but neither treatment differed from FSG (4.4%; P ≥ 0.23). Milk protein was greater for cows fed SSG (3.44%) or CON (3.44%) compared with cows fed FSG (3.40%; SE = 0.05; P = 0.01), but did not differ between CON and SSG (P = 0.99). Blood metabolites (BHBA, NEFA, and glucose) did not differ between treatments (P ≥ 0.32). No differences in sorting of the treatment TMRs were observed (P ≥ 0.18). Results suggest that feeding switchgrass can successfully replace wheat straw in lactating rations and that switchgrass harvested strategy may influence milk components in dairy cows.

Keywords: switchgrass, milk production, harvest strategy.