This study was conducted to evaluate the effects of perennial forage mixture (alfalfa, clover and tall fescue; control) seeded in a pure stand or with different annual companion forages [Sudangrass (SG), Sudangrass brown midrib (BMR) gene 12 (BSG) or Sorghum-Sudangrass BMR gene 6 (BSSG)] on ensiling characteristics, chemical composition and in vitro total-tract NDF digestibility (TTNDFD) of experimental silages. Field experimental plots (8 per treatment) were harvested at 60 d (1st cut) and 90 d (2nd cut) at the bud stage of alfalfa. Second harvest forages were ensiled in laboratory silos for 42 days. Silage indigestible NDF (iNDF) was calculated by in vitro incubation at 240 h whereas potentially degradable NDF (pdNDF) was calculated by subtracting iNDF from total NDF. Digestion rate (kd) of pdNDF was estimated by in vitro incubation at 24, 30 and 48 h. Data were analyzed as repeated measures using the MIXED procedure of SAS with fixed effects of treatment and cut. Chemical analysis of experimental silages showed that companion forages reduced lignin (P < 0.0001) and crude protein (P = 0.0006) concentrations but increased NDF and ADF contents (P < 0.0001) compared with the control. Neutral detergent insoluble protein, water soluble carbohydrates, total digestible nutrients, and net energy of lactation were similar across treatments whereas acid detergent insoluble protein was higher (P < 0.0001) for control than other treatments. Indigestible NDF fractions were lower (P = 0.002) in warm-season companion forages (average 19.5%) than control (28.9%). Digestion rate of pdNDF was higher (P < 0.0001) in SG, BSG and BSSG than control. In vitro TTNDFD followed the order (P < 0.0001): BSG and BSSG (average 64.7%) > SG (62.8%) > control (56.4%). It was concluded that seeding perennial forages with SG, BSG or BSSG may improve chemical composition and NDF digestibility of silages.
Key words: dairy cows, silage, fiber digestibility.
Published in the proceedings of the Animal Nutrition Conference of Canada 2020. For information on the event, past and future editions, check out https://animalnutritionconference.ca/.