To examine supplementation strategies — starch- or fiber-based concentrates offered with or without straw — for a high-quality grass silage, A. Craig, A.W. Gordon, S. Stewart and C.P. Ferris with the Agri-Food & Biosciences Institute in Northern Ireland recently conducted a three-period change-over design study using 24 mid-lactation multiparous Holstein-Friesian dairy cows.
The grass silage contained 418 g of dry matter per kilogram and, on a dry-matter basis, 170 g/kg of crude protein (CP) and 12.1 MJ/kg of metabolizable energy (ME).
Four treatments, in a 2 x 2 factorial arrangement, compared concentrate type (high-starch or high-fiber) and straw inclusion (straw or no-straw).
On a dry-matter basis, the high-starch concentrate contained 373 g/kg starch and 258 g/kg neutral detergent fiber (NDF), while the high-fiber concentrate contained 237 g/kg starch and 339 g/kg NDF, Craig et al. reported.
The researchers explained that in the no-straw treatments, silage and concentrates were offered as a total mixed ration in a 57:43 DM ratio, while in the straw treatments, chopped straw was added at 4% of total dry matter, replacing part of the silage component of the diet.
Following this study, the effect of diet on nutrient utilization efficiency was examined using four cows per treatment.
Craig et al. reported that there were no interactions between concentrate type and straw inclusion for any cow performance or digestibility parameters. Silage dry matter intake (DMI) and total DMI were reduced with the high-fiber concentrate (P = 0.001 and P = 0.006, respectively) and straw inclusion (P < 0.001 and P = 0.014, respectively), the researchers added.
Neither concentrate type nor straw inclusion had a significant effect on milk yield or milk fat content, Craig et al. observed.
They noted that the high-starch concentrate increased milk protein content (P < 0.001) while straw inclusion decreased milk protein content (P = 0.036). Treatment had no effect on cow bodyweight, condition score, fecal scores, digestibility coefficients or nitrogen and energy utilization efficiency.
Craig et al. concluded that supplementing a high-quality grass silage with a carefully formulated "high-starch" concentrate improved DMI and milk protein content with no adverse effects on cow performance. In this study, straw inclusion in the diet had no beneficial effects on DMI, milk production or nutrient utilization efficiency, the researchers added.
Craig et al. published their results in a recent edition of Livestock Science.