Using Eastern Gamagrass to Limit Weight Gains by Replacement Dairy Heifers: 1. Nutrient Intakes and Heifer Performance.

Previous research has shown that eastern gamagrass [EGG; Tripsacum dactyloides (L.) L.] will produce yields of DM in central Wisconsin ranging from 7,000 to 10,000 kg/ha annually when managed with a 1-cut harvest system. Our objective was to determine whether the fibrous nature of this perennial warm-season grass could reduce the caloric density and DM intakes of corn silage/alfalfa haylage diets for replacement dairy heifers. A total of 120 Holstein dairy heifers were blocked by weight (heavy, 424 ± 15.9 kg; medium, 369 ± 11.8 kg; light, 324 ± 22.4 kg), and then assigned to 15 individual pens comprised of 8 heifers/pen. Eastern gamagrass haylage was blended into corn silage/alfalfa haylage diets at rates of 0, 9.2, 18.4, or 27.6% of the total dietary dry matter (EGG0, EGG9, EGG18, and EGG27, respectively). These diets were offered during a 105-d evaluation period for ad-libitum intake; however, the EGG0 diet also was offered on a limit-fed basis (LF). Serial additions of EGG increased NDF in blended diets from 396 g/kg (EGG0) to 487 g/kg (EGG27), and reduced corresponding estimates of energy density from 682 to 613 g/kg TDN. Intakes of DM for all ad-libitum diets were greater than LF (9.06 vs. 8.07 kg/d; P < 0.001); however, DM intakes for diets containing EGG were reduced relative to EGG0 (9.40 vs. 8.94 kg/d; P = 0.001). Similar effects were observed for intakes of TDN. Over the 105-d trial, total weight gains ranged from 89 kg (0.85 kg/d) for heifers offered EGG27 up to 114 kg (1.09 kg/d) for those offered EGG0. Performance was numerically similar between heifers offered EGG27 and LF diets (0.85 vs. 0.88 kg/d). Eastern gamagrass haylage was a completely non-sortable additive within corn silage/alfalfa haylage diets, and limited undesirable weight gains by dairy heifers.