Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/2012
Publication Date: 10/3/2012
Citation: Coblentz, W.K., Hoffman, P.C., Esser, N.M., Bertram, M.G. 2012. Using eastern gamagrass to construct diets that limit intake and caloric density for dairy replacement heifers. Journal of Dairy Science. 95:6057-6071. Interpretive Summary: Dairy heifers consuming diets that contain significant proportions of corn silage or other high-energy forages often gain excessive weight, which negatively affects their future performance as lactating cows. Previous research has shown that eastern gamagrass will survive winter climatic conditions common throughout central Wisconsin and will produce adequate annual yields when managed with a 1-cut harvest system. The objective of this research was to determine whether the fibrous nature of this perennial warm-season grass could be effective in reducing the caloric density and dry matter intakes of corn silage/alfalfa haylage diets for replacement dairy heifers. When eastern gamagrass was included within the total mixed ration, there was no visual evidence of undesirable sorting behaviors by heifers, which is common when chopped straw is included in the diet. This is important because a functionally non-sortable diet potentially allows for greater flexibility with respect to bunk space; because less-desirable feed particles are not sorted, passive heifers have access to the same diet as aggressive heifers whenever they are able to reach the feedbunk. Based on our results, eastern gamagrass was effective in limiting caloric intakes by dairy heifers, and this was accomplished by diluting both the energy density of the diet as well as restricting dry matter intakes on the basis of gut fill. The practical benefit of reducing energy intakes was a reduction in average daily gain; this amounted to about 0.022 lb/day for each percentage unit of eastern gamagrass in the diet. As such, it was necessary to substitute eastern gamagrass primarily for corn silage until it comprised about 30% of the diet in order to reduce weight gains to typical targets (1.8 to 1.9 lb/day for 1000-lb heifers).
Technical Abstract: Previous research has shown that eastern gamagrass [EGG; Tripsacum dactyloides (L.) L.] will survive winter climatic conditions common throughout central Wisconsin, and will produce yields of DM ranging approximately from 7,000 to 10,000 kg/ha annually when managed with a 1-cut harvest system. The objective of this research was to determine whether the fibrous nature of this perennial warm season grass could be effective in reducing 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 each. Eastern gamagrass forage was harvested, ensiled, and subsequently incorporated into blended 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), which was set at 85% of the voluntary intake of EGG0. Serial additions of EGG increased concentrations of NDF in blended diets from 39.6% (EGG0) to 48.7% (EGG27), and simultaneously reduced the corresponding estimates of energy density from 68.2 to 61.3% TDN. Dry matter intakes for all diets offered ad libitum were greater than observed for LF (9.06 vs. 8.07 kg/d); however, DM intakes for diets containing EGG were reduced relative to EGG0 (9.40 vs. 8.94 kg/d). Similarly, intakes of TDN were greater for diets offered for ad-libitum intake than for LF (5.84 vs. 5.50 kg/d); however, inclusion of EGG reduced TDN intakes relative to EGG0 (6.41 vs. 5.65 kg/d). This reduction was explained by both linear and quadratic effects of the inclusion rate of EGG in the diet. 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 proved to be a completely non-sortable additive within corn silage/alfalfa haylage diets. It also was effective in limiting the caloric density and DM intake of these diets, as well as undesirable weight gains by dairy heifers.