A study was undertaken to compare Tifton 85 (T85) and Coastal (CBG) bermudagrasses for effects of cultivar and age at harvest on yields of DM and digestible DM, in vitro digestion, nutrient content, cell wall composition, in situ digestion kinetics, and feed intake and digestion by growing beef steers. In Exp. 1, T85 and CBG forages staged for growth in May or July of 1993 were harvested at 3, 4, 5, 6, 7, and 8 wk from subplots. Tifton 85 bermudagrass had 7.1% greater DM yield, 18.2% higher (P < .05) digestible DM yield, and 7.1% greater IVDMD than CBG, and, after 5 wk of forage growth, IVDMD of both T85 and CBG decreased with increased age at harvest (P < .05). In Exp. 2, T85 and CBG forages staged for growth in July 1997 were harvested at 2, 3, 4, 5, 6, and 7 wk from subplots. Even though T85 had higher concentrations of NDF and ADF than CBG, T85 had 34.1% higher DM yield, 47.9% higher digestible DM, 55.0% higher digestible NDF, 91.7% higher digestible ADF, greater IVDMD, in vitro NDF and ADF disappearances, and higher in situ DM and NDF digestion (P < .05). Coastal bermudagrass had higher concentrations of lignin and lower concentrations of total neutral sugars, arabinose, glucose, and xylose than T85 (P < .05). In vitro digestibilities of DM, NDF, and ADF were lower and concentrations of ADF and lignin were greater for 7- vs 6-wk harvests of both T85 and CBG (P < .05). In Exp. 3, T85 and CBG forages staged for growth in July 1997 were harvested as hay at 3, 5, and 7 wk from .8-ha pastures and fed to 36 individually penned growing beef steers (initial BW = 244 kg) to quantify ad libitum intake without supplementation. Tifton 85 bermudagrass had lower concentrations of lignin and ether-linked ferulic acid and greater concentrations of NDF, ADF, hemicellulose, and cellulose than CBG (P < .05). Steers fed T85 had higher (P < .05) digestion of DM, OM, NDF, ADF, hemicellulose, and cellulose than steers fed CBG. Digestion of NDF, ADF, hemicellulose, and cellulose decreased (P < .05) with increased age at harvest for both cultivars. In conclusion, T85 produced more DM and had more digestible nutrients in vitro, in situ, and in vivo than CBG, and 3 and 5 wk of growth would be recommended ages to harvest either cultivar.

No abstract

Three corn hybrids, Mycogen TMF94, Cargill F337 (which contains a brown midrib trait), and Pioneer 3861 were compared in a plot trial, an intake trial, and a lactation trial. In the plot trial, the three corn hybrids were planted in replicated 15.2 x 385-m plots. Mycogen TMF94 and Cargill F337 had lower yields of dry matter (DM), higher concentrations of neutral detergent fiber, and higher in vitro true DM disappearance compared with Pioneer 3861. Mycogen TMF94 had a higher yield of DM than Cargill F337 despite having a lower plant population. However, Cargill F337 had a higher in vitro true DM disappearance than Mycogen TMF94. In the intake trial, six individually penned Holstein heifers were blocked and assigned randomly to one of three total mixed rations containing 79% (DM basis) Mycogen TMF94, Cargill F337, or Pioneer 3861 corn silages in replicated 3 x 3 Latin squares. Heifers fed the Pioneer 3861-based TMR had lower DMI than heifers fed Mycogen TMF94 and Cargill F337-based TMR. In the lactation trial, 75 midlactation Holstein cows were blocked and assigned randomly to one of three total mixed rations containing 31% (DM basis) Mycogen TMF94, Cargill F337, or Pioneer 3861 corn silages used in the intake trial. Milk production was highest for cows fed Cargill F337-based total mixed rations. It is concluded from this study that Mycogen TMF94 was higher yielding, but less digestible, and resulted in lower milk production by lactating cows than Cargill F337. In addition, Mycogen TMF94 had higher in vitro true DM disappearance, and similar DM yield and milk production by lactating cows when compared with Pioneer 3861.

No abstract

Lactating cows were offered diets with increasing neutral detergent fiber concentrations to determine the effects on intake, milk yield and composition, blood hormones, and nutrient digestion during cool or hot weather conditions. Tifton 85 bermudagrass hay was substituted for corn silage so that the forage portion of diets were: 1) 40% corn silage (control), 2) 32.4% corn silage, 7.6% bermudagrass, 3) 24.8% corn silage, 15.2% bermudagrass, or 4) 17.2% corn silage, 22.8% bermudagrass (dry basis). Dietary neutral detergent fiber concentrations (% dry matter) were 30.2, 33.8, 37.7, and 42.0, respectively. Intake of dry matter declined with increasing dietary neutral detergent fiber during cool and hot periods, but intake adjusted for cool weather treatment differences did not change further during hot weather. Milk yield declined linearly with increasing neutral detergent fiber during cool weather and changed quadratically during hot weather. Milk temperature declined with increasing dietary neutral detergent fiber for the p.m. milking during the cool period and declined with increasing dietary neutral detergent fiber for the a.m. and p.m. milkings during the hot period. Digestibility of neutral detergent fiber improved and ruminal turnover of particulate digesta was increased with greater dietary neutral detergent fiber content. No dietary fiber level by hot weather interaction was observed, suggesting that total energy intake may have and a greater effect on milk yield than dietary fiber content during hot, humid weather.