Energy metabolism of lactating dairy cows fed 2 formaldehyde- and formic acid–treated forages with 2 nonstructural carbohydrate sources

The partial efficiency of ME used for net energy by growing ruminants is greater when fed alfalfa (ALF) than orchard grass (OG), but is unknown for lactating cows and may be influenced by varying the nonstructural carbohydrate (NSC) grain source. The NSC sources evaluated were corn grain (CG) and barley grain (BG). Individual treatments were ALF-CG, ALF-BG, OG-CG, and OG-BG arranged in a 4 × 4 Latin square having a 2 × 2 factorial arrangement of forage (FOR) and NSC sources. Four multiparous lactating Holstein dairy cows (milk = 33.8 ± 4.5 kg/d; BW = 599 ± 25.8 kg; DIM = 82 ± 20 d) were selected to measure whole-body energy balance via calorimetry. Forages were direct-cut and treated with formic acid and formaldehyde before ensiling. After 3 wk of adaptation, 6 d total collection energy and N balances were measured during the fourth week of each period. No FOR by NSC interactions were detected for lactational performance. Intake of DM (22.8, 23.5, 19.2, and 19.3 kg/d for ALF-CG, ALF-BG, OG-CG, and OG-BG, respectively), gross energy (106.6, 111.0, 91.6, and 90.0 Mcal/d) and N (681, 664, 561, and 521 g/d) were greater for lactating dairy cows fed ALF compared with lactating cows fed OG and similar for lactating cows fed CG compared with cows fed BG. Digestibility of DM (67.2%, 63.1%, 66.6%, and 64.1%) and gross energy (65.7%, 62.5%, 66.9%, and 64.0%) were similar when fed ALF and OG and increased when fed CG compared with BG. Intake of ME (60.5, 59.6, 51.9, and 48.5 Mcal/d) was greater for cows fed ALF compared with cows fed OG and similar when cows were fed CG and BG. However, heat production per unit of ME intake (56.8%, 53.7%, 59.4%, and 62.9%) was greater for cows fed OG compared with cows fed ALF, which reduced the efficiency of converting ME to net energy (NE; 43.2%, 46.3%, 40.6%, and 37.1%) for cows fed OG compared with cows fed ALF. The efficiency of converting ME to NE was similar when fed CG and BG. The consumption of O₂ L/kg DMI was greater when cows were fed OG compared with cows fed ALF and tended to be greater when fed CG compared with BG. Greater O₂ consumption for cows fed OG by the intestinal and liver tissues resulted in greater heat production per unit of ME indicating an increase in energetic costs associated with metabolism when feeding grass compared with legumes, thereby reducing ME for productive purposes and the partial efficiency of ME.