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Effect of dextrose and purified starch at two levels of rumen degradable protein on lactation performance and enteric methane emission in dairy cows
The objective of this study was to evaluate the effect of source of nonfiber carbohydrate (NFC) at two levels of rumen degradable protein (RDP) in the diet on lactation performance and enteric methane (CH4) emission. In addition, hourly CH4 emission rate relative to time of feeding was studied. Eighteen Holstein cows (mean ± SD; 148 ±10 days in milk, 644 ± 41kg of body weight), housed in a tie-stall barn were used in a split plot study. Cows were randomly assigned to either [dry matter (DM) basis] 11% (11-RDP) or 9% RDP (9-RDP) diets as whole plot. To lower diet RDP, soybean meal was partially replaced with expeller soybean meal and blood meal. Subplot treatments, which were allocated in three, 3 x 3 Latin squares (28d period) were (DM basis) 10% dextrose (DX), 5% dextrose and 5% purified starch (DX-ST), and 10% purified starch (ST). Cows were fed a total mixed ration with 61% forage and 39% concentrate, approximately 16.5% crude protein and 45.5% NFC once daily, and milked twice daily. During week 3 of each period, enteric CH4 emission was measured at 1, 2.5, 4, 5.5, 10, 11.5, 13, 14.5, 16, 17.5, and 22.5 hr after feeding, over a 4-d interval with GreenFeed (C-lock Inc, SD). The SAS mixed procedure with Tukey option was used to analyze the data. There was no NFC by RDP interaction (P> 0.05), and thus main effects are presented in table below. Cows fed 9-RDP had greater yield of fat-protein corrected milk (FPCM), milk (37.4 vs. 34.8 kg/d), milk fat (1.57 vs. 1.44 kg/d), and lactose (1.80 vs. 1.63 kg/d) compared to cows fed 11-RDP. Cows fed ST had lower dry matter intake (DMI), greater feed efficiency (FPCM /DMI) and lower enteric CH4 emission than cows fed DX and DX-ST. The hourly CH4 emission rate was lower for the 22.5 hr sampling time compared to all others (15.9 ± 2.8 vs. 20.1± 4.9 g/hr). Dietary treatments did not influence CH4/DMI (20.0 ± 3.5 g/kg) or CH4/FPCM (13.1 ± 2.6 g/kg). In conclusion, the level of RDP did not influence the responses to the source of NFC in the diet. Compared to dextrose as a source of NFC, starch reduced DMI, increased feed efficiency, and reduced daily CH4 emission.
Keywords: feed efficiency, greenhouse gas, nonfiber carbohydrate