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Effect of Rumen-Protected Lysine Supplementation of Corn-Protein Based Diets Fed to Lactating Dairy Cows
This trial tested whether rumen-protected Lys (RPL) supplementation would improve the nutritive value of RUP from corn protein. Thirty-two lactating Holstein cows were blocked by DIM and parity into 8 squares of 4 cows in replicated 4 x 4 Latin squares. Treatments were all supplemental CP from: 1) Soy [67% expeller soybean meal (ESBM) plus 33% solvent soybean meal (SSBM)]; 2) Soy/Corn [33% ESBM, 17% SSBM, 25% corn gluten meal (CGM) plus 25% distillers dried grains plus solubles (DDGS)]; 3) Corn (50% CGM plus 50% DDGS); or 4) Corn/RPL [diet 3 top-dressed with RPL (125 g Ajipro®/d, an estimated 20 g absorbed Lys/d)]. Diets contained (DM basis) 22% alfalfa silage, 43% corn silage, 18% ground high moisture and dry corn, 2.4% mineral-vitamin premix, 1.5-3.9% soyhulls, 15% CP, 30-32% NDF and, as predicted by NRC (2001), equal RDP, RUP and metabolizable protein. Cows within squares were randomly assigned to treatment sequences and fed diets for 4-week periods before switching; data from the last 2-week were analyzed using the mixed procedures of SAS. The table reports LS-means. Intake was highest on diet 1, intermediate on diets 2 and 3, and lowest on diet 4; BW change was highest on diet 3, intermediate on diets 1 and 2 and lowest on diet 4. Intakes and BW changes were reflected by differences in Milk/DMI, which was highest on diets 2 and 4 and lowest on diet 3. Milk yield was lower on diet 3 than on diets 1, 2 and 4 and protein yield was highest on diets 1 and 2, intermediate on diet 4 and lowest on diet 3. These results indicated that dilution of soybean meal RUP with that from corn protein did not reduce milk yield and adding RPL to the corn-protein based diet increased milk and protein yields.
| Item | Soy | Soy/Corn | Corn | Corn/RPL | SE | P > F |
| DMI, kg/d | 27.7a | 27.4ab | 26.9bc | 26.8c | 0.40 | < 0.01 |
| BW change, kg/d | 0.03bc | 0.59ab | 0.70a | -0.07c | 0.23 | 0.04 |
| Milk, kg/d | 45.8a | 46.1a | 44.3b | 45.4a | 1.17 | 0.01 |
| Milk/DMI | 1.66ab | 1.69a | 1.65b | 1.69a | 0.038 | 0.04 |
| Fat, kg/d | 1.87 | 1.87 | 1.83 | 1.83 | 0.060 | 0.37 |
| True protein, kg/d | 1.36a | 1.34a | 1.25c | 1.30b | 0.029 | < 0.01 |
| MUN, mg/dL | 10.6 | 10.6 | 10.8 | 11.1 | 0.25 | 0.06 |
abc(P < 0.05) |
Keywords:
Soybean meal
Corn gluten meal
Corn distillers dried grains
Rumen-protected Lys