Results and Discussion
The diets contained about 58% DM, 22.3% CP, 46% NDF, 25% ADF, and 4.3% fatty acids (Table 2). Protein and ADF were a little higher than the formulated targets, and NDF was about 33% higher than expected, probably because of the variability of fiber from nonforage sources given than ADF was not substantially higher. Total fatty acid concentration of the diets was lower than the formulated amounts.
| Item1 | Megalac | Rumolac |
| DM, % | 57.4 | 58.4 |
| -------- % of DM -------- | ||
| CP | 22.0 | 22.5 |
| NDF | 45.5 | 46.0 |
| ADF | 25.3 | 25.0 |
| Fatty acids | 4.32 | 4.24 |
| 1DM = dry matter, CP = crude protein, NDF = neutral detergent fiber, and ADF = acid detergent fiber. | ||
The DM intakes were not different between the two fat supplements (Table 3), with intakes being quite high given that the trial was conducted during summer months. Milk yield was similar and averaged about 92 lb/day. Milk fat and protein percentages and yields were similar between the treatments. The milk fat and protein concentrations were a little lower than typical but were not unreasonable. The milk fat and protein concentrations for the entire research herd during June, 2000 were 3.91% and 3.06%, respectively. However, days in milk averaged 239 for the herd and 146 and 155 days in milk for the two treatments.
| Item1 | Megalac | Rumolac | SE | P |
| DM intake, lb/day | 59.4 | 63.2 | 1.7 | 0.14 |
| Milk yield, lb/day | 91.5 | 92.9 | 2.2 | 0.65 |
| Milk fat, % | 3.38 | 3.33 | 0.10 | 0.72 |
| Milk fat, lb/day | 3.10 | 3.07 | 0.12 | 0.86 |
| Milk true protein, % | 2.88 | 2.84 | 0.04 | 0.48 |
| Milk true protein, lb/day | 2.63 | 2.62 | 0.06 | 0.89 |
| MUN, mg/dl | 16.0 | 16.0 | 0.5 | 0.99 |
| Milk SCC, (cells/ml) x 1000 | 377 | 481 | 162 | 0.66 |
| BCS1 | 2.28 | 2.35 | 0.09 | 0.61 |
| Change in BCS1 | -0.25 | -0.15 | 0.09 | 0.47 |
| 1DM = dry matter, MUN = milk urea nitrogen, SCC = somatic cell count, and BCS = body condition score. | ||||
The milk urea nitrogen was similar between the treatments but on the upper end of the desirable range, reflective of the high dietary concentration of protein. Milk somatic cell counts were not different between treatments. Body condition score averaged 2.3, and cows on both treatments decreased slightly in body condition from the beginning to the end of the trial, possibly because of the effects of environmental stress on feed intake.