The effect of silage and concentrate type on intake behavior, rumen function, and milk production in dairy cows in early and late lactation.

The objective of this experiment was to evaluate the effect of feeding total mixed rations (TMR) that differ in structural and nonstructural carbohydrates to dairy cows in early and late lactation on short-term feed intake, dry matter intake (DMI), rumen fermentation variables, and milk yield. A 5 x 5 Latin square experiment with 15 dairy cows was repeated during early and late lactation. The 5 treatments were a TMR with (all on dry matter basis) 55% roughage (a 50:50 mixture of corn silage and grass silage) and 45% concentrate (a 50:50 mixture of concentrate rich in structural carbohydrates and concentrate rich in nonstructural carbohydrates; treatment CON), a TMR with the concentrate mixture and 55% grass silage (RGS) or 55% corn silage (RCS), and a TMR with the roughage mixture and 45% of the concentrate rich in structural carbohydrates (CSC) or the concentrate rich in nonstructural carbohydrates (CNS). Meal criteria, determined using the Gaussian-Gaussian-Weibull method per animal per treatment, showed an interaction between lactation stage and treatment. Feed intake behavior variables were therefore calculated with meal criteria per treatment-lactation stage combination. Differences in feed intake behavior were more pronounced between treatments differing in roughage composition than between treatments differing in concentrate composition, probably related to larger differences in chemical composition and particle size between corn silage and grass silage than between the 2 concentrates. The number of meals was similar between treatments, but eating time was greater in RGS (227 min/d) and lesser in RCS (177 min/d) than the other treatments. Intake rate increased when the amount of grass silage decreased, whereas meal duration decreased simultaneously. These effects were in line with a decreased DMI of the RGS diet vs. the other treatments, probably related to the high neutral detergent fiber (NDF) content. However, this effect was not found in CSC, although NDF content of the TMR, fractional clearance rate of NDF, and fractional degradation rate of NDF was similar between CSC and RGS. Rumen fluid pH was lesser, and molar proportions of acetic acid and of propionic acid were lesser and greater, respectively, in RCS compared with all other diets. Milk production did not differ between treatments. There was no effect of type of concentrate on milk composition, but diet RCS resulted in a lesser milk fat content and greater milk protein content than diet RGS. Lactation stage did affect short-term feed intake behavior and DMI, although different grass silages were fed during early and late lactation. The results indicate that short-term feed intake behavior is related to DMI and therefore may be a helpful tool in optimizing DMI and milk production in high-production dairy cows.

Frequent allocation of rotationally grazed dairy cows changes grazing behavior and improves productivity.

Twenty Holstein cows were blocked in 2 groups according to milk yield to evaluate the effect of frequency of allocation to new grazing plots on pasture intake, grazing behavior, rumen characteristics, and milk yield. The 2 treatments, daily allocation to 0.125-ha plots (1D) or allocation every 4 d to 0.5-ha plots (4D) of Lolium perenne L., were tested in a randomized block design (2 rotations with 3 or 4 measuring periods of 4 d each) with mixed model analysis accounting for repeated measures. There were no differences in the chemical composition of offered pasture and in pasture dry matter intake (DMI) between 1D and 4D. However, an interaction between treatment and rotation indicated a difference in pasture DMI between treatments during the first rotation (4D, 16.5 vs. 1D, 18.3 kg/d) but not during the second rotation (4D, 15.0 vs. 1D, 14.7 kg/d), possibly a result of a greater pasture mass in the first rotation. Grazing time (average 562 min/d) and ruminating time (average 468 min/d), observed using IGER graze recorders, were similar between treatments, but grazing time increased numerically (549 to 568 min/d), and ruminating time decreased linearly (471 to 450 min/d) within periods in the 4D treatment. Mean rumen pH (6.16 vs. 6.05) and rumen NH(3)-N concentration (113.7 vs. 90.1 mg/L) were higher in 4D than in 1D, and total volatile fatty acid (VFA) concentrations did not differ. Molar proportions of VFA, except butyrate, differed between treatments, causing the nonglucogenic to glucogenic VFA ratio to be greater in 4D than in 1D. Within days in the 4D treatment, the molar proportion of acetate increased and those of all other VFA decreased linearly. Rumen NH(3)-N concentration within the 4D treatment declined quadratically from 170.3 mg/L on d 1 to 80.7 mg/L on d 4. In contrast to rumen NH(3)-N concentration, milk urea content did not differ between treatments, but decreased quadratically from d 1 to 4 in the 4D treatment (from 26.7 to 20.7 mg/dL). Mean fat- and protein-corrected milk was greater in 1D than in 4D (23.5 vs. 22.8 kg/d), mainly due to a difference in milk yield (24.5 vs. 23.7 kg/d). Fat and protein content were slightly lower in the 1D than in the 4D treatment (3.66 vs. 3.76% and 3.28 vs. 3.34%, respectively). This study confirmed that increasing pasture allocation frequency from once every 4 d to every day improved milk production in grazing dairy cows, especially when offered pasture was high.