Feeding behavior of Holstein and Jersey cows fed diets based on either alfalfa silage or corn silage at 2 forage fiber levels

Our objective was to assess the effects of 2 levels of forage NDF (FNDF), mainly from either alfalfa silage (AS) or corn silage (CS), on the feeding behavior of Holstein and Jersey cows. Twenty-four lactating primiparous cows (12 Holsteins and 12 Jerseys) were used in a triplicated split-plot 4 × 4 Latin square study in which breed formed the main plots and diets were arranged in a 2 × 2 factorial in the subplots. Dietary treatments were 2 FNDF levels (19% FNDF [low FNDF; LF] or 24% FNDF [high FNDF; HF]) and 2 FNDF sources (70:30 or 30:70 ratio of AS:CS). During each 28-d period, samples of TMR and individual cow refusals were collected to determine particle size distribution using particle separator with 3 sieves and a bottom pan. Eating time (ET, min/d) was recorded through visual observation, and rumination time (RT, min/d) was measured using a neck-collar recording system. Saliva samples were collected to determine concentration of urea-N and explore possible effects on N recycling. Compared with Holsteins, Jerseys had lower FNDF intake (kg/d; -25%) but greater FNDF intake as a percentage of BW (+12%). The particle size distribution of the DM consumed closely reflected the particle size distribution of the diet and did not differ between breeds. However, cows of both breeds sorted for long particles and against short particles, and compared with Holstein, Jersey cows exhibited more pronounced feed-sorting behaviors. Overall ET, RT, and chewing time (ET + RT) averaged (mean ± SD) 247 ± 60, 495 ± 110, and 739 ± 133 min/d. Eating time did not differ between breeds, but Jerseys had greater RT than Holsteins (519 ± 99 vs. 465 ± 113 min/d) and greater ET and RT expressed per kilogram of BW, DMI, and FNDF intake. Source, level, and interaction between source and level of FNDF influenced the percentage of DM consumed as long, medium, and short particles, but only FNDF level influenced the percentage of DM consumed as fine particles. Cows fed the HF diet based on AS had lower DMI (kg/d; -12%) but greater RT per kilogram of DMI (+22.9%) compared with cows fed other diets. The interaction between level and source of FNDF in the diet influenced ET and RT but not chewing time. In addition, ET was greater (+6.7%) when cows were fed AS-based diets than CS-based diets (255 ± 62 vs. 239 ± 58 min/d), and RT was greater (+8.1%) for HF-fed than LF-fed cows (512 ± 117 vs. 473 ± 98 min/d). Neither breed nor dietary treatment influenced saliva urea-N (11.6 ± 2.01 mg/dL). In brief, we found interactions between source and level of FNDF in the diet, most notably a reduction in DMI and cow performance when the FNDF level was increased with AS, but not with CS. Except for the sorting of fine particles, under the conditions of this study, both breeds responded in the same way to changes in the dietary particle size distribution associated with an increased level of FNDF regardless of forage source.