INFLUENCE OF FEEDING A RAPIDLY RUMEN DEGRADED DIETARY-PROTEIN AT NIGHT OR WITH A BASAL MIXED RATION ON PERFORMANCE OF DAIRY-COWS

Twelve multiparous and ten primiparous cows in late lactation were use d in a 16-wk study to determine the influence of feeding times of a pr otein supplement (PS) on dry matter (DM) intake, ruminal fermentation, milk yield and milk composition. One mixed ration consisting of 50% w hole crop oat silage, 10% alfalfa silage and 40% grain concentrate was offered twice daily with two-thirds at 08:00 h and the remainder at 1 8:00 h. In addition, a PS was offered in one meal per day at either 08 :30 h or 00:30 h at an amount equal to 12% of the mixed ration DM inta ke. Half of the cows were assigned to each of the two dietary treatmen ts which were designated as DAY (08:30 h) or NIGHT (00:30 h). Eight co ws in the production study, previously fitted with large-diameter rume n cannula, were used to study treatment effects on rumen fermentation and ruminal in situ nutrient disappearance. Rate of passage of PS was measured using chromium-mordanted PS. Time of feeding PS had no effect on DM intake or body weight. Milk yield and milk composition were not influenced by treatment. Treatment had no effect on in situ DM and cr ude protein disappearance or ruminal rate of passage of PS. Concentrat ions of all VFA were not influenced by treatments. All measured volati le fatty acid concentrations were higher during the period of 01:00 - 06:00 h for cows fed the PS at night. Results indicate that timing of feeding a PS can alter ruminal fermentation characteristic without inf luencing animal performance.