INFLUENCE OF SUGARY-BRAWN2 OR DENT CORN AT 2 FORAGE LEVELS ON INTAKE,DIGESTION, AND MILK-PRODUCTION BY DAIRY-COWS

Sugary-Brawn2 (su-Bn2) corn endosperm contains higher concentrations o f water-soluble polysaccharides than dent corn. Eight multiparous Hols tein cows averaging 48 d in milk and 667 kg BW at trial initiation wer e in a replicated 4 x 4 Latin square design with 28-d periods. Only co ws in one square were ruminally cannulated., Treatments were su-Bn2 or dent corn and 45 or 60% of ration DM as alfalfa silage arranged as a 2 x 2 factorial within each square. Diets, formulated to contain 19% C P, were fed as total mixed rations twice daily. Intake of DM and milk yield averaged 26.8 and 39.9 kg/d, respectively, and were not affected by treatment (P > .10). Sugary-Brawn2 corn decreased mill-fat percent age (3.21 vs 3.45%), particularly for the low-forage diet (3.15 vs 3.4 0%). Milk protein percentage was higher (3.15 vs 3.10%) for low-forage diets but was not affected (P > .10) by corn type. Ruminal pH was low er for low-forage diets. Feeding su-Bn2 corn decreased ruminal pH only at 4 h after feeding. Total VFA in ruminal. fluid (millimolar) 6 h af ter feeding were higher, whereas acetate molar percentage and acetate: propionate ratio were lower for su-Bn2 corn. Ruminal in situ evaluatio n of su-Bn2 and dent corn revealed a larger soluble fraction, a faster rate of degradation, and higher availabilities of both DM and starch for su-Bn2 corn. Ruminal in situ rate of degradation and availability of alfalfa hay DM were reduced by su-Bn2 corn. Total tract apparent di gestibilities of DM, CP, and starch were greater for su-Bn2 diets. Dig estion of a high-alfalfa silage diet was not improved by feeding corn with greater ruminal. availability. Because su-Bn2 corn adversely affe cted ruminal forage digestion and milkfat percentage and provided no i ncrease in milk yield, it is not recommended as the sole grain source for lactating dairy cows.