Influence of sugary-Brawn2 or dent corn at two forage levels on intake, digestion, and milk production by dairy cows.

Sugary-Brawn2 (su-Bn2) corn endosperm contains higher concentrations of watersoluble polysaccharides than dent corn. Eight multiparous Holstein cows averaging 48 d in milk and 667 kg BW at trial initiation were in a replicated 4 x 4 Latin square design with 28-d periods. Only cows 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% CP, 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 milkfat percentage (3.27 vs 3.45%), particularly for the low-forage diet (3.15 vs 3.40%). 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 lower 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 after feeding were higher, whereas acetate molar percentage and acetate:propionate ratio were lower for su-Bn2 corn. Ruminal in situ evaluation 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 digestibilities of DM, CP, and starch were greater for su-Bn2 diets.(ABSTRACT TRUNCATED AT 250 WORDS)