ABSTRACT
Summary The long-term feeding of corn silage as the sole forage to lactating dairy cows has had only limited success due to problems with production, reproduction, and health after one lactation. Consequently, a long-term study was begun in August 1975 with two groups of 19 cows, 15 2-year-old heifers, and 4 3-year-old cows assigned at random to each group as they calved. One group was fed a diet with corn silage as the sole forage and the other group a diet with a 50:50 ratio of forage as corn silage (CS) and low-moisture alfalfa-orchardgrass (AO) silage. Both rations contained a 60:40 ratio of forage to concentrate on a dry basis, 15% crude protein, 1.25% calcium, 0.50% phosphorus, 0.52% trace mineralized salt, 0.22% sulfur, 0.25% magnesium, and 4,400 units vitamin A, 2,200 units vitamin D, and 44 mg vitamin E/kg. The diets were blended in a mixer wagon with electronic load cells and fed once daily as a complete mix in feed bunks. All cows remained on their respective diets the entire experiment, including the dry period when they were fed controlled amounts of the lactating-cow diet. When the experiment was terminated in May 1980, there were 5 cows in the CS group and 3 in the other group. No cows were removed the first lactation. In succeeding lactations, cows were removed from the two groups, respectively, for the following: hardware, 2 and 0; aborted, 0 and 1; pneumonia, 1 and 0; udder problems, 3 and 3, leg problems, 3 and 2; low production, 2 and 3; failure to breed, 1 and 5; other, 2 and 2. There was little difficulty with digestive upsets and no problem with the fat cow syndrome. Milk production, fat tests, and fat production for 305-day lactations for the CS and the CS and AO group, respectively, were as follows: lactation: I, 6,686 kg, 3.62%, 238.5 kg (CS) and 6,535 kg, 3.67%, 237.7 kg (CS and AO); II, 7,462 kg, 3.64%, 271.9 kg (CS) and 6,800 kg, 3.63%, and 246.8 kg (CS and AO); III, 8,008 kg, 3.60%, and 288.3 kg (CS) and 6,989 kg, 3.68%, and 257.4 kg (CS and AO); IV, 8,338 kg, 3.51%, and 293.1 kg (CS) and 7,594 kg, 3.69%, and 280.4 kg (CS and AO). The differences were not significant (P > 0.05), although cows on the CS diet tended to produce more milk and fat. Higher than normal levels of limestone were used in these diets to reduce loss of starch in feces and to improve gastrointestinal and fecal pH. Cows in the CS and the CS and AO groups had average fecal pH of 6.58 and 6.61, respectively. Calving weights of cows were slightly higher for the CS group. Calf weights were similar for the two groups. These data indicate that corn silage can be used successfully as the sole forage in complete diets of lactating cows when diets are properly balanced.
