PREDICTING AD-LIBITUM DRY-MATTER INTAKE AND YIELD OF HOLSTEIN COWS

Two data files, one from New Hampshire (n = 3308) and one from Georgia (n = 678), containing 4-wk or weekly means, respectively, of ad libit um dry matter intakes (DMI) and related variables were used to predict DMI and yields of 4% fat-corrected milk and milk protein in lactating Holstein cows. The DMI. ranged from 5.9 to 30.4 kg/d, and milk yield ranged from 5.8 to 64.3 kg/d. Because of the lack of data from <14 d i n milk, prediction was not possible for the first 2 wk of lactation. F actors considered for inclusion in the DMI prediction model were parit y number (1 or greater than or equal to 2), treatment with bovine soma totropin (bST), day of year, days in milk, minimum (nighttime) tempera ture-humidity index, body weight, 4% fat-corrected milk yield, milk pr otein yield, and corn silage and total silage percentages in forage dr y matter. In separate models, the silage predictors were replaced with more specific descriptors of ration dry matter, including percentages of crude protein, fat (ether extract plus soaps of fatty acids), conc entrate, acid detergent fiber or neutral detergent fiber, and forage a cid detergent fiber or neutral detergent fiber. The square and sometim es natural logarithm of predictors were included in models, which then were subjected to a stepwise backward elimination option of a multipl e regression procedure. Several useful equations were developed to pre dict ad libitum DMI; the best models accounted for about 80% of the va riability in DMI, and standard deviations were <9% of mean DMI. Depres sion in DMI related to heat stress was higher in pluriparous cows than in primiparous cows (22% vs. 6%). The negative coefficient for effect s of bST treatment on DMI suggested that milk yield increased proporti onally more in response to bST than did DMI. About 74 to 77% of DMI pr edictions were within 2 kg/d of observed DMI.