Evaluation of ad libitum acidified milk replacer programs for dairy calves

Due to renewed interest in feeding acidified milk replacer (MR) for ad libitum consumption within North America, two 112-d trials were conducted using Holstein calves obtained from one dairy farm at 2 to 3 d of age. In trial 1, a 27% crude protein (whey protein), 17% fat MR powder was reconstituted with water to 14% solids and fed at 0.66 kg of dry matter (DM) per day for 42 d (CON) or acidified to pH 4.2 using citric acid and offered 24 h/d for d 0 to 35, then switched to 0.66 kg of DM without acid per d for 7 d (A4). In trial 2, the same MR was fed as CON, ad libitum pH 5.2 MR offered from 0600 to 0800 h and 1600 to 1800 h for d 0 to 21 (R5), ad libitum pH 5.2 MR offered 24 h/d for d 0 to 35 (A5), and ad libitum pH 4.2 MR offered 24 h/d for d 0 to 35 (A4). After the ad libitum period, calves on R5, A5, and A4 were switched to CON until d 42. Growth measures were made until d 112 in each trial. Data from each trial were analyzed as a completely randomized design with repeated measurements over time using an autoregressive type 1 covariance structure when appropriate. In each trial, calves fed CON had lower average daily gain (ADG) from 0 to 42 d and greater ADG from 42 to 56 d than calves fed the other treatments. In both trials, ADG from 0 to 56 d and 56 to 112 d were not greater for A4 or AS versus CON. From 56 to 112 d in trial 2, ADG was greater for R5 versus A5. Some calves completely rejected the MR at pH 4.2. Calves consumed more of the MR at pH 5.2 than 4.2. Calves fed A4 in trial 1 and treatments AS and A4 in trial 2 consumed >95% of their MR between 0600 to 0800 h and 1600 to 1800 h. Time spent standing did not differ by treatment in trial 1 and increased from 312 to 332 min/d from d 6 to 56. Under the conditions of these trials, results to 112 d showed no advantage to feeding calves MR acidified to pH 4.2 or 5.2 ad libitum from 0 to 35 d with gradually weaning by 42 d compared with calves fed the control MR fed at 0.66 kg of DM/d. Additionally, when calves were fed MR ad libitum, they consumed >95% of the MR between 0600 to 0800 h and 1600 to 1800 h and standing behavior was not greatly affected.