Conceptually, there are 2 feeding strategies for avoiding over-conditioning, which can be problematic for gravid dairy heifers that have reduced dietary energy density requirements relative to younger animals: (1) diluting the ad libitum-fed diet with low-energy forages; or (2) offering a diet of greater nutrient density but intentionally restricting the DM available for consumption (limit-feeding). Our objectives for this study were to evaluate the effects of feedbunk restriction and feed push-up frequency on the growth performance of gravid Holstein dairy heifers. A total of 128 Holstein heifers (434 ± 46.7 kg) were enrolled in the trial. Heifers were blocked by weight, and assigned to 1 of 16 identical research pens (4 pens/weight block; 8 heifers/pen), where the mean initial body weight (BW; ± SD) for the 4 blocks were 491 ± 19.0, 450 ± 16.5, 419 ± 10.6, 374 ± 23.0 kg. Within each block, a 2 × 2 factorial arrangement of treatments was assigned; treatments consisted of feedbunk access [full (FUL) or restricted (RES] and feed push-up frequency [1.5- or 3.0-h intervals]. The RES treatment was applied by covering 2 of the 8 head-locking feed gates in assigned pens with plywood partitions, thereby creating a feedbunk-stocking rate of 133%. A total mixed ration diet composed of alfalfa haylage (60.5%), corn silage (38.0%), and mineral (1.5%) was offered once daily for 91 d; daily feed allotments (overall mean = 9.11 kg dry matter (DM)/d) were generally consumed entirely within 9 h of feeding. Nutrient intakes were not affected by push-up frequency or the interaction of main effects, but all intakes were affected by feedbunk access, except for DM and neutral detergent fiber expressed as a percentage of BW (overall means = 1.93 and 0.80%, respectively). In each case, intakes for FUL were greater than those observed for RES; for DM intake, this amounted to a difference of 0.20 kg/d between those main-effect treatments. After 91 d, heifers without feedbunk restriction exhibited greater final BW, but total gain and average daily gain differed only numerically between FUL and RES. Under the conditions of this trial, heifers were blocked by weight, such that BW were relatively uniform within each pen, and head-locking feed gates were used, which also provided some protection from adjacent aggressive heifers. These results suggest heifers can exhibit acceptable growth performance on high-forage diets in a limit-feeding program that includes moderate feedbunk restriction provided other forms of stress are minimized.
Keywords: feedbunk access gravid heifers limit-feeding push-up frequency