1429 Effects of feeding alfalfa stemlage or wheat straw for dietary energy dilution on growth performance and sorting behaviors of Holstein dairy heifers.

Feeding high-quality forage diets may lead to excessive weight gains and overconditioning for pregnant Holstein heifers. Restriction of energy density and DMI by heifers by using low-energy forages, such as straw, is a good approach for controlling this problem. Alfalfa stems containing high fiber and moderate protein content have the potential to be used to replace straw to reduce dietary energy. The objective of this study was to compare the growth performance and sorting behavior of dairy heifers offered an alfalfa silage/corn silage diet (CON; 13.1% CP, 67.4% TDN, and 39.7% NDF) with two energy-diluted diets replacing the corn silage and alfalfa silage with either alfalfa stemlage (STM; 12.6% CP, 60.1% TDN, and 46.4% NDF) or wheat straw (STW; 12.6% CP, 62.7% TDN, and 43.7% NDF) to get a similar diet composition. Seventy-two pregnant Holstein heifers (16.8 ± 1.3 mo) were stratified (24 heifers/block) by initial BW (light, 440 ± 18.0 kg; medium, 486 ± 18.6 kg; and heavy, 534 ± 25.1 kg) and then assigned to 1 of 9 identical pens (3 pens/block and 8 heifers/pen), where each of the 3 diets was randomly assigned to 1 pen within each block. Diets were offered in a 56-d feeding trial. Statistical analyses were performed using a MIXED procedure in SAS 9.3 with pen as the experimental unit. Daily DMI was greater for CON than for diluted diets (11.3 vs. 10.3 kg/d; P = 0.01), with no differences observed between STM and STW (P = 0.61). Average daily gains were greater for heifers offered the CON compared with heifers offered diluted diets (1.32 vs. 1.00 kg/d; P = 0.02). The feed:gain ratio tended to be less for heifers offered the CON relative to heifers offered diluted diets (8.6 vs. 10.7; P = 0.08). There were no differences detected across all growth measures within the diluted diets (P > 0.05). Physically effective fiber (pef) particle content was relatively static across sampling times for CON (overall sorting factor mean = 1.02), which indicates minimal sorting. Sorting against pef particles was observed for diluted diets and much more severely for the STM diet (overall sorting factor mean = 1.14 vs. 1.06; P < 0.05). These results indicate that diets diluted with low-energy forages (both STM and STW) were effective in reducing intakes of DM and energy and maintaining appropriate weight gains and body condition for pregnant Holstein heifers.