Effects of straw processing and pen overstocking on the growth performance and sorting characteristics of diets offered to replacement Holstein dairy heifers

Authors: COBLENTZ, WAYNE; AKINS, MATTHEW - UNIVERSITY OF WISCONSIN; ESSER, NANCY - UNIVERSITY OF WISCONSIN; Ogden, Robin; GELSINGER, SONIA - UNIVERSITY OF WISCONSIN

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2017
Publication Date: 1/16/2018
Citation: Coblentz, W.K., Akins, M.S., Esser, N.M., Ogden, R.K., Gelsinger, S.L. 2018. Effects of straw processing and pen overstocking on the growth performance and sorting characteristics of diets offered to replacement Holstein dairy heifers. Journal of Dairy Science. 101:1074-1087.

Interpretive Summary: Dairy heifers are often fed straw to reduce the energy content of their diets and prevent over conditioning; but if the straw is not processed effectively, the heifers often sort out and refuse to eat it. In addition, sometimes heifers are overstocked in free-stall housing systems. The objectives of this study were to evaluate the effects of pen-stocking density and straw processing on the growth performance, feed-bunk sorting behaviors, daily behavioral traits, and hygiene of Holstein dairy heifers housed in a free-stall system. Diets were comprised of alfalfa haylage, corn silage, and either well-processed or poorly processed straw. In addition, heifers were stocked in pens at 100, 125, or 150% of capacity. Heifers sorted both diets, but exhibited more aggressive sorting behaviors when straw was poorly processed. In this study, heifers preferentially selected medium, small, and fine particles, but discriminated against large particles. Similarly, heifers favored specific nutrients, such as crude protein and energy, but actively discriminated against structural forage fiber components, such as lignin. However, during the 91-day feeding trial, it was not possible to relate feed-bunk sorting behaviors to heifer growth performance. Overall, the within-pen variability with respect to daily weight gains was increased with pen overstocking, although responses were not consistent across diets. Heifers within overstocked pens spent more time inactively standing and less time lying down than pens stocked at 100% of capacity. Hygiene scores remained acceptable for all heifers, indicating our free stalls provided good comfort; however, within-pen variability for hygiene increased sharply with stocking rate, suggesting that some heifers in overstocked pens were willing to accept a less-desirable lounging position out of fatigue, frustration, or lack of discernment. This information will help dairy producers and nutritionists improve heifer growth performance and well-being.

Technical Abstract: The effects of pen-stocking density and straw processing on the growth performance of Holstein dairy heifers housed in a free-stall system are not well understood. Our objectives were to evaluate these factors on the growth performance, feed-bunk sorting behaviors, daily behavioral traits, and hygiene of Holstein dairy heifers. Two corn silage-alfalfa haylage diets diluted with wheat straw were offered; diet composition was identical, except that one diet contained well-processed straw (SS; 46.0% NDF, 12.9% CP, 60.7% TDN), and the other poorly processed straw (LS; 46.5% NDF, 12.6% CP, 60.0% TDN). A 2 × 3 factorial arrangement of straw-processing (SS or LS) and pen-stocking-density [100, 125, or 150% of capacity] treatments was evaluated with 240 Holstein dairy heifers (410 ± 56.3 kg) that were blocked by weight, and then assigned to 24 pens with 4 pens/interactive treatment. For 91 d, diets were dispersed at 1100 h daily, and bunks were serial sampled during 3 evaluation periods throughout the trial. Diets were offered for ad-libitum intake, but with minimal orts (< 3%); as such, sorting factors were calculated as bunk value/initial value. For the LS diet, sorting factors for large particles increased linearly from 1.26 to 2.82 across sampling times, differing from the SS diet at 2200, 0100, 0600, and 0900 h (orts). Sorting factors for the SS diet also increased linearly across sampling times, but sorting was less severe (1.27 to 1.97). Overall, sorting factors for physically effective fiber (pef ) exhibited responses similar to those observed for large particles, except they were limited to narrower ranges for both SS (1.04 to 1.14) and LS (1.03 to 1.26) diets. Despite these differences in sorting behaviors, daily DMI was not affected by treatment (¯X = 9.65 kg DM/d), nor was daily intake of TDN (5.92 kg TDN/d). For SS, heifers housed within overstocked pens exhibited reduced ADG compared to the 100% stocking rate (0.93 vs. 0.99 kg/d). With LS processing, ADG differed between the 125 and 150% stocking rates (0.96 vs. 0.88 kg/d), as did the within-pen CV for ADG (10.7 vs. 18.6%). Hygiene scores (1 = clean, 4 = caked-on manure) for legs (2.1 to 2.3) and flanks (1.6 to 1.9) indicated heifers stayed acceptably clean, but the within-pen CV for legs (14.4 vs. 9.0%) and flanks (34.2 vs. 23.8%) was greater for overstocked pens compared to the 100% stocking density, thereby suggesting hygiene scores were more variable without a free stall for each heifer.