Performance, feed-sorting behavior, methane and carbon dioxide emissions, nitrogen balance, and nutrient digestibility of dairy heifers fed Kernza intermediate wheatgrass straw

Authors: PIZARRO, DANTE - University Of Wisconsin; Akins, Matthew; PICASSO, VALENTIN - University Of Wisconsin; WATTIAUX, MICHEL - University Of Wisconsin

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2025
Publication Date: 11/20/2025
Citation: Pizarro, D., Akins, M.S., Picasso, V., Wattiaux, M. 2025. Performance, feed-sorting behavior, methane and carbon dioxide emissions, nitrogen balance, and nutrient digestibility of dairy heifers fed Kernza intermediate wheatgrass straw. Journal of Dairy Science. Volume 109, Issue 1: page 346-359. https://doi.org/10.3168/jds.2025-27050.
DOI: https://doi.org/10.3168/jds.2025-27050

Interpretive Summary: The purpose of this study was to understand the growth and development, feed-sorting behavior, methane and carbon dioxide emissions, nutrient digestibility, and nitrogen balance of pregnant dairy heifers fed diet with 0, 20, or 40% Kernza intermediate wheatgrass straw. Compared to a corn-alfalfa control, introducing Kernza straw in the diet reduced feed intake, nitrogen intake, urinary nitrogen excretion, and altered the feed sorting behavior of heifers, but did not alter body condition score and methane production. Decline in average daily gain and fiber digestibility depended on the level of incorporation. Kernza straw can be used as a feed ingredient to modulate performance and manure nitrogen excretion of dairy heifers.

Technical Abstract: Kernza straw (KS) is a high-fiber, low-energy byproduct of intermediate wheatgrass (Thinopyrum intermedium [Host] Barkworth & D.R. Dewey) that may serve as an alternative forage to increase dietary fill and reduce the risk of over-conditioning in late-pregnant heifers. We hypothesized that inclusion of KS in the diet of late-pregnant heifers would reduce feed intake and BW gain, nutrient digestibility, and urinary N excretion, but increase enteric methane production depending on the level of inclusion. Thus, a complete randomized design study lasting 12 wk was conducted with 24 heifers (507 ± 2.87 kg BW) fed a TMR that included either 0% (0KS), 20% (20KS), or 40% (40KS) KS, with a 40:60 mixture of corn silage and alfalfa haylage (DM basis), and urea to equalize dietary CP. Heifers were evaluated for DMI, ADG, BCS, stature related body measurements, feed-sorting behavior, nutrient digestibility, methane and carbon dioxide emissions, and N balance. In this study, KS averaged 71.1% NDF, 4.8% CP, and 50.6% TDN (DM basis), TMR NDF was 41.0%, 47.1%, and 53.3%, and TMR CP was 13.3%, 12.8%, and 12.2% for the 0KS, 20KS, and 40KS diets, respectively. The DMI was 12.7 ± 0.13 kg/d for the 0KS diet but decreased to 11.7 ± 0.10 and 11.7 ± 0.14 kg/d when heifers were fed the 20KS and 40KS diets, respectively. In contrast, NDF intake was 5.0 ± 0.05 kg/d for the 0KS diet but increased to 5.4 ± 0.05 and 6.2 ± 0.08 kg/d when heifers were fed the 20KS and 40KS diets, respectively. The ADG was 1.35 ± 0.05 kg/d for the 0KS diet but decreased to 1.10 ± 0.05 and 0.86 ± 0.06 kg/d when heifers were fed the 20KS and 40KS diets, respectively. Change in BCS was lower when heifers were fed the 40KS diet compared with the other 2 diets, but dietary treatments did not alter stature-related body measurements. Heifers fed the KS diets sorted consistently against long particles but increasingly in favor of fine particles over time. Methane production and yield averaged 270 ± 5.70 g/d and 23.6 ± 0.50 g/kg DMI, but methane intensity increased when heifers were fed the 40KS diet compared with the 0KS diet (165 ± 7.89 vs. 207 ± 15.9 g/kg ADG.) The NDF digestibility declined when heifers were fed the 40KS compared with the 0KS diet (65.8% ± 0.36% vs. 61.8% ± 0.32%). Nitrogen intake was 356 ± 9.34 g/d for the 0KS diet but decreased to 312 ± 7.25 and 301 ± 11.1 g/d when heifers were fed 20KS and 40KS diets, respectively. Fecal N excretion was reduced when heifers were fed the 20KS compared with the 0KS diet (104 ± 4.86 vs. 79.7 ± 2.98 g/d), but urinary N excretion was reduced when heifers were fed the 40KS compared with the 0KS diet (212 ± 10.5 vs. 182 ± 6.71 g/d). This study demonstrated that KS can be used as a feed ingredient to modulate performance (DMI, ADG, BCS) and manure N excretion of dairy heifers.