|PIZARRO, DANTE - University Of Wisconsin|
|PICASSO, VALENTIN - University Of Wisconsin|
|WATTIAUX, MICHEL - University Of Wisconsin|
Submitted to: American Dairy Science Association Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 3/20/2023
Publication Date: 6/28/2023
Citation: Pizarro, D., Akins, M.S., Picasso, V., Wattiaux, M. 2023. Effect of kernza straw in forage-based diets on nitrogen balance and blood urea nitrogen in dairy heifers. American Dairy Science Association Abstracts. June 25-28, 2023.
Technical Abstract: Intermediate wheatgrass is a novel perennial grass used as a dual-purpose crop (i.e., grain for human and forage as a low cost feed for ruminants). Straw can be used to reduce energy density in the diet of heifers and their dry matter intake (DMI) to avoid over-conditioning. Our goal was to determine the effects of increasing dietary levels of intermediate wheatgrass straw on N excretion, N balance, and blood urea-N. The study was performed as a completely randomized design using 24 Holstein heifers. Eight heifers were fed 1 of 3 diets including (DM basis) either 0, 20 or 40% intermediate wheatgrass straw, a 40:60 mixture of corn silage and alfalfa haylage, and urea (0, 0.7, and 1.4%, respectively) for 12 weeks. On week 9, DMI was measured daily, bodyweight (BW, 577 ± 20 kg) was measured on 2 consecutive days, and fecal and spot urine samples were collected on 4 consecutive days (d 1 800h; d 2 1100h; d 3 1700h, and d 4 1400 h). Urine output was estimated using a creatinine excretion coefficient of 26.8 mg/kg BW. Fecal output was estimated using indigested NDF. Heifer was the experimental unit, and the model included the fixed effect of diet and the error term. On week 9, the 0, 20 and 40% straw diet contained 37.7, 42.0 and 50.6% NDF, and 15.6, 14.7 and 14.1% CP (DM basis). For heifers fed diets with 0, 20 and 40% straw, DMI was 12.5, 11.2, 11.3 kg/d (P = 0.03), N intake was 356, 312 and 301 g/d (P < 0.01), Fecal N excretion was 77.8, 59.5 and 64.9 g/d (P < 0.01), urine output was 30.1, 33.1 and 27.5 L/d (P = 0.35), urinary N excretion was 226, 215 and 211 g/d (P = 0.68), N balance was 52.7, 37.4 and 24.3 g/d (P = 0.10), urinary urea-N excretion was 157, 153 and 140 g/d (P = 0.10), and blood urea-N was 15.0, 16.3 and 16.7 mg/dL (P = 0.06), respectively. Inclusion of intermediate wheatgrass straw reduced DMI, N intake and fecal N excretion. There was no treatment effect on urine volume and urine N excretion, but tendencies for a reduction in N balance, a decrease in urinary urea-N excretion and an increase in blood urea-N. In this study, the high levels of urinary N excretion, urinary urea-N excretion, and blood urea-N might be associated with excess of rumen-degradable N.