Date of Award

Fall 2023

Project Type

Thesis

Program or Major

Animal Sciences

Degree Name

Master of Science

First Advisor

André F AFB Brito

Second Advisor

Peter S. PSE Erickson

Third Advisor

Md Elias MEU Uddin

Abstract

This study investigated the effect of an extruded flaxseed-based feed supplement ‘LinPRO-R (LNPR)’ on milk production and composition, milk FA profile, nutrient digestibility, ruminal metabolism, purine derivatives (PD) excretion, and enteric methane (CH4) emissions in grazing dairy cows during the summer season. Eighteen multiparous and 2 primiparous mid-lactating organic Jersey cows (128 ± 52 DIM) were used in a randomized complete block design. cows grazed mixed grass-legume pasture (Dactylis glomerata L., Trifolium repens L., Trifolium pratense L., Lolium perenne L., Phleum pratense L.) overnight (herbage allowance = 15 kg of DM/cow/day) following a strip grazing method and fed partial total-mixed ration (pTMR) in the barn during the day. The pTMR was formulated to contain (DM basis) 37.5% mixed, mostly legume baleage and 62.5% of a soybean meal/ground corn-based concentrate mash. Cows within pairs were randomly assigned to 1 of 2 diets: (1) pasture plus pTMR (control diet= CTRL) or (2) pasture, pTMR, and 6% LinPRO-R (LinPRO-R diet = LIN). Ground corn and soybean (extruded and roasted) were replaced with LinPro-R in the LIN diet. Diets were formulated to be isonitrogenous and to yield a 60:40 forage to concentrate ratio. Pasture averaged 17.5% CP and 53% NDF, and pTMR 9.7% CP and 15% NDF. The experiment lasted 12 wk with 2 wk for a covariate period followed by 3 sampling periods during wk 4, 7, and 10. Individual herbage intake was estimated using Cr2O3 and the in vitro dry matter digestibility (IVDMD) of the feeds. Two GreenFeed units were used to measure gaseous emissions throughout the study. Cows on LIN diet were observed to have a lower herbage intake (5.95 vs. 7.39 kg/d; P < 0.01) compared with CTRL, whereas the pTMR dry matter intake (DMI) was similar (mean = 14.7 kg/d) between the diets. Intake of OM (21.2 vs 20.3 kg/d), CP (3.82 vs 3.52 kg/d), NDF (7.55 vs 6.83 kg/d), and ADF (5.21 vs 4.80 kg/d) were greater (P ≤0.05) in CTRL compared to LIN. Contrarily, apparent total tract digestibility of DM (70.5 vs 69.5%), OM (71.5 vs 70.4%), and CP (65.7 vs 64.8%) were greater in LIN compared to CTRL whereas ADF and NDF digestibility did not differ. Treatments had no effect on milk yield (mean = 27 kg/d), and milk components. However, milk urea nitrogen (MUN) concentration was lower (P < 0.001) in LIN (8.38 mg/dL) than CTRL (11.0 mg/dL). No treatment effects were observed for total VFA concentration (mean = 89.8 mM), and the molar proportions of acetate, propionate, butyrate, and the acetate-to-propionate ratio (mean = 4.6). Similarly, production of CO2 (mean = 10.9 kg/d), enteric CH4 (mean = 351 g/d), CH4 yield (mean = 15.5 g/kg of DMI) and CH4 intensity (mean = 11.3 g/kg of ECM) did not differ with feeding CTRL vs. LIN. Most of the milk saturated fatty acids (SFA), Σ odd-chain, Σ branched -chain SFA, Σ<16C, Σ16C, and Σn-6 FA increased (P<0.01) in CTRL compared to LIN. In contrast, majority of the Σ18C FA, unsaturated fatty acids (UFA), trans-11 18:1, cis-9, cis-12, cis-15 18:3, cis-9, trans-11 18:2, and Σn-3 FA increased (P<0.01) in cows fed LIN diet than those fed CTRL. The Σn-6/n-3 ratio decreased with feeding LIN versus CTRL. In summary, LinPRO-R fed at 6% diet DM did not affect production performance and enteric CH4 emissions in grazing dairy cows but increased Σn-3 FA in milk. Thus, the profitability of LIN inclusion in the pasture based-dairy system will be contingent upon the cost involved and the industry acceptance of premium n-3 enriched milk.Key words: Extruded flaxseed, pasture, milk yield, α-linolenic acid, greenhouse gas

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