Date of Award

Fall 2023

Project Type

Thesis

Program or Major

Animal Sciences

Degree Name

Master of Science

First Advisor

Andre F Brito

Second Advisor

Peter S Erickson

Third Advisor

Amer AbuGhazaleh

Abstract

Molasses is a food byproduct rich in sucrose commonly added to the diets of cattle which has been reported to enhance milk production, promote rumen microbial growth, and increase digestibility of nutrients. Variable results obtained when partially replacing starch sources with molasses have led to an increased interest in the dietary conditions under which molasses could optimize the production of dairy cows. We aimed to investigate the effect of partially replacing ground corn with sugarcane liquid molasses on dry matter intake, milk yield and composition, enteric methane emissions, and N utilization in lactating Jersey cows fed red clover baleage. Eighteen multiparous and 2 primiparous Jersey cows averaging (mean ± standard deviation) 90 ± 34.7 days in milk, 27.8 ± 5.72 kg of milk, and 493 ± 61 kg of body weight at the beginning of the study were blocked in pairs based on milk yield, days in milk or parity and, within pair, randomly assigned to treatments in a randomized complete block design. The diets contained (dry matter basis) 60% red clover baleage, 5.8% soybean meal, 2.5% roasted soybean meal, 1.5% ruminally stable fat, 2.5% minerals and vitamins premix, and: 1) 27.7% ground corn (COR) or 2) 22.7% ground corn and 5% liquid molasses (MOL). Diets averaged 16.5% crude protein and 33% neutral detergent fiber. The study lasted 9 weeks with a 14-d covariate period directly preceding d 1 of the study. Data and sample collection were taken during the covariate period and weeks 6 and 9 of the study. Measurements of gaseous emissions were obtained using the GreenFeed system. Data were analyzed using the MIXED procedure of SAS with repeated measures over time. No treatment effects were observed for dry matter intake and milk yield, which averaged 20.1 and 30.5 kg/d, respectively. Feeding COR versus MOL also had no effect on concentration (mean = 5.0%) and yield (mean = 1.47 kg/d) of milk fat, as well as milk urea N concentration (mean = 8.65 mg/dL). In contrast, milk true protein concentration (3.34 vs. 3.27%; P < 0.01) and yield (1.01 vs. 0.93 kg/d; P = 0.01) decreased in cows fed MOL compared with COR. No treatment effects were observed for total urinary N excretion (mean = 252 g/d). However, decreases in excretion of urinary urea N excretion ( 94.5 vs. 116 g/d; P < 0.04), and urinary urea N excretion as a percentage of total urinary N (52.6 vs. 59.2% of total urinary N; P = 0.03) were observed in cows fed MOL when compared with COR. Feed efficiency calculated as 4% fat-corrected milk/dry matter intake (1.83 vs. 1.72 kg/kg; P < 0.01) and energy-corrected milk/dry matter intake (1.93 vs. 1.81 kg/kg; P < 0.01) were lower with feeding MOL than COR. Similarly, apparent total-tract digestibility of crude protein (59.7 vs. 56.6 %; P = 0.03) was lower in cows fed MOL than COR whereas that of dry matter (P = 0.08) and organic matter (P = 0.06) tended to decrease in MOL versus COR. Diets did not affect enteric CH4 production (mean = 398 g/d; P = 0.33) and CH4 intensity (mean = 10.0 g/kg of energy corrected milk; P = 0.44), but CH4 yield (20.4 vs. 19.5 g/kg of dry matter intake; P = 0.10) and CO2 production (11.1 vs. 10.8 kg/d; P = 0.06) tended to decrease in cows offered MOL. In summary, partially replacing ground corn with liquid molasses at a rate of 5% in the diet dry matter had no effect on enteric CH4 emissions, but decreased concentration and yield of milk true protein and feed efficiency in Jersey cows fed red clover baleage.

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