Date of Award

December 2020

Document Type


Degree Name

Doctor of Philosophy (PhD)


Animal and Veterinary Sciences

Committee Member

Gustavo J Lascano

Committee Member

Matias J Aguerre

Committee Member

Thomas Jenkins

Committee Member

William Bridges


Controlling dry matter intake (DMI) is one strategy to meet the animal’s requirements while reducing feed costs and increasing feed efficiency. Controlling intake through precision-feeding provides a more nutrient-dense diet, allowing an increase in energy and nutrient utilization efficiency while decreasing nutrient loss. The literature about precision feeding has provided information regarding optimal N intake and different dietary fiber proportions, but more information needs to be addressed. This is one of the first attempts to further our knowledge through the use of fat inclusion. In the present dissertation, a total of 4 in-vitro and in-vivo experiments were conducted. Simulated and applied precision feeding with different forage to concentrate (F:C) ratios and fat sources inclusion were used to determine the effect on Holstein and Jersey dairy heifer’s digestibility and fermentation.An introduction to the importance of investigating strategies to fat supplementation in precision feeding for dairy heifers is presented in Chapter 1. Background information and justification of the current dissertation is presented in the systematic Literature Review in Chapter 2. The objective of the first experiment presented in Chapter 3 was to screen the effects of including different types of fat to different F:C ratio on digestibility and in-vitro gas production (GP). Treatments included either low forage (LF; 35%) or high forage (HF; 70%) with 2 dietary fat concentrations (6 or 9% DM) screening for 6 different fat sources plus control (CON). The CON diet had a basal fat concentration in the diet [3% fat (0% fat inclusion); and fat sources were added to attain 6% or 9% fat and consisted of Coconut oil, CO; Poultry fat, PF; Palm oil, PO; Palm kernel oil, PKO; Ca Salts, MEG; Soybean oil, SOY]. Modules were randomly assigned to treatments in a 2×2×7 factorial design and incubated for four 24 h runs. The CO-fed module had the highest DM apparent digestibility (AD), followed by SOY and PF. The true DM digestibility (IVTDMD) and OM AD were the highest in CO than the other types of fat. The AD for DM, OM, NDF, ADF, and IVTDMD was higher in LF. Total VFA was lower in modules fed different fat types than the CON and acetate, while propionate was the lowest for the CON, which increased the A:P ratio. These results suggested that LF diets with high fat concentration can be used under a precision feeding system, and different types of fat sources may improve DM and fiber digestibility. The second experiment's objective presented in Chapter 4 was to evaluate the effects of fermentation and digestion of including different fat sources when high concentrate diets with high-fat inclusion are used to simulate precision feeding in continuous culture. Four treatments were randomly assigned to 8 continuous cultures in a randomized complete block design and ran for 2 periods of 10 d. Diets included high concentrate (HC; 65%) with high fat inclusion starting with a basal level of fat as CON [3% fat (0% fat inclusion); 9% fat (6% PF; CO; SO inclusion)]. The DM, OM, NDF, ADF, and hemicellulose digestibility coefficients (dC) were higher for PF-fed fermenter, and CO followed by SO and then CON. Total VFA was higher for CON, and there was a reduction in acetate and propionate with different fat treatments. These results suggest that simulated precision feeding with HC and high fat supplementation can improve digestibility. Chapter 5 presents the third experiment to determine the effects of simulated precision feeding of different PF levels at different F:C ratios on digestibility and fermentation in continuous culture. Treatments included 2 forage combinations, low (LF; 35% forage), and high (HF; 70% forage) and 4 levels of PF starting with a basal level of fat in the diet [3% fat (0% PF); 5% fat (2% PF); 7% fat (4% PF); and 9% fat (6% PF)]. Treatments were randomly assigned to 8 fermenters in a 2×4 factorial design and ran for 4, 10 d periods. The LF-fed fermenter had higher DM, OM, N, starch, and NFC dC than HF. Nutrients digestibility increased linearly with PF inclusion. Bacterial efficiency was decreased with PF inclusion. Total VFA was higher for LF, and there was a reduction in acetate with LF. The PF inclusion had a linear increase in total VFA, a linear reduction in acetate, and a linear increase in propionate. The A:P ratio decreased linearly in both LF and HF as PF increased. These results suggest that increasing PF in precision fed LF or HF can alter rumen fermentation and improve digestibility. Finally, the last experiment's objective in Chapter 6 was to evaluate the effects on nutrient digestion and rumen fermentation of including different levels of PF in precision fed Holstein and Jersey dairy heifers. Four Holstein and 4 Jersey cannulated heifers were randomly assigned to 4 treatments, included a 55% forage diet with 4 increasing PF inclusion starting with a basal concentration of fat in the diet [3% fat (0% PF); 5% fat (2% PF); 7% fat (4% PF); and 9% fat (6% PF)]. Treatments were administered according to a split-plot, 4×4 Latin square design for 4 periods of 21 d. Holstein-group had a lower DM, OM, NDF, ADF, and NFC AD than Jersey-group. The inclusion of PF did not affect AD. However, starch AD increased linearly as PF increased, whereas NFC AD decreased linearly. Manure output was higher for Holstein, and the PF inclusion showed a linear decrease in manure output. Total VFA, acetate decreased linearly as PF increased. Concurrently there was a linear increase in propionate, resulting in a linear reduction in the A:P ratio. These results suggest that Jerseys utilized nutrients more efficiently than Holsteins. Dietary PF inclusion up to 6% in the rations can further reduce DMI in precision feeding programs without compromising total-tract digestibility. Overall, these studie’s results indicate that PF can be used as a replacement for corn in precision-fed Holstein and Jersey dairy heifer diets up to 6% DM. Other fat sources with different characteristics can be utilized with relative success, but further research is needed. Incorporation of supplemental fat to controlled intake strategies such as precision-feeding can reduce feed intake for optimal growth, promising impacts on costs. Furthermore, nutrient digestibility, rumen fermentation, and animal performance can be enhanced with positive effects on environmental impact.



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