Document Type

Thesis - Open Access

Award Date

2023

Degree Name

Master of Science (MS)

Department / School

Dairy and Food Science

First Advisor

Md Elias Uddin

Keywords

Feed efficiency, rumen environment, rumen pH, volatile fatty acids

Abstract

The newly proposed physically adjusted NDF system (paNDF) system aims to maintain a favorable rumen environment (e.g., pH) by taking into account both the physical and chemical composition of diet. Thus, the objective of this study was to determine the effects of water-soluble carbohydrates (WSC) and non-forage NDF inclusion in a paNDF system on production performance, rumen pH and fermentation profile, rumen bacterial abundance, feeding behavior and nutrient digestibility in late-lactating Holstein cows. Nine fistulated multiparous Holstein cows (2nd and 3rd parity) were used in a triplicated 3×3 Latin Square experiment. Each period lasted for 21 d with 14 d of adaptation and 7 d of sampling. All three diets including control (CON), dextrose (DEX) and non-forage NDF (NFFS) had similar crude protein (16.5%), net energy for lactation (1.74 Mcal/kg DM), and forage NDF (19.1%). On contrary, CON diet contained greater starch than DEX or NFFS diet due to more corn grain inclusion whereas DEX and NFFS diet contained greater concentrations of WSC (replacing corn grain) and non-forage NDF (replacing soybean meal and corn grain with soybean hulls), respectively. Milk yield (MY) and dry matter intake (DMI) were recorded daily. Milk samples from AM and PM milking over 3 d (6 samples/cow in each period) were analyzed for milk components. Rumen fluid was collected for bacterial abundance, volatile fatty acids (VFA), and ammonia (NH3) whereas fecal spot samples (8 timepoints per cow) were collected for total-tract nutrient digestibility using indigestible NDF as marker. Feeding behavior and rumination was measured using an ear attached accelerometer. Statistical model included the fixed effects of period, Latin Square, diet, and diet × period interaction and a random effect of cow within parity. Although MY, fat-and-protein corrected milk yield and milk component yields were not affected by the diet, cows fed DEX had 6 and 9% greater DMI than CON and NFFS cows, respectively. Diet did not affect rumen pH, NH3-N and VFA, however, CON diet tended to have greater iso-butyrate and greater iso-valerate than DEX or NFFS. Inclusion of non-forage NDF increased DM and NDF digestibility of NFFS diet compared to CON or DEX diet whereas DEX had lower starch digestibility than CON or NFFS. Diet tended to affect the abundance of F. succinogenes, P. ruminicola and S. bovis being greater in abundance for DEX than NFFS whereas abundance did not vary between CON vs. DEX or CON vs. NFFS diet. Cows receiving the DEX diet tended to spend greater time eating than NFFS cows likely due to greater DMI. When expressed per unit of DM, NDF or forage NDF intake, DEX cows had lower rumination time than CON cows due to mainly increased DMI or NDF or forage NDF consumption. On contrary, eating and chewing time expressed per unit of NDF intake was greater in DEX than NFFS diet likely because DEX cows had greater DMI. Overall, our findings suggest that though replacement of corn grain either with dextrose or non-forage NDF in paNDF system affected DMI, nutrient digestibility, bacterial abundance and feeding behavior; however, implementing an adequate paNDF maintained a ruminal pH above 6.0 which most likely kept animals healthy without affecting lactation performance.

Publisher

South Dakota State University

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Dairy Science Commons

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Rights Statement

In Copyright