Date of Award:

2013

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Animal, Dairy, and Veterinary Sciences

Advisor/Chair:

Jong-Su Eun

Abstract

In two lactation studies reported in this dissertation, it was hypothesized that feeding 35% brown midrib corn silage (BMRCS) and 25% alfalfa hay (dry matter basis) would result in increased dry matter intake (DMI) around peak lactation compared with feeding conventional corn silage (CCS), causing longer peak milk production, and that feeding dairy cows in early lactation a 16% crude protein diet with fair quality alfalfa hay (FAH) in BMR-based diets would maintain milk production, reduce urinary N excretion, and improve N efficiency compared to those fed high quality alfalfa hay (HAH) in CCS- or BMR-based diets. A third experiment was conducted to assess in situ degradation kinetics of BMRCS harvested prior to or at maturity. The first lactation study was performed to determine the long-term effects of feeding BMRCS fed with a high dietary concentration of good quality alfalfa hay in a high-forage lactation diet on productive performance of Holstein dairy cows for the first 180 d of lactation. Feeding BMRCS-based diet did not affect milk production through peak lactation compared with a CCS-based diet; however, cows fed the BMRCS-based diet maintained heavier body weight through peak lactation and longer peak milk production, which resulted in increased milk yield post peak lactation, leading to greater overall milk production and milk protein yield. A second lactation experiment was performed to investigate if early lactating dairy cows fed with the FAH in BMRCS-based diets would reduce urinary N excretion and improve N efficiency compared to those fed the HAH in CCS- or BMR-based diets. Feeding BMR and HAH had better N utilization by decreasing concentrations of urea in blood, milk, and urine. In addition, feeding BMR-based diets decreased urinary N-to-fecal N ratio, and it was further reduced by feeding the HAH, which can represent an environmental advantage over traditional sources of forages in lactation dairy diets. A third experiment assessed in situ DM and neutral detergent fiber degradation kinetics for two new pre-matured BMR varieties (pmBMR1 and pmBMR2) that can be double-cropped by harvesting at tassel, compared with a sole crop mature BMR (mBMR) and CCS harvested at maturity in dry and lactating Holstein dairy cows. The potentially degradable NDF fraction was greater for BMR hybrids compared with CCS with the exception of the pmBMR2, which had the lowest potentially degradable NDF fraction in dry cows. Estimates of ruminal degradability of NDF were greatest for pmBMR1 in both dry and lactating cows. Feeding BMRCS exerted nutritive and environmental benefits when fed with typical Intermountain West lactation dairy diets. Further research is needed to understand interactive aspects of nutrient utilization with other dietary ingredients under different physiological conditions to take full potential benefits of BMRCS.

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