Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Animal and Veterinary Sciences

Committee Member

Dr. John Andrae, Committee Chair

Committee Member

Dr. Susan Duckett

Committee Member

Dr. Anibal Pordomingo

Committee Member

Dr. William Stringer


Annual ryegrass (Lolium multiflorum) is an important forage in Southeastern US. However, as in other winter annuals, concern exists about the balance between water soluble carbohydrates (WSC) and protein, which can lead to ruminal nutrient asynchrony. Lately, efforts have been done to increase the WSC content of ryegrass, and cultivars known as “high sugar varieties” have been released to the market. Several productive and environmental advantages have been suggested for these cultivars. The objective of our research was to compare conventional versus high sugar varieties under several conditions and from different approaches, to evaluate the potential of the high sugar varieties through a series of experiments. Our general hypothesis was that high sugar varieties would produce higher quality forage which in turn would lead to performance improvements and higher microbial protein synthesis. The first experiment evaluated four ryegrass varieties grown under greenhouse conditions varying in ploidy (diploid and tetraploid) and cycle length (annual or intermediate) to assess their chemical composition and digestibility. Later, two of those varieties which showed similar botanical characteristics and yields (Lonestar and Enhancer) were used in a two year experiment, to evaluate cattle performance, in vivo digestibility, and dry matter and forage intake, evaluating the interaction with corn supplementation as well. The next experiment involved the digestibility assessment of one of the varieties (Enhancer), grown in farm conditions, with four different in vitro methods: Daisy incubator system, batch culture, ANKOM gas production system and continuous culture fermenters, aiming to compare the results obtained by each of the in vitro method. In the last experiment, continuous culture fermenters were used to evaluate the effect of WSC and soluble protein levels on fermentation parameters, microbial protein synthesis and nutrient digestibility. Additionally, this dissertation includes a literature review on the potential of residual feed intake for cattle production efficiency improvement.