Submitted to: Canadian Journal of Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2016
Publication Date: 7/5/2016
Citation: Jensen, K.B., Robins, J.G., Rigby, C.W., Waldron, B.L. 2016. Comparative trends in forage nutritional quality across the growing season in thirteen grasses. Canadian Journal of Plant Science. doi: 10.1139/cjps2015-3208.

Interpretive Summary: Profitable livestock production from herbages depends largely upon the quantity and nutritive quality of the herbage produced and the animal's capacity to harvest and utilize efficiently. It is influenced largely by nutrient concentration, intake potential, and digestibility of the herbage. Based on recent climate change models, landscapes are likely going to get drier and hotter; thus, reducing the available water to support herbage production affecting the use of species dependent on greater water supplies for adequate herbage production and nutritional quality. This study looked at crude protein, neutral detergent fiber digestibility, digestibility, and neutral fiber in 13 grass species from 3 May to 3 August where the plots were harvested and from 15 September to 2 November on regrowth forage. Forage feed value under reduced irrigation and or precipitation remained above the critical level (105 g kg-1 crude protein) to maintain mother cows in crested wheatgrass, smooth bromegrass, RS-hybrid, and intermediate wheatgrass. Smooth bromegrass and crested wheatgrass digestible fiber concentrations were similar to orchardgrass and timothy. Concentrations of IVTD in crested wheatgrass and smooth bromegrass were similar to those observed in orchardgrass and timothy. Crested wheatgrass and smooth bromegrass have NDF concentrations similar to timothy, but less than orchardgrass. If forage producing environments do experience drier hotter conditions, many of the traditional herbage species will not persist and based on this study, there are grass species adapted to these environments capable of producing acceptable levels of forage feed values.

Technical Abstract: Based on recent climate change models, landscapes are likely going to get drier and hotter; thus reducing the available water to support herbage production in species heavily dependent on water for persistence and production such as perennial ryegrass (Lolium perenne L.), orchardgrass (Dactylis glomerata L.), timothy (Phleum pretense L.), tall fescue (Festuca arundinacea Schreb.) and timothy. Hence, there is a need to identify and describe herbage nutritive characteristcs in grasses that require less irrigation and or precipitation compared to those mentioned above. This study evaluated 13 cool-season grasses from May to August (growth phase-1) and from September to November (growth phase 2) in northern Utah during 2004 and 2005 for crude protein (CP) neutral detergent fiber digestibility (NDFD), in vitro true digestibility (IVTD), and neutral detergent fiber (NDF). Sampling date, year, and sampling date x species interation had a significant effect on CP, NDFD, IVTD, and NDF concentrations. In growth phase-1, there was a strong linear decline in CP, NDFD, and IVTD concentrations compared to a linear increase in NDF concentration as herbage matured. Herbage mean CP concentrations ranged from 83 to 251 g kg-1 in all species examined. Orchardgrass (Dactylis glomerata L.), smooth bromegrass (Bromus inermis Leyss.), RS-hybrid (Elymus hoffmannii K.B. Jensen & K.H. Asay), and crested wheatgrass [Agropyron cristatum (L.) Gaertn.] had herbage CP, NDFD, and IVTD concentrations similar to orchardgrass and timothy, but less than perennial ryegrass. Crested wheatgrass had herbage NDF concentrations similar to timothy, but less than orchardgrass. Of all the drought tolerant species examined, crested wheatgrass and smooth bromegrass herbage had the greatest nutritional quality. In the future, if herbage producing enviroments experience drier hotter conditions, shifting to these more drought tolerant grasses does not mean a reduction in herbage nutritional quality.