Relationship between temperate grass sward characteristics and grazing behavior of dairy heifers

Authors: Soder, Kathy; Brink, Geoffrey; Raynor, Edward; Casler, Michael

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2022
Publication Date: 6/30/2022
Citation: Soder, K.J., Brink, G.E., Raynor, E.J., Casler, M.D. 2022. Relationship between temperate grass sward characteristics and grazing behavior of dairy heifers. Agronomy. 12(7):1584. https://doi.org/10.3390/agronomy12071584.
DOI: https://doi.org/10.3390/agronomy12071584

Interpretive Summary: Cool-season grasses are the primary component of pastures grazed by dairy cows. The more high-quality grass that dairy cows are able to consume while grazing, the greater the potential milk production. The characteristics of grasses that may influence pasture consumption include yield, height, nutritive value, and distribution of the leaf and stem fraction. Our study determined which grass characteristics had the most influence on grazing behavior, including time spent grazing and number of bites per day, of cattle to better understand how productivity of grazing cattle can be improved. We found that grass species and sward structure had minimal impact on grazing behavior, with sward height and mass being the most important traits. These results suggest that dairy cows are quite adaptable at altering their grazing behavior to result in similar patterns of behavior across cool-season grass species as long as forage availability and nutritional quality are maintained at high levels.

Technical Abstract: Sward architecture mediates ruminant grazing behavior in temperate grazing lands. Temperate grasses differ in sward structure, which may influence grazing behavior of cattle. We determined relationships between grazing behavior of dairy heifers and sward structure of the temperate grasses meadow fescue [Schedonorus pratensis (Huds.) P. Beauv.], orchardgrass (Dactylis glomerata L.), quackgrass [Elymus repens (L.) Gould], and reed canarygrass (Phalaris arundinacea L.). Vegetative-stage grasses were rotationally grazed by Holstein heifers (average initial body weight of 460 kg) during 5-d periods in the spring, summer, and fall of 2007 and 2008. Herbage dry matter (DM) allowance was twice the expected daily intake (11 kg DM animal-1 d-1). Sward characteristics were measured before grazing (herbage height and mass, vertical distribution of leaf and stem fraction, nutritive value). Grazing behavior was quantified using automatic jaw movement recorders. Grass species had little effect on grazing behavior. However, bite rate was negatively correlated with herbage mass while number of bites was positively correlated with sward height and herbage mass. These results suggest that when herbage availability was not limited, grazing dairy heifers are quite adaptable in altering grazing behavior, resulting in similar behavior across grass species, sward structure, and seasons.