Effects of cultivar and grazing initiation date on fall-grown oat for replacement dairy heifers

Authors: Coblentz, Wayne; Brink, Geoffrey; ESSER, NANCY - University Of Wisconsin; CAVADINI, JASON - University Of Wisconsin

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2015
Publication Date: 8/16/2015
Publication URL: http://handle.nal.usda.gov/10113/61283
Citation: Coblentz, W.K., Brink, G.E., Esser, N.M., Cavadini, J.S. 2015. Effects of cultivar and grazing initiation date on fall-grown oat for replacement dairy heifers. Journal of Dairy Science. 98:6455-6470.

Interpretive Summary: Fall-grown oat shows promise for fall grazing, but the optimum date to initiate grazing has not been determined. Fall-oat forages typically exhibit very little regrowth potential, especially if the initial forage removal by grazing livestock occurs after plants have jointed and stem elongation has begun. Without potential for regrowth, initiating grazing too early will greatly restrict pasture productivity, but initiating grazing too late may depress the nutritive value of early-maturing cultivars as well as risk forage losses due to the onset of winter weather, particularly due to the necessary termination of grazing following heavy snowfall. In this study, heifer growth performance was evaluated from pastures seeded to an early-maturing or late-maturing oat with early (late-September) or late (mid-October) grazing initiation dates. Our results suggest that delaying grazing until mid-October will consistently suppress heifer growth performance, particularly if rapidly maturing cultivars are utilized. Several explanations for this response were identified, and include: i) potential forced early termination of grazing due to extensive snow cover; ii) sharp year-to-year differences in maturation rate by early-maturing, grain-type cultivars that may make the forage less acceptable to heifers; and iii) inadequate time for heifers to adapt properly to grazing routines, while also adapting to sub-freezing temperatures. Throughout central Wisconsin, grazing should be initiated in late September if fall-oat is established in early August.

Technical Abstract: Fall-grown oat has shown promise for extending the grazing season in Wisconsin, but the optimum date for initiating grazing has not been evaluated. Our objectives for this project were: i) to assess the pasture productivity and nutritive value of 2 oat cultivars (Ogle and ForagePlus; OG and FP, respectively) with late-September (EARLY) or mid-October (LATE) grazing initiation dates; and ii) to evaluate growth performance by heifers grazing these oat forages compared to that of heifers reared in confinement (CONTROL). A total of 160 gravid Holstein heifers (80 heifers/yr) were assigned to 10 research groups (8 heifers/group). Mean initial BW was 509 ± 40.5 kg in 2013 and 517 ± 30.2 kg in 2014. Heifer groups were assigned to specific pastures arranged as a 2 × 2 factorial of oat cultivars and grazing initiation dates. Grazing heifer groups were allowed to strip-graze oat pastures for 6 h daily before returning to the barn, where they were offered a forage-based basal TMR. Main effects of oat cultivar and sampling date interacted for forage characteristics in 2013, but not in 2014. During 2013, oat forage mass increased until early-November before declining in response to freezing weather conditions, thereby exhibiting linear and quadratic effects of sampling date, regardless of oat cultivar. Similar trends over time were observed in 2014. For 2013, the maximum forage mass was 5329 and 5046 kg/ha for FP and OG, respectively, while the mean maximum forage mass for 2014 was 4806 kg/ha. ForagePlus did not reach the boot stage of growth during either year of the trial; OG matured more rapidly, reaching the late-heading stage during 2013, but exhibited only minor phenological differences from FP in 2014. For 2013, ADG for CONTROL did not differ from grazing heifer groups (overall mean = 0.63 kg/d); however, ADG from FP was greater than OG (0.68 vs. 0.57 kg/d), and greater from EARLY compared to LATE (0.82 vs. 0.43 kg/d). For 2013, advantages in ADG for heifers grazing FP pastures were likely related to the greater energy density of FP oat throughout the fall that reached a maximum of 68.8% TDN on 27 November compared to only 63.7% for OG on 10 October. During 2014, ADG from CONTROL exceeded grazing heifer groups (0.81 vs. 0.57 kg/d), and ADG from EARLY again exceeded LATE (0.70 vs. 0.44 kg/d). These results suggest that delaying grazing until mid-October will consistently suppress heifer growth performance, particularly if rapidly maturing cultivars are utilized.