Refining Recommendations for Grazing Whole Plant Corn
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Study objectives were to assess the impacts of grazing allocation and fiber supplementation on animal performance, grazing preference and behavior, ruminal fermentation and whole-system economic costs. Field studies were carried out during the winters of 2015-16 (yr 1) and 2016-17 (yr 2) evaluating replicated (n = 2) whole-plant corn grazing systems: (i) 3d allocation with supplemental fiber (3DF); (ii) 3d allocation without supplemental fiber (3DNF); (iii) 9d allocation with supplemental fiber (9DF); and (iv) 9d allocation without supplemental fiber (9DNF). Ninety-six cows (yr 1 BW = 674 kg ± 53.1, yr 2 BW= 638 kg ± 49.9), including 16 ruminally cannulated cows, were allocated to 1 of 4 replicated systems for 84 and 88 d in yr 1 and 2, respectively. The same 2100 CHU hybrid (P7332R) was seeded in yr 1 and 2 (yr 1, CP =8.6 %, TDN = 69.5%; yr 2, CP = 8.3%, TDN = 70.72%) and a supplemental fiber source was offered each year, at 15% of total DMI in 3DF and 9DF treatment which was an alfalfa-grass mix hay (yr 1 CP = 12.9%, TDN = 60.2%; yr 2, CP =15.5%, TDN = 58.42%). Cow BW, rib fat, BCS, and ADG were not affected by treatment (P = 0.85). Total DMI was greater (P = 0.01) in 9D forage allocation compared to 3D allocation (12.8 kg hd-1 d-1, respectively). The proportion of cob was greatest (34.2%; P = 0.01) before a grazing allocation and decreased (1.1%) at the end of allocation, whereas the stem proportion was lowest (48.6%; P = 0.01) before and greatest at the end (87.4%) of allocation. When supplemental fiber was offered cattle spent less (48.6 vs. 63.5%, respectively; P = 0.03) time grazing corn compared to cows not provided supplemental fiber. Grazing selection results suggest that cobs were heavily selected for at the start of a grazing allocation, which would provide a highly fermentable starch source at the start of the grazing period. Rumen pH parameters were not affected by fiber supplementation or allocation duration (P > 0.05). The duration that ruminal pH < 5.8 was greatest (143.18 min; P = 0.01) at the start of the grazing allocation compared to middle and end (26.32 and 0.0 min, respectively) of allocation. Total SCFA concentration was greatest (102.12, 99.13 and 86.77 mM, respectively; P = 0.01) at the start and middle of allocation, compared to the end of allocation. The molar proportions of propionate (P = 0.03) and isovalerate (P = 0.01) were lower when fiber was supplemented to cows. Fecal starch was greatest (P = 0.01) at the start of 9D and middle of 3D grazing allocations but was not affected (P = 0.58) by fiber supplementation. Grazing systems costs were not affected (P = 0.73) by grazing treatment. Results from the current study suggest that trt had no impact on rumen fermentation however grazing selection as timing within a forage allocation impacts diet fluctuation in all trt. Offering fiber supplementation did not reduce selection of cob or improve forage utilization. Maintaining the current recommendation of 3 d allocation lengths will reduce the diet fluctuation by the animal and potentially improve forage utilization and economic costs.
DegreeMaster of Science (M.Sc.)
DepartmentAgricultural and Resource Economics
CommitteePenner, Greg; McKinnon, John; Brook, Ryan
Copyright DateFebruary 2020