395 The effect of forage allocation on steer performance when grazing cereal rye

Abstract With good winter tolerance and rapid spring growth, cereal rye can fill the early spring grazing gap in pasture productivity. However, there are little data regarding how to best use these acres in the Midwest. Thus, the objective was to study the effect of forage allowance on steer performance when rotationally grazing fall-planted cereal rye in the spring. Over 3 yr, steers (n = 170) were stratified by initial body weight (BW; yr 1 = 338 kg, yr 2 = 375 kg, yr 3 = 347 kg) and assigned to treatment groups of 5 to 30 depending on the year and desired stocking rate (range = 1.98 to 7.41 steers/ha) then assigned to a pasture. Experimental unit (EU) was pasture (n = 14), with three EU per year in yr 1 and 2 and eight EU in yr 3. Pasture size ranged from 0.81 ha to 6.1 ha. Pastures were divided into 2 paddocks for rotational grazing in yr 1 and 2, while pastures in yr 3 were divided into 4 paddocks. Grazing was initiated when average pasture height reached 12.7 cm and groups were rotated when paddock height reached 5 cm. Just before initiation of grazing in a paddock, forage mass and nutritive value were measured. The weighted average nutritive value of the cereal rye across the 3 yr was 69 ± 2.5% digestible organic matter (DOM) and 22.9 ± 5.1% CP. Data were analyzed using the regression procedure of SAS to test for a linear relationship between stocking rate and either forage offered or forage mass to determine if stocking rate effectively changed forage availability. Forage offered averaged 4.62 (SD ± 1.80) kg DM·100 kg BW-1·d-1 and had a moderate (R2 = 0.51) negative linear relationship (P < 0.01) to stocking rate. Mean forage mass was 947 (SD ± 301) kg DM·ha-1 was negatively linearly related (P < 0.01) to stocking rate with a moderate correlation of (R2 = 0.39). Additionally, a linear regression was used to analyze the relationship between average daily gain (ADG) and forage offered, forage mass, DOM offered, and CP offered. There was no correlation (P ≥ 0.75) between ADG (0.91 kg/d; SD ± 0.15) and the parameters of interest. The average DOM offered was 3.18 (SD ± 1.18) kg DOM·100 kg BW-1·d-1 and the average CP offered was 1.13 (SD ± 0.62) kg. When rotational grazing immature cereal rye, stocking rate did influence the amount of forage offered; however, ADG was not influenced by forage offered when it ranged from 1.4 to 8.5 kg DM·100 kg BW-1·d and there was no relationship between ADG and forage mass or nutrients offered. Lack of observed differences is likely due to the high nutritive value of the forage coupled with the close monitoring of forage height in the rotationally grazed system.