Shortgrass range vegetation and steer growth response to intensive-early stocking

Abstract

A 9-year grazing trial was conducted to compare shortgrass vegetation and steer responses under intensive-early stocking (IES) at 2 stocking rates to season-long stocking (SLS). The stocking rates were (1) equal to SLS, with twice as many steers used for the first half of the SLS grazing season (2X-IES), and (2) greater than SLS. with 3 times as many steers used for the same period (3X-IES). The hypothesis tested was that SLS and 2X-IES would be similar and sustainable in terms of productivity and vegetation composition, whereas 3X-IES would be different and not sustainable. The 3 treatments were assigned to 6 pastures in a randomized-complete block. Grazing was initiated on or near 1 May each year and continued until about 15 July for IES and about 1 October for SLS. Steers were weighted at initiation of grazing and in mid-July, and SLS steers were weighed in October. Vegetation data were collected in July and October in each pasture from 10 randomly located plots. Species composition of grasses was estimated, and grasses and forbs were clipped separately to determine biomass availability. Steer total gain and average daily gain (ADG) under SLS and 2X-IES were equal (P>0.10) during the early season, but 3X-IES gain and ADG were less (P<0.05). Total-season gain was greater under SLS (P<0.05 than either IES treatment, but total- season ADG was equal to that under 2X-IES. Steer production per ha was equal under SLS and 2X-IES, but greater under 3X-IES (P<0.05). Western wheatgrass [Pascopyrum smithii (Rydb.) Löve] and buffalograss (Buchloe dactyloides (Nutt.) Engelm.) composition did not change over time under SLS and 2X-IES, but decreased and increased, respectively, under 3X-IES (P<0.05). Blue grama (Bouteloua gracilis (HBK.) Lag. ex Steud.) and annual grasses displayed initial composition differences (P<0.10) among grazing treatments, but not differential composition shifts over time (P>0.10). Grass and total biomass availability were reduced (P<0.10) over time by 3X-IES. The hypothesis was supported: SLS and 2X-IES were equal in terms of both livestock performance and vegetation responses, but livestock performance and biomass availability were reduced and vegetation composition changed under 3X-IES. Thus, 3X-IES was not sustainable. While SLS and 2X-IES appear biologically equal, using them simultaneously on separate land areas may reduce market variability risk by marketing twice per year.