Effect of swath grazing on forage intake and wastage by ewes

Abstract

Sixty non-pregnant and non-lactating mature white faced ewes (Targhee 65.4 ± 5.84 kg BW in 2010 and Rambouillet 61.9 ± 6.28 kg BW in 2011) were used in a 2-yr study to evaluate intake, forage wastage, and nutrient composition of a pea/barley forage fed either as baled hay in confinement (CONFINEMENT) or swathed and left to graze (GRAZE). Forage DMI was estimated using IVDMD and chromic oxide as an external marker for estimating fecal output. Forage wastage was estimated by sampling and weighing the initial swath, standing, and baled forage, and weighing the forage again after a 7-d collection period, and subtracting the estimated forage DMI. Samples of baled, swathed, and any standing forage were collected in August and October and analyzed for DM, OM, CP, NDF, ADF, and in situ dry matter digestibility (ISDMD). There was no treatment by year interaction (P = 0.56) for BW change and no difference (P = 0.33) between treatments. There was a treatment by year interaction (P = 0.04) for DMI. In 2010, DMI was greater (P = 0.06) by CONFINEMENT ewes compared to GRAZE ewes (2.4 vs 1.7 kg x ewe -¹ x d -¹); however, in 2011, DMI did not differ (P = 0.25) between treatments. There was no treatment by year interaction (P > 0.22) for forage wastage either as a percent of beginning available forage or as kilograms of wastage. Although percentage wastage did not differ between treatments (P = 0.23), kilograms of wastage was greater (P = 0.03) for GRAZE than CONFINEMENT. For both years in the swathed forage, ISDMD and OM decreased while NDF and ADF increased. In 2010 CP increased, but in 2011 it remained the same. For both years in the baled forage, CP decreased while ISDMD and NDF increased. In 2010, ADF decreased and OM increased, but in 2011 ADF increased and OM decreased. Although nutrient content was lower in the swath, wastage and animal performance did not differ between the treatments. This research provides a sound biological basis for an economic assessment of using swath grazing in commercial sheep operations.