An evaluation of the biological implications of extended grazing within a wetland soil in the border midlands western region

The objective of this study was to investigate the effect of increasing stocking rate (SR) and/or extending grazing season (GS) length on pasture and animal productivity along with soil physical and structural properties on a wetland soil type. The study was a multi-year (2017 to 2020, incl.) whole farm systems evaluation with a 2 x 2 factorial experimental arrangement of treatments. The systems evaluated comprised 2 grazing season lengths (average (AGS; 205 days) and extended (EGS; 270 days) and 2 whole farm stocking rates (medium (MSR; 2.5 cows/ha) and high (HSR; 2.9 cows/ha). The study design was such as to create 4 grazing system intensities (500, 600, 700 and 800 grazing days per hectare yr-1). In 2017, cows were randomly allocated to one of the 4 whole farm systems pre-calving and remained on the same treatments for the duration of the study. Soil treading measurements were taken in 2018 and 2019. There were no significant differences in total average annual herbage production (14,133 +/- 538 kg DM per hectare) or sward chemical composition between GS and SR treatments over the 4 year period with the exception of CP content which was lower (P<0.01) for EGS (211 g/kg) compared with AGS (218 g/kg). Grazed pasture production was significantly (P<0.05) increased in EGS treatments (+758 kg DM/ha) compared with AGS (9,917 kg DM/ha), whereas conserved silage DM production was greater (P<0.05) for AGS (+716 kg DM/ha) compared to EGS (3,583 kg DM/ha). Neither GS nor SR had a significant impact on daily or cumulative lactation milk and fat plus protein production per cow (5,039 and +/-440 kg, respectively). While both Year and Season had a significant effect on soil treading characteristics, there was no significant impact of SR or GS. Increasing grazing days per hectare resulted in increased milk fat plus protein yield per hectare based on increased grazed pasture utilization resulting in an overall economic gain of €6.30 per additional grazing day per hectare. These results add further credence to the important additive contributions of both extended grazing and appropriate SR to maximise pasture and land resource utilization by increasing the number of grazing days per hectare in dairy systems on marginal soils with no negative effect on soil treading characteristics