Grazing season length and stocking rate affect milk production and supplementary feed requirements of spring-calving dairy cows on marginal soils

The objective of this study was to investigate the effect of increasing stocking rate (SR) and extending grazing season (GS) length on pasture and animal productivity on a marginal, poorly draining soil type. The study was a multiyear (2017 to 2020, inclusive) whole farm systems evaluation with a 2 x 2 factorial experimental arrangement of treatments. The systems evaluated comprised 2 GS lengths, average (AGS; 205 d) and extended (EGS; 270 d), and the 2 whole farm stocking rates were medium (2.5 cows/ha) and high (2.9 cows/ha). We used this study design to create 4 grazing system intensities (500, 600, 700, and 800 cow grazing days per hectare per year). In 2017, cows were randomly allocated to 1 of the 4 whole farm systems precalving and remained on the same treatments for the duration of the study. We found no significant dif-ferences in total average annual pasture production [14,133 & PLUSMN; 538 kg of dry matter (DM) per hectare] or sward chemical composition between GS and SR treat-ments over the 4-yr period, with the exception of aver-age crude protein content, which was lower for EGS (211 g/kg DM) compared with AGS (218 g/kg DM). Grazed pasture production was significantly increased in EGS treatments (+758 kg of DM/ha) compared with AGS (9,917 kg of DM/ha), whereas conserved silage DM production was greater for AGS (+716 kg of DM/ ha) compared with EGS (3,583 kg of DM/ha). Neither GS nor SR had a significant effect on daily or cumula-tive lactation milk and fat plus protein production per cow (5,039 and & PLUSMN;440 kg, respectively). Increasing SR resulted in increased milk fat plus protein yield per hectare based on increased grazed pasture utilization. These results add further credence to the important additive contributions of both extended grazing and SR intensification to achieve high levels of grazed pasture utilization and milk production per hectare while re-ducing supplementary feed requirements within spring-calving grazing systems.