Effect of autumn herbage mass on pasture productivity and animal performance in spring-calving grass-based dairy systems
Résumé
The objective of this study was to evaluate the impact of 3 available herbage mass strategies (HM) and 2 whole grazing intensities on the performance of spring calving dairy cows during late lactation. The 3×2 factorial design experiment was conducted in autumn over 3 years (2017, 2018 and 2019) and consisted of: Low Herbage Mass (LHM), Medium Herbage Mass (MHM) and High Herbage Mass availability (HHM) and 2 grazing intensities (GI; Medium Intensity (MI; 2.75 cows ha‑1) and High Intensity (HI; 3.25 cows ha‑1). Autumn mean pre-grazing biomass yield was 1,280, 1,731 and 2,080 kg dry matter (DM) ha‑1 for LHM, MHM and HHM, respectively resulting in post-grazing residual heights of 34.3, 36.8 and 37.3 mm, respectively. There was no difference in milk and fat plus protein yield between the 3 HM treatments during autumn (1 and 1.52 kg cow‑1 d‑1, respectively). Grazing intensity had no effect on pregrazing measurements, with the exception of daily herbage allowance which was higher (P<0.001) for MI compared with HI (+2.2 kg DM cow‑1 d‑1). The combination of increased GI and increased concentrate supplementation for HI GI resulted in a reduced post-grazing sward height (-3 mm) and an increased fat plus protein yield (0.04 kg cow‑1 d‑1). These results highlight the potential for high intensity grazing systems to maintain an extended grazing season by increasing HM during autumn without detriment to individual animal performance.