The Influence of Rotational Length, along with Pre- and Post-Grazing Measures on Nutritional Composition of Pasture during Winter and Spring on New Zealand Dairy Farms

Abstract

The quality of ryegrass–clover pasture was investigated between August (winter: start of calving) and November (spring: end of breeding) on pasture-based dairy farms (>85% of total feed from pasture) that had short (n = 2, Farms A and B; winter ~30 days, spring ~20–25 days) or long (n = 2, Farms C and D; winter ~35 days, spring ~25–30 days) grazing rotations to determine whether quality was affected by grazing rotation length (RT). Weekly assessments of pasture growth and herbage quality were made using a standardised electronic rising plate meter, and near-infrared spectroscopy, respectively. Data were subjected to repeated measure mixed model analysis, in which herbage quality was the outcome variable. The highest pre-grazing dry matter (PGDM) and height, post-grazing dry matter (DM) and height, and number of live leaves per tiller (leaf regrowth stage, LS) were present in late spring. Neutral detergent fibre (NDF), acid detergent fibre (ADF), metabolisable energy (ME), and organic matter digestibility (OMD) were positively correlated to each other (r2 ≥ 0.8) whilst ADF and lipid, and ADF and OMD were negatively correlated (r2 ≥ −0.8; p < 0.01). Metabolisable energy content was negatively correlated with ADF and NDF (r2 = −0.7, −0.8, respectively), and was inversely related to PGDM. Metabolisable energy was higher (p < 0.05) in farms with shorter (overall mean: 11.2 MJ/kg DM) than longer (10.9 MJ/kg DM) RT. Crude protein was also inversely related to PGDM and was higher with shorter (23.2% DM) than longer (18.3% DM; p < 0.05) RT. Pre-grazing DM affected the amount of pasture that was grazed and, hence, the amount of DM remaining after grazing (post-grazing DM or residual), so that PGDM was correlated with post-grazing height and residual DM (r2 = 0.88 and 0.51, respectively; both p < 0.001). In conclusion, RT, LS, and PGDM during winter and spring influenced the herbage quality, therefore, better management of pastures may enhance the productivity of dairy cows.

Grazing management practices on Waikato and Canterbury dairy farms diverging in bulk milk urea content

“…These are all likely to have been drivers behind the lower pasture CP content on the Low BMU farms. This is consistent with Kumara et al (2022) who reported lower CP and ME content of pasture with higher pre-grazing herbage mass (>3000 kg DM/ha), and with increased leaf stage above 3. They also determined that ME and CP were negatively correlated with both neutral detergent fibre and acid detergent fibre suggesting that longer grazing…”

“…In contrast, mean leaf stage was below 2.0 on Waikato farms, except in summer and autumn for Low BMU farms and in autumn for High BMU farms. Grazing before the 2-leaf stage for ryegrass would be expected to increase the N content of the pasture eaten (Fulkerson and Donaghy 2001;Kumara et al 2022). Grazing interval (days since last grazing) is a key factor influencing leaf stage and pre-grazing herbage mass; therefore, we also investigated differences in duration since last grazing between BMU groups.…”