The effect of stocking rate and calving date on milk production of Holstein-Friesian dairy cows

The objective of this study was to evaluate the effect of stocking rate (SR) and calving date (CD) on milk production, BW and BCS within grass-based production systems post-European Union milk quotas using modern grazing management practices and high genetic potential Holstein-Friesian (HF) spring calving dairy cattle over a two year period. Two groups of HF dairy cows with different mean CD were established from within the existing research herd at Moorepark (Teagasc, Ireland). Animals were assigned either to an early calving (mean CD: 12 February) treatment or a late calving (mean CD: 25 February) treatment. Animals within each CD treatment were randomly allocated to I of 3 SR treatments, Low (2.51 cows/hectare (ha), Medium (2.92 cows/ha) and High (3.28 cows/ha) which were designed to represent 3 alternative whole farm SR in a post-European Union milk quota, spring calving, grass-based milk production system. A total of 138 spring-calving dairy cows, comprised of two strains of HF (North American HF and New Zealand HF genetic strains), were used during 2009 and 2010, respectively. The effects of CD, SR treatment, genetic strain and their interactions on milk production per cow and per ha, body weight and body condition score were analyzed. Although reducing per animal production, increased SR resulted in increased milk and milk solids production per ha. The results also indicate that although CD had no effect on total lactation performance, adjusting mean CD may be an effective strategy to align animal requirements and grass supply and reduce the requirement for supplements at increased SR in early lactation. (C) 2013 Elsevier B.V. All rights reserved.