Association among pasture-level variables and dairy cow responses to supplements
C. Poole A B F , D. J. Donaghy A , R. R. White B and J. R. Roche C D EA DairyNZ Limited, Newstead, Private Bag 3221, Hamilton 3210, New Zealand.
B Department of Dairy Science, Virginia Tech, Blacksburg, Virginia 24061, USA.
C School of Agriculture and Environment, Massey University, Palmerston North 4410, New Zealand.
D School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand.
E Present address: Ministry for Primary Industries, Pastoral House, Wellington 6140, New Zealand.
F Corresponding author. Email: caitlynpoole93@gmail.com
Animal Production Science 60(1) 118-120 https://doi.org/10.1071/AN18581
Submitted: 10 September 2018 Accepted: 3 December 2018 Published: 8 October 2019
Abstract
In grazing systems, the marginal milk-production response to additional feed (i.e. supplement) is dependent on the relative feed deficit of the cow. We hypothesised that the relative feed deficit could be defined by post-grazing residual (PGR), with a greater PGR indicating a smaller relative feed deficit. The objective of our study, therefore, was to determine the relationship between post-grazing residual and the marginal milk-production response to supplements. We undertook a computerised literature search utilising keywords associated with grazing systems and supplementary feed. We collated data from 26 experiments and 90 treatments, wherein pasture-level, supplementary-feed, and milk-production variables were reported. A meta-analysis was undertaken using random coefficient regression fitted as a mixed model to determine the marginal milk-production response to supplements. On average, pasture DM intake declined (P < 0.001; –0.28 kg/kg supplement DM) and milk, fat and protein yields increased (P < 0.001; 0.64 kg, 20 g and 30 g/kg supplement DM respectively) with an increased supplement use. For every kilogram of DM supplement consumed, PGR pasture height and mass increased by 1.4 mm and 42 kg DM/ha. Associated with every 10-mm increase in post-grazing pasture height in the control treatment, marginal milk response declined (P < 0.05) by 9%. These results will enable farmers to use the change in PGR when feeding supplements, to estimate likely marginal milk-production response to supplementary feeds.
Additional keywords: grazing, marginal response, pasture residual.
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