Effect of supplementation and grazing residual on dairy cow production

Abstract

With the desire to increase milk production continuing the industry is developing ways to increase production without increasing costs. Two strategies to increase production are manipulating grazing residual to increase intake and pasture quality and through the addition of supplements into the system. There is ongoing debate over the most effective grazing residual to maximise milk production and maintain pasture quality. In this experiment the effect of post grazing pasture residual (PGPR) on long term pasture production, pasture quality and milk production has been investigated. Also the effect of supplementation on milk production and the interaction with PGPR has been examined. In a farmlet experiment, 32 mixed parity kiwicross cows were divided into four treatments low PGPR (grazed to 3.5 cm) without supplement (LR); high PGPR (grazed to 5cm) without supplement (HR); low PGPR with supplement (4kgDM/day)(LR+) and high PGPR with supplement (HR+). The experiment commenced in August 2012 and paddocks have been maintained under the same grazing management for two milking seasons with continual monitoring of milk production and pasture production and quality. In autumn 2014 additional measurements were taken to investigate the long term effect of PGPR on pasture characteristics. Increasing PGPR from 3.5 cm to 5cm reduced pasture production from 11,173 to 10,639 kgDM/ha for supplemented treatments and from 10,724 to 9,829 kgDM/ha (P<0.001) for un-supplemented treatments for the period 30/9/2013 to 12/5/2014. Botanical and nutritive composition changed throughout the season, but there was no significant difference between treatments. Milk production was greater for the supplemented treatments at 485 and 474 kgMS/cow/year for HR+ and LR+ respectively, and 425 and 418 kgMS/cow/year for HR and LR respectively. Milk solids per hectare was also increased with the addition of supplements at 2326, 2276, 1913 and 1880 kgMS/ha/year for the HR+, LR+, HR and LR treatments respectively (P<0.029). Milk composition was not affected by supplement although protein yield was greater under supplement treatments at 214, 207, 179 and 174 kg milk protein/cow/year for HR+, LR+, HR and LR treatments respectively (P<0.001). PGPR had no effect on milk production or milk composition. There were no long term effects of PGPR on pasture quality in autumn with some small effects on diet selection (NDF, P<0.029).