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Sward characteristics, grass dry matter intake and milk production performance are affected by pre-grazing herbage mass and pasture allowance

Curran, J., Delaby, L., Kennedy, E., Murphy, J.P., Boland, T.M., O'Donovan, M.
Livestock science 2010 v.127 no.2-3 pp. 144-154
dairy cows, milk protein yield, dry matter content, stocking rate, lactose, pastures, grazing, regrowth, Holstein, rumen fermentation, grazing management, leaves, sward, rumen fluids, dry matter intake, pH, vegetation structure
The objective of this study was to investigate the effect of pre-grazing herbage mass (HM) and pasture allowance (PA) on sward characteristics, milk production performance, dry matter intake (DMI) and rumen fermentation of spring calving dairy cows. Sixty-four Holstein-Friesian dairy cows (mean calving date, February 11) were balanced and randomly assigned to one of four treatments (n =16) in a 2×2 factorial design. Two swards, a low HM (L HM) sward (1600kg dry matter (DM)/ha) and a high HM (H HM) sward (2400kgDM/ha), were created by varying the regrowth interval before the study start date, with two PA, 15 and 20kg DM/cow/day imposed on each sward. Animals fitted with rumen cannula (n =4) moved in a complete Latin square to investigate the effect of HM and PA on rumen fermentation. The study lasted 30weeks and was analysed as two periods; PI (April 9-July 20) and PII (July 21-October 31). Sward structural characteristics, grass dry matter intake (GDMI) and rumen fermentation were investigated during PI and PII. The mean HM was 1551kgDM/ha and 2678kgDM/ha for L HM and H HM respectively in PI, and 1753kgDM/ha and 2281kgDM/ha for the L HM and H HM respectively in PII. During PII, the leaf proportion (> and <40mm) was higher in the L HM swards than the H HM swards. There was a lower dead proportion>40mm in the L HM swards compared to the H HM swards. In PI, the L HM treatments had significantly higher milk production (+0.9kg), milk protein yield (+42.4g/day) and milk lactose yield (+42.9g/day). Increasing PA increased milk yield (+1.1kg; +1.8kg), solids-corrected milk (+0.9kg; +1.3kg), protein (+67.9g/day; +63.5g/day) and lactose (+55.2g/day; +80.1g/day) yield in PI and PII respectively. The milk response per kilogram of GDMI was 1.13kg for the L HM animals compared to 0.65kg for the H HM animals. Rumen pH was lower for animals grazing the L HM swards (pH 5.69) than for animals grazing the H HM swards (pH 5.88) with no adverse rumen conditions evident. The results of this study suggest that L HM (1600kgDM/ha) and 20kg PA had a positive effect on sward characteristics which resulted in increased milk production and sward quality.