The objective of this work was to compare dry matter intake and grazing behaviour of different strains (S) of Holstein-Friesian dairy cows during early lactation. Three strains of different origin [two 1990’s genotypes of Holstein- Friesian from Overseas (OS90) or New Zealand (NZ90) origin and a 1970’s NZ Friesian (NZ70)] were offered low or high pre-grazing herbage mass (HM) (2100 vs 2800 kg DM/ha) at a common daily allowance (35 kg DM/cow) between September and November 2004. Pasture dry matter intake (IT) and digestibility (D) were determined using the n-alkanes methodology. Time spent grazing (GT) and ruminating (RT) were observed for 24 hours. Intake per empty body live weight unit (ILW) and rate of intake (IRATE) were calculated. There was a significant SxHM interaction (P < 0.001) for IT and ILW. IT was similar at low HM across strains, whereas at high HM, a lower IT was recorded for the NZ70 while it was higher for the OS90. At low HM, ILW was slighter lower in the OS90 than in the NZ90 (P = 0.06) while at high HM both NZ90 and OS90 showed a higher ILW. In vivo digestibility was similar across strains but was higher at high HM (P < 0.001). There was a significant SxHM interaction for GT (P < 0.01) with both NZ strains spending more time grazing at low HM, in contrast, GT was similar across strains at high HM. RT was higher for the OS90 strain than for both NZ strains (P < 0.05) and greater at high HM (P < 0.001). There was a significant SxHM interaction for IRATE (P < 0.05) with the NZ90 and OS90 strains showing similar IRATE at low HM but different at high HM. Results indicate a difference in the ability of the strains to adjust their grazing behaviour to different pre-grazing herbage mass. KEYWORDS: Holstein-Friesian; high-merit dairy cow; intake; grazing behaviour, herbage mass.

JL, Rossi, KA MacDonald, BS Thorrold, J Hodgson, and CW Holmes

Proceedings of the New Zealand Society of Animal Production, Volume 65, Christchurch, 236-240, 2005
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