Management decision rules (‘old’ rules) have been used at the Dexcel No. 2 Dairy Farm to remove subjectivity from the management of farm systems research and have also been promoted to the dairy industry. A trial involving these rules where three strains of Holstein-Friesian (HF) cows were compared has completed its third season. The trial included two high breeding worth (BW) strains of either North American (OS90) or New Zealand (NZ90) genetics, and one low BW strain of NZ genetics (NZ70). Under the ‘old’ rules the OS90 cows had fewer days in milk than the other two strains, mainly because they were dried off earlier due to their lower body condition score (BCS). In the third lactation ‘new’ rules were applied that allowed cows at the higher feed allowances to be dried off later (but at the same BCS) than would have been allowed under the ‘old’ rules. For the herds receiving the higher feed allowances, this change resulted in increased days in milk (NZ90 + 2 days; OS90 + 17 days) more milksolids (MS) per cow (NZ90 +2 kg; OS90 +21 kg), and more feed required (NZ90 + 10 kg; OS90 + 157 kg DM/cow) with all herds reaching target BCS by their next calving. It is calculated that this reduced the difference in economic farm surplus (EFS) per ha between the NZ90 and OS90 from $488 to $219. These results indicate the need to alter management rules to get the best performance from North American HF genetics. KEYWORDS: Holstein-Friesian; body condition score; drying-off decision rules.
Proceedings of the New Zealand Society of Animal Production, Volume 65, Christchurch, 40-45, 2005
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