An evaluation of traits other than production and its association with the survival of dairy cows milked once a day in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of AgriScience at Massey University, Palmerston North, New Zealand
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Date
2017
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Massey University
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Abstract
New Zealand dairy cows have traditionally been milked twice a day (TAD). However, an
increasing number of dairy farms have shifted to once a day (OAD) milking in the last few
years for several reasons. A particular emphasis has been placed on the cow’s conformation
and its management during the milking routine in OAD dairy farms, as these factors might
have altered the culling decisions of herds after shifting from TAD to OAD milking. This thesis
evaluates production traits and traits other than production (TOP) in the herd of Massey
University Dairy 1 since the start of OAD milking and for three consecutive seasons (2013-
2015), with an assessment of the influence that these traits have on the cow’s survival. Results
showed a significant effect of breed, season and lactation on TOP. The scores for most udder
traits showed a gradual decrease over lactations. The main reasons for culling were low fertility
(37.2%), poor udder conformation (19.9%) and low production (12.8%). Hazard ratios from a
Cox proportional hazard model showed that Holstein-Friesian and crossbred cows had a higher
likelihood of culling than Jerseys, which also had the highest scores for most udder traits. For
some TOP, such as adaptability to milking, rump angle and udder support, higher scores were
associated with a lower likelihood of culling. However, intermediate scores were optimum for
traits such as body capacity and leg conformation. The results of this thesis are the first to show
culling reasons and risk factors for survival in cows recently shifted from TAD to OAD. The
analyses of TOP over seasons and over lactations are also unique to this thesis as most studies
on this topic only include TOP on first lactation cows. The findings of this thesis indicate that
TOP would have a higher priority to make culling decisions in OAD herds during the transition
from TAD to OAD milking, compared to TAD herds and also established OAD herds that have
used this milking frequency for several seasons. Furthermore, besides body capacity and udder
support, traits such as adaptability to milking, rump angle and leg conformation could also
potentially be included in a new selection index for OAD dairy cattle.
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Keywords
Dairy cattle, Milking, New Zealand, Research Subject Categories::FORESTRY, AGRICULTURAL SCIENCES and LANDSCAPE PLANNING::Animal production