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Title: A phenotypic and genetic analysis of energy balance in dairy cows
Author: Coffey, Michael Peter
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2003
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In dairy cows, the failure or unwillingness to eat sufficient in early lactation when yield is high leads to a state known as negative energy balance (NEB). In this state, cows mobilise body tissue mostly in the form of body lipid in order to make up the difference in energy available from feed ingested and that required to sustain obligatory requirements, such as maintenance, and milk production. A large NEB is an undesirable state since it is associated with increased disease and reduced fertility. Body lipid content can be predicted from visual assessment of the tailhead of cows using a system known as body condition scoring (BCS). Changes in this score over time can therefore be used to predict body lipid changes. I investigated the feasibility of automating the process of collecting condition score using a digital camera and laser lights. The correlation between CS and shape over the tail-head was 0.55 suggesting that it may be possible in future to include digital images in an automated and integrated dairy farm management system. Using random regression analysis, I analysed changes in milk production, feed intake, liveweight and BCS over one to three lactations and calculated energy balance from these daily predictions. These analyses showed that energy balance can be predicted from body measurements without the need to measure feed intake making it practical to use nationally. Using these techniques enabled the genetic analysis of large volumes of field data to predict daily breeding values for energy balance for 1250 progeny test sires. Substantial genetic variation was found in energy balance profiles. The mean total daughter body energy loss at day 305 of lactation was 779 MJ (SD=224 MJ), equivalent in energy terms to about 189 kg milk. Future selection indices may contain an adjustment for the amount of body energy used to support the milk production of a bulls' daughters leading to a more complete assessment of the utility of a bull. Analysis of data from the Langhill Dairy Research Centre demonstrated that there are differences in the way dairy cows of differing genetic merit for production mobilise body lipid to support lactation and that the amount of concentrate fed also affects the recovery of lost body lipid. Select cows contained about 3200 MJ less energy than control cows at the end of the third lactation and lose and gain body lipid in a cyclical way. Parameters of these curves may be used in future selection indices to allow selection o f genotypes that have profiles of body lipid loss and gain commensurate with high yields and long herd life. This may also be useful in future when selection indices contain more traits and farmers and advisors tailor their management to suit the type of cow. It may also provide guidance on how future selection indices should be developed to incorporate traits such as body lipid, traits that enable the robust cow to thrive over many high yielding lactations.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available