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Factors associated with oestrous expression in dairy cows - AC0220

Description
Pregnancy failure or delay reduces the lifetime milk yield of cows and thereby increases the environmental footprint of dairy systems. Pregnancy depends not only on conception rate, but also on heat (oestrus) detection. If oestrus cannot be detected accurately, then a high proportion of cows will either not be inseminated at all, or will be mated at a time when they are unable to conceive. Heat detection rate has been declining for many years in the UK, as in other countries, and is currently about 50%. Coupled with an estimated pregnancy rate of 40%, this means that only 20% of ovulations actually result in the birth of a calf: 80% of opportunities are missed.

We have shown in our recent study for Defra (AC0205) that strength of oestrous expression varies considerably among cows. Some of this variation was explained by genetic markers (SNPs). A significant implication of these findings is that animals might be selected for stronger expression of oestrus using these markers. The mechanisms controlling expression of oestrus are poorly understood but, as shown in our fertility work, understanding of physiological mechanisms provides new insights leading to more robust solutions.

Expression of oestrus is driven primarily by oestradiol production just before ovulation. Consistent with this we have identified a SNP in the oestrogen receptor alpha promoter (SNP173) which initial analysis suggests is associated with activity at oestrus. In the proposed 6-month study we will extend our investigation of genetic markers associated with oestrogenic effects.

During oestrus dairy cows, like many species, produce pheromones. These volatile organic compounds cause behavioural reactions in other cattle and have been identified in saliva and urine from cows during oestrus. There is little information in the literature on pheromones produced by cattle. In the longer term we will investigate levels of these compounds in cows exhibiting different strengths of oestrous activity. As an initial objective we will investigate methods to collect pheromone samples from individual cows around the time of oestrus, using gas sampling.

The work will provide much needed information on plysiological factors that influence the strength and duration of oestrous expression. This information will have immediate application in developing strategies for better oestrus detection and, in the long term, possible genetic selection of cows for increased expression of oestrus. A significant output of this project will be DNA samples for genome-wide scanning in a future large collaborative programme. Together, these applications will help to reduce the unsustainable wastage of cows that currently contributes to the high environmental footprint of dairy systems.
Objective
The overall aim of the project is to investigate genetic markers associated with strength of oestrous expression and changes in pheromones associated with oestrus.

Objective 1 – to extend our database of genotyped cows to find further animals with the oestrogen receptor alpha SNP. Between 50 and 150 cows will be sampled for whole blood for genotyping at 17 previously identified loci.
Objective 2 – to investigate the possible significance of the oestrogen receptor alpha SNP 173 by determining whether the relevant DNA sequence is transcribed, and appears in messenger RNA.
Objective 3 – to carry out preliminary experiments to develop and test methods for pheromone collection from dairy cows.

Because the duration of the project is only 6 months, it is not appropriate to allocate a shorter timescale to any individual objective. All objectives will be ongoing and concurrent throughout the project period, with a milestone of 6 months.
Project Documents
• Final Report : Factors associated with oestrous expression in dairy cows   (778k)
• Summary Report : Factors associated with oestrous expression in dairy cows   (38k)
Time-Scale and Cost
From: 2009

To: 2010

Cost: £75,355
Contractor / Funded Organisations
University - Nottingham
Keywords
Agriculture and Climate Change              
Dairy              
Livestock              
Renewable materials              
Sustainable Farming and Food Science              
Fields of Study
Agriculture and Climate Change