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Seasonal Infertility in the domestic pig; database analyses to evaluate factors responsible - LS3307

Description
The two major manifestations of seasonal infertility in domestic pigs are low litter sizes in those animals conceiving in summer and late returns to oetrus. The latter of which may be a result of poor embryo survival leading to loss of pregnancy and an eventual return to oestrus (giving an oestrus to oestrus interval considerably longer than a normal cycle). It would appear that weaning to service intervals (whether resulting in conception or not) are of less importance. This suggests that the problem lies with ovulation / fertilisation / embryo and fetal survival. It is difficult to calculate the economic cost to the UK pig industry of the problems of seasonality; recent trade reports and discussions with the Meat and Livestock Commission have suggested that the figure is just over £5 million; based on an assumed UK outdoor sow population of 150,000 and a cost of £35/sow/annum. This does not include further problems associated with reductions in regularity of supply of finishing pigs as a consequence of lower than anticipated pig placements which would impact negatively both on producers and abattoirs.

There have been numerous extensive reviews of this subject published in the literature in recent years ranging from assessments of breeding activity in closed populations of the European wild pig to detailed physiological studies which have attempted to examine endocrinological patterns in response to changes in daylength, exogenous treatment (e.g. administration of melatonin), nutrient inputs, impact of ambient temperature and interactions between these, and other, factors; seasonal patterns in the boar (as evidenced by, for example, changes in semen quality and libido which are not thought to be influenced by those ambient temperatures normally encountered in the UK) are also important. A ‘boar’ effect in expression of seasonality in sows is also possible. All these investigations have been based on an assessment of phenotypic differences only.
It is considered by many that the problem of seasonality in domestic pigs, particularly those maintained outdoors, is related to the Wild pig from which the domesticate is derived. This suggests a genetic component to the problem as seasonality is not normally a selection trait in breeding programmes (selection for high prolificacy is concerned more with litter size). Indeed there has been a programme at Manchester / Roslin designed to locate markers linked to gene(s) responsible for seasonality. However, magnitude of genetic variation in addition to the underlying physiological mechanisms governing seasonality remain to be adequately defined.

It would appear that defining the extent of the problem is a fundamental initial step in any investigation. In addition, and bearing in mind the possible genetic component of seasonality, analyses of data should involve estimation of genetic and environmental effects as well as phenotypic effects. It is this complete analysis that has been essentially absent from previous studies. Cotswold Pig Development Company Ltd. have agreed to release the company database for the purposes of the programme. Records cover individual indoor sow performance (on a time basis - units of a week are straightforward) of 3 separate lines each of between 800 and 1500 breeding sows housed within 2 to 4 units. In addition to allowing an assessment of the phenotypic extent of the problem of seasonality by examining reproductive performance in individual sows, the data will also allow boar reproductive traits to be examined.

This represents an extremely powerful data set of enormous value, particularly as management practices are moderately uniform which would minimise an important but unquantifiable variable in analyses of herd data. It is for this reason that commercial units have not been contacted at this stage, although a major pig operation in Scotland with over 7000 outdoor sows is also prepared to release data. It should also be borne in mind that most commercial units with AI use mixed semen samples, thus an analysis of boar line effects would not be possible. Furthermore, records on most commercial units are not adequate for the purposes of the proposed study.

Thus the objectives of the programme are to establish the biological nature of the problem of seasonality (as analysed on a weekly rather than quarterly basis) based on litter size, returns to oestrus, farrowing rate, individual animal response, boar fertility and possible interactions with herd health; all analyses are to include a multi-generation pedigree component for sows and boars. The data set from Scotland is also available which will also be included in the analysis.

Seasonality in pig reproduction is a problem, which DEFRA recognises.
Analyses of data available would provide a particularly robust assessment of
the factors responsible, including genetic, and may inform future research priorities in reproductive physiology; Cotswold have indicated that they are prepared to support publication of any results both to the industry and in scientific journals. An economic analysis is also planned to identify the consequences of seasonality.
Objective
1. Cleaning up, preparation and amalgamation of breeding data provided by a large Scottish operation and Cotswold Pig Development Co Ltd.
2. Comprehensive phenotypic and genetic analyses of breeding data
3. Marginal cost assessment
4. Preparation of final report to DEFRA

The time allocated to the project is 18months.
Project Documents
• Final Report : Seasonal Infertility in the domestic pig; database analyses to evaluate factors responsible   (211k)
Time-Scale and Cost
From: 2002

To: 2005

Cost: £140,802
Contractor / Funded Organisations
University - Nottingham
Keywords
Farming              
Livestock Farming              
Pigs              
Reproduction              
Fields of Study
Livestock