Industry Partners

Prairie Swine Centre is an affiliate of the University of Saskatchewan

Prairie Swine Centre is grateful for the assistance of the George Morris Centre in developing the economics portion of Pork Insight.

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Author(s): Peet, Bernard
Publication Date: January 1, 2007
Country: Canada


Since the early 1990s, the application of genetic selection for litter size has led to an increase of up to 3.5 pigs per litter at dam line nucleus level, with the largest improvements shown in the French and Danish breeding programs. This has translated into the potential for a total litter size born of 15 or more piglets, providing the possibility for commercial producers to wean more than 30 pigs/sow/year (psy). However, there are a number of disturbing negative aspects of the rush towards increased sow productivity, which have implications for the sow and also her progeny’s health, growth, efficiency and carcass quality. Foxcroft (2007) described the phenomenon of pre-natal programming, and suggested that the large increase in ovulation rate in modern, higher parity, sows leads to uterine crowding, intra-uterine growth retardation in the embryo and foetus and a reduction in muscle fibre numbers. In practice, this leads to a number of problems, including lower immune status (Harding et al., 2006), and slower growth and poorer carcass quality in pigs from litters with a low average birthweight (Foxcroft et al., 2007). The other negative change that has taken place is that sow death rates have gone up significantly, especially in North America (Peet, 2005b). While the reasons are complex, there seems no doubt that the greater nutritional and physical strain on the sow as a result of the increased productivity is a major factor. Also, the decrease in gilt and sow backfat levels as a result of selective breeding for leaner, fast growing and efficient pigs, means that they have less tolerance to deficiencies in management, environment and nutrition. Lean animals are more prone to physical injury, which may lead to culling. Another factor is the intensification of production systems leading to harsher conditions, which are more likely to lead to injury, combined with a lack of suitable hospital facilities to deal with sick, injured or disadvantaged gilts and sows. The focus of management should be to nurture the gilt and second parity sow so that she reaches the highly productive 3-6 parity stage, thereby increasing average sow longevity. Foxcroft et al. (2007) reviewed information indicating that when high numbers of developing embryos implant in the uterus early in gestation (up to day 30), those that survive to term develop into compromised pigs with reduced growth potential. Piglets from litters with low average birthweight are all compromised, regardless of their relative birthweight within that litter. There are two aspects of dealing with this situation in respect to the gilt and sow. The first is to improve the nutritional status of the female in order to increase the nutrient supply to the developing embryos. The second is to improve the size and quality of the follicles released in order to reduce the “pre-natal programming” effect. Both of these will help to improve the quality of the piglet born and its growth potential. Herds with very high litter size tend to have a disproportionately high number of stillborn piglets, which is likely due to a lack of thriftiness caused by pre-natal influences. Therefore, close monitoring of farrowing, and management measures to reduce stillbirths, have become essential in herds with high numbers born. This will also lead to a reduction in post-farrowing piglet deaths by increasing piglet viability. Also, measures to increase survival, such as drying piglets off after birth, assisting them to suckle and placing them under a heat source, will be especially helpful to low birthweight litters. There is a wide range of nutritional and management strategies that can be used to counteract these potential problems. However, further work is required to understand the implications of higher litter size for management systems after weaning and the comparative economics of managing pigs based on their average litter birthweight or according to individual body weight.

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