New Opportunities for Reproductive Management

In examining data from a large database (Pig Champ® and Pig Champ, Inc., 2007) Dr. Flowers concluded that females are most likely to leave the herd during entry to first service and weaning-to-service after their first lactation. The situation with boars is somewhat different. Most boars in North America are replaced at 12-18 months after they enter production (Knox et al 2007).

This relatively short usage period is related to the need to maximize genetic improvement and typically is independent of a boar's performance. Even outstanding boars would be culled to make room for the next generation.

Both types of culling limit the reproductive efficiency of swine herds. For sows this type of culling creates a situation in which the majority of females are replaced before they reached their peak biological period of productivity, which typically occurs between parities three and six.

For boars, voluntary culling occurs during a period of time when their semen production and fertility is still increasing and also before it has reached optimum levels. From a management perspective, meat producers are forced with two different situations: one in which the longevity or productive life of sows needs to be increased; and another in which the output of boars needs to be increased during a relatively short period of time.

Most who have attempted to address these productivity issues have focused on the management of adult sows and boars, and often produce equivocal results on commercial operations (Flowers 1997; 1998). The observed variation in results with most of these intervention strategies suggests that they may be simply correcting problems inherent in and unique to a given production environment.

Dr. Flowers continues in his presentation that from a physiological perspective, important developmental events occur in both gilts and boars shortly after birth. These events establish the reproductive tools that animals have to work with as adults. In females, the number of egg nests and the formation of follicles in the ovary (Morbeck et al, 1993) and the size of the uterine endometrium (Bartal et al, 1993) increase during the first few weeks after birth. These are important observations because it means that there is a period of time shortly after birth during which management conditions have the potential to affect the number of eggs that sows can ovulate each time they are in estrus, and the number of fetuses that their uterus can maintain each time they become pregnant as adults. Similarly, the cells in the testicles and secondary sex glands that are responsible for the production of sperm and seminal fluids undergo two periods of rapid development (MaCoard et al, 2003). The first occurs during the first three weeks after birth and is thought to be the most critical for adult reproductive function. Consequently, the manner in which both potential replacement boars and gilts are managed early in life may present new opportunities for reproductive management.

The primary objective of this paper is to present some relatively new information with regards to how management early in the lives of gilts and boars can influence their reproductive performance as adults.

Experimental Method

I will briefly describe the method used by Dr. Flowers to conduct his study on gilts and boars. The study was done within an 80,000 sow unit that uses "in-house" gilt multiplication. Replacement gilts were divided at birth into two litter groupings: one ≥ 7 pigs and one ≥ 10 pigs and placed on sows. Each of these groups were further divided and half were exposed to boars at 140 days of age and half to boars at 170 days of age. Currently all of the gilts that went through this process remain in the herd and have just weaned their third litter. The result of this study clearly indicated that the neonatal environment, and the age at which puberty stimulation occurs has a significant influence. Based on estimations presented in Dr. Flowers work simply limiting the lactational litter size of future replacement gilts to seven piglets or less would increase the lifetime productivity of each sow that enters production by 3.3 pigs through three parities or roughly by 1.1 pigs per litter. A similar improvement of three pigs would be expected by providing boar exposure at 140 days of age. If both strategies were employed effectively then one would expect an improvement of six pigs per female over three parities or about two pigs per litter.

A.I. Boars

In the boar portion of the study, boars were separated at birth into litters of 6, and 9 or more. Litters were weaned at 18 days of age and managed according to normal industry standards through nursery and finishing phases. The only exception was that boars were allowed 4 and 10 square feet of floor space during nursery and finishing phases. At five months of age, boars were removed and placed in individual crates. At 5.5 months of age boars were trained for collection with a dummy sow and were collected once per week until they were at least two years of age.

The overall training period was significantly less (10 days) for boars from small litters, compared to 30 days for larger litters. These dates indicate that boars raised in small litters (six or less) had greater libido than boars raised in litters of nine or more. Boars raised in small litters also had increased testicular size at relatively young ages compared with boars raised in large litters. Numbers of spermatozoa per ejaculation are also greater in boars raised in small versus large litters. No significant differences among treatments in motility, morphology, acrosome morphology, acrosin activity or capacitation status were observed. Boars raised in small litters appear to be more fertile then boars raised in large litters.

Conclusion

Management of future replacement gilts and boars has a significant impact on their reproductive capabilities as adults. Strategies that reduce competition and enhance growth during the first three weeks of life positively affect the longevity and prolificacy of sows and the numbers and fertility of spermatozoa produced by boars. Reduction in the number of piglets in which replacement gilts and boars are raised is one such strategy that appears to be effective from both a practical and biological perspective.

Presented by Dr. William Flowers, North Carolina State University
Summarized by Ed Barrie - Swine Sow Nursery Specialist/OMAFRA
Published at the Ontario Ministry of Agriculture, Food and Rural Affairs website
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_{See the 2008 London Swine Conference Proceedings for references.}

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New Opportunities for Reproductive Management