Effects Litter sizes, sow housing and stress can affect how sows’ and boars’ reproductive organs develop
The North American pork industry is increasingly focusing on sow lifetime performance as a key goal for the breeding herd rather than pigs weaned per sow.
After all, if high replacement rates and moderate lifetime productivity can be improved, the cost of producing piglets will be reduced.
This was the theme of the recent Swine Breeding Management Workshop held at the University of Alberta, at which a panel of specialists from both Canada and the U.S., presented the latest research findings and practical experience.
One relatively new area of study is the impact of early life experiences on the productivity of the gilt through her breeding life and also the impact on the boar. Not only does this include the suckling and rearing phase, but also the embryonic and fetal stages of development.
Dr. Mark Estienne, from Virginia Tech in the U.S., described some of the effects that may influence gilt and boar performance.
“A growing body of evidence supports the notion that the maternal environment in which a gilt fetus develops plays an important role in the development of the reproductive and other physiological systems,” he says. “If you put stress on the female during its development, it can affect development of the reproductive organs, which won’t be evident until much later in life.”
The impact of the uterine environment has become a lot more relevant in high-litter-size females because some embryos may suffer from intrauterine growth retardation (IUGR) due to insufficient uterine capacity. Piglets in these low-birth-weight litters will have underdeveloped reproductive organs, compared to those in high-birth-weight litters.
“Low-birth-weight boars may have poorer reproductive performance at sexual maturity and preliminary evidence from our laboratory supports this hypothesis,” Dr. Estienne said.
He recently found that the birth weight of boars that were impossible to train for semen collection were lower than those that could be trained. Also, the low-birth-weight boars had lower sperm concentrations and total sperm per ejaculate than those classified as high birth weight. IUGR also impacts follicular development in gilts and the onset of puberty.
One of Dr. Estienne’s studies showed that age at first standing estrus was negatively correlated with birth weight. Stress during the gestation period is another factor that affects the fetus.
“A study in which sows were stressed by restraining them daily for five minutes during weeks 12-16 of gestation looked at how this impacted the onset of estrus in female offspring,” he said. “Age at first estrus was significantly delayed in gilts farrowed by stressed sows (average 172 days) compared to gilts farrowed by control females (average 158 days).”
The type of sow housing used in gestation can also influence growth performance of the sow’s offspring and their onset of puberty. Dr. Estienne and his team compared the progeny of sows housed in pens, stalls or stalls for 30 days after breeding, followed by stalls for the remainder of gestation.
“In our study, fewer gilts farrowed by females kept in crates throughout gestation reached puberty by 165 days of age compared with the other two groups,” he points out.
Research from nearly 40 years ago compared the performance of gilts reared in litters of six with those in litters of 12. “At 25 days post-mating, the gilts from small litters had more embryos than those from litters of 12 pigs,” notes Dr. Estienne. “Moreover, through three parities, sows raised in litters of seven pigs or less were less likely to be culled and had higher farrowing rates and larger litters than sows raised in litters of 10 or more pigs.”
Another study showed that boars raised in litters of six pigs or less reached puberty sooner and produced more sperm cells per ejaculate compared with boars raised in litters of nine pigs or more. “This all suggests that lactation litter size can impose some type of stress that negatively impacts future reproduction of the suckling pigs,” he said.
Environment and management during the rearing phase also influences subsequent reproductive performance. “Inadequate floor space during the grow-finish stage has been shown to affect the onset of puberty,” he said. “Also, one trial which compared gilts reared in pens of eight or 16 animals showed that females reared in the smaller groups ultimately farrowed one more pig per litter than gilts reared in the larger groups.”
Crowding during the nursery phase appears to have a significant impact on reproductive performance. “In one study, gilts kept in pens of 16 during a five-week nursery period subsequently farrowed 1.25 live pigs less during Parity 1 and 3.5 live pigs less during Parity 2, compared to gilts kept in pens of eight in the nursery,” Estienne said.
“Another study also showed the bigger impact of crowding on second-parity performance. These studies demonstrate that the potential detriment increases in Parity 2 after the female has experienced the normal rigours of the Parity 1 lactation.”
Clearly there are some significant effects of conditions in the uterus and in the early development of breeding boars and gilts on subsequent reproductive performance, in addition to those during the rearing phase. A better understanding of these factors will help to develop future management strategies that will contribute to higher lifetime performance.
“Research will continue to identify prenatal or early-in-life stressors and to develop management strategies for mitigating adverse effects on reproduction and increasing sow longevity,” concludes Dr. Estienne.