Low birth weights affect productivity

Pig researchers are finding that birth weight can have significant impact on an animal’s reproductive performance in later life.

And that’s not all, said Mark Estienne, a Virginia Tech pig physiologist.

“The way the sows are managed in gestation can also impact future reproduction in the gilts that are farrowed by those sows,” he told producers attending Ontario’s London Swine Conference held in March.

Estienne described the need to increase sows’ longevity as one of the biggest challenges facing the hog production.

“Fifty percent, 60 percent of our sows on commercial farms are culled each year,” he said, calling the lack of longevity terrible.

“We have got to get that worked out.”

Ensuring an animal produces at a high level throughout its lifetime is another important goal.

Selecting for animals that produce offspring with higher birth weights and careful management may be ways to achieve both goals.

Estienne cited recent studies that show pigs with lower birth weights reach puberty later than their heavier counterparts. Low birth weight pigs (a condition referred to as intrauterine growth retardation) will also show more growth problems, have a more difficult time surviving and present more carcass and pork quality problems after slaughter, he said.

In contrast, research indicates that a greater percentage of pigs with a heavier birth weight will reach six farrowings and therefore live longer than those with a low birth weight.

Achieving higher birth weights, however, faces an unusual challenge. As pig litter size increases, the proportion of both individual piglets and whole litters born with low birth weights also increases.

Research, some as recent as in 2016, shows that 15 percent of sows will have litters with low birth weights.

The tendency to produce animals with lower birth weights can carry into future generations, he added.

A study from Virginia Tech also indicates poorer pre-weaning survival rates of litters produced by gilts whose dams were under heat stress during gestation.

Researchers hypothesize that “enhanced secretion of maternal cortisol” stimulated by the stress is to blame, Estienne wrote in the paper that accompanied his presentation.

Gilts born from stressed sows also showed delays in the age when estrus first occurred.

Even the use of crates has an impact. Results from a 2010 study showed that gilts reached puberty later if they came from sows that had been kept in crates throughout gestation, compared to those whose dams gestated in group pens or spent only the first 30 days after mating in crates.

Estienne noted several new technologies that also promise breeding productivity improvements.

Post-cervical artificial insemination cuts time and reduces the number of sperm cells needed compared to the more traditional intracervical artificial insemination.

A new product released in the United States that induces ovulation increases the probability of fertilization in some instances, reduces the number of artificial insemination treatments and consequently reduces the labour involved in insemination and predicting estrus.

There have also been improvements in farrowing rates and litter sizes through the use of frozen semen, he said, referring to one study that looked at data over four years from a 1,800-sow farm in the U.S.

But to capitalize on the new technology, the production unit has to change, he said.

“You’ve got to have an animal that fits the system,” he said.

“There is a lot of stuff that we still need to learn, that we still need to manage at the pig level in order for us at some point to be able to fully capture the benefits of these new reproductive technologies that have been developed and are going to be developed.”

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