<?=getCodeSnippet(45);?>The results were presented last month at the 2007 Focus on the Future Conference in Saskatoon.

Larger Litters Result in Lower Birth Weights

“Work has shown that, as the litter size increases, that is the number of pigs born per litter, we get a lot more of these very small birth weight piglets,” says Dr. Denise Beaulieu, a research associate with the Saskatoon-based Prairie Swine Centre.

“When I first started raising pigs in the 1980’s, eight born alive per litter was the norm. And today we would expect between 11 and half and 12 for the progressive North American producers with respect to born alive per litter," recalls Dr. James (Jim) Lowe, the director of health and production services with the Maschoffs, a Carlyle, Illinois based family farming operation. Dr. Lowe told those on hand for the conference, “Most of that trend is really being driven by genetic improvement.”

Increased Liter Size a Result of Genetic Selection

“Our genetics companies have done a fantastic job selecting for increased litter size. It’s a highly heritable trait. We’ve been able to select that across time and so we’ve increased the number of litters strictly by genetic selection,” he explains.

“As litter size gets larger average piglet weight in that litter actually decreases. Although the pounds of litter is increasing, the average weight per piglet is decreasing so that puts more pigs in our lightweight less than 800 gram category.”

Dr. Beaulieu told those attending the conference, “The PigChamp records would show us, in about the last five years, we have increased [the number born alive] by almost one piglet per litter. However we do have some herds, even in Saskatchewan, that are now targeting 30 piglets per sow per year.”

Research Examines Impact of Litter Size on Performance and on Carcass and Meat Quality

In an effort to assess the impact of this genetic improvement, scientists at the Prairie Swine Centre are looking at the effect of birth weight on growth performance and on carcass and meat quality.

“We want to see if these smaller birth weight piglets have a lower level of performance than their more average littermates,” says Dr. Beaulieu.

As well, she notes, “There’s been some work out of Germany that has shown that these very small birth weight piglets are actually born with a different type of muscle fibre. We know that at birth or shortly after birth the number of muscle fibres does not continue to increase so the increase in size of the pig has to be due to an increase in size of muscle fibres.”

“So we want to see if these smaller birth weight piglets whether or not there's any effect on performance [and] if there's an effect on the ultimate eating quality of the meat.”

To accomplish that scientists followed a number of sows measuring when they farrowed, litter size and the order of birth of the piglets.

“We divided our litters into small, medium or large litter sizes from about 3 to 10, 11 to 13 or 14 to 19 piglets born per litter,” says Dr. Beaulieu

From there the pigs were managed normally and, once they reached standard market weight, they were marketed through Mitchell’s Gourmet Foods in Saskatoon, which provided carcass quality data, or they were sent to the Agriculture and Agrifood Canada research centre in Lacombe for a detailed assessment of carcass and meat quality.

Lower Weight Piglets Start Slow But Catch Up

“During the nursery [phase] the smaller birth weight piglets, as expected, did indeed grow slightly slower. However, by the time they were at seven weeks postweaning, they had caught up and were growing as well as their higher birth weight littermates,” Dr. Beaulieu reports.

“Our conclusion would be that increased litter size did result in more small birth weight piglets. However we saw no overall effect on average daily gain. They did take about ten more days to get to market. That is because they start at a smaller birth weight.”

No Impact from Birth Weight on Carcass or Meat Quality

As well, the research showed no effect on carcass quality.

“We looked at the normal parameters that you would get back when you send the pigs to slaughter so things like millimeters of backfat, millimeters of loin, lean yield index, carcass premiums, those types of things,” says Dr. Beaulieu.

“We divided the piglets up by birth weight,” she explains. “From the very small, from about 800 grams, to about 1.5 kilos [and] we saw no effect on carcass quality.”

Although the evaluation of meat quality and taste is still underway at Lacombe, preliminary indications are there is no significant difference.

“Some of these measurements were done both by a taste panel, by trained taste panelists, and also using instrumental analysis and our overall conclusion would be that if there are any effects they are very minimal,” says Dr. Beaulieu.

“Preliminary analysis would indicate, overall, there certainly does not seem to be any effect on, for example, palatability. No effect on color. No effect on perceptible tenderness of the meat. The overall perception of the meat [was that] there was no effect.”

Lower Birth Weights Create Management Challenges

Although the research suggests these lower birth weights do not negatively impact ether performance or meat quality, they do present an increased challenge in terms of management.

Dr. Lowe notes that if they wean successfully they are O.K., but the data would suggest those pigs under 800 grams are 10 to 20 times more likely to die prior to weaning.

“Low birth weight pigs don’t have as much body mass. They tend to get cooler right after birth. That drop in body temperature leads to a reduction in colostrum intake, or the first milk intake, which really predisposes those pigs to preweaning mortality.”

Management Key to Survivability

“That’s where we’ve learned to be better in the farrowing house,” Dr. Lowe says. “It has a lot to do with getting those pigs started right which means getting them warm [and] there are several techniques for doing that.”

“Getting the heat lamp, or the alternate source of heat, is important but then there’s some other things we can do. Some of those include using survivability boxes which is a tub that we place a heat lamp or heat source over for 20 or 30 minutes to allow them to dry off. The other alternative is, which we use today because it’s less likely to spread disease, would be to use towels and dry these pigs off immediately after birth. [We] use one towel per litter so we don’t cross-contaminate and spread any diarrhea that can be there. That’s been very effective for us to get those pigs warmed. Get them rubbed off, get them back underneath the heat lamp and get them to get up and suckle.”

Limits to Genetic Improvement Still Unknown

Dr. Lowe notes, the controlled research still isn’t in place to be fully sure of the overall limits to genetic improvement.

“We do know that we’ve been able to maintain our pre-weaning losses to ten percent or less as we’ve increased total born. If you look at the research data larger litter sizes are certainly associated with higher preweaning mortality. We’ve not seen that trend as we’ve increased litter size so we think our management strategies are at least bucking the trend that we’d expect biologically with those lower birth weight pigs.”

However, he observes, “The Europeans, particularly the Danes, have selected very heavily on litter size for longer than we have. The typical Danish farm would be significantly above one to two pigs born alive better than the typical North American herd today which probably shows us what the genetic potential is today.”

He concedes, “We think there’s probably some biological maximum. Her uterus is only so big. But we said that 20 years ago when we had eight per litter. So I think we certainly could look at that 13 to 14 born alive routinely if we can continue to have the genetic improvement, the management capabilities.”

Dr. Lowe stresses, “It’s all about people. And so it is about people taking care of the pigs every day. That sounds simple and it sounds a little bit homey but it’s having a thorough understanding, by the guy that does the work or the lady that does the work every day, of what their job is and how it’s important their job is to the process. That’s absolutely critical.”

April 2007