Pork producers and managers commonly give sows a subjective condition score based on their apparent level of “fatness.” This score is used to guide how a sow is fed in gestation.
Problem is, the push toward leaner genetic lines has created compositional changes in popular sow lines that aren't readily apparent.
Indiana swine practitioner Tom Gillespie began addressing the sow conditioning issue about two years ago. After purchasing a Renco ultrasound machine, he began measuring backfat depths on select sow herds. After considerable sampling of several different genetic lines, Gill-espie soon verified that modern-day sows were generally much leaner than he or his producer-clients thought.
Early into his crusade, the Rensselaer, IN, veterinarian ran across some research by Frank Aherne, swine nutritionist at the Alberta (Canada) Pork Research Centre. Widely recognized for his sow nutrition work, Aherne was also studying the effectiveness of condition scoring.
In a June 2001 report, Aherne also challenged popular thinking and the oft-cited research data supporting the idea that sow “fatness” and visual scoring serves as a good guide to the metabolic status and lifetime performance of sows. Some guides rely solely on visual appraisal, while others combine a visual appraisal with palpation of the hipbones to arrive at a condition score.
Aherne chose a popular 1- to-4 scoring guide with sketches of four example sows, ranging from very thin to obviously fat. Producers using this scoring system generally aim for a condition score of 2.5 to 3, adjusting gestation feed to hit that goal.
Like Gillespie, Aherne was dubious about the ability to accurately judge sow condition using these subjective scores. He also selected a Renco ultrasound machine to test the validity of the assumptions being made while scoring sows. These assumptions include:
Condition scores accurately reflect overall fatness of the sow.
Those doing the scoring can assign scores consistently over a wide range of animals and over an extended period of time.
Those assigning scores generally agree about various degrees of condition.
There is a logical basis for assigning feeding levels based on specific condition scores.
Aherne tested these assumptions on three different farms over a 12-month period. Backfat depths were measured at the commonly accepted position known as “P2.” This position is easily found by locating the last rib, moving perpendicular to the spine, then moving 2½ in. down to pinpoint the P2 location.
In Aherne's trial, two pairs of evaluators scored the same sows for condition to check their consistency of scoring. One evaluator in each pair was also tested for consistency of scoring over time.
Aherne's concerns were confirmed. Backfat levels measured ultrasonically varied widely within each condition score. “This data indicates that, although condition scoring may reflect the shape of the sow, it does not accurately reflect the backfat level of the sow,” he reports. Other conclusions included:
Evaluators assigned different scores to the same sows.
Evaluators were not consistent in assigning scores.
There was no scientific basis for assigning feeding levels to a particular condition score.
Small differences in daily feed allowance of gestating sows led to large differences in the weight gain and backfat levels of sows.
Aherne's results confirmed what Gillespie was seeing. Not only were the scoring procedures inaccurate for estimating condition, they served as a poor guide to managing feed intake during gestation.
Over the past two years, Gillespie has introduced the backfat/conditioning initiative to about half of his client herds. Gillespie believes that with a concerted effort, a six-month commitment to measure backfat is adequate for this retraining process. Periodic, random measuring will help keep this ability sharp.
He begins by sampling 30-40 sows across all parities. Measuring all sows being moved to one or two farrowing rooms works well. He then graphs those backfat measurements for a clearer picture of the range of backfat levels in the herd.
“That usually gets their attention, because the sows are usually a lot leaner than they perceive them to be,” he says. “It takes a little time for them to accept that the sow they used to call ‘fat’ is really an ‘average’ sow today.”
Some producers find that if they palpate over the sows' hipbones, they can also develop a “feel” for the amount of cover there. Gillespie suggests 0.7-0.8 in., last-rib backfat as a good target.
The next step is to measure the same sows when litters are weaned. Gill-espie's goal is to minimize backfat loss during lactation to under a tenth of an inch, across all parities.
Full-Cycle Sow Feeding
As producers gain a better understanding of condition levels in their herds, Gillespie introduces them to a gestation-feeding program that also has “desired” backfat levels (see Figure 1). He feels strongly that feeding in gestation has a great deal to do with how well a sow eats during lactation, and consequently, how much backfat will be lost.
“The key is trying to be a little more aggressive in feeding during early gestation,” he says. “Let's get their body condition recovered, then maintain it.”
Gillespie suggests feeding 4 to 5 lb./day for a week after first service. Then, for the next 60 days, bump feed to 8 lb./day. On Day 65, drop back to 6.5 lb./day, or maintenance levels, depending on body condition and environmental conditions. Maintain that level until farrowing.
“Many nutritionists agree that we need to feed about 7,000 Kcals of ME (metabolizable energy) per day for the modern sow. That compares to 6,000 Kcals/day recommendations just a few years ago,” says Gillespie. “It varies according to individual and parity, of course.
“No matter what condition a sow's in, the last couple of weeks [of gestation] she starts to allocate resources to her mammary and reproductive systems. If she's too lean, she either cannot allocate enough [resources] or something gives — in either her or the pigs,” he says.
In one field trial, Gillespie measured last-rib backfat on 325 sows before they farrowed, covering a 13-week stretch in late spring and early summer 2001 (Figure 2).
Gillespie used the P2 positioning to get consistent backfat readings on sows entering the farrowing crates and again when litters were weaned. The P2 position was identified with a permanent marker, thereby insuring the backfat reading was taken at the exact same place both times.
Eliminating the first seven sows because of their extremely low backfat readings (.28-.35 in.), Figure 2 shows that as backfat increased, so did the likelihood that sows would return to estrus by the fourth day after weaning.
Gillespie uses the wean-to-first service interval as another indicator of whether sow condition is being misjudged. A review of this herd's reproductive records showed a general trend — 40% of sows were bred on Day 4 (after weaning), 35% were bred on Day 5 and 10-12% were bred on Day 6.
This herd had averaged 20-22 pigs/mated female/year in recent years. After greater attention was paid to backfat levels, their average crept up to 23 pigs/mated female/year.
Gillespie knows from experience that attention to backfat levels and fine-tuning producers' abilities to see sow condition will pay dividends. As sow condition improves, pigs per mated female will edge upward, and culling and mortality rate should decline. “If we learn to feed sows to improve their overall condition, who knows what the modern sow can do?” he concludes.