Withdrawing feed just once before slaughter has little affect on net revenue from hogs and a positive impact on meat quality.

In a study by North Carolina State University (NCSU) for the National Pork Producers Council, a team of researchers investigated the impact of 0-, 12- or 24-hour feed withdrawal regimens in three, equal-sized marketing groups over a three-week period prior to slaughter. The first marketing group had feed withdrawn once at 0, 12 and 24 hours; the second group had feed withdrawn twice at 0, 12 and 24 hours; and the third marketing group had feed withdrawn three times at 0, 12 and 24 hours (Table 1).

Withdrawing feed one time at 0, 12 and 24 hours reduced hot carcass weight, but had little affect on fat or muscle depth, says the North Carolina research team. And the procedure produced improvements in color scores and color redness in the first marketing group.

In contrast, there were significant affects for 24-hour feed withdrawal in the second and third marketing groups. Reduced carcass weight where feed was withdrawn two or three times as compared to control groups appears to be the main factor in reducing net revenues from hogs.

Figure 1 illustrates carcass weight of pigs for 0-, 12- and 24-hour feed withdrawal and number of marketings for each of the three treatment groups. Researchers noted there was an interaction between the effect of length of feed withdrawal and carcass weights. The lightest carcasses came from hogs on the longest feed withdrawal and in the third marketing group, which had feed withdrawn three times. Prevalence of ulcers increased from the first to the third marketing group, leading researchers to conclude that the impact of chronic ulcers on growth of pigs may be greater than is widely believed.

To counteract the risks inherent in carcass contamination, the research team at NCSU developed some other objectives for the different feed withdrawal marketing procedures. Those included evaluation of gastrointestinal tract lesions, prevalence of salmonella at slaughter and prevalence and severity of gastric ulcers.

One theory going into the study was that withholding feed from pigs prior to slaughter decreases gastrointestinal contents and appears to reduce the risk of gastrointestinal spillage and thus carcass contamination. But feed withdrawal may produce some stress in itself and increase the number of pigs excreting salmonella organisms. Feed withdrawal could also have the effect of increasing the level of gastric ulcers.

Average ulcer scores differed for 0-, 12- and 24-hour feed withdrawal groups, but not significantly. As earlier results indicated, damage started to show up in the pigs that were marketed later and as the number of feed withdrawal treatments increased. Overall, prevalence of severe ulcers was 13.7%; 57.9% of chronic ulcers occurred in the third marketing group.

Prevalence of esophageal constrictions was 10.4%, with 66.7% in stomachs of animals from the third marketing group. The NCSU research team stressed that it appeared stomach damage was worse in the three-times treatment group, not related to the length of feed withdrawal.

Feed withdrawal treatments or marketing group had no impact on gastrointestinal lacerations.

Figure 2 depicts percentage of pigs with severe damage from feed withdrawal.

Tests revealed 62% of pig intestines were positive for salmonella at slaughter. The percent positive declined from the first to the last marketing group. As Table 2 indicates, there were no differences in positives for pigs with feed withdrawn once, twice or three times vs. their respective control groups that didn't have feed withdrawn.

The NCSU team says that 12- and 24-hour feed withdrawal before loading for slaughter didn't boost the percentage of intestinal samples testing positive for salmonella post-slaughter.

These findings support the hypotheses of others that the prevalence of salmonella in pigs in finishing pens doesn't correlate well to levels of salmonella at slaughter. Transport, holding pens at slaughter and close contact with other pigs are more likely factors linked to salmonella prevalence at slaughter.

The feed withdrawal study involved close to 1,100 nursery pigs assigned by weight, 30 head/pen.

Researchers: Morgan Morrow, DVM; Todd See; Joan Eisemann; Peter Davies, DVM; and Kelly Zering, North Carolina State University. Phone Morrow at (919) 515-4001 or e-mail morgan_morrow @ncsu.edu.