Walking the fine line when restricting feed before slaughter

Monday, October 6, 2014

U.S. research indicates that, while feed withdrawal offers savings in feed costs, it shouldn't exceed 24 hours in order to maximize pork quality

by JANICE MURPHY

Feed deprivation in finishing pigs is inevitable prior to slaughter, considering the time spent in transit and in lairage. Withdrawing feed prior to loading on the truck reduces intake and saves on the cost of expensive feed. Further benefits are realized since pigs are not travelling with a full stomach, which can make them easier to handle and less likely to experience transport sickness. Fasting also reduces gut fill, which decreases the likelihood that the carcass will be contaminated inadvertently during evisceration and ultimately minimizing waste at the packing plant.

Research has also proven that feed withdrawal before slaughter improves pork quality by reducing muscle glycogen levels at the time of exsanguination, resulting in a higher ultimate pH, lower drip loss and a decreased likelihood of pale, soft and exudative (PSE) pork.

However, producers must walk a fine line when it comes to feed restriction since extended periods, greater than 24 hours, can cause increased pig aggression, resulting in skin and carcass damage. Feed restriction beyond 18 hours may also result in excessive shrinkage and increase the risk of dark, firm and dry (DFD) pork.

Due to the long list of potential negative effects of excessive feed withdrawal, recommendations for feed withdrawal times currently range from eight to 24 hours. To date, little research has been done to evaluate the economic implications of increasing feed withdrawal prior to slaughter. Researchers at Kansas State and Iowa State universities recently performed two experiments to examine the effects of varying feed withdrawal length on weight gain, carcass characteristics and measures of food safety.

In Experiment 1, 728 pigs (128.9 kilograms) were allotted to one of four treatments with feed withdrawal times of eight, 24, 36 or 48 hours and 12 replicate pens per treatment. Prior to feed withdrawal, pigs were fed a standard corn-soybean meal diet containing dried distillers grains with soluble (DDGS), bakery co-products and five milligrams per kilogram of ractopamine HCl.

In Experiment 2, 843 pigs (125.4 kilograms) were used to determine the impact of feed withdrawal on growth, carcass characteristics and meat quality. There were four treatments with feed withdrawal times of eight, 12, 24 or 36 hours and 10 replicates per treatment. In this study, pigs received a common corn-soybean meal–based diet containing 20 per cent DDGS and five milligrams per kilogram of ractopamine HCl.

Both trials were conducted at commercial research finishing facilities in southwestern Minnesota. At the end of the finishing phase, pigs were transported 95 kilometres for slaughter at a commercial abattoir in Minnesota, spending approximately two hours in transit. This time period was included in the respective treatment durations in both experiments.

The results for Experiment 1 are summarized in Table 1. Pigs that experienced increased periods of feed withdrawal were significantly lighter at load-out and at the abattoir, resulting in a larger weight change from 48 hour pre-slaughter up to unloading and weighing at the abattoir. This effect was most drastic beyond 24 hours of feed withdrawal. Feed withdrawal time also significantly decreased hot carcass weight (HCW) and backfat depth, while significantly increasing percentage yield and fat-free lean index (FFLI). Withholding feed significantly decreased feed intake per pig marketed, resulting in increased feed savings of over five kilograms per pig from eight to 48 hours.

The results for Experiment 2 are summarized in Table 2. As in Experiment 1, withholding feed significantly decreased live weight, resulting in decreased HCW. Unlike experiment 1, there were no differences in FFLI or backfat, but percentage yield increased significantly with longer withdrawal times. Withholding feed significantly increased 45-min pH, ultimate pH and visual marbling score while blood lactate, visual colour score and purge loss were unaffected. Withholding feed significantly decreased feed intake, this time resulting in feed savings of up to three kilograms per pig.

The results of both experiments showed that feed withdrawal time increased carcass yield – by two per cent at 48 hours in Experiment 1 and 1.8 per cent at 36 hours in Experiment 2. This type of increase is likely linked to the decrease in overall viscera weight, particularly gut fill and liver weight. Liver weight in particular, has been described by previous researchers as occurring rapidly over the first 24 hours and then stabilizing once the liver reaches approximately 80 per cent of initial unfasted weight.

In Experiment 2, measurements were also captured for carcass contaminations by stomach contents escaping from the oral cavity after shackling (leaking ingesta) or visible fecal contamination of the exterior of the carcass (runny bung). Feed withdrawal time did not affect runny bung, but it significantly increased the incidence of leaking ingesta. The greatest effect was seen in the 36-hour treatment, where 19.6 per cent of pigs in each pen exhibited leaking ingesta compared to only 3.2 per cent in the control group. Visible leaking ingesta is a major concern, since it is a criterion for head condemnation and results in a loss of approximately 2.5 per cent of the overall carcass value.

The data from these experiments indicate feed withdrawal times should not exceed 24 hours in order to minimize HCW loss and the impact on carcass composition while maximizing pork quality. Feeding patterns are an important consideration; since feed intake is typically lowest overnight, loading pigs early in the morning may capture some of the benefits of feed withdrawal in the time period below 12 hours. A major concern with feed withdrawal times exceeding 12 hours is the incidence of leaking ingesta. However, the researchers suggest that additional research is needed to determine the true impact of this issue on condemnations and carcass value. BP

Janice Murphy is a former Ontario agriculture ministry swine nutritionist who now lives and works in Prince Edward Island.

Source: H.L. Frobose, S.S. Dritz, M.D. Tokach, K. J. Prusa, J.M. DeRouchey, R.D. Goodband, and J.L. Nelssen. 2014. Effects of pre-slaughter feed withdrawal time on finishing pig carcass, body weight gain and food safety characteristics in a commercial environment. J ANIM SCI
92:3693-3700