Feed withdrawal of less than 36 hours prior to slaughter can be an effective tool to maximize carcass value by reducing market hog weights, saving producers unnecessary feed costs. But increased feed withdrawal time caused losses up to $3-4/carcass in studies at New Horizon Research Farm in Minnesota.

Two studies were conducted to assess the effects of feed withdrawal time on carcass composition and net returns.

In the first experiment, 728 pigs weighing an average of 286 lb. were marketed from 48 pens. They were randomly assigned to one of four treatments: feed withdrawal times of 7 (control), 24, 36 or 48 hours before harvest (Table 1).

Longer feed withdrawal time reduced live weight, hot carcass weight and backfat depth. Percentage yield and percentage lean increased with longer withdrawal periods.

Withholding feed also increased live and carcass prices, due in part to increased premiums and decreased weight discounts.

As a result, total value and net revenue received were similar between treatment groups as hot carcass weight declined in fasted pigs, but feed intake also decreased, resulting in feed savings of up to $0.78/pig. Withholding feed for 24 hours resulted in an increase in net revenue of $0.89/pig compared to 7 hours (Table 1).

In the second experiment, the 48-hour feed withdrawal time was removed and replaced with a 12-hour treatment to more accurately determine the proper time to implement feed withdrawal (Table 2).

The incidence of runny bung (anus) and leaking ingesta (from the digestive tract) were also recorded to assess whether a relationship existed between feed withdrawal and the occurrence of these processing concerns.

A total of 843 pigs were assigned to one of four treatments: withholding feed for 7, 12, 24 or 36 hours prior to harvest. Only 26 of 40 pens were used in this second experiment because of misidentification by plant employees, which may have disrupted the results.

Unlike the first experiment, no differences were observed in hot carcass weight, percentage lean or backfat depth across treatments. However, similar to the first trial, percentage yield increased as feed withdrawal time increased. Although withholding feed had no effect on the level of runny bung, it did boost the incidence of leaking ingesta.

As in the first experiment, withholding feed increased live price, and fasted pigs had increased carcass value. Premiums were similar, but withholding feed decreased weight discounts. Total value and net revenue were similar across treatments.

Overall, feed withdrawal can be an effective means of avoiding weight discounts in heavyweight pigs without hurting carcass composition and maintaining overall revenue per pig. However, these advantages come with a potential reduction in carcass weight and increased incidence of leaking ingesta, which can result in condemned heads at inspection and losses of $3-4/carcass.

Researchers: H.L. Frobose, S.S. Dritz, M.D. Tokach, J.M. DeRouchey, R.D. Goodband and J.L. Nelssen, all of Kansas State University; and L.N. Edwards and K.J. Prusa of Iowa State University. For more information, contact Frobose by phone (419) 308-9053, fax (785) 532-7059 or e-mail Frobose@ksu.edu.