Nutrition

On-Farm Tests Indicate No Advantage with Diet Acidification

Adding organic acids to high-quality North American nursery diets is unlikely to improve pig performance, according to University of Illinois research results. Researchers acknowledged that lactic acid changed the gut environment, but not enough to improve growth performance.

Two experiments were conducted to evaluate how weaned pigs respond to lactic acid in nursery diets. Pigs were weaned at less than 3 weeks of age and were housed in large groups on a commercial farm. Each experiment was conducted using 48 pens of approximately 33 pigs/pen. Pigs were divided into six replicates of four treatments. A series of four diet phases were fed.

The goal was to evaluate the effect of lactic acid in the diet on the growth performance and health of young weaned pigs in typical commercial pork production systems.

Experiment 1 was conducted over six weeks to assess the ability of lactic acid to improve growth performance and health status of nursery pigs in the presence or absence of dietary lactose. Pigs averaged 14.8 days of age and 9.5 lb. at the start of the test.

The first experiment included a negative control diet, in addition to animal-grade lactose fed at 21, 14, 7 and 0% in phases 1-4. The other two treatments in the first experiment included lactic acid fed at 0.75% in Phases 1-3 and a dietary treatment combining both lactose and lactic acid at the same levels. Negative control diets contained considerable amounts of corn starch.

The lactose and/or lactic acid were substituted for the corn starch in the other experimental diets. All diets in the first experiment contained carbadox.

The experimental treatments did not affect average daily gain (ADG) nor health status (Figure 1). However, the inclusion of lactose significantly increased the average daily feed intake (ADFI) during Week 1 and Week 2, making the gain:feed ratio significantly decreased in Week 1 and overall. The use of lactic acid significantly reduced the percentage of pigs given medical treatments during Week 1, then significantly increased the same variable during Week 2.

A second experiment also lasted six weeks. Researchers evaluated the effect of increasing lactic acid levels to improve nursery pig growth performance and health status. Pigs were weaned averaging 17.3 days of age and 12 lb. Diets included 0, 0.75, 1.50 and 2.25% lactic acid, respectively, during Phases 1-3. Lactic acid was substituted for the corn starch that was included in the control diets at low levels. All pigs received a common Phase 4 diet. No antimicrobial was fed.

An outbreak of diarrhea occurred near the end of the second week of the experiment. All pigs were provided medicated water containing oxytetracycline HCL at 264 mg./l of water for three days, starting on Day 13.

The results for Experiment 2 did not show clear responses to increasing levels of lactic acid. The experimental treatments did not affect ADG nor health status (Figure 1). ADFI showed a linear positive response in Weeks 3 and 4 and quadratic responses in Weeks 5 and 6, and overall.

The quadratic responses showed the greatest ADFI on the extreme treatments of base diet and 2.25% lactic acid. Responses also showed lower ADFI on the lower lactic acid inclusions. There was a similar quadratic effect on gain:feed ratio during Week 1, and a different quadratic effect on gain:feed ratio, with the maximum value at 1.50% lactic acid, during Weeks 5 and 6.

Under the conditions of this study, researchers reported no consistent benefits were found when lactic acid was fed, either in the presence or absence of lactose.

Previous research conducted by other institutions had shown lactic acid, formic acid and benzoic acid to provide benefits when diets were formulated with cereals and plant proteins. The fact that these research trial diets contained only modest levels of cereal and plant proteins may explain the lack of response to lactic acid. The diets in these research trials more realistically reflect the most common swine diets fed in North America.

Some researchers have found the response to acids has been smaller when diets with milk products are fed to nursery pigs vs. diets without milk products. Lactose from milk products is converted to lactic acid, perhaps creating desirable changes in the gastric environment and thus reducing the benefits of acidification.

Neither lactose nor lactic acid improved growth performance or measures of health, such as number of pigs removed or number of medical treatments, in either experiment.

“These results can save producers the cost of organic acids for addition to nursery diets, a cost that could reach 20¢/pig,” states Jim Pettigrew, faculty excellence professor, University of Illinois. “Perhaps, more importantly, this research can direct research attention to other, more useful products. The industry has a rich supply of feed ingredients purported to improve growth and health of young pigs, but most have not been adequately tested. We have a pressing need to identify those that will help pork producers.”

Researcher: Jim Pettigrew, University of Illinois. Contact Pettigrew at (217) 244-6927.

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