Testing New & Cheaper Catfish Feed Formulations

In 2008, three 32 per cent protein diets (an industry standard, an alternative and a corn gluten feed diet) and a 24 per cent protein diet were tested. The 32 per cent industry standard diet resulted in significantly greater yield of carryover fish. Feed conversion ratios of the standard and alternative diets were significantly lower than those of the 32 per cent corn gluten and 24 per cent protein diets, but visceral fat content was higher for the standard and alternate diets. The 32 per cent industry standard diet was economically preferable to the alternative diets because the additional revenue from the greater yield of fish fed the 32 per cent protein industry standard diet more than offset the reduced cost of the alternative diets evaluated.

In 2009, three 28 per cent protein feeds (premium, standard or a sub-optimal diet) were tested in ponds. Total yield (gross and net) did not differ between fish fed the premium as compared to the standard diet, but that of the premium diet was significantly higher than that of fish fed the sub-optimal diet. The feed conversion ratio (FCR) did not differ between fish fed the premium and standard diets, but was lower than the FCR of fish fed the sub-optimal diet. There were no differences found in processing yields among treatments. Given the lower cost of the 28 per cent standard diet and yields equivalent to those of the 28 per cent premium diet, the 28 per cent standard diet was economically preferable to the other diets tested.

A multi-state pond study was initiated in April 2010, as an outcome of the regional USDA Catfish Forum, to evaluate alternative (low-cost) feeds as compared with traditional catfish feeds. The 2010 trials were conducted with channel catfish in Mississippi and Arkansas, while Alabama tested the diets with channel-blue hybrid catfish.

The 2010 study evaluated four diets (traditional or alternative 28 per cent and 32 per cent protein diets). The two traditional diets (28 per cent or 32 per cent protein) were similar to those used in the industry several years ago when feed prices were relatively low. The traditional diets included soybean meal, cottonseed meal, corn, wheat middlings and animal protein (pork meat and bone/blood meal). The two alternative feeds (28 per cent or 32 per cent protein) contained corn gluten feed and supplemental lysine, less corn and wheat middlings and no animal protein. All diets were formulated to meet or exceed the known nutrient and energy requirements of channel catfish. The diets were also manufactured by a single feed mill to minimize variations from mill to mill.

In the Arkansas study, channel catfish were stocked April 21-22, 2010 into five 0.25-acre ponds per diet. Each pond was stocked with 6,000 fingerlings per acre (5-8 inches; averaging 65 pounds per 1,000) and 2,000 pounds per acre of larger, carryover fish (0.40-1.50 pounds each). Fish were fed once daily to apparent satiation, and ponds were managed in a manner similar to that of commercial farms.

Subsamples of fish were weighed three times throughout the study to measure growth. Fish were harvested October 19-21, 2010. Gross and net yield, growth, survival, feed conversion ratio, total feed fed, mean daily feed fed and processing (carcass and fillet) yields were determined. Fillet proximate nutrient composition will also be determined.

A partial budget was used to compare the economics of the various diets fed. It measured the changes in costs and benefits from switching from the 32 per cent reference diet to each of the other diets. Feed costs at the time the feed was formulated were: $431 per ton for the 32 per cent reference diet; $421 per ton for the 32 per cent alternative diet; $409 per ton for the 28 per cent reference diet; and $399 per ton for the 28 per cent alternative diet. While bagged feed costs more than bulk feed, partial budgets consider only the differences in feed cost per ton across the various diets. The relative differences were approximately $10 per ton. However, since the relative costs of various ingredients change, feed price differentials were also varied from the $10 per ton of the initial prices to $30 per ton, in increments of $5 per ton. Stockers were valued at 80 cents per pound in the initial analysis. Sensitivity analyses of stocker prices were then conducted with stocker prices of 60 cents per pound, 40 cents per pound and 20 cents per pound and a high price of $1 per pound.

Results

The following tables summarize the results of the 2010 feed study. The values in the tables are the averages of the five ponds fed each diet. The number following the + sign indicates the standard deviation, or how variable the values were across the five ponds that were fed the same diet. The columns in Tables 1, 2 and 3 with the P-values heading show results of statistical analyses. A P-value of 10 per cent (0.10) as the cutoff was used to decide if the differences are real (due to the diet) or if they are due to normal pond-to-pond variation. Thus, any variable with a P-value less than 0.10 is considered to have a significant effect.

The column labeled Overall lists the P-values for a one-way Analysis of Variance that shows if the different diets resulted in any differences in survival, yield, mean weight at harvest, total feed fed, FCR or processing yields. The other columns, labeled Protein, Quality and Interaction show results of a two- way factorial analysis that separates and compares results of the 28 per cent vs. 32 per cent diets (Protein) and the reference diets vs. the corn gluten feed diets (Quality). The Interaction heading shows that the protein levels and diet ingredients did not combine to produce significant effects.

Table 1 shows that the overall P-values are all above 0.10 except for the yield of fingerlings (0.06). This means that the only significant effect of the different diets was on the yield of fingerlings. In looking at the P-values for Protein and Quality, it is clear that the difference is due to the protein level, not its composition. In other words, the fingerlings fed the 28 per cent diets (both the reference and corn gluten feed) had lower yields (both gross and net) than those fed the 32 per cent protein diets. However, there was no difference due to the ingredient composition of the diets. There also was no interaction between protein and quality. There were no differences in the amount of feed fed across the diets (Table 2). FCR had a P-value of 0.09 for protein effects. This is because fewer pounds per acre (of fingerlings) were produced for the same amount of feed.

There were some differences in processing yields (Table 3). The quality of the diet affected the headed-gutted and shank fillet yields and visceral fat content. Fish fed the corn gluten feed diets had lower yields as well as less visceral fat than the fish fed the reference diets.

Economics

Decisions related to which feed is best to use should be made after considering a number of alternatives. The business short and long-term goals, financial position and cash flow position must all be considered, in addition to the overall profitability and economic efficiency of the feed used. The best feed for a farmer will vary with individual farms depending on their situation with regard to the above-mentioned factors.

In terms of relative profitability, the only change that would be economically preferable would be to switch from the 32 per cent reference diet to the 32 per cent corn gluten feed diet (only positive net change value in Table 4). While the 28 per cent diets are less expensive, the reduced cost of the feed is more than offset by the reduced yield of fingerlings fed the 28 per cent as compared to the 32 per cent diets. Since there was no reduction in yield measured with the 32 per cent corn gluten feed diet as compared to the 32 per cent reference diet, the lower cost of the corn gluten feed diet resulted in a positive net change for the partial budget. The sensitivity analyses of the differences in costs among the various diets showed that, regardless of the feed price differential, the 32 per cent corn gluten feed diet continued to show the greatest relative economic advantage. When the 28 per cent alternative diet was $75 per ton less expensive (an unrealistic difference), it became more profitable than the 32 per cent reference, but not the 32 per cent corn gluten feed diet. The price of stockers did not affect the results until they reached 20 cents per pound (an unrealistically low price for stockers), at which point the 28 per cent reference diet became economically preferable.

It should be noted that this effect on relative profitability will occur in year two; there was no difference in yield of the carryover fish that would be sold in year one. It should also be noted that the partial budget analysis does not indicate overall whether the farm is profitable; only if it would be more or less profitable with the various feeds tested.

The lower yields of fingerlings fed the 28 per cent protein diets will weaken the farms balance sheet and financial position in year one. The inventory value of fish in ponds at the end of the year will be lower. Thus, current and total asset values will be lower and will reduce net worth and financial ratios that compare assets to liabilities.

However, some farms are faced with serious cash flow problems, and have business goals that are based on surviving the coming year. Since there was no difference in the yield of carryover fish or the amount of feed fed, for a farmer concerned primarily with cash flow in year one, the 28 per cent alternative (corn gluten feed) diet will result in the best year one cash flow. The yield of marketable fish would be the same, but at a lower total feed cost. The 28 per cent alternate diet would also work well for ponds that have mostly larger fish that are in final growout and have few understocked fingerlings, as long as the fish are fed daily.

Table 1. Survival, yield, and mean weight at harvest of catfish fed four different diets, Arkansas.

Table 2. Total feed fed, mean daily feed rate, and feed conversion ratio of catfish fed three different diets, Arkansas.

Table 3. Processing yields of catfish fed four different diets, Arkansas.

Table 4. Partial budget of experimental pond results of catfish fed four different diets (32% and 28% protein with and without corn gluten feed). The 32% reference diet (without corn gluten feed) was used as the base. Analysis was done on a per-acre basis.