Nutrition: Irradiation of feed ingredients - a new frontier in nursery diets?

Tuesday, February 16, 2010

Experiments have shown that irradiation improves nursery pig growth and efficiency of gain compared with pigs fed traditional spray-dried animal plasma and meal diets

by JANICE MURPHY

Modern nursery diets commonly include expensive specialty protein sources, such as spray-dried animal plasma, dried whey and fish meal, to encourage young pigs to eat after weaning. These starter pig diets are typically fed in a pelleted form to overcome problems with flowability of the feed.

Recently, studies have suggested that nursery pigs started on pelleted diets have a definite advantage, realizing increased weight gain and feed intake compared with pigs that started out on meal diets. It appears that the heating and conditioning of the ingredients themselves can affect microbial populations in complete pelleted feeds.

The effects of bacteria from non-pelleted ingredients on pig growth performance are not very well understood. Research from a variety of sources has demonstrated improvements in growth performance when nursery pigs were fed diets containing irradiated ingredients, suggesting that bacterial populations in the ingredients may affect growth performance in nursery pigs fed meal diets.

Researchers at Kansas State University have been assessing the impact of irradiation and pelleting on feed ingredients and complete rations for the past decade. They recently conducted two experiments to evaluate the effects of irradiated ingredients in meal and pelleted diets on nursery pig performance (average of 21 days of age).

In the first experiment, 192 pigs (6.0 kilograms initial weight) were placed on one of four treatments to assess diet form (meal or pellet) and either irradiated or non-irradiated spray-dried animal plasma included at a rate of five per cent. Treatment diets were fed from day 0 to 11, followed by a standard meal diet from days 11 to 25.

The second experiment used 350 pigs (4.9 kilograms initial weight) to determine the effects of feeding irradiated protein sources in meal and pelleted diets on pig performance. Pigs were allotted to one of 10 treatments – a single diet formulation fed in either meal or pellet form containing either no irradiated protein sources or irradiated spray-dried animal plasma, soybean meal, fish meal, or all three. In this second experiment, the treatment diets were fed from day 0 to 11, followed by a standard meal diet from days 11 to 22.

In experiment 1, the irradiated spray-dried animal plasma had a lower total bacterial count compared to non-irradiated spray-dried animal plasma; pelleted diets also exhibited less bacteria than diets fed in meal form (Table 1). However, the complete diets had similar bacterial profiles, regardless of whether or not they were irradiated.

Overall (day 0 to 25; Table 2), when pigs were fed the irradiated spray-dried animal plasma in meal form, average daily gain (ADG) increased compared to pigs fed the non-irradiated meal diet, but there was no change in ADG when pigs were fed pelleted diets.

In addition, from day 0 to 11, pigs fed irradiated spray-dried animal plasma or pelleted diets had significantly greater efficiency of gain (G:F) compared with pigs fed traditional spray-dried animal plasma and meal diets, respectively.

These results translate into a 14 and 12 per cent improvement in ADG and G:F, respectively, from day zero to 11, but only a six per cent improvement in G:F overall. The researchers suggest that, for the first few days after weaning, it is reasonable to anticipate greater than a 10 per cent improvement in ADG and feed conversion with pelleting. However, the response falls off to approximately five to six per cent as the pigs become older.

In experiment 2, the irradiated protein sources also tended to have lower total bacteria counts compared with non-irradiated spray-dried animal plasma, and the pelleted diets had lower bacteria counts compared with meal diets.

The results showed that, from day 0 to 11, pigs fed diets containing irradiated protein sources had significantly greater G:F compared with pigs fed the control diets, though there was no difference in ADG or average daily feed intake (ADFI; Table 3).

In that first phase and overall (day 0 to 22), pigs fed pelleted diets achieved greater G:F compared to pigs on meal diets, again with no difference in ADG and ADFI.

In contrast to the results in experiment 1, the second experiment showed no advantages to pelleting the diet on ADG. There was, however, a six per cent improvement in G:F from day 0 to 11, dropping down to a four per cent improvement from day 0 to 25. The researchers are at a loss to explain this difference in response to pelleting, but do point out that the pigs in experiment 2 were one kilogram lighter and only consumed two-thirds of the amount of feed compared to the pigs in the first experiment.

Based on these results, the researchers concluded that both irradiation and pelleting are manufacturing processes that can contribute to reduced bacteria counts in feed ingredients and diets.

In the first experiment, both pelleting and irradiation improved nursery pig growth, with a greater impact in meal-fed diets. Irradiation of spray-dried animal plasma, soybean meal, and fish meal improved G:F compared with control diets containing non-irradiated ingredients.

There were some discrepancies between the two experiments, but these may be related to the difference in initial starting weight of the pigs and, ultimately, the speed with which the pigs themselves could adapt to dry feed at weaning. BP

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

Source: C. N. Groesbeck, J. M. DeRouchey, M. D. Tokach, R. D. Goodband, S. S. Dritz and J. L. Nelssen. 2009. Effects of irradiation of feed ingredients added to meal or pelleted diets on growth performance of weanling pigs. J. Anim. Sci. 87:3997-4002.