*John H. Goihl is president of Agri-Nutrition Services Inc., Shakopee, Minn. To expedite answers to questions concerning this article, please direct inquiries to Feedstuffs, Bottom Line of Nutrition, 7900 International Dr., Suite 650, Bloomington, Minn. 55425, or email [email protected].

MANY research trials have demonstrated that reducing the particle size of corn with a hammer mill or a roller mill improves nutrient digestibility and feed efficiency in pigs.

Pelleting complete feeds for pigs has also been shown to improve nutrient digestibility and feed efficiency.

The process of reducing particle size and pelleting has some negative effects. Fine-grinding corn decreases bulk density, production rate and flowability of feed and also increases the dustiness of the feed and the amount of energy required for processing. Pelleting will improve flowability and reduce dustiness but adds energy costs for the pellet processing.

Fine-grinding corn is necessary to make a good pellet. However, pelleting increases the incidence and severity of ulceration of the pars esophageal region of the pig's stomach, which can result in death.

Poultry researchers have shown that the negative effects of fine grinding and pelleting in poultry could be reduced by adding 35% coarse-rolled corn to a pelleted protein supplement without having negative effects on broiler performance.

Swine researchers C.B. Paulk, J.D. Hancock, A.C. Fahrenholz, J.M. Wilson, L.J. McKinney, K.C. Benhke and J.C. Nietfeld of Kansas State University conducted four experiments to determine the effects of supplementing cracked corn in nursery and finishing pig diets on growth performance and milling efficiency.

In experiment 1, 144 pigs weaned at 21 days of age were allotted to pens of three barrows and three gilts and assigned to one of four treatments: (1) complete mash, (2) complete pellets, (3) all corn ground plus the balance of the diet pelleted and (4) all corn cracked plus the balance of the diet pelleted.

The pigs were fed a common pelleted diet for the first seven days postweaning before starting on trial for 28 days. The diets were fed in two phases: phase 1 from days 0 to 14, which contained whey, plasma and fish meal, and phase 2 from days 14 to 28, which was a basic corn/soybean meal diet. Pigs and feed were weighed on days 0, 14 and 28. Particle sizes were: 0.4 mm pellets, 618 mm ground corn and 3,444 mm cracked corn.

Table 1 summarizes the performance results for the 28-day trial of experiment 1.

The researchers provided the following observations:

* The energy used for pelleting diet 2 was approximately five times more than the mash diet 3.

* The pelleting of ingredients other than corn in diets 4 and 5 reduced energy costs but also resulted in a slight reduction in average daily gain (ADG) and gain:feed.

* The conditioning retention time was not measured in this experiment. However, the researchers referenced other studies where increasing the conditioning time of diets before pelleting resulted in decreased ADG.

Experiment 2

Experiment 2 used 224 pigs weighing 7.4 kg at 21 days of age. Pigs were allotted to pens of seven barrows and seven gilts and assigned to the same four treatments as used in experiment 1, except 50% of the corn in treatments 3 and 4 was incorporated into the pellet and the other 50% of the corn was fed ground or cracked.

The particle size of the ground corn in treatment 3 was 445 mm, and the cracked corn in treatment 4 was 2,412 mm. The same weighing protocol was followed as in experiment 1.

Table 2 summarizes the performance results for the 28-day trial of experiment 2.

The researchers provided the following observations from experiment 2:

* The energy cost was slightly less for treatments 3 and 4. ADG and gain:feed were also lower compared to treatments 1 and 2.

* Pigs fed treatment 1 had increased average daily feed intake (ADFI) and decreased gain:feed compared to pigs fed treatment 2.

* Pigs fed treatments 3 and 4 had increased ADFI and decreased gain:feed for the 28-day trial compared to pigs fed treatment 2.

Experiment 3

Experiment 3 was conducted for 63 days and used 208 finishing pigs with an initial weight of 62.6 kg. The pigs were allotted to pens of 13 barrows or 13 gilts and assigned to one of four treatments (Table 3). The corn/soybean meal-based diets were fed in meal form, with different percentages of cracked corn.

The pigs and feed were weighed on days 0 and 63. On day 63, all pigs were harvested. Various carcass measurements were obtained and stomachs removed. The esophageal region of the stomach was removed and scored for ulcers and keratinization.

Table 4 summarizes the performance results and stomach morphology scoring of experiment 3.

The researchers provided the following observations from experiment 3:

* As the percentage of cracked corn increased, there were no significant differences in ADG or ADFI, but gain:feed tended to decrease.

* Gain:feed improved by 0.8% for every 10 mm reduction in mean particle size.

* Increasing the percentage of cracked corn had no effect on hot carcass weight, backfat thickness or fat-free index percentage, but carcass dressing percent decreased.

* The scores for keratinization and ulcers decreased with an increasing percentage of cracked corn in the diet.

Experiment 4

Experiment 4 was conducted for 80 days in an environmentally controlled finishing facility with slotted floors and 0.93 sq. m per pig of floor space. The 252 finishing pigs were allotted to pens of four barrows and three gilts and assigned to the same four treatments as described in experiment 2. The diets were fed in three phases: phase 1 was fed from 40 to 69 kg, phase 2 from 69 to 98 kg and phase 3 from 98 to 127 kg.

The complete pellet diet 2 and pelleted supplements in diets 3 and 4 were pelleted using a die with 4.8 mm holes.

Pigs and feed were weighed on days 0, 26, 54 and 80. Carcass data and stomachs were collected in the same manner as experiment 3. The particle size was 493 mm for the ground corn and 2,841 mm for the cracked corn.

Table 5 summarizes the results of experiment 4 growth performance, carcass measurements and stomach morphology.

The researchers provided the following observations from experiment 4:

* Pigs fed treatment 2 had increased ADG and a slight increase in gain:feed compared to the pigs fed treatment 1.

* Pigs fed treatments 3 and 4 had decreased ADG and gain:feed and a slight increase in ADFI compared to pigs fed treatment 2.

* Pigs fed treatment 2 had a tendency for increased hot carcass weight and backfat thickness but a slight reduction in fat-free loin index and decreased carcass yield compared to pigs fed treatment 1.

* Pigs fed treatment 4 had the lowest keratinization and ulceration scores. Pelleting the complete diet 2 increased ulceration scores compared to pigs fed the all-mash complete diet 1.

* Pelleting compete diets, or part of the diet, significantly increased the energy cost of processing compared to an all-mash diet.

The Bottom Line

This study demonstrated some of the variability involved in pelleting diets and pelleting trials. Pelleting the complete diet for nursery pigs improved efficiency of gain in one of the two experiments. Adding a percentage of the corn post-pelleting appears not to be an option for nursery pigs.

In finishing pigs, pelleting improved performance but increased feed mill energy consumption and increased the incidence of pars esophageal lesions in the stomach. However, the negative effects were reduced by adding 50% of the corn post-pelleting as cracked corn.

Reference

J. Anim. Sci. Vol. 93, No. 4.

Volume:87 Issue:20