Particle size of corn in lactation diets for mixed-parity sows Particle size of corn in lactation diets for mixed-parity sows

performance but increased feed intake and digestibility of nutrients and reduced nutrient excretion in sows


Introduction
The ever increasing productivity in sows results in greater and greater demand for digestible nutrient intake to support milk production.If this demand is not met by the diet, the sow mobilizes body reserves, which can result in a poor body condition at the end of lactation.Thus, longevity of the sows can be compromised, and turnover rate in the sow herd becomes a costly problem.Data from our lab indicate that reducing particle size of corn from 1,200 to 600 microns in diets for first-litter sows increased feed intake, digestibility of nutrient, and ME content of the feed.However, we continue to field questions about feed intake and performance of older sows when fed diets of small particle sizes.Thus, we designed an experiment to determine the effect of particle size of corn in lactation diets of mixed-parity sows.

Procedure
A total of 107 sows was used in a 21-d lactation experiment.The sows were fed 4 lb/d of a sorghum-based gestation diet for the first 110 days of pregnancy.Then they were moved to a farrowing facility and fed the corn-based experimental diets at 6 lb/d.After farrowing, the sows were allowed ad libitum consumption of feed and water.Crossfostering was completed among litters within 48 hours after farrowing.Treatments were three corn particle sizes (approximately 1,500, 900, and 600 µm) with the coarsest particle size prepared in a roller mill and the other two particle size treatments achieved with a hammermill.All other ingredients were the same in all experimental diets (Table 1).Each time the diets were processed, samples of ground corn and the complete diet were collected for particle size determination.
Sows were weighed and scanned for backfat at farrowing and weaning.Water and feed consumption of the sows were recorded each week, and total litter weight and number of pigs were recorded after cross-fostering and at weaning.Finally, samples of feces were collection (one collection per sow) for moisture content and the chromic oxide (0.25%) added to the diets allowed calculation of nutrient digestibilities.All data were analyzed using the Proc Mixed Procedure of SAS with polynomial regression used to describe the shape of the response to reducing particle size in the lactation diets.

Results and Discussion
Analyses of the corn samples collected during the course of the experiment indicated that the particle size was 1,600, 824 and 619 µm for the 1,500, 900 and 600 µm treatments, respectively (Table 2).Thus, the particle sizes were reasonably close to the original targets.By decreasing particle size from the targets of 1,500 to 600 µm, ADFI (Table 3) and water usage were increased by approximately 9 and 42%, respectively (linear effects, P<0.02).Loss of backfat thickness for the sow was decreased (quadratic effect, P<0.03) as particle size decreased, and the trend for sow BW loss during lactation was in the same direction as that for fat loss, although for BW loss the effect was not statistically significant.Also, measurements of piglet growth and survivability were not different among sows fed diets with different particle sizes (P=0.15 or greater).
Apparent digestibility of DM and N were improved from 79.9 to 85.0% and 83.0 to 86.7% (linear effects.P<0.001) as particle size of corn was reduced from 1,500 to 600 µm (Table 4).These improvements in nutrient digestibility resulted in 19 and 18% decreases in excretion of DM and N (linear effects, P<0.002).These improvements in nutrient digestibility are consistent with the general trends in sow and litter performance that suggest better energy balance in the sows fed the diets with the more finely ground corn.
In conclusion, by decreasing particle size of corn we were able to increase water and feed intake.Also, sows fed diets with smaller corn particle sizes had less loss of backfat,  greater digestibilities of DM, N and GE, and returned to estrus more quickly.Thus, use of finely ground corn in lactation diets for multiparous sows is recommended to improve body condition of the sows at weaning and to reduce the environmental impact of swine production.

Table 3 . Effects of Corn Particle Size on Sow and Litter Performance
a Dashes indicate P=0.15 or greater.

Table 4 . Effects of Corn Particle Size on Apparent Digestibility, Intake, and Excretion of Nutrients
a Dashes indicate P=0.15 or greater.