Summary and Implications

Record-breaking heat and lack of rainfall during the 2012 growing season resulted in drought-stressed growing conditions. An experiment was conducted to investigate the impact of these conditions on nutrient composition and apparent total tract digestibilities (ATTD) of energy in corn, and determine if relationships exist between corn quality measurements, nutrient content, and digestibility of energy.

Twenty-eight samples of corn from the 2012 crop, plus two samples of corn from the 2011 crop to serve as a positive control, were collected across the Midwest using yield as an initial screen for drought impact. Each sample was graded by an official US grain inspection agency and analysed for ether extract and crude protein content.

Diets were formulated using each of the 30 corn samples plus vitamins, minerals and 0.4 per cent titanium dioxide as an indigestible marker.

Sixty individually-housed barrows (mean initial bodyweight = 34.2kg) were randomly allotted in an incomplete crossover design with 30 diets and four collection periods.

Comparing 2011 with 2012, there were no differences in ether extract or crude protein, nor were there any differences in any single corn quality measurement or energy digestibility.

In conclusion, corn grown under drought-stressed conditions was not different in energy content from that grown in the previous year under 'normal' conditions.

Introduction

Record-breaking heat and lack of rainfall during the 2012 growing season resulted in drought-stressed growing conditions.

There are no data in the literature describing the nutritional value to pigs of corn grown under these conditions. Therefore, an experiment was conducted to investigate the impact of these conditions on nutrient composition and ATTD of energy in corn and determine if relationships exist between corn quality measurements, nutrient content, and digestibility of energy

Materials and Methods

Corn samples

Twenty-eight samples of corn from the 2012 crop, plus two samples of corn from the 2011 crop to serve as a positive control, were collected across the Midwest using yield as an initial screen for drought impact.

Corn was collected using five yield categories: <50 bushels per acre, 50-100 bushels per acre, 100-150 bushels per acre, 150-200 bushels per acre, and >200 bushels per acre.

Care was taken to ensure enough samples were collected from each yield category. Each sample was graded by an official US grain inspection agency and analysed for ether extract and crude protein content.

Test Diets

Diets were formulated using each of the 30 corn samples plus vitamins, minerals and 0.4 per cent titanium dioxide as an indigestible marker. Diets were fed at a level of approximately 2.6 times the estimated energy required for maintenance (NRC 2012) based upon the average initial bodyweight of the pigs at the beginning of four collection periods.

Animals

This experiment was conducted at the Iowa State University Swine Nutrition Research Farm under the approval of the Institutional Animal Care and Use Committee (#9-12-7441-S). In this experiment, 60 individually-housed barrows (PIC 359 × C29; initial bodyweight = 34.2±0.18kg) were randomly allotted in an incomplete crossover design with 30 diets and 4 collection periods.

Each of the four collection periods consisted of six days adjustment to the test diet followed by three days of faecal sample collection followed by five days of feeding a fully balanced grower diet; the latter was fed to ensure that the protein-deficient test diets did not impair digestion functions in subsequent collection periods.

Analysis

Diet and faecal samples were analysed for DM, titanium dioxide and GE. ATTD coefficients were then determined.

Data were analysed using the PROC MIXED procedure of SAS (SAS Inst. Inc., Cary, NC) with the individual pig and corn sample as the experimental unit for analysing the data from the digestibility trial and analysis of the chemical constituents, respectively.

Results and Discussion

Mean ATTD coefficients of GE between the 2011 and 2012 corn samples were not different (84.3 versus 83.1 respectively; P>0.10).

Comparing 2011 with 2012, there were no differences in ether extract (4.07 per cent versus 3.96 per cent; P>0.10) or crude protein (8.56 versus 9.19 per cent; P>0.10).

There were no differences in physical characteristics, except for 1,000-kernel weight, which varied among samples by 220 per cent (176 to 386g).

No relationships were found between any single corn quality measurement, physical or chemical, and digestibility of energy (P>0.10).

In conclusion, ATTD of corn grown under drought-stressed conditions was not different in energy content from corn grown in the previous year under 'normal' conditions.

The authors of this paper - published in Iowa State University Animal Industry Report 2014 - were Monica Newman (Graduate Research Assistant), John Patience (Professor, Department of Animal Science) and Charles Hurburgh (Professor, Agriculture and Biosystems Engineering).

Acknowledgements: The authors gratefully acknowledge the Iowa Pork Producers Association for funding this experiment (Project #12-193).

Further Reading

You can see other papers in the Iowa State University Animal Industry Reports 2014 by clicking here.

May 2014