Mineral composition of two genetic lines of barrows and gilts from twenty to one hundred twenty-five kilograms of body weight1,2

Abstract

Two genetic lines of barrows and gilt pigs with lean BW gain averages of 280 and 375 g/d were used to evaluate their macro- and micromineral contents at BW intervals from 20 to 125 kg of BW. The experiment was a 2 x 2 x 5 factorial arrangement of treatments (i.e., 2 sexes, 2 genetic lines, and 5 BW intervals) conducted in a completely randomized design in 6 replicates using a total of 120 pigs. Initially, 12 pigs (3 from each genetic line and sex) were killed, and then at approximately 25 kg of BW intervals to 125 kg. Pigs were fed vitamin and mineral fortified corn-soybean meal diets. At slaughter the total body (except digesta and blood) of each pig was ground and analyzed for their macro- and micromineral contents. The high-lean genetic line (P < 0.03) pigs and barrows (P < 0.01) reached their targeted BW an average 3 d earlier than the low-lean genetic line and gilts. Total macro- and micromineral contents increased as BW increased, generally in a linear or quadratic (P < 0.01) manner. There was an increasing difference between genetic lines in some minerals as BW increased. Total body Ca content was greater in the low-lean genetic line with increasing differences occurring as BW increased resulting in a BW x genetic line interaction (P < 0.05), whereas P was similar for both genetic lines. The quantity of K (P < 0.01) and S (P < 0.01) increased at a greater rate in the high-lean genetic line as BW increased, resulting in BW x genetic line interactions (P < 0.01). Body Cl (P < 0.01), Mg (P < 0.06), Mn (P < 0.05), Se (P < 0.01), and Zn (P < 0.01) were greater in the high-lean genetic. As BW increased, the Ca:P and the P:K ratios were increasingly greater (P < 0.01) in the low-lean genetic line, whereas the K:Na ratio was greater (P < 0.01) in high-lean genetic line. Although K and Fe were greater (P < 0.05) in gilts than in barrows, other mineral content differences were not significant. When minerals were expressed on a per kilogram of empty BW basis, the macro- and microminerals differed (P < 0.01) as BW increased indicating a response by body maturity. Genetic line had a greater effect on mineral content per kilogram of empty BW than sex. These results indicate that differences in mineral content are largely affected by BW or physiological age and by genetic line. Best-fitting equations were developed to determine macro- and micromineral contents of both genetic lines.