Nutritive value of Manitoba-grown corn (Zea mays L.) cultivars for swine
Opapeju, Florence O.
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Three experiments were conducted to evaluate the nutritional value of Manitoba-grown corn cultivars for swine. In Experiment 1, the effect of corn heat units (CHU) rating of corn cultivars and field location on the chemical and nutrient composition of thirty-six corn cultivars replicated in two locations (St. Pierre and Reinland) in Manitoba was determined. Cultivars from each location were further subdivided into low CHU rated cultivars (less than 2300 CHU) and high CHU rated cultivars (2300 or more CHU). Samples were analyzed for dry matter (DM), crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), fat (hexane extract), ash and total and phytate phosphorus. Data on yield, bushel weight and moisture content at harvest were also collected as agronomic parameters. As expected, there was a significant effect (P<0.05) of location on DM, CP, ADF, and phytate and total phosphorus contents and on yield. Corn heat units rating had an effect (P<0.05) on CP, bushel weight and yield with the low CHU rated cultivars having higher CP and bushel weight but lower yield than the high CHU rated cultivars. In Experiment 2, the digestible energy, CP and amino acids (AA) contents of the two most widely grown corn cultivars in Manitoba obtained from three locations were determined using six ileal cannulated barrows with an average initial body weight (BW) of 21.5 +- 0.9 kg (mean +- SD) according to a 6 x 6 Latin square design. There was an effect (P<-0.05) of location on apparent ileal digestible CP and AA and on digestible energy (DE). Location significantly affected (P<0.05) the digestible contents of all AA except lysine, threonine, alanine, glycine, proline and serine. Cultivar had an effect on apparent ileal digestible CP and AA and on DE. Cultivar significantly affected (P<0.05) the digestible contents of all AA except lysine, phenylalanine, valine and cysteine. Overall the digestible energy, protein and AA in the two corn cultivars averaged 3662 kcal kg-1, 5.95% and 0.40%, respectively. Based on the results of Experiment 2, Experiment 3 was conducted to determine the performance and carcass characterisitics of growing-finishing pigs fed diets based on the two corn cultivars. Twenty-four Cotswold pigs with an average initial BW of 41.4 +- 1.4 kg (mean+-SD) were blocked by BW and sex and randomly alloted to one of three dietary treatments based on; 1) barley (control), 2) corn cultivar 1 and 3) corn cultivar 2 on a three-phase feeding program for the 20-50 kg, 50-80 kg and 80-110 kg BW range. The diets were formulated to contain 3,500 kcal kg-1 DE and 0.95%, 0.75% and 0.64% total lysine for phases I, II and III, respectively. There were no effects (P>0.05) of dietary treatments on average daily gain (ADG), average daily feed intake (ADFI) and gain:feed ratio (G:F) in all the three phases. The overall ADG, ADFI and G:F averaged 0.87 kg, 2.43 kg and 0.36, respectively. Carcass length, dressing percentage, loin eye area, loin depth, midline backfat thickness, 10th rib backfat thickness, belly firmness fat color and the amount of saturated fatty acids, monounsaturated fatty acids and total unsaturated fatty acids in belly fat and backfat were similar (P>0.05) across dietary treatments. Pigs fed diet based on corn cultivar 2 contained a higher (P<0.05) amount of polyunsaturated fatty acids in their backfat compared with those fed barley-based diet. The results from the three experiments show that the nutritional composition of corn varies with field location and CHU rating and that digestible energy, protein and AA contents of corn vary with location and cultivar. Furthermore, growth performance and carcass characteristics of pigs fed diets based on Manitoba-grown corn cultivars were similar to those fed barley-based diets.