Winter weathering effects on corn grown for grazing in a short-season area

Winter grazing can reduce over-winter feeding costs of beef cows and, recently, the selection and marketing of corn (Zea mays L.) varieties for grazing has increased the interest of Alberta beef producers. The objective of this study was to compare grazing corn varieties with early conventional corn hybrids for winter grazing potential. Five corn varieties (one grazing, one short-stature and three conventional types) were compared for whole-plant yield and forage quality at Lacombe and Brooks, AB, at four harvest times (two in September, one in December and one in January), in each of 2 yr. Forage quality analyses were in vitro digestible organic matter (IVDOM), neutral (NDF) and acid detergent fiber (ADF) and crude protein concentration. Averaged over varieties and years, yield decreased (P ≤ 0.05) by 13% between September and January at Lacombe, and by 39 and 16% at Brooks in 1999 and 2000, respectively. At Brooks, yield losses from September to January, averaged over years were 38 to 18% for a grazing and a conventional variety, respectively. At Lacombe, IVDOM concentration declined (P ≤ 0.05) by 6.3 and 3.6% between September and January during 1999 and 2000, respectively; NDF concentration increased (P ≤ 0.05) by 10% over the same interval for both years. At Lacombe there were no differences among varieties for nutritive value by January harvests. Trends for reduced forage quality with harvest were not clear at Brooks but the grazing-type variety had higher (P ≤ 0.05) NDF and ADF concentrations than the other varieties after the first harvest. In general, projected energy and crude protein concentrations of corn during winter exceeded minimum requirements an were adequate, respectively, for non-lactating, pregnant beef cows. Grazing and short stature corn varieties were not superior to early conventional corn genotypes for winter grazing potential. Thus, choice of variety for winter grazing should be made on the basis of cost of production and early maturity.