Effect of different grazing strategies on dry matter yields and nutritive characteristics of whole crop cereals

Abstract

Forage cereals offer the potential to increase the amount of forage grown and consumed on dairy farms in southern Australia. The effect of single or multiple grazing of winter cereal forages by lactating dairy cattle on dry matter (DM) yield and nutritive value at grazing and on subsequent silage production harvested at the soft-dough stage of growth was determined in three studies in south-western Victoria. In the first two studies, a range of forage cereals and an annual ryegrass were grazed either once (G1) during tillering (GS 21–29), followed by locking up for silage, grazed twice (G2) (GS 21–29 and GS 32–34), followed by locking up for silage, or not grazed (NG) and harvested for silage only. In the third study, two forage cereals were either ungrazed (NG) or grazed at either GS 21, GS 24, GS 30 or GS 32 and subsequently locked up and harvested for silage. All silage harvests occurred at GS 84 (soft dough). In all studies, grazing at early tillering resulted in DM yield of less than 1.4 t DM/ha, although crude protein (CP) (30–37% DM) and estimated metabolisable energy (ME) (12.2–14 MJ/kg DM) were high. Deferring grazing until the start of stem elongation resulted in higher DM yields (1.8–4.3 t DM/ha). Silage DM yields were higher (P < 0.05) for G1 and NG treatments than for G2 in all cases apart from McKellar wheat in study 1. At silage harvest, CP and estimated ME contents of cereals were lower than for annual ryegrass. In general, total DM yields across the growing season were higher for the G1 and NG treatments compared with forages that were grazed twice before silage harvest. Deferment of a single grazing from early tillering to stem elongation did not adversely affect total DM production. However, delaying grazing until stem elongation resulted in significant declines in CP concentration and estimated ME. These studies highlight the potential of cereal forages to contribute to DM production on dairy farms in southern Australia. They can provide additional flexibility into forage systems through the provision of forage for a single grazing in early winter and in the production of high DM yield silage harvests. Cereals grazed in early winter have a high estimated ME and CP content, whereas the nutritive characteristics when harvested for silage at soft dough are of only moderate feed value. Consideration is required as to how best to incorporate these into diets of lactating dairy cattle.