Grazing preferences by dairy cows for 14 forage species

Abstract

The objective of this study was to quantify the grazing preference of dairy cows for eight grass, four legume and two herb species in eight seasons over 2 years. All species were grown at the same site, under the same climatic conditions, and with soil moisture and nutrient availability being non-limiting to plant growth. The forage species evaluated were cocksfoot (Dactylis glomerata cv. Kara H0265), perennial ryegrass (Lolium perenne cv. Bronsyn), short rotation ryegrass (Lolium multiflorum cv. Concord), fescue (Festuca arundinacea cv. Advance Maxp.), phalaris (Phalaris tuberose cv. Holdfast), paspalum (Paspalum dilatatum cv. Poir. Common), kikuyu (Pennisetum clandestinum cv. Whittet), prairie grass (Bromus willdenowii cv. Matua), lucerne (Medicago sativa cv. Sceptre), persian clover (Trifolium resupinatum cv. Maral), red clover (Trifolium pretense cv. Astred), white clover (Trifolium repens cv. Kopu II), chicory (Cichorium intybus cv. Grouse) and plantain (Plantago lanceolata cv. Tonic). The 14 forage species treatment plots were laid out in a completely randomised block design with three replicate blocks. The treatment plots were around the circumference of a circle so that the three cows used in each test had unbiased access to all forage species within the blocks. The tests comprised observing the forage being grazed at 10-s intervals for 1 h. The cow preference was recorded as time (min) spent grazing on each forage species. Three Holstein Friesian dairy cows of similar dominance were selected and had grazed all 14 forage species before tests. Cows were fed to requirements before each test so that they would be selective in choice of forages. The most preferred species over the whole year was prairie grass followed by kikuyu and then white clover, despite the fact that kikuyu was not available in winter. Fescue was the least preferred grass species. The mean grazing times for prairie grass and kikuyu during the 1-h test periods of grazing was 11.6 and 10.5 min, respectively. White clover and lucerne were the most preferred legumes (9.6 and 9.0 min, respectively), whereas chicory and plantain were little consumed (3.5 and 3.2 min, respectively). A prediction equation comprising water soluble carbohydrates (WSC%) and nitrate-nitrogen [NO3-N (g/kg DM)] over all seasons and forage species accounted for more variation in cow preference than any other single or combination of variables measured: cow preference [time (min) on plots] = 1.86 + 0.67 WSC% – 1.9 NO3-N (g/kg DM) (r2 = 0.76; s.e. = 2.22; n = 109). The results indicate that the relative palatability of forages can be reasonably well predicted from WSC% and NO3-N concentration, having a positive and negative effect on cow preference, respectively. The prediction equation was improved for groups of species if neutral detergent fibre (NDF%) was included: grasses, cow preference [time (min) on plots] = 24.5 + 0.42 WSC% – 1.31 NO3-N (g/kg DM) – 0.39 NDF% (r2 = 0.87; s.e. = 1.62; n = 57); legumes, cow preference [time (min) on plots] = 3.02 + 0.98 WSC% – 2.15 NO3-N (g/kg DM) – 0.08 NDF% (r2 = 0.92; s.e. = 1.38; n = 36); and herbs, cow preference [time (min) on plots] = 19.41 + 0.22 WSC% – 1.74 NO3-N (g/kg DM) – 0.69 NDF% (r2 = 0.53; s.e. = 1.81; n = 19).