Single and mixed grazing of cattle, sheep and goats

Abstract

The objectives of the research were to: achieve a method of grazing species comparison in which grazing behaviour would be unconfounded by stocking rate: to compare the grazing behaviour of cattle, sheep and goats under equivalent pasture conditions: to observe the interaction of animal species during periods of mixed grazing: and to define grazing strategies which would fit the observations. Three species of domestic ruminant (cattle, sheep and goats) were repeatedly observed during progressive defoliation of temperate, ryegrass/white clover pastures at an equal rate of disappearance of pasture mass (RDPM). Eight grazing experiments were conducted, each for a period of between 4 and 21 days, during winter, spring and summer. Animal intake was estimated from apparent disappearance of pasture mass and faecal recovery, using Cr₂O₃ as a marker. Diet composition and quality was measured in the extrusa (OE) obtained from oesophageal fistulae of six individuals of each species. RDPM was controlled at similar values across species (±13 kgDM/ha) in the range of 110-365 kgDM/ha/day over all experiments. It was concluded that RDPM was a suitable, if laborious, method to compare intake behaviour. Digestible organic matter intake (DOMI) of each species declined from a mean maximum, ad libitum value of 48.7 (cattle), 40.0 (sheep) and 47.3 (goats) gDOM/kgw·75 at the beginning of each experiment, to below 10 gDOM/kgW'75 at mean pasture masses (PM) of below 1300 kgDM/ha for cattle and sheep and below 2000 kgDM/ha for goats. The DOMI response was the result of a decline in both dry matter intake (DMI) and diet digestibility (DMD) during the grazing period. At PM above 1700 kgDM/ha cattle had a significantly (p<0.05) higher DOMI (29.7 gDOM/kgW.75) than sheep (19.7 gDOM/kgW.75). Goats were intermediate (26.1 gDOM/kgW.75). Cattle also had the lowest rate of decline of intake (RDI) in the first half of a grazing period (6.6%/day cf. 13.6% and 10.1% for sheep and goats respectively) and were thus termed the most tolerant of the species. Overall, goats were the least tolerant of pasture disappearance. In summer pastures, green material was consumed in greater quantities by sheep (total 160 gDOM/kgW.75) than by cattle (113 gDOM/kgW.75) or goats (107 gDOM/kgW.75). Clover was present in greater proportions in OE of all species than in the pasture being grazed (by +7.9% (cattle). 41.7% (sheep) and 24.1% (goats). The similarity between OE composition and composition of pasture was 0.76 (cattle). 0.58 (sheep) and 0.71 (goats). Composition of cattle OE was more similar to that of the entire pasture than to any particular horizon in the pasture. Composition of sheep OE was most similar to that of the pasture horizon between 40 and 80mm above the ground and that of goats most similar to the herbage growing above 8Omm. Mixed grazing of cattle with either sheep or goats increased DOMI of sheep (10.7%) and goats (43.0%). decreased DOMI of cattle grazing with sheep (18.7%: competition) and increased DOMI of cattle grazing with goats (24.4%: complementarity). These interactions were of sufficient magnitude to account for the animal production differences observed in previous mixed grazing research. Likely grazing strategies were postulated for the three species in which primary motivations were defined as maximisation of intake mass (cattle). maximisation of intake quality (sheep) and maximisation of intake of fresh growth (goats). The observed grazing interactions of the species could be explained by reference to these strategies.