Effects of grazing by sheep on barley grass (Hordeum leporinium Link) infestation of pastures.

Abstract

Proc. Aust. Soc. Anim. Prod. (1972) 9: 221 EFFECTS OF GRAZING BY SHEEP ON BARLEY GRASS (HORDEUM LEPORINUM LINK) INFESTATION OF PASTURES J. M. GEORGE* Summary In spring 1967 the density of barley grass inflorescences was estimated in a study of the productivity of two breeds of sheep at three stocking rates, lambing at three seasons on two pasture types. Infestation by barley grass, as measured by inflorescence density, was 20 per cent higher on fescue than on phalaris pastures (P < O.Ol), and 250 per cent greater when grazed by Merinos than when grazed by Dorset Horns (P < 0.001). Significantly more inflorescences were found in paddocks stocked at 12/ha than at 8 or 16/ha (P < 0.001). Merino ewes and lambs were severely infested with barley grass seed around the face and crutch, but no Dorset Horn ewes and few lambs -were infested. I. INTRODUCTION The occurrence of barley grass (Hordeum Zeporinum Link) in pastures is widespread, but the effect of grazing management on the degree of infestation is not well documented. Barley grass invaded an experimental area in which ewes were stocked at three rates on two pasture types, and opportunity was taken to examine the effect of treatments on the number of inflorescences present. II. MATERIALS AND METHODS The .measurements were taken after the experimental area had been continuously grazed for 5 years. The treatments were two breeds (Merino and Dorset Horn), three stocking rates (8, 12 or 16/ha) and two pasture types (Phalaris tuberosa/Trifolium repens and Festuca arundinacea/Trifolium repens) arranged in a factorial design. The area received 250 kg superphosphate/ha annually. Quadrat frames measuring 1 x 0.5m were located at random on ten sites in each of the 36 treatments on November 8 and 9, 1967, and a number of inflorescences of barley grass in each frame was counted. 1000 inflorescences were collected from one of the heavily infested treatment paddocks, and the number of seeds per inflorescence counted. At the same time all sheep were examined and the number of ewes and lambs with one or both eyes affected by barley grass was recorded. At this time, only lambs born in spring were present. In analyses of variance of the data, square root transformations were used for inflorescence counts and arcsine transformations for proportions. TSIRO, Division of Animal Physiology, Pastoral Research Laboratory, Armidale, New South Wales, 2350. III. RESULTS An analysis of variance of the number of barley grass infiorescences per m2 revealed there were significant differences between breeds (P < O.OOl), pasture species (P < 0.01) and stocking rates (P < 0.001). There were 2.5 times as many inflorescences in the pastures grazed by Merinos as there were in pastures grazed by Dorset Horns (648 vs. 254/mz), and 20 per cent more inflorescences in the fescue than in the phalaris pastures (492 vs. 409/mg). The mean numbers of barley grass inflorescences/mz were 363, 742, and 264 at stocking rates of 8, 12, and 16 sheep/ha respectively (Table 1). TABLE 1 The number of barley grass culms per m2 for each stocking rate (ewes/ha) and each lambing group for pastures grazed by Merino and Dorset Horn ewes The average number of seeds per inflorescence was 20 (range 9-32). Differences between stocking rates were not significant. It was calculated that the most heavily infested paddock could produce 39 X 109 seeds/ha (16 X 109 seeds/acre). No Dorset Horn ewes and only a few lambs were infested by barley grass seed. The proportion of Merino ewes and lambs that had eyes affected by barley grass seed on one or more occasions is recorded in Table 2. The barley grass seed infestation in the eyes of Merino ewes differed significantly between stocking rates TABLE 2 Percentage of Merino ewes and lambs with one or both eyes affected by barley grass seed, November 1967 222 (P < 0.05). Most lambs were affected on many occasions (on some days up to six seeds per eye were removed) and many required daily attention. Seeds in the ears, crutch, vulva and under the legs were common in the Merino ewes and lambs, and two of the lambs that died were found, on post-mortem examination, to have barley grass seeds lodged in the oesophagus. IV. DISCUSSION The difference in the numbers of barley grass inflorescences between fescue and phalaris pastures could possibly be explained by the different horizontal distribution of these two species or the proportion of bare ground. In the fescue paddocks, barley grass became established more easily between plants, whereas in phalaris paddocks there was little space between plants. Although barley grass invasion may be an indicator of high soil fertility (Campbell 1961; Squires 1963; Gunning 1966), the density of the invasion may also indicate the degree of loss of vigour of the sward. Moore (1970) suggested that annual species such as barley grass which are shallow rooting take advantage of a redistribution of nutrients in the soil profile under grazing. Barley grass seed infestation was reduced at high stocking rates, probably because of defoliation due to the increased grazing pressure. At low stocking rates, plant competition possibly suppressed barley grass germination and establishment, and inflorescences only occurred in small areas that had been grazed more intensively than the remainder of the paddock. Barley grass seeds were most frequently found about the eyes of sheep, causing inflammation and ocular discharge whsich attracted flies and presumably led to infection. Seed under the shoulders and in the groin and feet frequently impaired walking ability and reduced condition, sometimes to the point of death. The virtual absence of wool on the face and crutch of Dorset Horn lambs and ewes may account for the fact that this breed was not adversely ,infested by barley grass seed. Further, the lower density of barley grass in paddocks grazed by Dorset Horns reduces the opportunity for the animals to become infested. Dorset Horn sheep were seen to eat seed heads of barley grass without any apparent discomfort in the mouth, whereas Merinos appeared to avoid eating the awned seeds. Sheep which are dipped when infested by grass seeds are likely to become infected by organisms causing numerous small subcutaneous abscesses, or by Clostridia, spp. and die of septicaemia (Barry 1971). Although no post-mortem examinations were made on a number of sheep that died of `post-dipping infection' each year, it would seem reasonable to attribute at least a proportion of these deaths to infections caused by barley grass seed. Little is known of the effect of barley grass seed on sheep production. The awns of barley grass seed penetrate the skin of Merinos, but no evidence of damaged Dorset Horn skin was seen in this experiment. In New Zealand a bonus for pelts free from punctures and damage by barley grass seed has been proposed (Quinn 1968). It was estimated that more than 10 per cent of all sheep and lamb skins in New Zealand were damaged by barley grass seed and this has been conservatively estimated to cost $500,000 per year (K. J. George 1969). There does not appear to be any published information on the extent of grass 223 seed damage to skins in Australia, and investigations of this type of loss to the Australian industry would be desirable. Results from the present study point to the extremely high seed production per unit area that can be expected, values comparable to those of Meeklah (1966) in New Zealand. K. J. George (1969) states that little if any barley grass seed remains viable in the soil for more than two seasons; while Meeklah (1966) found that great quantities of seed resulted in a lower viability. It is recognized that barley grass possesses many advantages such as early germination, cold tolerance and provision of early winter feed, especially in southem Australia (Smith 1967, 1968). The present study #indicates that infestation from barley grass seed is a function of sheep management (stocking rate), and is in agreement with Gunning's (1966) finding that a drop in the barley grass content of pastures usually accompanies a rise in stocking rate. It is suggested that maturation of barley grass seed may be controlled by grazing management of the pastures when the inflorescence is developing. Alternatively, the inflorescences could be mown or slashed before maturity, but this would involve labour and equipment. Merry (1960) claims that after cultivation, areas remained free from barley grass for 3 to 4 years, but this would result in land being out of production until the new pasture was established. Chemical control has been shown to be effective (Campbell 1961; Squires 1963) but this could cost $7.20/ha ($3.00 per acre) per annum at current prices for chemicals alone, and could also reduce pasture production. Meeklah (1966) concluded that eradication programmes based on spring application of chemicals are likely to fail through re-infestation from viable seed, and Gunning (1966) considered the chemical control of barley grass was impractible if the whole property was infested. V. ACKNOWLEDGMENT The technical and field assistance given by Messrs. R. McArthur and J. Elliott is gratefully acknowledged. VI. REFERENCES Barry, M. R. (1971). 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