An assessment of overgrown Phalaris tuberosa as shelter for newborn lambs.

Abstract

AN ASSESSMENT OF OVERGROWN PHALARIS TUBEROSA AS SHELTER FOR NEWBORN LAMBS J.K. EGAN*; R.L. THOMPSON* and J.S. McINTYRE* Stlmm;l.ry Results are presented from an experiment which evaluated overgrown Phalaris tuberosa as shelter for Merino lambs born in August in western Victoria. In each from grazing equivalent to strategic use of twin lambs of four years an area of dense phalaris pasture between October and the following August. The one hectare for each 250 ewes joined. During of the area for lambing significantly reduced from birth to 48 h by about 50%. was excluded area was wet weather, the mortality It is concluded that overgrown phalaris is an effective alternative to traditional shelterbelts for use in lambing systems. I. INTRODUCTION Cold wet and windy conditions during spring in western Victoria are held to be responsible, indirectly at least, for excessive mortalities et McLaughlin et al. (1970) and Egan - al. (1972) amongst newborn lambs. described the strategic use of cypress hedges to provide shelter from strong winds and demonstrated that lamb survival was markedly improved. However, on many properties the shelterbelts, if they exist, are either inadequate or inconveniently located for use at lambing. This paper presents observations on the use of overgrown Phalaris tuberosa as a form,of natural shelter for newborn lambs. II. MATERIALS AND METHODS (a) Location and animals The observations were made in 1971-74 at the Pastoral Research Station, Hamilton, in western Victoria. During March each year a flock of Merino ewes, two to five years old, was joined to Merino rams fitted with crayons. Crayon marks were recorded twice weekly for two weeks and ewes not returning to service within four weeks were allocated to two groups according to mating date, age and live weight at joining. (b) Experimental site The observations were made on a total area of 4 ha of dense pasture which, in 1970, comprised in excess of 80% by dry weight of phalaris. Each year an area of' 0.5 ha within the larger area was closed to grazing from mid-October until the following lambing. The overgrown area was double fenced (1 m apart) to prevent trampling of the edges. By lambing in each year there was a dense growth of phalaris to a height of approximately 0.5 to 1.0 m. * Department of Agriculture, Victoria, Pastoral Research Station, _ Hamilton. 157 Prior to lambing the overgrown area was subdivided into five equal areas and tracks 2 m wide slashed in a zigzag pattern through the length of each small paddock to facilitate the-movement of sheep. Similar subdivision of a grazed area was prepared for the control group of ewes. (c) Treatment of groups Immediately before lambing the ewes were separated into their groups and further split into drafts expected to lamb in each week of the experiThereafter, each draft was introduced to the experiment two days ment. before the first ewe was due to lamb. (i) Sheltered group During fine weather the ewes were drift lambed (Dun 1966; Giles If 1968) in two paddocks each of 0.6 ha adjacent to the overgrown area. rainfall was imminent during the day or likely overnight, unlambed ewes were moved into the sheltered area with not more than 40 ewes in each Ewes with newborn lambs were also moved to one of the small paddock. sheltered paddocks. Each morning, ewes without lambs were released from the sheltered Ewes with lambs remained area unless wet conditions still prevailed. in the sheltered area until the lambs were 48 h old and then released to a collecting paddock. (ii) Exposed group The ewes in the exposed group lambed without shelter but otherwise under identical conditions of management. (d) Observations Both flocks were inspected twice daily at 0900 h and 1600 h and newAll dead lambs were autopsied born lambs were identified and weighed. and those without obvious aeration of the lungs were classified as dead at birth. Daily wind travel 0.5 m above ground level was measured at a central Tempsite in the exposed area and at two sites in the overgrown area. erature and rainfall were recorded at a meteorological station immediately south of the experimental area. III. RESULTS (a) Weather A summary of the weather conditions in each year of the experiment is presented in Table 1. TABLE 1 Weather conditions during-experimental periods 1971-74 158 Conditions for lambing were generally more severe in 1971 than in Table 2 presents a description of the any of the subsequent years. weather conditions for days on which rainfall exceeded 1.5 mm, defined The data illustrate the association for present purposes as wet'days. between heavy rainfall and low temperatures in 1971. TABLE 2 fMean rainfall, maximum temperature and windspeed on wet days (b) Lamb birth weights The mean birth weight of single lambs varied between years from 3.95 to 4.25 kg and of twin lambs from 3.06 to 3.50 kg. Within years there was no difference between treatments in the birth weight of single or twin lambs. (c) Lamb deaths Approximately 3.5% of all single lambs and 1.5% of twins were classified as dead at birth. Deaths from 48 h to marking at about three weeks average age totalled 4% of all single lambs and 10% of twin lambs. Some variation existed between years but there were no apparent differences between treatments. In Table 3 the proportion of lambs born alive which died between birth and 48 h in both groups is presented for each year. In addition, the data have been pooled between years to examine the effect of shelter on the mortality of lambs born on wet days. Since only six twin lambs were born in the sheltered group in 1974 they have been excluded from the analysis. TABLE 3 159 Significantly fewer twin Ianibs died in the sheltered group than in the exposed group in 1971 and 1972, but the survival of singles was not significantly improved by the provision of shelter in any year. The pooled data reveal that the sheltering treatment resulted in a marked reduction in the mortality of twin lambs born on wet days; there was not a corresponding effect for single born lambs. IV. DISCUSSION It is concluded from measurements of windspeed and the distribution of lamb deaths that overgrown phalaris provides shelter which effectively The average windspeed within reduces the mortality of newborn lambs. the shelter was usually less than 50% of that outside and during wet weather the loss of twin lambs from birth to 48 h was reduced by half. We infer from these results that overgrown phalaris is potentially as useful as the cypress hedges tested by McLaughlin - al. (1970) and Egan et et m - al. (1972). In our experiment maximum use was made of a limited area of shelter at the expense of capital for intensive subdivision and labour to manage many small flocks. Further work is required to incorporate overgrown phalaris into a simplified lambing system readily acceptable to sheepowners. For some areas the possibility of deaths amongst ewes grazing phalaris cannot be discounted although these are thought to be rare during spring in western Victoria. However, for some situations the evaluation of alternative non-toxic species could be warranted. v. ACKNOWLEDGMENT This study was supported by funds from Wool Research Trust Fund. VI. REFERENCES Proceedings N.S.W. Division Australian Veterinary DUN, R.B. (1966). Association, p.61. EGAN, J.K., MCLAUGHLIN, J.W., THOMPSON, R.L., and MCINTYRE, J.S. (1972). Australian Journal of experimental Agriculture and Animal Husbandry 12~470. GILES, J.R. (1968). . Proceedings Australian Society of Animal Production 7:235. MCLAUGHLIN, J.W.': EGAN, J.K., POYNTON, W.McL., and THOMPSON, R.L. (1970). Proceedings Australian Society of Animal Production z:33'7. 160