Abstract:
OVlNE NEONATAL MORTALITY IN WESTERN QUEENSLAND By I. D. SMITH* I. INTRODUCTION Lamb losses contribute western Queensland and the Smith (1962, 1964) on three including desertion, account largely to the observations of flocks indicate for the majority low reproductive rates of sheep in Moule (1954) on eleven flocks and that predation and maternal factors, of lamb deaths in Merinos in this The present observations were undertaken in order to extend information concerning lamb mortality in Merino flocks in central western Queensland, and to define the factors involved in lamb mortality in a Border Leicester flock in south-western Queensland. II. MATERIALS AND METHODS (a) Merinos (i) Description of flocks Observations were made on five groups of 800-1400 medium wool Peppin Merino ewes, 3-6 years old, during the spring of 1960, 1961, 1962 and 1963, on properties in central western Queensland. These properties are situated between 24' and 25's. latitude and between the 15 and 20 inch (381 and 508 mm) isohyets. The natural pasture is a Mitchell grass (Astrebla spp.) association. growing on grey-brown soils of heavy texture; shade is provided by gidyea (Acacia cambagei), boree (Acacia cana) and mimosa (Acacia farnesiana). The stocking rate is usually one ewe to four acres. Water is provided mainly by drains and tanks supplied by artesian and sub-artesian bores. Lamb-marking percentages on these properties are usually 80-90s and lambing usually commences while the pastures are dry and of poor quality. The frequency of effective rainfall is least during August, September and October; in two-thirds of the years for which there are accurate rainfall records. effective rainfall was received during two summer months and two winter months (Everist and Moule 1952). During four months of the year mean maximum daily temperatures exceed 95�F (35�C) (Farmer, Everist and Moule 1947). Species considered locally to be predators, i.e., wild pigs (Sus scrofa), foxes (Vulpes vulpes), wedgetailed eagles (Aquila audax) and crows (Corvus spp.), are common in this area. (ii) 0 bservations during lambing The lambing period in each case was of six to eight weeks' duration. Througklout this period, eight to twelve hours daily were spent in the surveillance of the ewes and lambs,' commencing at about the time of sunrise. The paddocks, which varied in size from 2,000 to 7,400 acres were inspected as thoroughly as possible <` Department of Animal Husbandry, University of Queensland. 100 at least once daily; however, most of the time was spent in the observation of ewes and lambs near watering points and shaded areas. Where defective maternal behaviour was observed, the ewe and lamb were not disturbed until the end of the day' observations, when the lamb was eartagged for identification. The age of the s ewe was determined from earmarks. The newborn lambs were not weighed in these observations as it was considered that, under the prevailing conditions, this would disturb normal maternal behaviour and cause an increased incidence of deserted lambs. (iii) Post mortem examination Dead lambs in which post mortem decomposition was slight, and lambs which were moribund at the time of discovery, were submitted to a post mortem. examination. Foetal membranes were collected and examined whenever possible. Cotyledonarv impression smears and smears of abomasal contents were examined after staining with Gram and modified acid-fast stains. The lamb deaths were classified according to the criteria suggested by McFarlane ( 1961) . Lamb death was attributed to predation where the predator was seen to attack the lamb or where there was clear evidence of the lamb having been alive at the time of attack (viz., haemorrhage from wounds or lamb still living when seen after attack). (b) Border Leicester-s Observations were also carried out during July and August in 1962 and 1963 on a flock of 216 Border Leicester ewes of mixed ages on a property at latitude 26' ' in south-western Queensland. The average annual rainfall is 23 inches, 40 s. falling mainly during the summer. Blue grass (Dichanthium sericeum) is the main pasture species and shade is provided by myall (Acacia pen&da). At lambing time the ewes graze on oats (Avena byzantium) at the rate of one ewe per 2 acres. All lambs were eartagged and weighed at birth and otherwise the same methods were used as in the observations on the Merinos. During all of these observations, crows were shot and trapped in order to allow identification. III. RESULTS (a) Merinos The incidence of the various classes of lamb deaths in the Merinos is shown in Table 1, which summarises the results of the post mortem examination of 98 1 lambs. Examination of lambs dying before and during parturition revealed no evidence of pathogens; dystocia due to gross oversize of the foetus accounted for most parturient deaths. The recorded incidence of parturient deaths may be disproportionately high since ewes in which parturition was prolonged were easily detected and thus lambs dying from this cause rarely escaped detection; lambs dying from other causes were sometimes not found until post mortem decomposition was too far advanced to allow classification, and are therefore excluded . from Table 1. Approximately 10% of dead lambs had failed to either stand or suck. In the group which had stood but failed to suck, failure of the ewe to allow sucking appeared to be the most important cause (Table 2). The incidence of lambs which had sucked and in which undigested milk remained in the abomasum at the time 101 TABLE 1 TABLE 2 Factors associated with death due to starvation, of death was low; eleven were killed by predators and seven showed pneumonic lesions in the right apical and cardiac lobes. No attempts to isolate the causative organisms were made. Evidence of desertion and starvation was found in almost 70% of the lambs examined, including those attacked by predators. Death due to starvation appeared to be related to parity, cutaneous myiasis (fly strike) and poor body condition in the ewe, whilst in the lamb it was related to heat prostration and blindness caused by either entropion or irritation by the ant, Iridomyrmex obscurus (Table 2). Most deserted lambs survived for 2-3 days before dying. Although predators had attacked 27% of the lambs examined, there was clear evidence (viz., fat depletion) that over one-third of these lambs were starving at the time of death, and thus would have died even if they had not been killed by the predators. Of the lambs killed by predators and whose carcases were not eviscerated, only 14% were not starving at the time of death. Crows and eagles were observed to be responsible for many of the deaths in lambs immediately after birth and some of the deaths of older deserted lambs. The importance of the predators is difficult to assess since the lambs are often devoured almost completely, particularly in the case of the feral pig. (b) Border Leicesters In the Border Leicester flock, 258 lambs were weighed and eartagged at birth. The birth weights ranged from 1.36 to 6.23 kg with a mean of 4.16 kg in the single lambs, and from 1.45 to 5.09 kg with a mean of 3.80 kg in the 103 twins (Table 3). Lambs which died tended to be lighter than lambs which survived. &ring 1962, 44 twin and 6 single lambs were found dead before having been weighed; if these are included, it appears that mortality amongst twins was greater than amongst single lambs (1962: 46 -6 and 33 ~7% respectively, x2 = 352. P < 0.10; 1963: 68.4 and 22.7% respectively, x2 = 17.29, P < O*OOl). `In both years the most important cause of mortality was predation by the crow and there was a significantly higher mortality due to this cause in twin than in single lambs (51.4 and 13 -7% of all deaths respectively, ~2 == 45.4, P < 0.001). The lambs were usually attacked soon after birth, while still poorly coordinated; the crows pecked at the eyes, tongue, ears, umbilicus and perineum. Not all lambs were killed immediately; many had their tongues removed but survived for several days and many lambs which survived showed evidence of crow pecks about the ears and perineum. All of the twins which died were attacked by crows and the mortality thus attributed to crows doubtless includes some lambs which would have died from other causes. Five lambs, four of them males, were dead at birth as a result of dystocia. The mean birth weight of these lambs was 5 18 kg; however, their weights were not included in the analysis of birth weights since they may have gained weight due to oedema about the head and neck. Pneumonic lesions were observed in five lambs dying 5-10 days after birth; all were in the right apical lobe, extending into the cardiac lobe with an adjacent pleurisy and epicarditis. Entropion was prevalent during both years and although most cases were corrected when the lambs were weighed, two deaths occurred, at 6 and 9 days, TABLE 3 Mortality in relation to the birth weight of Border Leicester lambs 104 due to blindness. The ant, 1. obscwus, caused chemosis and blindness in one lamb which was attacked before it stood for the first time; it died at 5 days. Two lambs were abandoned by their primiparous mothers, before they had sucked and another two lambs were unable to suck efficiently due to abnormalities of the maxilla. During the two years, seven lambs were born with weights betlveen 1.36 and 2.04 kg. Six were singles and five of these died. Crows killed two of the lambs and three died in hypothermia. One lamb (female, 1.36 kg) had a rectal temperature of less than 95�F (35�C) 2'/2 hours after birth at an air temperature of 81 'F (27~2�C). A twin female, weighing 1.45 kg, litter mate to a male of 4.45 kg, was removed from its mother at birth and successfully reared artificially. The mean growth rate ( t standard deviation) of Border Leicester lambs, born in 1962, during the first six weeks was 0.29 t 0.05 kg/day for singles and O-27 t 0.08 kg/day for twins. (c) Identification of crows A total of 47 crows were shot and trapped during the observations on the Merino and Border Leicester flocks. All were identified as Corvus coronoides, more correctly known as ravens. IV. DISCUSSION The causes of lamb mortality in the Merino flocks were similar to those previously observed in western Queensland (Moule 1954; Smith 1962), desertion of lambs which had sucked being the most important cause. In the Border Leicester flock, however, the most important cause of mortality was predation by ravens and desertion was of minor importance. The observations on desertion are consistent with those of Moule (1954) concerning the effect of poor body condition, of Alexander (1960) concerning the effect of parity, and of Gill and Graham (1940) concerning the effect of cutaneous myiasis. Desertion has been observed to be much less frequent in flocks in western Queensland which lamb during the autumn, due presumably to more favourable pasture conditions (Smith 1964). The high air temperatures during lambing in the Merino flocks caused heat prostration of the newborn lambs and this has previously been observed as a cause of desertion (Smith 1961). In the Border Leicester flock mortality was high amongst the heavier single lambs but was highest amongst the lightest lambs. This is in accord with the observations of Moule (1954), Alexander, McCance and Watson (1955), Alexander and Peterson (1961) and Watson and Elder (1961). The only physiological explanation available is that of Alexander (1962), who showed that there is a lower level of summit metabolism in lighter lambs,. thus predisposing to hypothermia and reduced activity. Hypothermia has been observed as a cause of mortality elsewhere by Moule (1954), Alexander and McCance (1958) and Alexander and Peterson (1961). Predation was an important cause of mortality and although there is some doubt as to the importance of predators in the Merino flocks, the raven was responsible for a mortality rate of 36.2% in the Border Leicester flock, twins being more prone to be attacked than single lambs. Predation has also been observed as an important cause of lamb mortality in other flocks in this environment by Moule (1954) and Smith (1964). JO5 Although of minor importance, attack by ants appears to be a consistent cause of mortality in this environment; deaths due to I. obscurus have been reported by Smith (1962, 1964) and Moule (1954) has reported death resulting from attack by an unidentified species, possibly also I, obscures. Other than pneumonia, there was no evidence of infectious conditions causing mortality. The cause of pneumonia is unknown but it was responsible for only O-84 and 3 -8% of mortalities in the Merino and Border Leicester flocks respectively. These observations support those of Moule (1954), Alexander, Peterson and Watson (1959), Alexander and Peterson (1961) and Smith (1962, 1964) who found that perinatal infection is not normally an important cause of lamb losses in eastern Australia. V. ACKNOWLEDGMENTS The author wishes to thank Mr. I. Rowley, C.S.I.R.O. Division of Wildlife Research, Canberra, for his assistance in the identification of the Corvus sp. VI. REFERENCES ALEXANDER, G. (1960). Maternal behaviour in the Merino ewe. Proceedings of the Australian Society of Animal Production 3: 105. ALEXANDER, G. (1962). Temperature regulation in the new-born lamb. V. Summit metabolism. Australian Journal of Agricultural Research 13: 100. of Agricultural Research 9: 339. ALEXANDER, G., and MCCANCE, I. (1958). Temperature regulation in the new-born lamb. I. Changes in rectal temperature within the first six hours of life. Australian Journal LEXANDER A A LEXANDER lambs from one flock. 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