Abstract:
The Effect of the Physical Environmfent Upon Ovine Reproduction in Tropical Queensland by % IAN D. SMITH' SUMMARY The principle cause of low reproductive rates in semi-arid tropical Queensland appears to be a combination of adverse nutritional status and high atmospheric temperatures. Two of the most important ways in which reproductive rates are affected are: (9 seasonal anoestrus; (ii) lowered conception rates. In most of this region higher-than-average lamb-marking percentages can be obtained from ewes joined during the hot summer months provided that pastoral conditions are favourable at the time, and that they are joined long enough to ensure a high proportion of conceptions. Lambs produced from such matings are usually born when pastoral conditions are still quite favourable and there is a low neonatal mortality rate. INTRODUCTION Lamb-marking percentages in Merino sheep in north-western Queensland are notoriously low and in some districts there is reported to have been a marked decline in lamb-marking percentages in the last forty years. This decline coincides with closer settlement of the area and subdivision of the original holdings. In February, 1959, an investigation into the problem of ovine reproductive failure in tropical Queensland was initiated and an attempt made to define the factors involved. The work was carried out at ' Bowen Downs ', a property 42 miles north of Aramac, in central-western Queensland (approximatelv 22.4'S latitude). The country consists almost entirely of open downs and the pasture is predominantly a Mitchell-Flinders grass association. This environment has been described more fully by Moule (1950, 1956). MATERTALS AND METHODS The lamb-marking percentages on ' Bowen Downs' have declined since original settlement, when the property was much larger. Average Lamb-marking Percentages on ' Bowen Downs' Aramac , 1882 - 1901 - 59.8% 1902 - 1921 - 53.476 1922 - 1941 - 35.7% 1941 - 1960 - 37.2% The rainfall in this area is monsoonal and on ' Bowen Downs' the mean annual rainfall (over a 77 year period) is 18.35 inches, ranging from 4.66 inches in 1926 to 60.09 inches in 1956. Reliability of effective rainfall (Everist and Moule, 1952) exceeds 50% only during February, when it is 63.6%; it exceeds 30% during five months-January, February, March, June and December. Groups of Merino ewes were joined on five different occasions during the year, and the various sources of reproductive wastage were studied on each occasion. The ewes, which were two years old, were joined with at least 2% rams in each case and were run under normal conditions in small paddocks, the smallest being approximately 200 acres in area and the stocking rate not being heavier than 1 sheep to 3 acres. The * Department Queensland. of Animal Husbandry, Veterinary School, University of 115 animals were yarded at least every second day and were under constant surveillance. Incidence of oestrus was measured by use of ewe-marking crayons on the rams (Radford, Watson and Wood, 1960). Conception was assessed by the production of a lamb 140-155 days after mating- this method was satisfactory in this instance as the ewes were under constant surveillance and the possibility of infectious ovine abortion had been eliminated bv constant observation, . serology and bacteriology. RESULTS Mean maximum and minimum temperatures (recorded in the shade, four feet above the ground) during the period over which the observations were made are shown in Table I. TABLE I. Monthly Atmospheric Temperatures (O Fahrenheit). Month Mean Maximum Daily Temperature Mean Minimum Daily Temperature March ...... April ...... ...... May June ...... July ...... August ...... September October ...... November ... December ... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... 102.3 93.8 89.4 84.5 83.3 86.7 ............ ............ ............ ............ ............ ............ 71.7 62.1 54.9 44.2 41.9 46.4 93.2 96.0 102.5 106.1 ............ ............ ............ ............ 55.1 58.8 70.4 74.2 Effective rain fell only during two months in 1959; 564 points being recorded in January and 351 points in May. Observations on factors responsible for low lambing percentages have been divided into two parts: ( i ) incidence of oestrus; and (ii) conception rates. Incidence of Oestrus Observations during 1959 (Table II) indicated a high incidence of oestrus from March (when observations were initiated) to July, declining to a negligible incidence from mid-September until late December. During this latter (anoestrous) period, the ewes were on a declining plane of nutrition and were losing body-weight. Rains fell in late December and oestrus was observed in January; however, it was not possible to measure percentage incidence on this occasion. TABLE II. Seasonal Variation in Incidence of Oestrus. Time of Joining Number of Ewes Mated Incidence at 3 Weeks Incidence at 4 Weeks 19/3/1959 ...... ...... ...... ...... 152 64 54 80 60 2/4/1959 ...... 10/6/1959 ...... 84.75% 73.2% 88.8% 86.16% 23/g/1959 ...... . ...... ...... 21/11/1959 ... Nil Nil 1.25 % Nil 116 Conception Rates Conception rates were studied in ewes joined at different times on ' Bowen Downs ' and there was an obvious difference between summer and winter conception rates. TABLE III. Seasonal Variation in Conception Time of Joining Number of Ewes Joined Rates. Concept ion Rate of initial Oestrus 19/3/1959 ...... ...... 2/4/1959 ............ 10,` 6/1959 ...... ...... 152 64 54 ...... ...... ...... 33.6% 39.0% 84.0% Further, in those ewes joined on 19/3/1959, there was an obvious difference in conception rates at initial oestrus and at the recurrent oestrus in those ewes which failed to conceive at thle initial oestrus (Table IV). Examination of semen from the rams during this period showed an improvement in semen quality and it is suggested that the reason for the increased conception rate at recurrent oestrus is due to improving ram fertility. TABLE IV. Conception Rates in Ewes Joined 19/3/1959-26/4/1959. Conception rate at initial oestrus (119 ewes) 33.6% Conception rate at recurrent oestrus (64 ewes) : : 46.9% Incidence of early prenatal failure in those ewes joined 19/3/1959 was assessed at 22.5%, using the method of Morley (1954). DISCUSSION The principal factors responsible for low lambing percentages in this area it would appear are: ( i ) seasonal anoestrus, (ii) low conception rate. The oestrous behaviour pattern observed at Aramac did not deviate radically from those patterns observed elsewhere in Australia (Kselley & Shaw, 1943)) although there was an extended period of anoestrus. Moule (1950)) however, has reported figures for incidence of oestrus during October-November in this region as high as 99% in Merino ewes during the first three weeks of joining, Indeed, on ' Bowen Downs' in previous years when pastoral con , ditions have been more favourable during this period (SeptemberDecember), higher-than-average lamb-marking percentages have b' een recorded from ewes joined at this time, indicating a high incidence of oestrus : Number of Ewes Date Joined Lambs Marked 7,076 13,292 ...... ...... November-December, 1937 September- October, 1956 ...... ...... 59.5 % 45.6 % On both of the above occasions, good rain fell shortly before joining. In South Africa, a similar situation apparently exists and although sometimes Merino sheep exhibit oestrus activity throughout the year, on other occasions there is a definite anoestrous period which extends from July or August to January or February (Roux and Hoffman, 1937). The reason for this delayed sexual activity is thought to be the low rainfall, it being considered that droughts delay the breeding season and that ewes come on heat about fourteen days after the first good rains. Examination of data from observations 117 carried out in tropical Western Australia (Suijdendorp, 1959) indicates the effect of good rainfalls upon oestrous activity of Merino ewes during the spring period, there being a marked increase in incidence of oestrus about one month after the rainfall. Hafez (1952) showed that, in British breeds, a submaintenance diet does not delay onset of the breeding season, which is at variance with observations on Merino ewes in South Africa and Queensland. However, as this author explains, these observations were made at 52' N latitude where the daylight environment varies considerably according to the season and the animals are more responsive to daylight changes which probably dominate other environmental factors including nutrition. Hunter (1959) found, that, in the more arid parts of South Africa, the percentage of ewes ovulating, as well as the mean ovulation rate per ewe, may remain relatively constant throughout the year, although the ewes may be anoestrous during spring and early summer. From their observations in the sweet veld and karoo areas of South Africa, Quinlan and Mare (1931) concluded that if conditions are suitable, oestrous activity is maintained throughout the year. In a season of good rainfall, these authors found that 53.0% of ewes showed signs of oestrus during November, while in a dry year, only 29.2% of the ewes came into oestrus during that month. It-is reasonable to assume that the good rainfall exerts its effect by causing an increase in the plane of nutrition. It does, therefore, appejar likely that in semi-arid, tropical Queensland, particularly during spring and Iearly summer, nutrition is a major factor controlling oestrus in the ewe and in many cases, reproductive failure of ewes joined at this time is due to anoestrus. It is possible that there is a threshold requirement of nutritive intake for oestrous activity, whilst, however, subliminal levels do not necessarily cause cessation of ovulation. If it is desired to join ewes during the late spring and early summer months and pastoral conditions are poor, it is suggested`that supplementary feeding may be of definite value. Associated with high summer temperatures, there is a lowered conception rate in the ewe. It is difficult to access whether the low conception rate is due to failure of fertilisation, failure of implantation or failure of the implanted embryo to survive till parturition. However, Morley (1954) in his analysis of lambing data from Merino ewes in South Africa and at Trangie, obtained a figure of 25-30% for the incidence of early prenatal failure in Merino ewes; those ewes which did not return to oestrus within 19-20 days and which failed to lamb were considered to exhibit evidence of nrenatal failure. Using Morley' method the incidence of nrenatal failure s Merino ewes mated on ` LBowen Downs' during March, 1959 WE assessed as 22.5%. This would appear to indicate that the major reason for lowered conception rate is failure of the ovum to be fertilised. It is not certain whether this is due entirely to seasonal infertility of the ram or whether there is also an effect of high atmospheric temperatures on the Merino ewe. Despite the fact that high atmospheric temperatures during summer are an important cause of ram infertility (Gunn et al, 1942) and lowered conception rates, they are not so important as a cause of reproductive failure provided that the joining period is extended. Thus, even where conception rate is 30%, 51% of ewes will have conceived after two dioestrous periods, whilst after four dioestrous periods, 76% of ewes will have conceived. In semi-arid tropical Queensland, unless sheep are joined in the summer, pastoral conditions are usually unsatisfactorv either at the time of joining or at lambing. Reliabilitv of effective rainfall is greatest during those months (December to March) when the mean maximum daily temperature may be expected to exceed lOOoF, and thus it might be anticipated that the major factor responsible for a low reproductive rate in ewes joined on good feed during the l summer months would be a low conception rate. However the problem of reduced conceptions does not appear to be insuperable as an extension of the joining period largely overcomes the problem. ACKNOWLEDGMENT S It is desired to acknowledge the co-operation of the Scottish Australian Company in making facilities for this work available at ' Bowen Downs' Aramac. The observations were made as part of , a project conducted under a grant from the Commonwealth Wool Research Trust Fund. REFERENCE S Everist, S. L. and Moule, G. R. (1952)-Q' J. agric. Sci., 9: 185. ld Gunn, R. M. C., Sanders, R. N. and Granger, W. (1942)-Bull. Coun. Sci. industr. Res. Aust., No. 148. Hafez, E. S. E. (1952)-J. agric. Sci., 42: 189. Hunter, G. L, (1959)-J. agric. Sci., 52: 282. Kelley, R. B. and Shaw, H. E. B. (1943)-Bull. Coun. Sci. industr. Res. Aust., No. 166. Morley, F. H. W. (1954)-Aust. vet. J., 30: 125. Moule, G. R. (1950)-Aust. vet. J., 26: 29. Moule, G. R. (1956)-Aust. vet. J., 32: 289. Quinlan, J. and Mare, G. S. (1931)-17th Rept. Div. Vet. Serv. Anim, Ind., Onderstepoort, p. 663. Radford, H. M., Watson, R. H. and Wood, G. F. (1960)-Aust. vet. J., 36: 57. ROUX, L. L. and Hoffman, F. E. (1937)-Fmg. in S. Afr., 12: 116. Suijdendorp, H. (1959)-J. Agric. West Aust., 8: 711. DISCUSSION Dr. R. B. Dun (N.S.W.).-There is some evidence to suggest that late foetal loss is relatively unimportant in sheep which are mated in autumn. With a spring or early summer joining, embryonic or foetal loss may be involved in the poor conception rates observed by Mr. Smith. Dr. E. A. Campbell (Qld.).- Protein levels can affect oestrus. In experimental animals, oestrus cycles are affected when the protein level drops below 5% and return to normal when the protein'level is above 10%. Is there evidence that this applies in the sheep? Answer.-In Queensland pastures, pro tein 1 evels after rain are approximately 6% while three months later they may be down to 3%. Professor T. J, Robinson (N.&W.) suggested that ram fertility may be important, perhaps not with ewes exhibiting regular oestrus but when irregular oestrus occurred. He suggested that the anoestrus observed in these data might be, in fact, a silent oestrus. A silent oestrus may be due to the stress effect of high temperatures and inadequate nutrition. 119