Effect of paddock size, stocking rate, anthelmintics, and trace elements on the weight gain of young cattle.

Abstract

EFFECT OF PADDOCK SIZE, STOCKING RATE, ANTHELMINTICS, AND TRACE ELEMENTS ON THE WEIGHT GAIN OF YOUNG CATTLE W. H. SOUTHCOTT*, M. K. HILL, B. R. WATKIN, and J. L. WHEELER* Summary A total-of 444 heifers, eight to ten months old, average initial liveweight 207 kg, grazed for nine months on three areas of sown pasture (8, 16, 36 ha) at two stocking rates (1 per 0.4 ha and 1 per 0.8 ha). Anthelmintic (methyridine) and trace element (selenium) treatments were superimposed on the main comparisons. Weight gain was not affected by paddock size or selenium, but there were significant increases due to methyridine (24 g/day) and the lower rate of stocking (187 g/day). A second experiment that was curtailed by drought after four months provided additional information. Replacement heifers (initial average liveweight 174 kg) gained significantly more weight (271 g/day) at the lower than at the higher rate of stocking, and those given anthelmintic (thiabendazole) also grew faster (104 g/day). Paddock size and a trace element (cobalt) had no effect. I. INTRODUCTION Very few studies have been made on the effect of paddock size on animal production although subdivision has considerable economic significance. Shepherd (192 1) made observations on cattle in paddocks of 30, 50, 70 and 100 acres?t but used different stocking rates for each paddock. Southcott, Roe and Turner (1962) investigated the effect of paddock size on sheep performance. Over a period of three years, sheep at a constant and low rate of stocking (l/at) on native pasture in paddocks of 4, 8, 16 and 30 acres had similar levels of production. Sheep in a two acre paddock showed a significant decline in production but this was associated with aberrant grazing behaviour. Suckling (1962) reported that the Iiveweight and wool production from ewes stocked at about five per acre on sown pastures varied little between paddocks of sizes 5, 10 and 50 acres. Similarly, Elliott (1966) found no difference in the production of wethers grazing sown pastures of 5 or 107 acres, and 5 or 40 acres. The present paper is an interim report on a study of the effect of paddock size on the performance of young cattle. The design permitted the simultaneous evaluation of the effects of anthelmintic treatment for control of roundworm infections. In addition, further sub-treatments with the trace elements selenium and cobalt were included because signs of deficiency had been observed in the area. II. EXPERIMENTAL The observations were made at Jeogla near Armidale on the Northern Tablelands of N.S.W. on grey-brown podzolic soils (Jessup 1965). T.S.I.R.O., Pastoral Research Laboratory, Armidale, N.S.W. -i-University of New England, Armidale, N.S.W. $Massey University, Palmerston North, New Zealand. $7 lac= 0.40 ha approx. 118 The experimental areas had been sown several years previously with phalaris (P. tuberosa), cocksfoot, perennial rye grass and white clover and had been topdressed with superphosphate. After subdivision and for about six months before the experiment commenced, the paddocks were stocked uniformly with one cow plus calf per 1.2 hectares. The factorial design involved three sizes of paddock, approximately 8, 16 and 36 hectares, stocked with recently weaned eight to ten month old Hereford heifers at two rates, either 1 per 0.4 ha or 1 per 0.8 ha. There were two replicates. Balanced subtreatments of anthelmintic and trace elements were superimposed. The 444 heifers required were weighed and allocated randomly to the 12 paddocks and their sub-groups, i.e. control, anthelmintic, trace element, and anthelmintic plus trace element. There were two experiments. The first extended from August 1963 to May 1964. The second, using freshly weaned heifers, ran from August to December 1964 when it was curtailed by drought. The cattle were fasted overnight and weighed at the start of the experiments and then every three-four months. The mean initial liveweights were 207 kg and 174 kg respectively. Anthelmintic and trace element treatments were given and faecal samples were obtained when the cattle were weighed. The faecal samples TABLE 1 Efj'ect of treatments on average daily gain of heifers-Experiment I (g/head) (two or three per sub-group) were used for worm egg counts and were cultured to obtain larvae for identification of species. At the outset of the first experiment, all the heifers were given hexachlorethane to control liver fluke infections. The anthelmintic used in this experiment was methyridine* (200 mg/kg) and the trace element selenium (10 mg Se) was given as sodium selenate by mouth. In the second experiment, the anthelmintic was thiabendazolet, and the trace element cobalt (20 g) was given as a slow release pellet$ (Skerman et al. 1959). III. RESULTS Mean liveweight gains of the heifers in respect to paddock size, stocking rate and anthelmintic are summarized in Tables 1 and 2 respectively. Weight gains were significantly higher at the lower rate of stocking, were increased by anthelmintic treatment, but were not affected by size of paddock or by trace elements. The stocking rate x anthelmintic and stocking rate x paddock size interactions were not significant. In the first experiment, the liveweight response to the anthelmintic was more marked in the immediate post-weaning period than later but the anthelmintic x time term was not significant. A significant (P<O.O5) negative interaction between anthelmintic and selenium was recorded but was probably of no biological significance. TABLE 2 E#ect of treatments on average daily gain of heifers-Experiment 2 (g/head) 120 TABLE 3 mintics on species incidence was detected. Worm species present in greatest numbers were Trichostrongylus axei, Coop&a spp., Oesophagostomum radiatum, Haemonchus placei and Haemonchus contortus. There was a low incidence of Ostertagia spp. and Bunostomum phlebotomum. Proportions of species varied with time but no differential effect of the anthel- IV. DISCUSSION As in published work with sheep, paddock size over the range selected did not affect the productivity of young female cattle. However, the experimental period was short and further continuous observations must be made over several years. Stocking rate had a significant effect on the rate of liveweight gain but even at the higher rate the average liveweight gain was 477 g/day in the first and 426 g/day in the second experiment. The worm egg counts were not high initially and in both experiments fell below levels generally considered to be important for health (Roberts, O'Sullivan and Riek 195 1). Nevertheless, the effect of anthelmintic treatment on weight gain was substantial. A concomitant decrease in worm burden as evaluated by worm egg counts was not found, but the interval between successive examinations allowed time for reinfections to develop and short term changes caused by the anthelmintic would not have been detected. The grazing together of'the treated and untreated heifers provided an opportunity for reinfection of the former and may have lessened the liveweight response. TABLE 4 121 The greatest liveweight response to anthelmintic treatment in the first experiment was in the immediate post-weaning period when worm egg counts were highest. Thereafter, worm egg counts in all heifers progressively declined, probably indicating a developing resistance, and at the final examination when the cattle were about 18 months old worm burdens were apparently negligible (Table 3). At the heavier rate of stocking, contamination of the pasture with excreta was approximately doubled, and the growth rate of the catt1.e was reduced. These circumstances could have favoured parasitic infection and there was some evidence of a lesser reduction in worm egg counts at the heavier stocking rate in the immediate post-weaning period (Tables 3 and 4). However, these differences were not statistically significant. Neither selenium nor cobalt administration was associated with growth response but as the manifestation of selenium (Cousins and Cairney 1961) and cobalt (Lee 1950) deficiencies may vary from year to year, the present results are not conclusive. V. ACKNOWLEDGMENTS We are indebted to Mr. B. A. Wright of Jeogla Station for providing the land, stock and assistance for this investigation, and to Australian Wire Industries Pty Ltd. for the fencing materials. The supply of anthelmintics by Imperial Chemical Industries of Australia and New Zealand Ltd., and Merck Sharp and Dohme (Aust.) Pty. Ltd., is gratefully acknowledged. VI. REFERENCES C OUSINS, F. B., and C AIRNEY, I. M. ( 1961). Aust. J. agric. Res. 12: 927. ELLIOTT, N. M. ( 1966). Proc. Aust. Anim. Prod. 6: 177. JESSUP, R. W. (1965). Soil Pub/. C.S.I.R.O. Aust. NO . 21. L EE, H. J. (1950). Aust. vet. J. 26: 152. R OBERTS , F. H. S., O'SULLIVAN , P. J., and R IEK, R. F. ( 195 1) . Aust. vet. J. 27: 16. S HEPHERD , J. H. ( 1921). Bull. 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