Trop. Anita. Htth Prod. (1995) 27, 1-8

EFFECT OF STOCKING RATES AND ANTHELMINTHIC T R E A T M E N T S O N W E I G H T G A I N S IN W E A N E D N E L L O R E C A T T L E O N I M P R O V E D P A S T U R E IN T H E B R A Z I L I A N CERRADO I. BIANCHIN,M. R. HONER,S. G. NUNESand Y. A. DO NASCIMENTO EMBRAPA--Centro Nacional de Pesquisa de Gado de Corte ( CNPGC), Caixa Postal 154, CEP 79.002.970 Campo Grande, Maw Grosso do Sal, Brazil

SUMMARY

The results are presented of 6 years of field trials with weaned Nellore cattle on improved pasture in the midwest of Brazil, using 2 stocking rates and 4 anthelminthic treatment regimes. The most profitable regime included treatments in May, June and September, which yielded an additional 41 and 42 kg of liveweight on the 2 stocking rates. No significant additional gains were obtained by treating during the rainy season, or by treating animals more than 24 months of age. The higher stocking rate (1"8 AU/ha) proved excessive on the improved pasture which deteriorated during the 6 year experimental period, yielding suboptimal liveweight gains. INTRODUCTION

The treatment of helminthosis of beef cattle raised in the Brazilian savanna region ("cerrado") has been described (Bianchin and Honer, 1987a, 1987b; Honer and Bianchin, 1987; Bianchin et al., 1990, 1992). Over the years, native pastures have been replaced on a large scale with imported grasses, especially Brachiaria species, in an attempt to accelerate liveweight gains, and stocking rates have been increased. The nutritional value of these forages is correlated with the cyclic variation in climatic conditions (Bianchin and Honer, 1987a). Helminth infections (principally Cooperia spp., Haemonchus contortus, Trichostrongylus axei and Oesophagostomum radiatum) remain the principal limiting disease factors to improved production (Bianchin et al., 1992). This paper describes a study to quantify the various components of this situation, comprising 3 growth trials, each of 2 years duration, carried out from 1983 to 1989. MATERIALS AND METHODS

The trials were carried out at the National Centre for Beef Cattle Research (CNPGC), of the Brazilian Corporation for Agricultural Research (EMBRAPA), in Mato Grosso do Sul State in the midwest of the country, an important region for raising beef cattle. Three consecutive trials, each of 2 years duration, were carried out from May 1983 to April 1989. In each trial 128 weaned (6 to 9 months old) Nellor¢ calves were used, allocated to 16 paddocks, each of 4ha of Brachiaria brizantha, (Hochst ex A. Rich., Stapf. cv. "Marandu"), a cultivar developed and introduced by the CNPGC. This pasture was sown in October 1982 in a cleared area of"cerrado" and following local practice, no fertilisers were used. The stocking rate (SR) was 1.4 Animal Units (AU)/ha (SR1) in 8 of the paddocks and 1.8 AU/ha (SR2) in the remaining 8 paddocks, one AU being defined as 450kg of animal liveweight on pasture. These densities were maintained by using animals of the same

BLANCHINET AL, Temperatures °C

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FZGt 1. Mean (50 year) values for rainfall, maximum, minimum and mean temperatures for the Campo Grande region, showing the wet and dry seasons typical of the cerrados.

origin and age and adjusting their numbers according to their weight. Each stocking rate was subjected to one of 4 regimes: A = no drenching with anthelmintics, B = drenching in July and September, C = drenching in May, July and September, and D = drenching in May, July, September and December. Avermectin was administered in the September treatment and levamisole in the other months, although during the second and third trials, group D was treated with disophenol 1983 1983/84 1984 1984185

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Fio 2. Deviations from the 50-year average rainfall values for the dry and rainy seasons during the trials, 1983 to 1988/89, CNPGC, Campo Orande.

STOCKING RATES AND ANTHELMINTHIC TREATMENTS OF CATTLE Log DM kg/he 10000 "r

t

r :-0.7447

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SR2-2

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Stooking retes ($R) v Triers ( I - B )

FIG 3. Reduction in the availability of dry matter (DM), expressed as log DM kg/ha for the three trials and two stocking rates. The regression hne for overall reduction ts shown (r = -0.7447, R" - 55.5 '/e).

in December. The experimental design was of randomised blocks, with 2 repetitions; each treatment consisted of 8 experimental animals. These were weighed individually at intervals of ca 60 days, when forage samples were taken from each paddock to quantify the dry matter availability (DM kg/ha) and quality (protein content and digestibility of organic matter), using the techniques of Harris (1970) and Tilley TABLE I

Mean percentage protein content and digestibilities for the dry and rain), seasons in three trials, and two stocking rates (SR1 and SR2) SRI Trial/Season Trial 1 dry rainy Trial 2 dry rainy Trial 3 dry rainy

SR2

% protein

% digestibility

% protein

% digestibility

6"0 6.2

47.9 48.7

6.4 7.3

46.1 49.3

5-6 6-2

41.8 47.2

6-2 8-3

47.2 53-3

4"0 6-0

34"6 45-0

4"6 7"1

39"2 49-6

Trial 1 = May 1983 to April, 1985; Trial 2 = May 1985 to April 1987; Trial 3 = May 1989 to April 1989. SR 1 = stocking rate 1.4AU/ha; SR2 = stocking rate l'8AU/ha. A - No drenching; B --- Drenching in July and September;, C - Drenching in May, July and September, D = Drenching in May, July, September and December.

4

BIANCHIN ET AL° TABLE II

Mean weight gains (kg)* for the three trials (1-3), two stocking rates (SR) andfour anthelmintic treatments

(A-D) SR 1 Trial 1 2 3 Mean

Overall

SR 2

A

B

C

D

A

B

C

D

245 b 226 b 143b 205 b

259 ab 241 b 140b 213 b

273 a 250ab 215 a 246 a

269 a 267 a 203 a 246 a

235 a 140b 63 b 146b

237 a 192a 119a 183a

242 a 197a 125a 188a

236 a I95a 138a 190a

228°

177r

*Mean weight gains in each row with identical superscripts are not significantly different (P > 0.050, by analysis of variance and Duncan's test. F o r details of Trials see footnote of Table I.

and Terry (1963). The weight gain data obtained during the 3 trials was subjected to analysis of variance (3 trials, 2 grazing densities and 4 treatments) at the 5% level, in the model: Yijkt = M -t- Bi 4. Cj 4. Kk 4. CKjk 4. Tt 4- CTjt 4- KTkt 4. CKTjkt 4- Eij~t where Yijkt is the weight gain i*kt, M = mean, Bi = block (i = 1, 2), Cj = trial (j = 1, tj 2, 3), K k = stocking rate (k = 1, 2), Tt = treatment (t = 1, 2, 3, 4) and E i j k t experimental error. Meteorological data were collected at the CNPGC synoptic weather station located about 1 km from the experimental site. RESULTS

During the 3 trials the temperature ranges were normal for the region when compared to mean values calculated over 50 years, i.e. mean minimum temperatures were above 17°C and the mean maximum below 35°C; mean annual temperatures were approximately 25°C. The normal rainfall values for the rainy and dry seasons are 1,230 and 287 mm respectively (Fig. 1); Fig. 2 shows the variations in rainfall from these normal values which occurred during the trials. Fig. 3 shows the decline (r - -0.7747) in pasture availability during the trials, for both stocking rates (SR1 and SR2) and Table I shows the protein content and in vitro digestibility of the various herbage samples. Liveweight gains are shown in Fig. 4 and the total gains are summarised in Table II where Duncan's test was used to analyse mean liveweight gains between groups. Fig. 5 shows weight gains and losses (kg/ha), during rainy and dry seasons for comparison with the rainfall data of Fig. Z DISCUSSION

Dry conditions predominated during the course of the trials with 3 rainy and 3 dry seasons being drier tl~mn normal, (Figs I and 2). The succession of abnormally dry conditions from the dry period of 1984 to that of 1986 clearly had a deleterious effect on forage production and growth performance, especiaUy in cattle on the higher stocking rate (SR2). This explains why the liveweights of the experimental animals at both stocking rates tended to stabilise or diminish from July to October in each trial (Figs 4 and 5), sinc~ this was related directly to the decline in the availability

STOCKING RATES AND ANTHELMINTHIC TREATMENTS OF CATTLE 450

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Fm 4. Growth curves (kg liv~,veight) for 3 consecutive 2-year trials. SR1 = stocking rate 1-4 AU/ha;

SR2 = 1-8 AU/ha; A = no anthclmintic treatment, B -- treatments in July and September, C =treatments in May, July and September, D = treatments in May, July, September and December.

6

BIANCHIN ET AL.

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Fm 5. Positive and negative mean weight gains per treatment durin S the dry and rainy seasons for 3 consecutive 2-year trials.

STOCKING RATES AND ANTHELMINTHIC TREATMENTS OF CATTLE

of forage (DM/kg/ha) in the paddocks (Fig. 3) which accompanied the fall in in vitro digestibility and protein content (Table I). Within the SR1 stocking rate, there was no significant difference (P > 0-05) in weights gained in calves subjected to treatment regimes C and D, but these differed significantly from animals in treatment B and from the untreated controls (A); the treatments C and D resulted in a mean gain in liveweight of 41 kg more than the untreated animals in A (Table II). This effect was most pronounced in animals between 18 and 24 months of age, after which the difference was maintained until the end of each trial. A similar effect occurred in animals subjected to the higher stocking rate (SR2), where the weight gains of animals in all treatment regimes (B, C and D) were similar but significantly greater than those of the untreated controls (A). These observations confirm the necessity of treating beef cattle between 18 and 24 months of age, when they are most susceptible to helminth infection. After this age, a certain degree of immunity is developed and anthelmintic treatments, although diminishing pasture contamination, do not result in weight gains as great as before. On the other hand cattle at high densities are forced to graze less selectively and closer to the dung pats on pasture, thus acquiring higher worm burdens. Together with the decline in forage quality, this may lead to an interference in their immunocompetence resulting in ill-thrift or even mortalities under certain conditions (Hansen et al., 1989; Bianchin et al., 1992). Daily weight gains declined from the first to the third trial in all groups. This is related to the general fall in forage availability during the course of the experiment (Fig. 3), due to pasture ageing and degradation exacerbated by the dry weather conditions. The rate of degradation was higher at the higher stocking rate (SR2, Fig. 3). Such rapid pasture degradation is common in cattle raising on improved pastures in the cerrado since pasture management is almost absent. It is thus clear that merely replacing native pastures with improved ones, without pasture management, is unprofitable in the long run under these conditions. The justification for anthelmintic treatments and their timing has been considered previously (Bianchin and Honer, 1987a). The field trials reported here have shown that the most profitable regime is that which includes treatments in May, July and September (treatment C), since this yielded an additional 41 and 42 kg of liveweight in the SR1 and SR2 stocking rates, respectively (Table II). A fourth anthelmintic treatment in December yielded no additional significant gains, probably because pasture contamination and infection translation is high during the rainy season (Bianchin and Honer, 1987a). It may be concluded from these trials that the stocking rate of 1-8 AU/ha is excessive for this type of improved pasture which, without management, will degenerate within a few years of its f o r m a t i o n a 6 years in the present study--resulting in suboptimal weight gains. It may also be concluded that there is no economic benefit to be gained by increasing the number of anthelmintic treatments from 3 to 4, or of applying them in older animals when sufficient nutritive forage is available. ACKNOWLEDGEMENTS The authors are grateful to the Conselho Nacional para Pesquisa e Tecnologia (CNPq) for research scholarships, and to the Technicians of the Helminthology Laboratory, Ananias Louvera, Arami da Silva Charao and Antonio Sergio Silva. Acceptedfor publicationApril 1994

8

BIANCHIN ET AL. REFERENCES

I k ~ c t i ~ , I. & H o a x , M. IL (1987a). Helminth parasites of beef cattle in the cerrado region of Brazil. Tropical Animal Health and Production, 19, 39-45. Bt~cm~, I. & Ho~eR, M. R. (1987b). Endoparasites of cattle in the tropical savannah of South America. In: Symposium "The economic impact of parasitisln in cattle". XXIII World Veterinary Congress, Montreal, pp 49-51. B ~ c m N , I., H o a x , M. R. & N~SCIM~CrO,Y. A. Do (1990). Epidemiology of helminths in Nellore beef cattle in the cerrados of Brazil. In: Symposium "Epidemiology of bovine nematode parasites in the Americas", XVI World Buiatries Congress, Salvador, pp 41--47~ Bt~qcemq, I., HONER,M. R. & NASC~4E~rO,Y. A. do (1992). Fatores chaves na prevalencia e patogenicidade de Trichostrongylus axei em bovinos de corte. Revista Brasileira da Parasitologia Veterinltria, I, 1--6. HANS~'~,J. W., Z~^c, A. M., Evesso~, D. E. & GemcJ~N,H. J. (1989). The effect of stocking rate and parasite control on the performance of replacement beef heifers on pasture. Veterinary Parasitology, 34, 103-115. H ~ s , L. E. (1970). Os m6todos quimicos e biol6gicos empregados na an/tlise de alimentos. University of Florida, Galnsville, Fa. VoL I, np. HONE~ M. R. & BtANCmS, L (1987). Considerafoes bfisicas para um program de controle estrat~gico da verminose bovina em gado de corte no Brasil. Circular T~cnica No. 20, il., CNPC~, Campo Grande, 53 p. Tila~ev, J. M. & T ~ v . R. A. (1963). A two-stage technique for the "in vitro" digestion of forage crops. Journal of the British Grassland Society, 18, 104-111. INFLUENCE DES TAUX DE CHARGE ET DES TRAITEMENTS ANTHELMINTHIQUES SUR LES GAINS DE POIDS DE BOVINS NELLORE SEVRES, ENTRETENUS SUR PATURAGE AMELIORE DU CERRADO BRESILIEN Des essais sex le terrain ont 6t~ rballis~spendant 6 ans avec des bovins sevnh de race Nebore, sur paturage am~lior~ dans le moyen ouest bt~silien. Denx taux de charge ont ~t~ utilis&set quatre traitements anthelminthiques ont ~t~ administr~ aux animaux. Les traltements les plus profitables ont ~t~ ceux effectu~s en mai, juin et septembre avec un rendement additionnel de 41 et 42kg de poids vif avec les deux taux de charge. Aucun gain additionnel significatif n'a 6t¢~obtenu avec un traitement pendant la saison des pluies, ou chez des animaux ~g~s de plus de 2 ans. Le taux de charge le lus 61ev6(1,8 AU/ha) s'est rev61~ excessif sur le p~turage am~lior~ qui s'est d~'t~rior~ pendant les 6 arts d'exl~rience, avec un rendement inf'erieur en gain de poids vif. EFECWO DE LA TASA DE CARGA ANIMAL Y TRATAMIENTOS ANTIHELMINTICOS SOBRE LA GANANCIA DE PESO DE GANADO DESTETADO NELLORE EN PASTURAS MEJORADAS EN EL CERRADO BRASILENO Resmaen-Se presentan resultados de 6 afios de pruebas con ganado Nellore destetado pastoreando praderas mejoradas en el oriente medio de Brasil, usando 2 tasas de carga animal y 4 reglmenes de tratamiento con antihelminticos. El mejor r~gimen fue aquel qoc incluy6 tratamientos en mayo, junio y septiembre, mediante el cual se obtuvo 41 y 42kg adicionales de peso corporal bajo los 2 tipos de carga. No se obtuvo gammcias adicionales ~uando los animales se trataron durantc la estaci6n 11uviosa, o enando se trataron

animales mayores de 24 meses. La carga m/ts alta (1.8 UA/ha) foc delet~rea para la pradera mejorada, la que se deterior6 durante los 6 afios de periodo experimental, rindiendo tasas inferiores de ganancia de peso.