Performance and nematode infection of ewe lambs on intensive rotational grazing with two different cultivars of Panicum maximum

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1 DOI /s ORIGINAL ARTICLE Performance and nematode infection of ewe lambs on intensive rotational grazing with two different cultivars of Panicum maximum R. L. D. Costa & M. S. Bueno & C. J. Veríssimo & E. A. Cunha & L. E. Santos & S. M. Oliveira & E. Spósito Filha & I. P. Otsuk Accepted: 14 February 2007 # Springer Science + Business Media B.V Abstract The daily live weight gain (DLWG), faecal nematode egg counts (FEC), and packed cell volume (PCV) of Suffolk, Île de France and Santa Inês ewe lambs were evaluated fortnightly for 56 days in the dry season (winter) and 64 days in the rainy season (summer) of The animals were distributed in two similar groups, one located on Aruana and the other on Tanzânia grass (Panicum maximum), in rotational grazing system at the Instituto de Zootecnia, in Nova Odessa city (SP), Brazil. In the dry season, 24 one-year-old ewe lambs were used, eight of each breed, and there was no difference ( p>0.05) between grasses for DLWG (100 g/day), although the Suffolk R. L. D. Costa Apta RegionalExtremo Oeste, Andradina, SP, Brazil M. S. Bueno : C. J. Veríssimo : E. A. Cunha : L. E. Santos : I. P. Otsuk Instituto de Zootecnia/APTA/SAA-SP, Nova Odessa, SP, Brazil S. M. Oliveira : E. Spósito Filha Instituto Biológico/APTA/SAA-SP, São Paulo SP, Brazil C. J. Veríssimo (*) Rua Heitor Penteado, 56, C.P 60, Nova Odessa- SP, CEP , Brazil cjverissimo@iz.sp.gov.br had higher values ( p<0.05) than the other breeds. In the rainy season, with 33 six-month-old ewe lambs, nine Suffolk, eight Île de France and 16 Santa Inês, the DLWG was not affected by breed, but it was twice as great (71 g/day, p<0.05) on Aruana as on Tanzânia grass (30 g/day). The Santa Inês ewe lambs had the lowest FEC ( p<0.05) and the highest PCV ( p<0.05), confirming their higher resistance to Haemonchus contortus, the prevalent nematode in the rainy season. It was concluded that the best performance of ewe lambs on Aruana pastures in the rainy season is probably explained by their lower nematode infection owing to the better protein content of this grass (mean contents 11.2% crude protein in Aruana grass and 8.7% in Tanzânia grass, p<0.05) which may have improved the immunological system with the consequence that the highest PCV ( p<0.05) observed in those animals. Keywords Haemonchus. Sheep Panicum maximum. Pasture Abbreviations ADF acid detergent fibre CP crude protein DLWG daily live weight gain epg eggs per gram of faeces FEC faecal nematode egg count NDF neutral detergent fibre PCV packed cell volume

2 Introduction During the last few years, sheep breeding has been increasing in the tropical areas of Brazil. Roughage supplied by direct grazing is the cheapest means of ruminant feeding. Intensive rotational grazing is a good alternative for small and medium farmers to achieve high lamb meat production. Grasses of the genus Panicum are the most promising forage for ruminant pastures, including sheep, in the south-east region of Brazil. They have African origin and need medium to high soil fertility and high temperatures and rainfall to grow well. They have high productivity per area, good nutritive value and high acceptability for ruminants, and they have the advantages of being propagated by seeds. Nowadays there are many cultivars of Panicum maximum available for pastures in Brazil; the majority were developed for cattle and are tall, and are therefore difficult for sheep grazing. Aruana grass is a short grass (50 80 cm high), developed by Instituto de Zootecnia in the 1990s. It is suitable for small ruminants owing its short height and is being used by many sheep farmers in Brazil, mainly in São Paulo State. Tanzânia grass is a tall grass ( cm), developed by Empresa Brasileira de Pesquisa Agropecuaria (Embrapa) in It was developed for cattle but, despite its height, is being used for small ruminants as well. The two cultivars are being used for sheep grazing and were recommended by Santos and colleagues (2002) as alternative forages, in tropical and subtropical areas, owing to their many advantages in intensive grazing systems. Gastrointestinal nematode infections are an important source of economic losses for small-ruminant breeding in the tropics. Among them, Haemonchus contortus, a haematophagous parasite, is responsible for reduced packed cell volume (PCV) as well as losses of others blood constituents such as macro and micro elements and vitamins (Bowman, 2002), which may lead to reduction of performance and to death (Amarante et al., 2004). This nematode is prevalent around the year in the majority of flocks, mainly in intensive grazing system (Bueno et al., 2002). This work aimed to evaluate the performance and the level of gastrointestinal nematode infection in ewe lambs of different breeds, grazing on two different cultivars of Panicum maximum Jacq. naturally infected by gastrointestinal nematodes, during the dry (winter) and rainy (summer) seasons. Material and methods Study location The trial was carried out at the Instituto de Zootecnia, Nova Odessa city, São Paulo State, Brazil, located at S and W with a Cwa climate (Köppen), characterized by rainy summers and dry and mild winters. The trial was carried out during the two most typical south-eastern Brazilian seasons: dry season (09 July to 03 September, 2001) and rainy season (28 January to 02 April, 2002). Experimental area and rotational grazing The experimental area was 1.2 ha and was divided into 16 paddocks of ha each, eight paddocks of Aruana grass (Panicum maximum Jacq. cv. Aruana) and eight of Tanzânia grass (Panicum maximum Jacq. cv. Tanzânia). Grasses were seeded in early December 2000 and after 45 days of growth the area was grazed (55 head/ha) by naturally infected ewes (mean value of faecal egg count was 1000 eggs per gram of faeces) before area subdivision. The goal was to reach a significant and uniform level of infestation in the grazing area. The area was fertilized annually with 150 kg of nitrogen/ha: one-third at the beginning of the rainy season and the remainder at the end of the rainy season. In both seasons, pastures were managed in a rotational grazing system and the stocking rate was adjusted weekly, according to forage availability, with additional Santa Inês ewe lambs, similar to the experimental animals in terms of age and weight. Forage availability was evaluated immediately before animals entrance into each paddock. During the experimental period, experimental animals entered each paddock when grasses were fully developed, around 30 days in the rainy season and 40 days in the dry season. Grazing periods in each paddock were around 6 days in the rainy season and 8 days in the dry season. Stocking densities were adjusted in each paddock, through forage availability, attempting to reduce grass height to cm. The

3 post-grazing residue was evaluated immediately after removing animals from the paddock. In each paddock, the estimation of pre-grazing available forage and post-grazing residue was performed by randomly cutting four squares of 0.25 m 2 (0.5 m 0.5 m) in the paddock. These samples were weighed and dried at 65 C in a forced-air oven for further chemical analysis. Experimental animals In the dry season, a group (n=24) of Santa Inês (n=8), Suffolk (n=8) and Île de France (n=8) ewe lambs, months of age, were distributed into two groups according to breed and live weight. One group grazed on Aruana and the other on Tanzânia grass for 56 days. In the rainy season, 33 six month-old ewe lambs (16 Santa Inês, nine Suffolk and eight Île de France) were distributed in two groups according to breed and live weight. One group grazed on Aruana and the other on Tanzânia grass for 64 days. As the experimental ewe lambs used were different between seasons, the statistical analyses were performed separately by season and their performance was not compared. All experimental animals were drenched with an organophosphate product (100 mg/kg, Neguvon, Bayer do Brasil, S.A.) before starting the experimental grazing period to reduce their faecal egg count to zero at the beginning of the trial. Tracers Tracer sheep (n=14) were placed on Aruana and Tanzânia pastures to evaluate the level of pasture infestation and verify the gastrointestinal nematodes species in each season (dry and rainy seasons). These animals were 6-month-old wool wethers with average live weight kg; they had previously been dewormed (Neguvon, 100 mg/kg live weight (LW)) and confined in pens, where they received parasite-free food. Before grazing, animals were monitored to confirm a faecal egg count value equal to zero during at least three consecutive faecal examinations. In total, 14 tracers were used: three per pasture in the dry season and four per pasture in the rainy season. The tracers and the ewe lambs grazed together for 7 days. After this period they were removed and maintained in pens for 14 days on a worm-free diet. They were slaughtered and the gastrointestinal tracts were removed, opened and processed according to Costa and colleagues (1970). Adult worms were identified, according to Yamaguti (1961), and counted. Animal performance The ewe lambs were weighed at the beginning and end of the experimental period to calculate daily live weight gain. Fortnightly weighing was performed to check animal development and health. Faeces and blood samples were collected fortnightly. Blood samples were taken from the jugular vein using vacuum tubes containing EDTA for determination of PCV. During the dry season, blood samples were taken on the 28th, 42nd and 56th days of trial and faecal samples were collected fortnightly. Faecal samples were taken directly from the rectum to determine faecal egg counts (FEC) of Trichostrongylidae (Ueno and Gonçalves, 1998) in order to monitor the level of re-infection as well as the necessity of de-worming (when FEC>1500 eggs per gram (epg)). Larvae cultures were prepared for identification of prevalent nematodes in each season according to Roberts and O Sullivan (1950). Statistics The statistical design was a completely randomized in a 2 3 factorial scheme (two grass cultivars and three breeds) for performance, FEC values and PCV. The performance of the experimental animals was evaluated on the basis of daily live weight gain (DLWG) in each season. Transformed values (log x+1) of FEC observed at the penultimate sampling of each period (42nd day of the dry season and 49th day of the rainy season) were used for statistical analysis. This time was chosen because of the high FEC values in the rainy season, when eight Suffolk, two Île de France and two Santa Inês had FEC higher than 1500 epg and had to be drenched (Neguvon, 100 mg/kg LW). For statistical analysis of PCV data, mean values from each animal in each season were considered. Data on Haemonchus and Trichostrongylus counts in tracer animals were analysed in a completely randomized design in 2 2 factorial scheme (two grass cultivars and two seasons).

4 Results The availability and chemical composition of forages are shown in Table 1. The average forage availability in the dry season was similar between grasses, with values of 2.86 and 2.94 t DM/ha for Aruana and Tanzânia grass, respectively. In the rainy season, Aruana paddocks had lower average forage availability than Tanzânia. The Aruana grass had higher crude protein (CP) content and lower neutral detergent fibre (NDF), acid detergent fibre (ADF) and lignin content than Tanzânia in both season. The mean DLWG, FEC and PCV for breeds and grasses evaluated in the dry season are shown in Table 2. There was no grass cultivar effect on animal performance ( p>0,05), with a average value for live weight gain around 100 g/day and low values for FEC and high values of PCV. There was an effect of breed ( p<0.05) on animal performance. The Suffolk ewe lambs had the highest live weight gain (134 g/day), while the Île de France showed intermediate gain (104 g/day) and Santa Inês ewes the lowest (64 g/day). There was no effect of breed on FEC values, and the mean values were less then 500 epg. Average values of PCV in Santa Inês and Île de France ewes were higher ( p<0.05) than those observed in Suffolk ewe lambs, all values being higher than 30%. The larval cultures performed during this period found infective larvae of Haemonchus (97.9%), Trichostrongylus (1.8%) and Cooperia (0.3%). The necropsies of tracer animals slaughtered in the dry season showed Trichostrongylus colubriformis (67.9%), Haemonchus contortus (26.2%) and Cooperia curticei (5.9%), and also the cestoid Moniezia benedeni. Table 2 Mean values for daily live weight gain (DLWG, g/day), faecal egg count (FEC, epg) and packed cell volume (PCV, %) of ewe lambs in rotational grazing on Aruana or Tanzânia grasses in the dry season N 1 DLWG (g/day) FEC (epg) 2 PCV (%) Breed Santa Inês 8 64 b 50 (1.00) a 33.9 a Suffolk a 238 (1.05) a 30.6 b Île de France ab 425 (1.55) a 34.4 a Grass Tanzânia a 217 (1.15) a 33.3 a Aruana a 258 (1.25) a 32.7 a Overall mean CV (%) a,b Means in the same row with different superscript letters are statistically different by F-test ( p<0.05). 1 N=number of animals. 2 Numbers in parenthesis are log x+1 transformed means. 3 CV=coefficient of variation. The average DLWG, FEC and PCV for different grasses and breeds during the rainy season are shown in Table 3. The DLWG was affected by grass cultivar ( p<0.05) but was not affected by breed ( p>0.05). Ewe lambs grazing on Aruana gained twice as much weight (71 g/day) as those grazing Tanzânia grass (30 g/day). Mean FEC values did not show a statistical difference between grasses, although the animals that grazed on Aruana showed half of the value found on Tanzânia (1596 vs 3095 epg). There was also a significant effect ( p<0.05) of breed on FEC, since the Santa Inês showed lower FEC (825 epg) than the Suffolk (4888 epg) and the Île de France ewe lambs had intermediate values (1325 epg). Table 1 Chemical composition of Aruana and Tanzânia grasses and forage availability Grass Season CP a (%) NDF b (%) ADF c (%) Lignin (%) Forage availability(t DM/ha) Aruana Dry Tanzânia Aruana Rainy Tanzânia a Crude protein. b Neutral detergent fibre. c Acid detergent fibre.

5 Table 3 Mean values for daily live weight gain (DLWG, g/day), faecal egg count (FEC, epg) and packed cell volume (PCV, %) of ewe lambs in rotational grazing on Aruana or Tanzânia grasses in the rainy season N 1 DLWG (g/day) FEC (epg) 2 PCV (%) Breed Santa Inês a 825 (1.52) b a Suffolk 9 51 a 4888 (3.19) a b Île de France 8 41 a 1325 (2.85) a b Grass Tanzânia b 3095 (2.81) a b Aruana a 1596 (2.24) b a Overall mean CV(%) a,b Means in the same row with different superscript letters are statistically different by F-test ( p<0.05). 1 N=number of animals. 2 Numbers in parenthesis are log x+1 transformed means. 3 CV=coefficient of variation. There were grass cultivar effects on PCV ( p< 0.05), with animals grazing Aruana grass having higher values. There was a breed effect ( p<0.05) on PCV, since the Santa Inês ewe lambs had higher average value (31.12%) than those found in Île de France and Suffolk, which were not statically different (27.97 and 26.26%, respectively). Larval cultures derived from faecal samples collected during the rainy season showed infecting larvae of Haemonchus (89.6%), Trichostrongylus (10.25%) and Cooperia (0.15%), and also of Strongyloides papillosus. The necropsy of tracer animals showed the presence of H. contortus (69.99%), T. colubriformis (27.58%), S. papillosus (2.32%) and C. curticei (0.11%), and also of M. benedeni. In the rainy season, there were good conditions for development of eggs and larvae of Haemonchus and Trichostrongylus. Hence during this period, mean FEC increased at each sampling and exceeded 2000 epg after 49 days (Fig. 1), when eight of nine Suffolk, two Île de France and two Santa Inês ewe lambs were drenched because they had a FEC higher than 1500 epg. At this time, one Suffolk ewe lamb had to be excluded from the trial owing to severe clinical signs of haemonchosis (FEC= epg and PCV=16). After drenching, low values were achieved. There was no effect of season or grasses on number of H. contortus or T. colubriformis specimens recovered from tracers (Table 4), but it is interesting to note that the number of T. colubriformis was twice as high in the dry season (1533) as in the rainy season (710), while H. contortus was three times higher in the rainy season (1803) than in the dry season (592), indicating a higher prevalence of this nematode during this period of the year. Discussion The most prevalent nematode species found in the animals were H. contortus and T. colubriformis, which is in accordance with the findings of Bueno et al. (2002) and Amarante et al. (2004) in Brazil. The H. contortus is a blood-suckling parasite of the abomasum and causes acute anaemia and may cause death. The T. colubriformis, a small-intestinal parasite that causes intestinal mucosal lesions, provoking loss of appetite, poor absorption of nutrients and exudations of serum protein to intestinal lumen. The Fig. 1 Mean values of FEC (Trichostrongylidae; epg) according to breed in the rainy season FEC Santa Inês Suffolk Ile de France Days

6 Table 4 Mean values and standard deviation of Haemonchus contortus and Trichostrongylus colubriformis number in tracer sheep on Aruana or Tanzania grasses N 1 Haemonchus 2 Trichostrongylus 2 Season Dry 6 592±970 (2.22±0.42) a 1533±367 (3.16±0.36) a Rainy ±840 (2.53±0.36) a 710±318 (2.16±0.31) a Grass Tanzânia 7 924±907 (2.33±0.39) a 991±344 (2.47±0.34) a Aruana ±907 (2.42±0.39) a 1253±344 (2.85±0.34) a Overall mean (2.40) 1063 (2.59) CV (%) a,b Means in the same row with different superscript letters are statistically different by F-test ( p<0.05). 1 N=number of animals. 2 Numbers in parenthesis are log x+1 transformed means. 3 CV=coefficient of variation. Trop Anim Health Prod parasitism leads to a negative nitrogen balance in the organism, mainly due to excessive loss of blood protein, and also of macro and micro elements and vitamins (Bowman, 2002). The blood drainage and nutrient losses induced by nematode infection can diminish performance and can be partially compensated by highly nutritive diet, mainly with high protein content (Abbott et al., 1986, 1988; Bricarello et al., 2005). Good forage quality was maintained in both seasons and had a marked effect on grass cultivars, since Aruana grass always had a higher value of crude protein and lower values of fibre components than Tanzânia grass (Table 1). It is interesting to note that the forage quality was better in winter than in summer, which was due to the grass regrowth even in poor weather conditions. The forage availability showed a great difference between seasons, which allowed distinct stocking density in the two seasons (Table 1), since the rainy season gave better conditions for grass development than the dry winter. In the dry season, the average forage availability was 2.9 t DM/ha and the stocking rate ewe lambs/ha; in the rainy season the average forage availability was 4.5 t DM/ha and the stocking density ewe lambs/ha. Average forage availabilities of Aruana and Tanzânia pastures, evaluated before grazing in each paddock, were similar and were adequate for the mean stocking densities adopted, in both the dry and the rainy seasons. During the dry season, the experimental animals used were near to one year of age and nematode infections were probably not a limiting factor for their performance owing to their higher resistance to worms. There was no difference in live weight gain among animals on different grasses and this is probably due to the nutritive value of both forages, which had good crude protein and fibre contents that allowed moderate live weight gains. The daily live weight gains are satisfactory for ewe lambs on tropical pastures, since Carnevalli and colleagues (2001) found lower values for lambs that grazed on Cynodon pastures, as did Barbosa and colleagues (2003) for ewe lambs grazing on the same cultivars. The values of PCV were well above 20%, considered adequate for sheep (Fraser, 1991) and showed that the levels of nematode infection did not impair the animals. In this season, the Suffolk ewe lambs, which are characterized by their high live weight gain potential, showed the best performance, regardless of the grass cultivars. In the dry season average FEC values were always below 500 epg and no animal had to be drenched. The numbers of H. contortus found in tracer sheep in the dry season was three times lower than that found in the rainy season. Characteristics of the dry season in south-east Brazil are the low rainfall and mild temperatures. In this period, mean temperature was 19.8 C but the low rainfall (57 mm) would have had a negative effect on the life cycle of nematodes. In contrast, during the rainy season, the higher rainfall (359.2 mm) and temperatures probably favoured the life cycle of H. contortus. It was suggested by Amarante and colleagues (1996) that

7 Fig. 2 Mean live weight (kg) of Santa Inês, Suffolk and Île de France ewe lambs in the experimental period during the rainy season Live weight Santa Inês Suffolk 20 Ile de France Days rainfall enhances high larval migration to the forage from faeces previously accumulated in pasture. In Africa, Ndamukong and Ngone (1996), verified that no larvae were recovered from eggs on pasture during dry the season and concluded that humidity was the most important climatic factor influencing the survival and development of Haemonchus and Trichostrongylus larvae on pasture. Infective larvae of gastrointestinal nematodes cannot survive for long on pasture when environmental conditions are not favourable, especially under low relative humidity (Charles, 1995; Tembely, 1998). In addition, as animals age, they become more resistant to nematodes (Colditz et al., 1996). This aspect, associated with adequate availability of forage, especially in Aruana paddocks, explains the better performance of older ewe lambs, even in the dry season. During the rainy season, there was a marked effect of grass on live weight gain that was probably due to the great difference in chemical composition of the two grasses as well as to the nematode infection. The higher nutritive value of Aruana grass, mainly its higher CP content in the rainy season, might explain the lower levels of parasite infection for the animals on this treatment, and is in agreement with Barbosa and colleagues (2003). Higher dietary protein can improve sheep resistance to H. contortus (Abbott et al., 1986, 1988; Bricarello et al., 2005). Nutritional status affects the development of the immunological system in young animals (Shaw et al., 1995; Kambara and McFarlane, 1996). There was no effect of breed on the daily live weight gain of ewe-lambs. On the other hand, the higher resistance to Haemonchus shown by Santa Inês ewe lambs was verified by their lower values of FEC (p<0.05) when compared to Suffolk, which resulted in higher PCV values (p<0.05) in relation to those found in Île de France and Suffolk animals, considered susceptible breeds (Morais et al., 2000; Bueno et al., 2002; Amarante et al., 2004). Amarante and colleagues (2004) did not detect statistical differences in daily weight gain among lambs of these three breeds when they were subjected to natural infection by gastrointestinal nematodes during one year, and observed that Santa Inês sheep were more resistant and needed less anthelmintic treatment. The animals live weight during the rainy season (Fig. 2) showed a slight fall on for Suffolk and Île de Fig. 3 Packed cell volume (PCV, %) of Santa Inês, Suffolk and Île de France ewe lambs in the experimental period during the rainy season PCV Santa Inês Suffolk Ile de Fraace Days

8 France ewe lambs after 35 days of the experimental period owing to infection by nematodes (see Fig. 1). A similar trend was found for PCV (Fig. 3), which showed decreases for all breeds, with an accentuation from the 35th day of the trial, anticipating the peak of FEC values (Fig. 1) observed on the 49th day of the trial when many animals had to be treated with anthelmintics. References Abbott, E.M., Parkins, J.J. and Holmes, P.H., The effect of dietary protein on the pathophysiology of acute ovine haemonchosis. Veterinary Parasitology, 20, Abbot, E.M., Parkins, J.J. and Holmes, P.H., Influence of dietary protein on the pathophysiology of haemonchosis in lambs given continuos infections. Research in Veterinary Science, 45, Amarante, A.F.T., Padovani, C.R. and Barbosa, M.A., Contaminação da pastagem por larvas infectantes de nematódeos gastrintestinais parasitas de bovinos e ovinos em Botucatu-SP. Brazilian Journal of Veterinary Parasitology, 5, Amarante, A.F.T., Bricarello, P.A., Rocha., R.A. and Gennari, S.M., Resistance of Santa Ines, Suffolk and Île de France sheep to naturally acquired gastrointestinal nematode infections. Veterinary Parasitology, 120, Barbosa, C.M.P., Bueno, M.S., Cunha, E.A., Santos, L.E., Estrada, L.H.C., Quirino, C.R. and Coelho da Silva, J.F., Consumo voluntário e ganho de peso de borregas das raças Santa Inês, Suffolk e Île de France, em pastejo rotacionado sobre Panicum maximum Jacq. cvs. Aruana ou Tanzânia. Boletim da Indústria Animal, 60, Bowman, D.D., Georgis Parasitolgy for Veterinarians, 8th edn, (W.B. Saunders, Philadelphia). Bricarello, P.A, Amarante, A.F.T., Rocha, R.A., Cabral Filho, S.L., Huntley, J.F., Houdijk, J.G.M., Abdalla, A.L. and Gennari, S.M., Influence of dietary protein supply on resistance to experimental infections with Haemonchus contortus in Île de France and Santa Inês lambs. Veterinary Parasitology, 134, Bueno, M.S., Cunha, E.A., Veríssimo, C.J., Santos, L.E., Lara, M.A.C., Oliveira, S.M., Spósito Filha, E. and Rebouças, M.M., Infección por nematodos en razas de ovejas cárnicas criadas intensivamente en la región del sudeste del Brasil. Archivo de Zootecnia, 51, Carnevalli, R.A., Silva S.C., Carvalho, C.A.B., Sbrissia, A.F., Fagundes, J.L., Pinto, L.F.M. and Pedreira, C.G.S., Desempenho de ovinos e respostas de pastagens de Coastcross submetidas a regimes de desfolha sob lotação contínua. Pesquisa Agropecuária Brasileira, 36(6), Charles, T.P., Disponibilidade de larvas infectantes de nematódeos gastrintestinais parasitas de ovinos deslanados no semi-árido pernambucano. Ciência Rural, 25, Colditz, I.G., Watson, D.L., Gray, G.D. and Eady, S.J., Some relationship between age, immune responsiveness and resistance to parasites in ruminants. 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Yamaguti, S., Systema Helminthum, vol. 3, (Interscience, New York). Performances et infections par nématodes des agneauxbrebis élevés dans des pâturages en rotation intensifs avec deux cultivars différents de Panicum maximum Résumé Le gain de poids vif journalier (DLWG), le nombre d'œufs de nématodes fécaux (FEC) et le taux d'hématocrite (PCV) des agneaux-brebis Suffolk, Île de France et Santa Inês ont été évalués tous les quinze jours pendant 56 jours durant la saison sèche (hiver) et pendant 64 jours durant la saison des pluies (été) de Les animaux ont été répartis dans deux groupes similaires, l'un localisé à Aruana et l'autre sur les prairies de Tazânia (Panicum maximum), dans le cadre d'un système de pâturage en rotation à l'instituto de Zootecnia, dans la ville de Nova Odessa (SP), au Brésil. Durant la saison sèche,

9 24 agneaux-brebis d'un an ont été évalués, huit de chaque race, et aucune différence (P>0.05) n'a été notée entre les pâturages pour le DLWG (100 g/jour), bien que la race Suffolk ait enregistré des valeurs plus élevées (P<0.05) que les autres races. Durant la saison des pluies, avec 33 agneaux-brebis de six mois, neuf Suffolk, huit Île de France et 16 Santa Inês évalués, le DLWG n'a pas été affecté par la race, mais il a été deux fois plus élevé (71 g/jour, P<0.05) sur les pâturage d'aruana que de Tanzânia (30 g/jour). Les agneaux-brebis Santa Inês ont enregistré le FEC le plus bas (P<0.05) et le PCV le plus élevé (P<0.05), confirmant ainsi leur résistance plus élevée à Haemonchus contortus, le nématode prévalent durant la saison des pluies. Il en a été conclu que les meilleures performances des agneaux-brebis dans les pâturages d'aruana durant la saison des pluies pourraient être probablement expliquées par leur taux plus bas d'infections par nématodes en raison de la meilleure teneur en protéines de cette herbe (teneur moyenne de 11,2% CP dans l'herbe d'aruana et de 8,7% de CP dans l'herbe de Tanzânia (P<0.05)) qui a peut-être amélioré le système immunologique, avec pour conséquence le PCV plus élevé (P<0.05) observé chez ces animaux. Rendimiento e infección por nematodos de borregas en un sistema de pastoreo rotacional e intensivo con dos cultivares diferentes de Panicum maximum Resumen Se evaluaron quincenalmente durante 56 días en la estación seca (invierno) y 64 días en la estación lluviosa (verano) de : la ganancia o aumento de peso vivo diario (DLWG), el recuento de huevos de nematodos fecales (FEC), y el volumen de células empaquetadas (PCV) de borregas Suffolk, Ile de France y Santa Inês. Los animales se distribuyeron en dos grupos similares, uno ubicado en Aruana y el otro en pastos de Tanzania (Panicum maximum), en un sistema de pastoreo rotacional en el Instituto de Zootecnia, en la ciudad de Nova Odessa (SP) en Brasil. En la estación seca se utilizaron 24 borregas de un año de edad, ocho de cada raza, y no hubo diferencia (P>0.05) entre los pastos para la DLWG (100 g/día), aunque las de Suffolk tenían valores más altos (P< 0.05) que las otras razas. En la estación lluviosa, con 33 borregas de seis meses de edad (nueve de Suffolk, ocho de Ile de France y dieciséis de Santa Inês) la DLWG no se vio afectada por la raza, pero fue dos veces mayor (71 g/día, P< 0.05) en pastos de Aruana que de Tanzania (30 g/día). Las borregas de Santa Inês tenían el FEC más bajo (P<0.05) y el PCV más alto (P<0.05), confirmando con ello su resistencia más alta al Haemonchus contortus, el nematodo predominante en la época lluviosa. Se concluyó que el mejor rendimiento de las borregas en los pastos de Aruana en la estación lluviosa podría seguramente explicarse por su menor infección de nematodos, debido a los mejores contenidos proteicos de estos pastos (contenidos medios de 11.2% de proteína cruda en pastos de Aruana y 8.7% de PC en pastos de Tanzania, P< 0.05), lo que quizás mejoró el sistema inmunológico y produjo en consecuencia el más alto PCV (P<0.05) observado en esos animales.