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Absence of biochemically demonstrable stress in early weaned half-bred Zebu calves.

2003; Pontifical Catholic University of Chile; Volume: 30; Issue: 2 Linguagem: Inglês

10.7764/rcia.v30i2.268

0718-3267

J. A. Coppo, N. B. Mussart, M. A. Revidatti, A. Capellari,

Ruminant Nutrition and Digestive Physiology

Early weaning is carried out in northeastern Argentina to increase beef cattle reproductive performance. This practice reduces calfs growth rate, a result attributable to stress. To verify this hypothesis, a prospective case control study was performed in 120 calves, 60 in lactation (controls, lot C) and 60 submitted to early weaning and supplemented with balanced pellets (experimental, lot E), during 120 days of follow up for 4 successive years on natural pasture. Levels of weight and stress blood indicators were measured in days 0, 7, 14, 21, 28, 60, 90 and 120. Significant cortisol increase (initial: 2.4±0.6 versus final: 3.7±0.9 ug·dl -1 ) and aldosterone decrease (351±13 versus 291±14 pg·m -1 ) were verified in E (time effect) during calf development. The differences between C and E (treatment effect) were not significant in any of the studied hormones. In E (versus C), less weight gains were verified (139.4±11.6 versus 158.7±11.7 kg, P<0.001). Significant increases (P<0.05) in total leukocytes (12.08±1.08 versus 9.76±0.90 G·l -1 ), neutrophils (4.12±0.59 versus 3.78±0.59 G·l -1 ) and lymphocytes (7.26±0.95 versus 5.39±0.76 G·l -1 ) were also confirmed in E, increases beginning between 7 and 28 days after weaning. No significant fluctuations were observed in monocytes, eosinophils, sodium, potassium and chloride. Modifications were attributed to combined effects of ontogeny (growth) and sympathetic alarms (catecholamines), rather than stress (cortisol, aldosterone). Para incrementar la performance reproductiva del ganado para carne, en el nordeste argentino se efectua destete precoz. Esta practica provoca menor velocidad de desarrollo de los terneros, circunstancia que se atribuye al estres. Para verificar tal hipotesis, en 4 anos sucesivos fueron realizados ensayos de 120 dias de duracion, sobre pastura natural, empleando 120 terneros: 60 en amamantamiento (controles, lote C) y 60 sometidos a destete precoz y suplementados con alimento balanceado (experimentales, lote E). Los examenes fueron realizados a los 0, 7, 14, 21, 28, 60, 90 y 120 dias, consistiendo en pesajes y determinaciones hematicas de parametros indicadores de estres, bajo un diseno de medidas repetidas. Durante el desarrollo de los terneros, en E se incremento el cortisol (inicial: 2,4±0,6 versus final: 3,7±0,9 ug·dl -1 ) y disminuyo la aldosterona (351±13 versus 291±14 pg·mχ -1 ), en ambos casos significativamente (efecto tiempo). Al final, no hubo diferencias significativas entre C y E (efecto tratamiento) para ninguna de las hormonas estudiadas. Culminados los ensayos, en E (versus C) fueron verificadas menores ganancias de peso (139,4±11,6 versus 158,7±11,7 kg) (P<0,001) y significativos aumentos (P<0,05) de leucocitos totales (12,08±1,08 versus 9,76±0,90 G·l -1 ), neutrofilos (4,12±0,59 versus 3,78±0,59 G·l -1 ) y linfocitos (7,26±0,95 versus 5,39±0,76 G·l -1 ). Las diferencias significativas entre C y E se iniciaron entre los dias 7 y 28 post-destete. No se registraron variaciones significativas de monocitos, eosinofilos, sodio, potasio ni cloruro. Las modificaciones se atribuyen a los efectos conjuntos de ontogenia (crecimiento) y alarmas simpaticas (catecolaminas), antes que al estres (cortisol, aldosterona).