Multivariate analysis about causes of growth delay in early weaned calves

Resumen

The purpose of this trial was to check if early weaned calf growth delay is due to stress or inadequate feeding. In 4 successive years, assays of 120 days each were carried out, using in total 120 half-bred Zebu calves (2 months old) grazed on natural pasture. Sixty animals were controls fed on maternal milk (C), and other 60 made up the experimental group (E), which was submitted to early weaning and supplemented with balanced food. Weightings and blood extractions were made in days 0, 7, 14, 21, 28, 60, 90 and 120. Hematological and biochemical determinations (42 parameters) included stress and malnutrition indicators, which were evaluated by radio-immune-assay, chemoluminiscency, spectrophotometry, electrophoresis, and electronic particle recount. Such procedures generated more than 40,000 data, which were statistically processed by multivariate techniques, to eliminate the additive effect of random intervention probability (alpha error), characteristic from univariate methods that comprise numerous dependent variables. Variables that obtained significant differences for treatment and/or time effects in repeated measures univariate techniques, were selected for analysis of principal components. Four orthogonal supervariables, susceptible to stress, malnutrition and ontogeny, were created. Weight gains were 79.9 kg (666 g/animal/day) in C, and 61.6 kg (513 g/animal/day) in E. Variations of cortisol, aldosterone, fructosamine, glucose, sodium, potassium, leukocytes, gamma globulins and enzymes suggested absence of stress, examined under an ontogenic frame. On the other hand, decrease of protein, carbohydrate, lipid, and mineral nutritional indicators, revealed malnutrition in E. Selected principal components indicated that most of total variance was due to malnutrition and ontogeny, but not to stress. It is important to develop more appropriate balanced supplements for early weaned calves.