Intensive milk feeding in calves affects growth performance, metabolic and endocrine traits, but not rumen development
Restricted milk feeding during the pre-weaning period is supposed to stimulate solid feed intake, but growth performance is insufficient in calves. The objective of the present study was to compare feed intake, growth performance, metabolic traits, and rumen development during the pre-weaning period in calves with different milk feeding levels. The hypothesis was tested that intensive milk feeding supports metabolic changes related to enhanced growth, but does not impair solid feed intake and rumen development. Four d after birth, 28 Holstein × Charolais calves (male and female) were fed either 6 L milk replacer (MR; 125 g powder/L)/d for 8 wk (RES) or unlimited amounts of MR up to d 35 of life (AL) that was stepped down to 6 L/d afterwards. Concentrates and hay were available ad libitum for both groups. Blood samples were taken weekly for determination of plasma concentrations of glucose, triglycerides, NEFA, BHBA, urea, insulin, IGF-I and IGF binding proteins (IGFBP). Calves were slaughtered at d 60 ± 2 and rumen tissue samples were taken for measurements of papilla size. Data were analysed by the Mixed Model of SAS with feeding, sex, time, and feeding × time interaction as fixed effects. MR intake increased (P < 0.001) in AL to 14.5 ± 0.4 L/d in wk 5 of life, but did not change in RES calves. Concentrate intake increased (P < 0.001) in both groups from wk 4 on, but did not differ between groups. Body weight and ADG were greater (P < 0.001) in AL than in RES calves. Plasma concentrations of triglycerides, glucose, insulin, and IGF-I were higher (P < 0.05) and concentrations of NEFA, urea, and IGFBP-2 and -4 were lower (P < 0.05) up to d 35 of life in AL than in RES calves. Plasma concentrations of BHBA tended to be higher (P < 0.1; mainly from d 21 to d 35 of life). Rumen empty weight and papillae length were not different, but papillae densities in atrium and ventral sac were greater (P < 0.05) in RES than in AL. Intensive milk feeding resulted in enhanced body growth and changes in metabolic and endocrine traits supporting anabolic metabolism in AL calves. Intensive milk feeding did not impair concentrate intake and slightly affected rumen papillae growth.
Keywords: calf, milk feeding, rumen development