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Nitrogen metabolism of Holstein calves on high or low pre- and post-weaning feeding plan.

G. Antunez



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Nitrogen metabolism of Holstein calves on high or low pre- and post-weaning feeding plan.
G. Antunez*1, C. Cajarville1, C. Fernandez1, L. Artus1, J. Dayuto1, F. Correa1, G. Oleggini2, J. Repetto1. 1Departamento Producci�n Animal de Veterinaria (IPAV), Facultad de Veterinaria, UdelaR Libertad, San Jos�, Uruguay, 2CONAPROLE Montevideo, Uruguay.

The aim was to study the effects of the pre- and post-weaning nutritional plans on N metabolism of calves. Twenty 4 female Holstein calves (41 � 0.5 kg BW; 6 � 2 d old), were blocked by birthdate, and randomly assigned to 4 nutritional levels (Trt): 1) high pre- and high post-weaning (HH), 2) high pre- and low post-weaning (HL), 3) low pre- and high post-weaning (LH), or 4) low pre- and low post-weaning (LL). Calves had free access to water and starter (21% CP, 15% NDF). Milk replacer (MR; 25% CP, 20% EE; 12% of DM) was provided twice daily at 10% (LH and LL) or 20% (HH and HL) of initial BW, stepping-down the offer since d 49 MR until weaning (d 56). After weaning calves were fed with different amounts (H or L) of a diet (50% starter and 50% hay; 18% CP; 40% NDF). Feed intake was recorded daily, and total feces were collected during wk 7, 9, and 11 to determine N excretion (NE), N balance (NB), N efficiency (Nef), and N absorbed (Nab). Spot samples of urine were taken for 3 d on wk 7, 9, and 11 to determine urine volume and N excreted by urine by creatinine concentration. The mixed model of SAS was used, considering calf as experimental unit, Trt as fixed effect and block as random. Means were compared by Tukey (P < 0.05). On wk 9, calves on HH and LH had more NE than calves on HL and LL and had negative NB (Table 1). No differences were observed on Nef (wk 7: 56 � 10.2%, P = 0.89; 9: −6 � 10.2%, P = 0.89; 11: 37 � 8.1%, P = 0.73) or Nab (wk 7: 91 � 1.0%, P = 0.82; 9: 74 � 4.1%, P = 0.13; 11: 86 � 1.4%, P = 0.15). Weaning seems to have affected N metabolism of calves (wk 9), but a high nutritional plane after weaning allowed to recover N intake and N balance 3 wk after weaning.Table 1.

Wk 7, g/kg BW0.75
 N intake2.
 N output1.
 N balance1.
Wk 9, g/kg BW0.75
 N intake1.
 N output1.5a1.2b1.7a1.2b0.12<0.01
 N balance−0.4b0.3a−0.3b0.3a0.180.04
Wk 11, g/kg BW0.75
 N intake2.9a2.0b3.2a2.2b0.14<0.01
 N output1.
 N balance1.

Keywords: nitrogen, digestibility, heifer.