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<p>This study evaluated the optimal dietary crude protein (CP) level for growth, digestibility, and feed efficiency in crossbred bull calves (local indigenous zebu, <i>Bos indicus</i> × Holstein Friesian, <i>Bos taurus</i>) reared under tropical conditions in Bangladesh. Twenty-one calves (78 ± 5&#xa0;kg BW, 12–15 months) were randomly assigned within blocks (<i>n</i> = 7 per treatment) to three isoenergetic diets containing 10.12% (T0), 11.25% (T1; NRC (Nutrient requirements of beef cattle, 7th rev edn, 1996) recommendation), or 12.50% (T2) CP for 75 days following a 14-day adaptation period. A 7-day total fecal collection assessed nutrient digestibility. Increasing dietary CP improved CP and metabolizable energy intake without significantly affecting dry matter intake. Average daily gain (ADG) increased linearly (<i>P</i> &lt; 0.001) from 0.36 to 0.53&#xa0;kg d⁻¹, with only T2 reaching the target 0.5&#xa0;kg d⁻¹. Feed conversion ratio improved from 6.22 to 4.69 (<i>P</i> = 0.003), and the energy cost of gain decreased from 66.1 to 50.1&#xa0;MJ kg⁻¹. Apparent digestibility of dry matter, crude protein, and crude fiber increased by 7–8% points (<i>P</i> &lt; 0.05), raising total digestible nutrients from 59.6% to 64.6%. Nitrogen retention improved from 10.8 to 15.9&#xa0;g d⁻¹, with nitrogen use efficiency rising from 28.2% to 32.1%. Elevated heat and humidity likely increased maintenance demands and nitrogen turnover, making protein the primary limiting nutrient. The results suggest that crossbred bull calves need approximately 12–12.5% dietary CP, about 10% higher than temperate-zone standards, to achieve efficient 0.5&#xa0;kg d⁻¹ growth under tropical heat stress conditions. Moderate CP enrichment enhanced digestibility, feed efficiency, and nitrogen utilization without excessive waste, demonstrating that precise protein supplementation provides an economically and environmentally balanced approach for sustainable beef production in humid tropical regions.</p>

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Optimal dietary crude protein for growth, digestibility, and feed efficiency in crossbred bull calves under tropical conditions in Bangladesh

  • 期刊论文

  • 发表日期：

    2026年3月31日

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  • S. H. Joya,
  • Z. H. Khandaker,
  • M. B. Kakee,
  • R. S. Heera,
  • M. T. Islam

摘要

This study evaluated the optimal dietary crude protein (CP) level for growth, digestibility, and feed efficiency in crossbred bull calves (local indigenous zebu, Bos indicus × Holstein Friesian, Bos taurus) reared under tropical conditions in Bangladesh. Twenty-one calves (78 ± 5 kg BW, 12–15 months) were randomly assigned within blocks (n = 7 per treatment) to three isoenergetic diets containing 10.12% (T0), 11.25% (T1; NRC (Nutrient requirements of beef cattle, 7th rev edn, 1996) recommendation), or 12.50% (T2) CP for 75 days following a 14-day adaptation period. A 7-day total fecal collection assessed nutrient digestibility. Increasing dietary CP improved CP and metabolizable energy intake without significantly affecting dry matter intake. Average daily gain (ADG) increased linearly (P < 0.001) from 0.36 to 0.53 kg d⁻¹, with only T2 reaching the target 0.5 kg d⁻¹. Feed conversion ratio improved from 6.22 to 4.69 (P = 0.003), and the energy cost of gain decreased from 66.1 to 50.1 MJ kg⁻¹. Apparent digestibility of dry matter, crude protein, and crude fiber increased by 7–8% points (P < 0.05), raising total digestible nutrients from 59.6% to 64.6%. Nitrogen retention improved from 10.8 to 15.9 g d⁻¹, with nitrogen use efficiency rising from 28.2% to 32.1%. Elevated heat and humidity likely increased maintenance demands and nitrogen turnover, making protein the primary limiting nutrient. The results suggest that crossbred bull calves need approximately 12–12.5% dietary CP, about 10% higher than temperate-zone standards, to achieve efficient 0.5 kg d⁻¹ growth under tropical heat stress conditions. Moderate CP enrichment enhanced digestibility, feed efficiency, and nitrogen utilization without excessive waste, demonstrating that precise protein supplementation provides an economically and environmentally balanced approach for sustainable beef production in humid tropical regions.