Calcium, Phosphorus and Magnesium, but not Protein alone, Drive Growth in Pre-pubertal Captive Grasscutters (Thryonomys swinderianus)

Abstract

This study examined the interactive effects of dietary crude protein (CP), calcium (Ca), phosphorus (P), and magnesium (Mg) on pre-pubertal growth in captive grasscutters. Fifty weaned grasscutters (6 weeks old; initial mean weight 0.582 kg) were assigned to a 5 × 2 factorial design (diets × sex; n=10/treatment, 1:1 sex ratio). Treatments comprised four pelleted concentrate diets and fresh elephant grass (control, mimicking farmers' practice): Diet 1 (15% CP, 1.2% Ca, 0.6% P, 0.3% Mg); Diet 2 (15% CP, 1.5% Ca, 0.75% P, 0.33% Mg); Diet 3 (18% CP, 1.2% Ca, 0.6% P, 0.3% Mg); Diet 4 (18% CP, 1.5% Ca, 0.75% P, 0.33% Mg); elephant grass (11.37% CP, 0.9% Ca, 0.19% P, 0.13% Mg). Dietary CP influenced feed intake: Diets 1 and 2 (110.4 g/d) > Diets 3 and 4 (103.0 g/d), but elephant grass provoked the highest intake (160.1 g/d). Mineral synergies showed no clear feed intake effects (e.g., Diet 4 = 102.2 g/d vs. Diet 3 = 103.8 g/d; Diet 2 = 109.1 g/d vs. Diet 1 = 111.7 g/d). Water consumption increased with elevated mineral levels: Diets 2 and 4 (114.3 ml/d) > Diets 1 and 3 (106.7 ml/d). At 15% CP, elevated minerals (Diet 2) boosted average daily gain (0.013 kg vs. 0.010 kg), total weight gain (1.540 kg vs. 1.240 kg), and final body weight (2.132 kg vs. 1.808 kg) compared to Diet 1. At 18% CP, minerals had minimal impact (Diet 4 vs. Diet 3: 0.014 kg vs. 0.014 kg daily gain; 1.736 kg vs. 1.693 kg total gain; 2.317 kg vs. 2.275 kg final weight). It is concluded that synergies of elevated Ca, P, and Mg drive growth in CP-restricted diets (≤15%) beyond CP alone, and even at 18% CP, a mineral threshold is required to optimize pre-pubertal growth of captive grasscutter.