Effects of restricted feed intake on heat energy by different goat breeds

Sixteen Boer (B) goat doelings, 16 Spanish (S) doelings, and 8 Angora (A) doelings and 8 wethers, 283, 316, and 330 d of age initially (SEM = 5.0), respectively, were used to evaluate effects of nutrient restriction on heat energy (HE). During the first and second 10-wk phases, 8 animals of each breed were fed a 50% concentrate pelletized diet at a level adequate for maintenance and moderate energy accretion (CONT). Other animals were fed approximately 50% of these amounts in phase 1 relative to initial BW, followed by the higher level of feeding in phase 2 based on initial or actual BW when greater (REST). Average daily gain was 43, -20, 16, -78, 8, and -48 g in phase 1 (SEM = 5.0) and 26, 44, 50, 65, 27, and 32 g in phase 2 (SEM = 3.5) for A-CONT, A-REST, B-CONT, B-REST, S-CONT, and S-REST, respectively. Total HE was greater for CONT vs. REST in both phases (P < 0.001), greater in phase 1 for A than for B (P < 0.01) and S (P < 0.01), and greatest (P < 0.01) in phase 2 among breeds for A [481, 347, 430, 356, 424, and 338 kJ/kg BW0.75 per day in phase 1 (SEM = 11.1), and 494, 479, 445, 397, 444, and 406 kJ/kg BW0.75 per day in phase 2 (SEM = 11.3) for A-CONT, A-REST, B-CONT, B-REST, S-CONT, and S-REST, respectively]. Equations describing the temporal pattern of HE (kJ/kg BW0.75 per day), expressed as a percentage of the wk-0 value and corrected for corresponding breed × week CONT means, in phase 1 were: 95.8 ± 2.43 – (8.18 ± 1.144 × wk) + (0.655 ± 0.1098 × wk2) (R2 = 0.58) for A, 95.3 ± 2.63 – (4.34 ± 1.237 × wk) + (0.271 ± 0.1187 × wk2) (R2 = 0.41) for B, and 97.4 ± 2.21 - (4.69 ± 1.068 × wk) + (0.282 ± 0.1021 × wk2) (R2 = 0.53) for S. Phase 2 equations were: 78.9 ± 2.22 + (8.74 ± 1.036 × wk) - (0.608 ± 0.0095 × wk2) (R2 = 0.60) for A, 77.5 ± 2.10 + (3.30 ± 0.978 × wk) - (0.153 ± 0.0942 × wk2) (R2 = 0.39) for B, and 80.6 ± 2.50 + (4.50 ± 1.165 × wk) - (0.208 ± 0.1122 × wk2) (R2 = 0.43) for S. These equations indicate that changes in HE in response to nutrient restriction and realimentation were more rapid and of greater magnitude in A vs. B and S. The temporal pattern of decline in HE by B and S during restriction was similar, but the subsequent rise with realimentation was slower and smaller for B. In conclusion, most appropriate methods of predicting change in the maintenance energy requirement during and after periods of limited feed intake may differ among breeds of goats.