Effects of supplementation and body condition on intake, digestion, performance, and behavior of yearling Boer and Spanish goat wethers grazing grass/forb pastures

Abstract

Sixteen Boer and 16 Spanish (Span) yearling wethers were used, with eight of each breed in different initial body condition (IBC; High and Low). Initial BW was 40, 25, 29, and 22kg (SE=1.4) and body condition score (BCS; 1=extremely thin and 5=very obese) was 3.9, 2.4, 3.6, and 2.7 (SE=0.12) for Boer-High, Boer-Low, Span-High, and Span-Low, respectively. There was one wether per breed×IBC treatment in each of eight 0.4-ha grass/forb pastures. Wethers in four control (Con) pastures were not supplemented with concentrate, whereas those in supplement (Sup) pastures received 0.9% BW (DM basis) of concentrate. The experiment was 126 days, with four periods 39, 28, 37, and 22 days in length. Forage mass was 2466, 2496, 3245, and 2495kg/ha for Con and 2226, 2378, 3100, and 2724kg/ha for Sup in periods 1, 2, 3, and 4, respectively (SE=199.0). The difference in intake of digested OM between breeds was much greater with than without supplemental concentrate (485 and 741g/day for Boer and 413 and 561g/day for Span without and with supplementation, respectively; SE=23.2). In accordance, supplementation increased (P<0.05) ADG by Boer but not Span wethers (6, 32, 82, and 51g for Boer-Con, Span-Con, Boer-Sup, and Span-Sup, respectively; SE=13.1). There was a trend (P=0.070) for greater ADG by Low vs. High IBC wethers (56 vs. 30g; SE=0.4), in agreement with overall greater (P<0.05) total DM intake relative to BW by Low IBC wethers (3.16 and 2.78% BW; SE=0.065). However, converse to the breed comparison, IBC and supplement treatment did not interact in ADG. Grazing time was less (P<0.05) with than without supplementation (5.8 vs. 6.9h; SE=0.22) and greater (P<0.05) for Boer vs. Span in period 1 (8.0, 6.9, 6.3, and 7.2h for Boer and 4.7, 5.9, 5.7, and 6.4h for Span in periods 1, 2, 3, and 4, respectively; SE=0.45), although IBC did not influence grazing time (6.2 and 6.6h for High and Low, respectively; SE=0.22) despite the difference in ADG and greater total DM intake relative to BW. In conclusion, supplementation increased ADG by Boer but not Spanish wethers and lessened grazing time, low IBC resulted in compensatory growth with increased DM intake relative to BW and ADG without affecting grazing time, and supplementation interacted with breed though not IBC.