Dorper × Santa Ines F1 crossbred lambs under different grazing times and supplement levels in tropical regions: performance and macromineral requirements

Abstract

The objective of this study was to evaluate the performance and net requirements for calcium (Ca), phosphorus (P), magnesium (Mg), potassium (K) and sodium (Na) in Dorper × Santa Ines F1 crossbred lambs under different grazing times and supplement levels. We used 36 uncastrated male lambs with initial body weights (BW) of 15.5 ± 1.9 kg. Twelve animals were used as a reference group, and the remaining 24 animals were divided into three treatments according to grazing time and supplement level: 9 h × 1.2% BW, 6 h × 0.84% BW and 3 h × 0.48% BW. There were increases in the final BW, average daily gain (ADG) and dry matter intake (DMI) of pasture (p < .05) in lambs that grazed longer (9 h × 1.2% BW). Feed efficiency (G/F ratio) was similar between the 9 h × 1.2% BW and 6 h × 0.84% BW groups and both the groups were greater than the 3 h × 0.48% BW. However, there was a reduction in the DMI of concentrate, total DMI, and Ca, P, Mg and K intake (p < .05) for lambs that grazed longer. However, pasture DMI and sodium intake increased (p < .05) in animals that grazed for less time (3 h). The chemical composition of the empty bodies in DM, fat, ash, Ca and P showed the greatest values (p < .05) in groups with animals grazing 9 h with a supplement level of 1.2% BW. Net maintenance requirements were 0.101–0.202 g Ca/day, 0.204–0.408 g P/day, 0.053–0.105 g Mg/day, 0.386–0.771 g K/day and 0.105–0.211 g Na/day for crossbred lambs between 15 and 30 kg BW. For the same group, net requirements to gain 100/200 g/day BW were 1.171/2.341–1.667/3.333 g Ca/day, 0.694/1.398–0.998/1.995 g P/day, 0.027/0.054–0.032/0.063 g Mg/day, 0.098/0.195–0.091/0.182 g K/day and 0.315/0.629–0.311/0.621 g Na/day. Lambs grazing longer (9 h × 1.2% BW) displayed increased ADG and concentrate intake and reduced forage intake, which increased intake and body retention of Ca, P, Mg and K.