A new insight about the selection and intake of forage by ewes and lambs in different production systems on pasture

Keeping lambs with their dams and providing concentrate supplement for weaned lambs are two strategies used in lamb meat production systems on pasture that may affect the way that lambs explore, select, and ingest the forage while grazing. Thus, this study aimed to evaluate the selection and intake of forage by ewes and lambs using the continuous bite monitoring method in two pasture-based production systems: non-weaned and nonsupplemented lambs (NW); and weaned lambs supplemented with concentrate (WS). Continuous bite monitoring is based on a bite-coding grid that allows the estimation of bite mass, intake rate, selection of plant species and plant parts by grazing animals. Two experiments were carried out during September-November of two subsequent years on a mixed pasture of black oat (Avena strigosa Schreb.) and annual ryegrass (Lolium multiflorum Lam.) established over a perennial Tifton 85 (Cynodon spp.) pasture. On the second year, a third treatment including only the dams of weaned lambs - dry ewes - was also evaluated. In the WS system, lambs were supplemented with concentrate feed at 2% of body weight (BW)/day on a dry matter (DM) basis. Both experiments lasted 46 days, and a continuous stocking management with the forage allowance maintained at 16% BW in DM/day for all treatments. There was a high degree of variability on botanical and morphological composition of forage that was ingested by lambs and ewes, with ranges of 3-14 and 8-11 bite categories for NW lambs and ewes, respectively; 12-15 bite categories for WS lambs, and 8 bite categories for dry ewes. There was similarity between the forage ingested by lambs and ewes in the NW system, except for inflorescences of black oat and annual ryegrass, that were ingested in greater proportions by ewes. WS lambs ingested the most diverse forage diet, which appeared to explore the superior strata of pasture (above 10-15 cm of height) more frequently, and grazed inflorescences and senescent material in higher proportions than NW lambs. Dry ewes showed higher intake of Paspalum spp., Kikuyu grass and other voluntary species and weeds compared to NW ewes. These results suggest that the production system affects the way that lambs explore the pasture and compose their forage diet, with WS lambs ingesting the most diverse diet. The increased intake of inflorescence and, eventually, voluntary species and weeds may be a strategy used by lactating and dry ewes to extend the vegetative stage of high-quality forage species and reduce the population of low-quality plant species on pasture.