A diverse diet increases animal growth performance and carcass yield of grazing lambs

Abstract

The current experiments were conducted across two lamb finishing seasons (2019 [experiment 1; Exp1] and 2020 [experiment 2; Exp2]). In both experiments lambs were provided a monotonous (MON) diet (annual ryegrass [Lolium multiflorum L.] during 2019 and perennial ryegrass [L. perenne L.] and white clover [Trifolium repens L.] during 2020) or a diverse (DIV) diet composed of spatially separated strips sown to chicory (Chicorium intybus L.), plantain (Plantago lanceolata L.), perennial ryegrass, lucerne (Medicago sativa L.), and dock (Rumex obtusifolius). During Exp1, the DIV lambs had a stocking rate (SR) of either 80, 95, 100, or 110 m²/lamb/wk, whereas the MON lambs had a 100m²/lamb/wk SR. In Exp2, the SR aimed to allocate the MON lambs with twice the forage allowance (kg DM/lamb/d) as DIV lambs. In Exp1, all lambs provided DIV had a greater (P < 0.01) average daily gain (ADG; + 130%) than MON rams, independent of the SR. Accordingly, DIV had greater (P < 0.05) hot carcass weight (HCW; + 26%) and aged carcass weight (CW; + 27%) compared with MON, across all SR. The 80 m²/lamb/wk SR tended to have a greater (P = 0.10) dressing percentage and had similar (P = 0.29) drip loss percentage to the MON lambs, while the other DIV lamb SR all had greater (P < 0.05; +12%) dressing percentages and lower (P < 0.05) drip loss percentage than MON lambs. In Exp2, DIV lambs had greater (P < 0.01) ADG (+37%), HCW (+15%), and dressing percentage (+6%) compared with MON lambs. This improved animal performance occurred despite being offered 57% less (P = 0.01) dry matter (DM), 56% less (P < 0.01) digestible DM, and 57% less (P = 0.02) metabolizable energy per lamb per day. Ultimately, these experiments demonstrate that providing growing lambs a functionally diverse diet improves animal growth performance and carcass weight compared with a monotonous diet of annual ryegrass or a mixed sward containing perennial ryegrass with white clover. LAY SUMMARY Recent research has demonstrated that offering dietary diversity to growing lambs may improve well-being and growth performance relative to monotonous diets that are traditionally fed. Two experiments were conducted over 2 yr to determine the growth-promoting benefits of offering a diverse diet composed of spatially separated sown strips of perennial ryegrass, plantain, chicory, broad-leaf dock, and alfalfa compared with monotonous diets of Italian ryegrass (experiment 1, Exp1) or perennial ryegrass with white clover (experiment 2, Exp2). In Exp1 the monotonous treatment group were stocked at a rate of 100 m²/lamb/wk, while the diverse fed lambs were stocked at either 80, 95, 100, or 110 m²/lamb/wk. In Exp2, the lambs were stocked at 122.5 m²/lamb/wk in the monotonous treatment, while the diverse lambs were stocked at 74.3 m²/lamb/wk, on average. Lambs offered diverse swards in the 80m²/lamb/wk group in Exp1 and the lambs offered diverse swards in Exp2 were allocated much less area, dry matter, crude protein, and metabolizable energy than the lambs offered monotonous swards, yet still had 34% or greater average daily gain and 13% or greater hot carcass weight. These results suggest that lambs will grow at appreciably faster rates when offered functionally diverse swards, resulting in greater saleable carcass weight compared with lambs offered monotonous swards of Italian ryegrass or Perennial ryegrass with white clover.