Effect of supplementing veld hay with tropical legumes Desmodium uncinatum, Stylosanthes guianensis and Macroptilium atropurpureum on intake, digestibility, outflow rates, nitrogen retention and live weight gain in lambs

In 2 consecutive years using fresh batches of lambs, poor-quality veld (natural pasture) hay dominated by Hyparrhenia grasses (23 g crude protein per kg dry matter) was fed ad libitum either alone or with one of three herbaceous tropical legumes at the rate of 0.25 of total feed consumed. The legumes Desmodium uncinatum (Silverleaf desmodium), Stylosanthes guianensis (Oxley fine-stem stylo) and Macroptilium atropurpureum (Siratro) contained 143, 114 and 159 g crude protein per kg dry matter, respectively, and, to varying degrees, increased feed intake, digestibility, energy intake and nitrogen retention and reduced live weight loss (P < 0.05). Legume supplementation also marginally increased the fractional outflow rate of particles from the rumen from 0.015 to 0.020 per hour (P > 0.05). Average daily consumption of total dry matter was 465 g in animals given veld hay alone compared with 636, 681 and 754 g in those supplemented with D. uncinatum, S. guianensis and M. atropurpureum, respectively. The daily intake of the basal veld hay was significantly increased (P < 0.05) by M. atropurpureum (574 g) but not by S. guianensis (514 g) and D. uncinatum (480 g). Average apparent digestibility coefficients of organic matter were 0.394, 0.440, 0.466 and 0.464 with veld hay alone, veld hay/D. uncinatum, veld hay/S. guianensis and veld hay/M. atropurpureum, respectively. Proportions of metabolisable energy intake relative to that required for maintenance were 0.61, 0.96, 1.11 and 1.20 in animals given veld hay alone and with D. uncinatum, S. guianensis and M. atropurpureum, respectively. Average calculated microbial nitrogen production was 3.46, 5.33, 6.07 and 6.58 g per day, respectively, in animals given veld hay alone and with D. uncinatum, S. guianensis and M. atropurpureum. Respective values for nitrogen retention and live weight gain were −1.44, 0.29, 0.70 and 1.06 g per day, and −98, −32, 0 and −8 g per day. Relative to nitrogen consumed per day, animals given D. uncinatum tended to excrete more nitrogen in their faeces (0.83) than those given S. guianensis and M. atropurpureum (0.71) probably due to a higher content of acid detergent insoluble nitrogen in D. uncinatum (608 g per kg total nitrogen) than in the other legumes (273 to 285 g per kg total nitrogen). Overall, M. atropurpureum appeared to be the best legume supplement for veld hay, followed by S. guianensis.