Average daily gain and blood fatty acid composition of cattle grazing the nonbloating legumes birdsfoot trefoil and cicer milkvetch in the Mountain West

Birdsfoot trefoil (BFT; Lotus corniculatus L.) is a tannin-containing, nonbloating forage legume that is productive and persistent under irrigation in the Mountain West region of the United States. The unique type and concentration of condensed tannins in BFT increase ruminant production. The hypothesis of this study was that the ADG of cattle grazing monoculture BFT would be greater than that of cattle grazing cicer milkvetch (CMV; Astragalus cicer L.), a nonbloating forage legume that does not contain tannins. Weaned, fall-born Tarentaise calves (mixed sex; n = 3) grazed monoculture legume pastures for 2 periods of 30 and 31 d beginning 3 June 2008 and 2 periods of 45 and 32 d beginning 3 June 2009 (steers; n = 2). Initial BW were 301 ± 15 kg and 282 ± 12 kg in 2008 and 2009, respectively. Treatments were Norcen and Oberhaunstadter BFT, previously shown to have low and medium tannin concentrations, respectively, and nontannin Monarch CMV, all similar in forage nutritive value to alfalfa (Medicago sativa L.). In 2008, ADG was greater for the medium-tannin BFT than for CMV in the first period (P = 0.07) but greater for CMV in the second period (P = 0.09). In 2009, gains were greater for both BFT cultivars than for CMV in the first period (P < 0.01) and did not differ among legume treatments in the second period. Weighted mean ADG in 2008 were 1.42, 1.35, and 1.64 kg/d for CMV, low-tannin BFT, and medium-tannin BFT, respectively, and in 2009, were 0.97, 1.25, and 1.40 kg/d for those respective legume pastures. Mean cattle blood plasma omega-6 to omega-3 fatty acid ratios ranged from 1.39 to 1.91 and were greater on BFT than CMV pastures (P < 0.01 to 0.02). Although based on limited cattle numbers, this study shows that perennial nonbloating legume pastures have the potential to produce high ADG in cattle.