Effects of V a R Y I N G Zinc Concentrations on Quality of a L F a L F a for Lambs 1'2

Zinc concentrations in alfalfa hay were varied using a N-Zn liquid fertilizer as a foliar applicant (.34 or .68 kg Zn/ha) or as a soil fertilizer (4.07 kg Zn/ha). Mean concentrations of Zn across five cuttings of alfalfa in 2 yr were 18, 27, 41 and 21 mg Zn/kg DM for control, low foliar, high foliar and soil treatments, respectively. Each treatment was fed in ad libitum amounts to eight crossbred wether lambs (20 to 35 kg) in 6-wk growth and intake trials, followed by 2-wk digestibility and balance trials with individual lambs. For one cutting, hays were also fed in an 81-d trial to four ram lambs (30 to 35 kg) and live weight gain and testicular development were measured. Average daily gain (ADG) and intake over 6 wk differed (P<.O1) with cutting but not with Zn treatment. Average daily gain and testes weight of ram lambs also were not affected by treatment. In the metabolism trials, Zn treatment did not alter (P>.05) intake or dry matter digestibility (DMD) of alfalfa, but did influence digestibility of neutral detergent fiber (NDF). Digestible NDF (%) was higher (P<.05) for high foliar than for low foliar treatments. Apparent absorption and retention of Zn was significantly greater for control than for Zn-treated alfalfas and did not differ with cutting. Mean serum Zn concentrations for control, low and high foliar, and soil treatments were .79, .81, .78 and .75 tag Zn/ml, respectively, for all cuttings, with no differences due to treatment. Results do not suggest an appreciable response in lamb growth or Zn status to increased levels of Zn in a forage diet containing a marginal level of the element. (