INTAKE AND DIGESTION OF LOW-QUALITY, MEDIUM-QUALITY, AND HIGH-QUALITYGRASS HAYS BY LAMBS RECEIVING INCREASING LEVELS OF CORN SUPPLEMENTATION

Thirty wether lambs (52.5 +/- 1.5 kg) were used in a replicated 3 x 5 factorial treatment arrangement and four periods to determine dietary intake and digestibility of three ground forages with increasing level s of supplemental ground corn. Forages were a mature, low-protein gras s hay (LQH; 5.2% CP), an immature, medium-protein grass hay (MQH; 10.2 % CP), and an immature, high-protein grass hay (HQH; 14.2% CP). Supple mentation treatments were no supplement (NS), a protein supplement (PS ), protein plus .25% BW of corn (LC), protein plus .5% BW of corn (MC) , and protein plus .75% BW of corn (HC). Crude protein intake (1.4 g/k g BW) from supplements was equalized with soybean meal and corn gluten meal. Lambs were housed in metabolism crates. Supplements were fed at 0700 each morning after orts from the previous day's feeding were rem oved. Hay was subsequently offered at approximately the previous day's consumption plus 25%. Each of the four periods lasted 21 d. Sixteen d ays were allowed for diet adaptation. Feces were collected with fecal bags during d 17 to 21. Lambs receiving LQH and PS had higher forage ( P <.04) and total DMI(P <.001) than lambs fed LQH and NS. Corn supplem entation decreased forage intake (quadratic effect; P =.08), total int ake (quadratic effect; P = .08), and increased apparent DM digestibili ty (linear effect; P <.04) with lambs receiving LQH. Protein supplemen tation did not affect forage or total DMI (P >.11), and corn supplemen tation did not affect total DMI (P >.20) with either MQH or HQH. Forag e DMI by lambs fed MQH and HQH decreased linearly (P < .005) as corn s upplementation increased. Apparent DM digestibility increased linearly (P <.001) as supplementation increased for both MQH and HQH, and star ch digestion by lambs receiving all forages increased (P <.009) quadra tically as level of supplemental corn increased. Digestible DMI increa sed (P =.04) quadratically with lambs receiving LQH as level of supple mental corn increased, and digestible DMI increased (P =.05) linearly with lambs consuming MQH as level of supplemental corn increased. Inta ke of DE by lambs fed MQH increased linearly (P <.05) as corn suppleme ntation increased. Corn supplementation did not affect (P <.66) digest ible DMI or DE intake with HQH. These data suggest that response of la mbs to increasing levels of supplemental corn is dependent on forage q uality.