Intake and digestion of low-, medium-, and high-quality grass 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 levels of supplemental ground corn. Forages were a mature, low-protein grass 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). Supplementation 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/kg 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 removed. Hay was subsequently offered at approximately the previous day's consumption plus 25%. Each of the four periods lasted 21 d. Sixteen days 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 supplementation decreased forage intake (quadratic effect; P = .08), total intake (quadratic effect; P .08), and increased apparent DM digestibility (linear effect; P < .04) with lambs receiving LQH. Protein supplementation did not affect forage or total DMI (P > .11), and corn supplementation did not affect total DMI (P > .20) with either MQH or HQH. Forage DM by lambs fed MQH and HQH decreased linearly (P < .005) as corn supplementation increased. Apparent DM digestibility increased linearly (P < .001) as supplementation increased for both MQH and HQH and starch digestion by lambs receiving all forages increased (P < .009) quadratically as level of supplemental corn increased. Digestible DMI increased (P = .04) quadratically with lambs receiving LQH as level of supplemental corn increased, and digestible DMI increased (P = .05) linearly with lambs consuming MQH as level of supplemental corn increased Intake of DE by lambs fed MQH increased linearly (P < .05) as corn supplementation increased. Corn supplementation did not affect (P < .66) digestible DMI or DE intake with HQH. These data suggest that response of lambs to increasing levels of supplemental corn is dependent on forage quality.