Individual mineral supplement intake by ewes swath grazing or confinement fed pea-barley forage
Sixty mature ewes (non-pregnant, non-lactating) were used in a completely randomized design to determine if feeding method of pea-barley forage (swath grazing or hay in confinement) had an effect on individual ewe mineral consumption and variation in supplement intake. Thirty ewes were randomly allocated to 3 confinement pens and 30 ewes were randomly allocated to 3 grazing plots. The study was conducted September 25 to October 15, 2010 and September 6 to 19, 2011. Targhee ewes (65.4 ± 5.84 kg BW) were used in 2010. Rambouillet ewes (61.9 ± 6.28 kg BW) were used in 2011. Ewes had ad libitum access to food, water, and a mineral supplement containing 11 to 12.5% salt with 2% titanium dioxide added as an external marker to estimate individual mineral intake. Forage intake was calculated using estimates of fecal output obtained by dosing gelatin capsules containing 2 g chromic oxide every day for 14 d, and in vitro 48-h DM indigestibility. Fecal grab samples were collected from each individual ewe for a period of 7 d and composited by ewe. Forage and mineral intakes were analyzed using individual ewe as the experimental unit. A year x treatment interaction (P < 0.01) existed for forage DMI and mineral DMI. Ewes in confinement consumed more forage than grazing ewes in 2010 (2.60 vs. 1.86 kg/d, respectively), but less than grazing ewes in 2011 (1.99 vs. 2.49 kg/d, respectively). Mean mineral intake was highest (P < 0.01) by grazing ewes in 2011 and 2010 (average 69 g/d), intermediate by ewes in confinement in 2010 (57 g/d), and lowest by ewes in confinement in 2011 (31 g/d). A year x treatment interaction (P = 0.05) existed for mineral DMI CV. Mineral DMI CV was higher (P = 0.04) for the confinement treatment than the grazing treatment in 2011 (67.2 vs. 33.7%), but similar for confinement and grazing treatments in 2010 (55.4 vs. 46.5%, respectively). In this study, both swath grazing ewes and ewes in confinement consumed more mineral than recommended by the mineral manufacturer and the NRC indicating that more research is needed to develop a better understanding of the factors that regulate and impact mineral intake.