Mineral Concentrations of Cool Season Pasture Forages in North Florida During the Winter-Spring Grazing Season: II. Trace Minerals

ABSTRACT

Trace mineral concentrations of annual cool season pasture forages grazed by growing beef cattle during late fall-winter-spring grazing season were evaluated during two experimental cool season grazing studies, each lasting two years at the North Florida Research and Education Center (NFREC), Marianna, Florida. Eight 1.32 ha fenced pastures or paddocks were divided into two groups of pasture land preparation/planting methods, four pastures for the sod seeding treatments (SS) and four for the prepared seedbed treatments (PS). Two different pasture forages, small grains, (rye/oats mix) with or without ryegrass for the first two years (Study 1); and oats with ryegrass or ryegrass only for the last two years (Study 2) were planted in these pasture lands. Each of the four forage, type, and cultivation combination treatments was assigned to two pastures each year, thereby giving two replicates per pasture treatment per year. Forage samples were collected at the start of pasture grazing and twice monthly thereafter until the end of grazing season, pooled by month, and analyzed for copper (Cu), iron (Fe), zinc (Zn), manganese (Mn), cobalt (Co), molybdenum (Mo), and selenium (Se). Liver biopsies and blood plasma samples were collected from the tester cattle only during the spring of year two of Study 2. Liver was analyzed for Cu, Fe, Mn, Co, Mo, and Se and plasma for Cu, Fe, Zn, and Se. Forage trace mineral concentrations were found to differ by month in Cu (P < 0.01), Fe and Zn (P < 0.0001) in both studies, and with Mn (P < 0.0001) in Study 2 only. Pasture forage type effects on Cu (P < 0.05), Fe and Zn (P < 0.01), and Se (P < 0.05) and forage type by month interactions on Cu and Mn (P < 0.0001), and Zn (P < 0.05) were observed in Study 2. Forage concentrations of Cu, Zn, Mn, and Mo in Study 1 and Mn, Mo, and Se in Study 2 were affected (P < 0.05) by pasture land preparation/planting methods in that these minerals were found to be lower from forages of sod-seeded treatments than from those of prepared seedbed treatments. Forage Cu concentrations were lower than the minimum requirements (10 ppm, DM) for beef cattle among months in both studies. Oats-ryegrass pastures of Study 2 had surprisingly low Fe concentrations (P < 0.01) in all months of the winter-spring grazing season. Cobalt, Mn, Mo, and Se did not vary much month to month during the winter-spring grazing months. All mean forage Se concentrations were lower than the requirements (0.10 ppm, DM) for grazing beef cattle. There were no differences (P > 0.05) in mean Se values between the two studies. Liver Cu, Fe, Co, and Se concentrations were sufficient to indicate adequate status of these minerals in tester animals from both forage types. Liver concentrations of Mn and Mo were slightly low, indicating a low status or these minerals. Plasma concentrations of Cu, Fe, Se, and Zn were all above the recommended concentrations for beef cattle. In conclusion, trace minerals deficient in North Florida during the cool season were Cu, Co, and Se, and a special consideration should be given to include adequate amounts while supplementing the mineral mixtures to growing beef cattle since forage samples reflected deficient concentrations of these minerals.

Keywords:

• forages
• Florida
• trace minerals
• deficiencies

Notes

^a Study 1; year 2001-2002 and 2002-2003 and Study 2: year 2003–2004 and 2004–2005. Late fall-winter-spring grazing season from November to June

^b Level of significance:

(∗) P < 0.05,

(∗∗) P < 0.01,

(∗∗∗) P < 0.0001.

^c LP: pasture land preparation/planting methods (sod-seeded or prepared seedbed).

^d For: pasture forage type (rye/oats or rye/oats/ryegrass for Study 1, and oats/ryegrass or ryegrass only for Study 2).

^e For∗month: no significant effects for study 1.

^a Study 1 (2001–2002 and 2002–2003); year was highly significant for Cu (P < 0.0001), significant for Fe (P < 0.01) and Zn (P < 0.05), and not significant (NS) for Mn (P > 0.05). Pasture land preparation/planting method (LP): significant for Cu and Zn (P < 0.01) and Mn (P < 0.05), and NS for Fe (P > 0.05). Pasture forage type (For): NS for all. LP∗For: NS for all. Month: highly significant for Fe and Zn (P < 0.0001), significant for Cu (P < 0.01), and NS for Mn (P > 0.05).

^b Mean = least square means.

^c SEM = standard error of mean; n = 2, 8, 4, 16, 16, 16, and 6 for Nov, Dec, Jan, Feb, Mar, Apr, and May, respectively.

^a Study 1 (2001–2002 and 2002–2003); year was not significant (NS) for Co, Mo, and Se (P > 0.05). Pasture land preparation/planting method (LP): significant for Mo (P < 0.01), and NS for Co and Se (P > 0.05). Pasture forage type (For): NS for all (P > 0.05). LP∗For: NS for all (P > 0.05). Month; NS for all (P > 0.05).

^b Mean = least square means.

^c SEM = standard error of mean; n = 1, 3, 4, 7, and 1 for Dec, Feb, Mar, Apr, and May, respectively.

^a Study 2 (2003–2004 and 2004–2005): year was highly significant for Fe. Treatment values: least squares means. Pasture forage type (For): significant for Cu (P < 0.05), and highly significant for Fe and Zn (P < 0.01). Pasture land preparation/planting method (LP): not significant (NS) for all minerals (P > 0.05). LP∗For: NS for all (P > .0.05). For∗month: highly significant for Cu (P < 0.0001), significant for Zn (P < 0.05), and NS for Fe (P > 0.05). Month: Significant for Cu (P < 0.05) and Fe (P < 0.01), and highly significant for Zn (P < 0.0001).

^b Pasture forage type 1 (For 1): oats/ryegrass.

^c Pasture forage type 2 (For 2): ryegrass.

^d SEM: standard error of mean; n = 4, 4, 8, 8, 16, 16, 16, and 8 for Nov, Dec, Jan, Feb, Mar, Apr, May, and June, respectively.

^a Study 2 (2003–2004 and 2004–2005): year was not significant (NS) for Mn, Co, Mo, and Se. Treatment values: least squares means. Pasture forage type (For): significant for Se (P < 0.05) and not NS for Mn, Co, and Mo. Pasture land preparation/planting method (LP): highly significant for Mn (P < 0.01) and Mo, significant for Se (P < 0.05) and NS for Co (P > 0.05). LP∗For: NS for all (P > 0.05). For∗month: highly significant for Mn (P < 0.0001) and NS for Co, Mo, and Se. Month: highly significant for Mn (P < 0.0001) and NS for Co, Mo, and Se.

^b Pasture forage type 1 (For 1): oats/ryegrass.

^c Pasture forage type 2 (For 2): ryegrass.

^d SEM = standard error of mean; n = 4, 4, 8, 8, 16, 16, 16, and 8 for Mn for Nov, Dec, Jan, Feb, Mar, Apr, May, and June, respectively and n = 9, 5, and 2 for Co, Mo, and Se for Mar, Apr, and May, respectively.

^a Samples collected; March of 2005. LP, For, and LP∗For; not significant (P > 0.05) for all the above trace minerals.

^b LP: pasture land preparation/planting method (sod-seeded or prepared seedbed).

^c For: pasture forage type (oats/ryegrass or ryegrass).

^a Samples collected; March of 2005. Pasture land preparation/planting method (sod-seeded vs prepared seedbed) and pasture forage type: not significant (P > 0.05). LP∗For: not significant (P > 0.05).

^b Pasture forage type 1 (For 1): oats/ryegrass.

^c Pasture forage type 2 (For 2): ryegrass.

^d Mean = least square means.

^e SEM = standard error of mean; n = 16 for Cu, Fe, and Mn and n = 6 for Co, Mo, and Se.

^a Samples collected; March of 2005. LP: significant for Fe and Se (P < 0.05). For, and LP∗For: not significant for all the above trace minerals (P > 0.05).

^b LP: pasture land preparation/planting method (sod-seeded or prepared seedbed).

^c For: pasture forage types (oats/ryegrass or ryegrass).

^a Samples collected; March of 2005. Pasture land preparation/planting method (LP): significant (P < 0.05) for Fe and Se only. Pasture forage type (For) and LP∗ For: not significant for all the above microminerals (P > 0.05).

^b Mean: least square means

^c SEM: standard error of means; n = 16.

^d Pasture forage type 1 (For 1): oats/ryegrass.

^e Pasture forage type 2 (For 2): ryegrass.