Mineral Concentrations of Cool Season Pasture Forages in North Florida During Winter-Spring Grazing Season. I. Macrominerals and Forage Organic Constituents

ABSTRACT

Two experimental late fall-winter-spring grazing studies, each lasting two years, were conducted at the North Florida Research and Education Center (NFREC), Marianna, Florida to evaluate the organic constituents and macromineral concentrations of annual cool season pasture forages grazed by growing beef cattle. Eight 1.32 ha fenced pastures or paddocks were divided into two pasture land preparation/planting methods, four pastures for the sod seeding treatments and four for the prepared seedbed treatments. These pastures were planted with two different forage combinations: 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). Each of the four forage/land preparation combination treatments was assigned to two pastures each year, thereby giving two replicates per year. Forage samples were collected at the start of grazing and twice monthly thereafter until the end of grazing season for each year, pooled by month, and were analyzed for calcium (Ca), phosphorus (P), sodium (Na), potassium (K), magnesium (Mg), dry matter (DM) yield, crude protein (CP), and in vitro organic matter digestibility (IVOMD). Blood plasma samples were also collected from the tester cattle during the spring season of year 2 of Study 2 and were analyzed for Ca, P, and Mg. Month differences were observed in forage concentrations of P and K (P < 0.0001), and Mg (P < 0.05) in both studies, Ca (P < 0.01) in Study 1 only, and Na (P < 0.05) only in Study 2. Year affected P, K, and Mg concentrations in Study 1 and Ca, P, and Na concentrations in Study 2. In Study 2, forage type by month interactions on Ca, K, and Mg concentrations were noticed (P < 0.01). Forage Ca was lower (P < 0.05) than the critical level for all months from the oat plus ryegrass pastures, and for early winter months and late spring months from ryegrass only pasture. Forage Na concentrations were consistently low throughout the grazing season and unaffected by forage type or land cultivation methods used in both studies. Low Mg concentrations of both forage types in Study 2 (also with high K concentrations) were indicative of a potential risk of grass tetany (hypomagnesemia) for grazing ruminants. Forage DM yields were highly variable with fluctuations among the experimental months and were found to be highest in the spring months, with decreasing yields towards the end of the grazing season in both studies (P < 0.0001). The CP concentrations were greater than the required levels and both CP and IVOMD decreased gradually by month in both studies (P < 0.0001). Normal blood plasma concentrations of Ca and P obtained were indicative of a good overall status of these minerals in the animal's body. Plasma Mg concentrations were slightly above the critical level for cattle from both forage types. In summary, the macrominerals most likely to be deficient in North Florida during the cool season would be Ca, Na, and Mg. Special attention should be given to supplementation of Mg since forages reflected a marginal deficiency of this mineral and high K concentrations were found.

Keywords:

• macrominerals
• winter-spring
• grazing
• forages
• Florida
• 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 method (sod-seeded vs. 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: not significant (P > 0.05) for Study 1

^a Study 1 (2001-2002 and 2002-2003): year highly significant for P (P < 0.01) and significant for K and Mg (P < 0.05) and not significant(NS) (P > 0.05) for Ca and Na. Pasture land preparation/planting method (LP) and pasture forage type (For): NS (P > 0.05) for all the minerals. LP∗For: NS (P > 0.05) for all. Month: significant for Ca (P < 0.01) and Mg (P < 0.05) and highly significant for P and K (P < 0.0001) and NS (P > 0.05) for Na

^b Mean = least square mean

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

^b Level of significance: , ,

(∗) P < 0.05

(∗∗) P < 0.01

(∗∗∗) P < 0.0001

^c LP: pasture land preparation/planting method (sod-seeded vs 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 highly significant for IVOMD (P < 0.0001), and not significant (NS) for DM and CP (P > 0.05). Pasture land preparation/planting method (LP); significant for IVOMD (P < 0.01) and CP (P < 0.05), and NS for DM (P > 0.05). Pasture forage type (For) and LP∗For: NS for all three (P > 0.05). Month: highly significant for DM, IVOMD and CP (P < 0.0001)

^b Mean = least square mean

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

^a Study 2 (2003–2004 and 2004–2005): year significant for Ca (P < 0.05) and P (P < 0.01). Treatment values: least squares means

^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 significant for Na (P < 0.05) and not significant (NS) for K & Mg (P > 0.05)

^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 highly significant for CP (P < 0.01) and not significant (NS) for DM and IVOMD (P > 0.05). Treatment values: least squares means; Pasture forage type (For): significant for IVOMD (P < 0.05) and NS for DM and CP (P > 0.05). Pasture land preparation/planting method (LP): significant for IVOMD (P < 0.05), and NS for DM and CP (P > 0.05). LP∗For: NS for all (P > 0.05). For∗Month: highly significant for DM and CP (P < 0.01), and NS for IVOMD (P > 0.05). Month: highly significant for DM, IVOMD and CP (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, 10, 12, 16, 16, and 16 for IVOMD and CP and n = 4, 6, 12, 12, 16, 16, and 16 for DM for Nov, Dec, Jan, Feb, Mar, Apr, and May, respectively

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

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

^c For: pasture forage type (oats/ryegrass or ryegrass); NS (P > 0.05)

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

^b Mean: least square mean

^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