Effects of Copper, Zinc, and Manganese Source on Mineral Status, Reproduction, Immunity, and Calf Performance in Young Beef Females over a Two-Year Period1,2,3

Professional Animal Scientist, Aug 2005 by Ahola, J K, Baker, D S, Burns, P D, Whittier, J C, Engle, T E

Abstract

Crossbred beef females (n = 43 nulliparous heifers, yr 1; n = 37 primiparous cows, yr 2) were used to evaluate the effects of Cu, Zn, and Mn source on mineral status, reproduction, immunity, and performance in young grazing cattle in Eastern Colorado over a 2-yr period. Pregnant nulliparous heifers were stratified by expected calving date, BW, body condition score (BCS), and liver mineral status and assigned to treatments, which included 1) organic (ORG; 50% organic and 50% inorganic Cu, Zn, and Mn) and 2) inorganic (ING; 100% inorganic CuSO^sub 4^, ZnSO^sub 4^, and MnSO^sub 4^) trace minerals. Treatments were provided via ad libitum mineral feeders from 54 d (yr 1) and 81 d (yr 2) prior to the average calving date through 119 d (yr 1) and 135 d (yr 2) post-calving. Final liver Cu concentrations were greater (P

(Key Words: Beef Cattle, Performance, Trace Mineral Source.)

Introduction

Source (organic vs inorganic) of trace minerals such as Cu, Zn, and Mn has been shown to affect the performance of grazing beef cattle. Improved pregnancy rate to AI (Stanton et al., 2000), reduced postpartum interval to breeding (Swenson et al., 1998), and enhanced repair of uterine tissue following parturition (Manspeaker et al., 1987) have been associated with organic trace mineral supplementation. When organic trace minerals were supplemented to dams, suckling calves had enhanced performance (Kropp, 1990; Stanton et al., 2000) and immune response (George et al., 1997; Ward and Spears, 1999) compared with calves whose dams received inorganic trace minerals.

Other experiments, however, showed no effect of trace mineral source on reproductive performance (Olson et al., 1999) or calf performance (Olson et al., 1999; Muehlenbein et al., 2001). Because of reports of enhanced cattle performance and increased bioavailability associated with organic trace minerals, some cow-calf producers have begun to include organic trace minerals in grazing cow and calf mineral supplements (Spears, 1996). Comparisons of inorganic and organic trace mineral supplements on grazing cattle performance at NRC (1996) recommended concentrations for >1 yr are limited, particularly in young cows. Therefore, the objectives of this study were to determine the effects of Cu, Zn, and Mn source (at current NRC recommendations) on mineral status, reproductive performance, immune response, and calf performance over a 2-yr period in nulli- (yr 1) and primiparous (yr 2) grazing beef females.

Materials and Methods

Prior to the initiation of this experiment, all animal use, handling, and sampling techniques described herein were approved by the Colorado State University Animal Care and Use Committee.

Experimental Design. Over a 2-yr period, Red Angus-based beef females (n = 43 nulliparous heifers, yr 1; n = 37 primiparous cows, yr 2) at the Eastern Colorado Research Center (Akron, CO) were utilized for this experiment. Beginning 12 d prior to the initiation of the experiment in yr 1 (January 2001), 43 pregnant nulliparous heifers in the last trimester of gestation were stratified based on expected calving date, BW, body condition score (BCS), and liver mineral status and randomly assigned to one of six replicates (Table 1). Replicates were then assigned to one of two trace mineral treatments (n = 6 to 8 heifers per replicate). Treatments consisted of 1) organic (ORG; 50% organic and 50% inorganic Cu, Zn, and Mn; n = 21) and 2) inorganic (ING; 100% inorganic CuSO^sub 4^, ZnSO^sub 4^, and MnSO^sub 4^; n = 22) trace minerals.

All procedures described subsequently were repeated over 2 consecutive yr, except where noted. All females remained on the same treatment for both years. Inorganic trace minerals were supplemented as CuSO^sub 4^, ZnSO^sub 4^, and MnSO^sub 4^, whereas organic trace minerals were provided from a commercially available mineral proteinate source (Bioplex® trace minerals; Alltech Inc., Nicholasville, KY). Salt (NaCl) was added to the supplements to limit consumption of Cu, Zn, and Mn to approximately NRC (1996) recommended concentrations. Vitamins A, D, and E were added to meet NRC (1996) recommendations and were mixed thoroughly by hand at the time of mineral delivery to ad libitum trace mineral feeders. Ingredient composition and laboratory analysis of the trace mineral treatments are listed in Table 2. Basal forage and water trace mineral concentrations were determined using samples collected from pasture (freshly consumed forage was collected on a section of pasture representative of the pastures used in the experiment via two fistulated mature cows; samples were collected after rumens were evacuated and cows were allowed to graze for approximately 30 min), stored hay, and water sources. Trace mineral concentrations were as follows: pasture = 13.1 mg Cu/kg DM, 16.1 mg Zn/kg DM, and 36.6 mg Mn/kg DM; stored hay = 19.6 mg Cu/kg DM, 32.1 mg Zn/kg DM, and 52.2 mg Mn/kg DM; and water

After replicates and treatments were assigned, animals were housed by replicate in six separate native pastures consisting primarily of blue grama (Bouteloua gracilis), prairie sandreed (Calamovilfa longifolia), and needle and thread grass (Stipa comata). Early in yr 1 of the experiment (December through March), supplemental millet hay and range cubes were provided to compensate for poor winter forage quality. Estimated intakes of millet hay and range cubes were similar across treatments. Forage and range cube supplementation were discontinued as range quality increased during early spring.

Mineral treatments were provided at a single location in each pasture in ad libitum mineral feeders beginning 54 d (d -54; yr 1) and 81 d (d -81; yr 2) before the average calving date (d 0) of the females. Mineral treatments remained available for ad libitum consumption for 119 d (d 119; yr 1) and 135 d (d 135; yr 2) after the average calving date. Mineral treatments were also made available exclusively to the calves via creep feeders in each pasture when calves within the pasture averaged 98 d (yr 1) and 111 d (yr 2) of age. All calves received the same respective trace mineral treatment as their dams. In yr 1, on d 119 after the average calving date, treatments to cows were discontinued, and all cows within a treatment were combined and given access to a basal trace mineral supplement that did not contain any supplemental Cu, Zn, or Mn for a period of 160 d. Calves continued to have access to their respective mineral treatments via creep feeders until weaning at an average age of 185 d (yr 1) and 176 d (yr 2). On d -81 in yr 2, cows were sorted back into the same respective treatment groups as in yr 1, assigned to new replicates, and maintained on treatments until d 135 of yr 2. At the beginning of yr 2, there were six fewer females in the experiment (n = 37) compared with the beginning of yr 1 (n = 43) because some females were culled from the herd and removed from the experiment because they were not pregnant at the final pregnancy diagnosis at the end of yr 1 or for other reasons unrelated to this experiment. Of the six females removed, four were from the ORG treatment and two were from the ING treatment.