A randomized complete block experiment was conducted in 24 replicates using a total of 1,060 pigs. Pigs were bled at the 28-d period and plasma was analyzed for Zn and Cu. Because two stations weaned pigs at < 15 d (six replicates) and five stations at > 20 d (18 replicates) of age, the two sets of data were analyzed separately. The early-weaned pig group had greater (P < 0.05) gains, feed intakes, and gain:feed ratios for the 28-d postweaning period as dietary ZnO concentration increased. Later-weaned pigs also had increased (P < 0.01) gains and feed intakes as the dietary ZnO concentration increased. Responses for both weanling pig groups seemed to reach a plateau at 2,000 mg Zn/kg. Plasma Zn concentrations quadratically increased (P < 0.01) and plasma Cu concentrations quadratically decreased (P < 0.01) when ZnO concentrations were > 1,000 mg Zn/kg. Experiment 2 was conducted at seven stations (KY, MI, MO, NE, ND, OH, and OK) and evaluated the efficacy of an antibacterial agent (carbadox) in combination with added ZnO. The experiment was a 2 × 3 factorial arrangement in a randomized complete block design conducted in a total of 20 replicates. Carbadox was added at 0 or 55 mg/kg diet, and ZnO was added at 0, 1,500, or 3,000 mg Zn/ kg. A total of 918 pigs were weaned at an average 19.7 d of age. For the 28-d postweaning period, gains (P < 0.01), feed intakes (P < 0.05), and gain:feed ratios (P < 0.05) increased when dietary ZnO concentrations increased and when carbadox was added. These responses occurred in an additive manner. The results of these studies suggest that supplemental ZnO at 1,500 to 2,000 mg Zn/kg Zn improved postweaning pig performance, and its combination with an antibacterial agent resulted in additional performance improvements.
Nursery studies evaluating the efficacy of pharmacological concentrations of dietary Zn on postweaning pig performance have generally demonstrated positive growth responses (Holm, 1988, 1990; Poulsen, 1989; Hahn and Baker, 1993). These responses have been achieved at dietary concentrations of 2,000 to 4,000 mg Zn/kg (Poulsen, 1995; Smith et al., 1997; Hill et al., 2000). The oxide form of the mineral seems to be critical in achieving these response benefits and is less toxic than other inorganic Zn sources (Hahn and Baker, 1993; McCully et al., 1995; Schell and Kornegay, 1996). High dietary concentrations of ZnO increased liver Zn (Schell and Kornegay, 1996; Carlson et al., 1999) but decreased liver Fe concentrations (Cox and Hale, 1962). Carlson et al. (1999), however, did not affect liver Cu or Fe concentrations when high dietary ZnO concentrations were fed to weanling pigs for a 2- to 4-wk period.
Copper sulfate provided at dietary concentrations substantially higher (125 to 250 mg Cu/kg) than the NRC (1998) requirement (6 mg Cu/kg) has also resulted in improved nursery pig performance (Braude, 1967; Prince et al., 1979; Edmonds et al., 1986). The data from Beames and Lloyd (1965) demonstrated an additive growth response when a high dietary Cu concentration was fed in combination with an antibiotic. Studies using various antibiotics or antibacterial agents in combination with CuSO4 have also demonstrated an additive performance effect with weanling pigs (Stahly et al., 1980; Roof and Mahan, 1982). When high concentrations of CuSO4 (250 mg Cu/kg) or ZnO (2,000 or 3,000 mg Zn/kg) were tested, growth responses occurred with each mineral source but were not additive (Smith et al., 1997; Hill et al., 2000). Experiments were conducted by the North Central Regional Swine Nutrition Committee (NCR-42) to further evaluate the 1) feeding of various dietary concentrations of ZnO on postweaning pig performance and blood Zn and Cu concentrations and 2) feeding of an antibacterial agent in combination with ZnO on weanling pig performance.
Materials and Methods
The first experiment evaluated the efficacy of five dietary concentrations of supplemental ZnO fed to postweaning pigs in a randomized complete block design. The concentrations evaluated were 0, 500, 1,000, 2,000, and 3,000 mg Zn/kg using a common source of ZnO that contained 72% Zn (Prince Agri Products, Quincy, IL). Seven university research stations (IA, MI, MN, MO, NE, ND, and OH) participated in the experiment for a total of 24 replicates (each contributed a minimum of two replicates). The experiment included 1,060 crossbred pigs of various genetic crosses that were weaned at an average age of 19.1 d (range 11 to 25 d) and an average BW of 6.0 kg (range 3.9 to 8.4 kg). Upon weaning, pigs were allotted to treatment pens on the basis of weight, sex, and litter using an equal number of pigs per pen within each replicate. Each station differed in its facility, management, and laboratory methodology, but the procedures followed within each replicate were identical. Pigs were housed in nursery facilities that contained either slotted concrete or plasticcovered wire, mesh-floored pens, with room temperatures adjusted when needed to meet the comfort zone of the pig. Pig information and other experimental conditions for the seven stations that conducted the experiment are presented in Table 1.
Postweaning diets contained both animal and vegetable protein sources and were formulated to provide a dietary lysine concentration of 1.35% (total) for the initial 14-d postweaning period and 1.15% (total) lysine for the 14- to 28-d postweaning period. Vitamin and trace mineral premix compositions differed among stations but each premix met or exceeded NRC (1988) requirements. Each station added the antibiotic chlortetracycline at 220 mg/kg to the nursery diets. Supplemental ZnO was added to treatment diets at the appropriate concentration at the expense of corn. The composition of the basal diets is presented in Table 2. Diets were subsampled at mixing and subsequently analyzed for Zn, Fe, and Cu. The analyzed basal diets averaged 291 and 300 mg Zn/kg, 265 and 280 mg Fe/kg, and 16 and 15 mg Cu/kg for the two production phases, respectively.
Pigs consumed their treatment diets on an ad libitum basis in meal form during the 28-d experimental period. Pig weights and feed intakes were collected weekly. At the end of the 28-d study, blood was collected from the vena cava from all or from randomly selected pigs within each treatment pen; a similar number of pigs was bled in each pen for each replicate. Pigs from six replicates (n = 350 pigs) in the early-weaned group and 14 replicates (n = 480 pigs) in the later-weaned group were bled, and the blood was centrifuged and the plasma separated, frozen, and subsequently analyzed for Cu and Zn.
Because of the positive growth response to added ZnO in Exp. 1, this experiment was conducted to evaluate whether there was an interaction between ZnO and an antibacterial agent. The experiment was a 2 × 3 factorial arrangement of treatments and was conducted in a randomized complete block design. Carbadox (Mecadox; Pfizer Animal Health, Terre Haute, IN) inclusion (0 or 55 mg/kg) was the first factor and the dietary concentration of ZnO (0, 1,500, or 3,000 mg Zn/kg) was the second factor tested. The experiment was conducted at seven university research stations (KY, MI, MO, NE, ND, OH, and OK). Each station contributed a minimum of two replicates for a total of 20 replicates. A total of 918 crossbred pigs of differing genetic crosses were weaned at an average age of 19.7 d (range 14 to 21 d) and an average BW of 6.5 kg (range 5.8 to 7.0 kg). Although cooperating stations were not identical to those of Exp. 1, experimental conditions were generally similar to those in the previous experiment and identical within replicate. Pig and experimental facility information for the cooperating stations is presented in Table 1.