Effects of Increasing Zinc, Using Zn Hydroxychloride, on Growth Effects of Increasing Zinc, Using Zn Hydroxychloride, on Growth Performance, Carcass Characteristics, and Economic Return of Performance, Carcass Characteristics, and Economic Return of Pigs Housed in a Commercial Environment Pigs Housed in a Commercial Environment

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Introduction
The addition of Zn to diets is a common practice in the swine industry.Several supplemental Zn sources are commercially available and have been extensively researched since the 1990s.The beneficial effects of added Zn for nursery pigs are well described; however, data are lacking regarding the impact of added Zn on performance and carcass characteristics of grow-finishing pigs.Recently, a study conducted by Carpenter et al. 3 compared increasing levels (50, 100, and 150) ppm of added Zn from two sources (ZnSO 4 and Zn hydroxychloride) in finishing pigs.They observed no effect of Zn source on growth performance.However, pigs fed diets with 100 ppm added Zn had greater ADG and final BW.Carcass yield increased linearly when pigs were fed diets with increasing Zn, and those fed Zn hydroxychloride had heavier HCW than those fed ZnSO 4 .Although growth performance was maximized with 100 ppm added Zn, the linear response in carcass yield might suggest an even greater requirement estimate to maximize carcass characteristics.Moreover, the improved carcass weight observed in pigs fed diets containing Zn hydroxychloride warrants further investigation.Thus, the objective of this study was to determine the impact of increasing Zn from Zn hydroxychloride on growth performance and carcass composition of pigs housed in a commercial environment.

Procedures
The Kansas State University Institutional Animal Care and Use Committee approved the protocol used in this experiment.The study was conducted at a commercial research facility in southwestern Minnesota.The barns were naturally ventilated and doublecurtain-sided.Each pen was equipped with a 5-hole stainless steel dry self-feeder and a bowl waterer for ad libitum access to feed and water.
A total of 2,430 pigs (PIC 337 × 1050; initial BW of 66.3 ± 1.55 lb) were used in a 113-d growth trial.Two identical barns were used in this trial for a total of 18 pens per treatment with 27 pigs per pen.Daily feed additions to each pen were accomplished using a robotic feeding system (FeedPro; Feedlogic Corp., Wilmar, MN) able to record feed amounts for individual pens.
Pens were randomly assigned to dietary treatment within weight blocks.The 5 dietary treatments consisted of 50, 87.5, 125, 162.5, and 200 ppm added Zn from Zn hydroxychloride (Intellibond Z, Micronutrients, Indianapolis, IN).A trace mineral premix without any added Zn was used for all experimental diets.Dietary treatments (Table 1) were offered in 5 phases.
Pens of pigs were weighed on d 0, 14, 27, 42, 59, 73, 90, and 113 of the trial to determine ADG, ADFI, and F/G.On d 90, the 3 heaviest pigs in each pen were tattooed with a treatment identification number and transported to a USDA-inspected packing plant (JBS Swift and Company, Worthington, MN) for carcass data collection.On the last day of the trial, final pen weights were taken and the remaining pigs were tattooed with a pen identification number and transported to the same packing plant for carcass data collection.Carcass measurements included HCW, loin depth, backfat, and percentage lean.Percentage lean was calculated from plant proprietary equation.Carcass yield was calculated by taking the pen average HCW divided by the pen average final live weight obtained at the farm.

Swine Day 2017
An economic analysis was performed to determine the financial impact of dietary treatments.The base diet cost in phases 1 to 5 was $ 223.83, $217.39, $210.68, $207.45, and $218.24,respectively.Intellibond Z was valued at $2.95/lb.Total feed cost per pig was calculated by multiplying the ADFI by the feed cost per pound and the number of days in each period, then adding the values of each period.Feed cost per pound of gain was calculated by dividing total feed cost per pig by overall gain.Gain value was obtained by multiplying carcass gain by an assumed value of $70.00 per cwt of carcass.Income over feed cost (IOFC) per pig was calculated by subtracting total feed cost from gain value.Data were analyzed using the GLIMMIX procedure of SAS version 9.4 (SAS Institute, Inc., Cary, NC) with pen as the experimental unit.The statistical model included dietary treatment as a fixed effect and barn and block nested within barn as random effects.Results were considered significant at P ≤ 0.05 and marginally significant at 0.05 < P ≤ 0.10.

Results and Discussion
Chemical analyses of complete diets are presented in Tables 2 and 3. Crude protein, total Ca, and total P levels were similar within dietary phase.The total analyzed Zn concentrations for diets formulated to 50, 87.5, 125, 162.5, and 200 ppm added Zn ranged from 89 to 173, 108 to 121, 134 to 147, 172 to 201, and 183 to 231 ppm, respectively.Of the 25 experimental diets, only 1 was outside the 20% analytical variation limits for Zn. 4rom d 0 to 42, increasing Zn decreased ADFI (linear, P = 0.043; Table 4) with a marginal decrease in ADG (linear, P = 0.092).The reduction in ADG elicited a marginal linear decrease in BW (P = 0.078).
From d 42 to 113, increasing Zn resulted in quadratic response (P = 0.042) in ADFI with intake decreasing, then returning to control values as dietary Zn increased.Pigs fed 87.5 ppm of Zn had the lowest ADFI.As a result of the decreased ADFI, increasing Zn marginally improved F/G (linear, P = 0.063).
For overall growth performance (d 0 to 113), there were marginally significant quadratic responses in ADFI (P = 0.073) and F/G (P = 0.067), with the lowest ADFI observed at 87.5 and the best F/G observed at 125 ppm added Zn.There was no evidence for differences in overall ADG, final BW, HCW, backfat, loin depth, lean percentage, mortality, and removal rate (P > 0.10).
Regarding economic effects, there was a marginally significant (P = 0.075) quadratic response in feed cost per pig with the lowest cost observed at 87.5 ppm added Zn.There was a marginally significant (P = 0.088) effect for a quadratic response in feed cost per pound of gain, with the lowest cost observed at 125 ppm added Zn.There was no evidence for differences in gain value and IOFC (P > 0.10).
In summary, increasing added Zn beyond 50 ppm to a basal diet negatively affected ADFI and ADG from d 0 to 42.However, F/G from d 42 to 113 tended to improve with increasing Zn.Overall, 50 ppm added Zn maximized ADG, but feeding 125 ppm Zn resulted in the best F/G with no evidence for differences in carcass characteristics.

Table 1 .
Composition of base diets (as-fed basis) 1

Table 3 .
Chemical analysis of phase 4 and 5 diets (as-fed basis) 1

Table 4 .
Effects of increasing added dietary Zn hydroxychloride on finishing pig growth performance, carcass characteristics, and economics1,2