Zinc, not arginine may boost piglet growth, oxidative status

Adding supplemental zinc may boost piglet growth and oxidative status, while supplemental arginine in feed has a limited influence on oxidative status or piglet growth, say researchers.

A team of researchers from the University of Laval in Canada explored the use and influence of arginine and zinc in the diets of weanling piglets. The team published its work in the journal, Animal Nutrition​​​.

“The objective of this study was to determine the impact of dietary arginine and zinc supplements on antioxidant and inflammatory status in weanling piglets raised in a conventional pig production facility,” ​the researchers said. “Our hypothesis is that this status should improve under the supplemented condition and lead to better growth performance.”​

The researchers found that adding the zinc supplement improved average daily gain (ADG), average daily feed intake (ADFI) and the gain to feed ratio (G:F) and that using either supplement lowered the malondialdehyde concentration. However, total antioxidant capacity and a drop in glutathione (GSH) grew from day 8 to 15 of the feeding trial – regardless of diet – although, total and oxidized GSH levels were higher on day 8 for piglets on the combined supplements diet.

Piglets receiving a diet with supplemental zinc also saw a reduced serum haptoglobin level, they said. Adding, “Increasing the dietary intake of zinc had a positive effect on the growth performance of weanling piglets through a mechanism that remains to be determined but likely involves improvement of the systemic antioxidant capacity (estimated as malondialdehyde concentration) and control of inflammation (haptoglobin concentration).”​

“Increasing the dietary intake of arginine had no positive effect on growth performance despite a positive impact on malondialdehyde status,” ​the researchers said. “Zinc and arginine supplements may act synergistically on GSH metabolism, but the mechanism involved remains to be determined.”

Why zinc and arginine?​

Weaning piglets in a commercial situation tends to start at 3 to 4 weeks of age, unlike what has been described as a “natural” process which starts at about 10 weeks, the researchers said. Commercially raised piglets are also separated from the sow and re-housed with new cohorts.

The change in diet, location and social environment brings on systemic inflammation, increased haptoglobin – a market of acute-phase inflammation – a high expression of pro-inflammatory cytokines in the intestine along with other symptoms of “systemic and intestinal oxidative stress,”​ they said.

“Oxidative stress is an unbalanced equilibrium between reactive oxygen species (ROS) production and the antioxidant system of the animal, resulting in an increase in oxidation products such as malondialdehyde, an indicator of oxidative stress,”​ they said.

Several previous studies found that adding doses of zinc to piglet diets – 2,000 to 3,000 mg/kg – during weaning helps growth performance and lowers incidents of diarrhea, the researchers said. Studies also explored the use of L-arginine at 0.5% to 1% of dry feed to boost growth and feed efficiency.

Arginine is an essential element involved in the synthesis of nitric oxide, they said. Higher production of nitric oxide has been linked to zinc release and increased metallothionein expression.

“Metallothioneins are Zn-storing sulfo-proteins involved in zinc homeostasis and have significant antioxidant properties,”​ they added.

Zinc supplementation also has been helped lower plasma malondialdehyde levels for piglets, the researchers said. It also supported antioxidant status during stress, especially when arginine levels were supplemented.

But no work has been done exploring a potential zinc-arginine interaction during periods of chronic “lipopolysaccharide-induced inflammation and oxidative stress,”​ they said.

Falling sanitary conditions can alter the antioxidant status of piglets, which is measurable by tracking decreased GSH levels and increased plasma haptoglobin, they said. In lab tests, injections of lipopolysaccharide can be used to stimulate the immune system and produce oxidative stress, but the conditions do not fully replicate the immune system changes and antioxidant response during commercial production.

Feed trial details​

During the feeding trials, 288, 21-day-old piglets were provided one of four diets for a 15-day period, the researchers said.

The diets included a corn-soybean meal control (NC0ARG0) feed, that feed supplemented with 2,500 mg/kg zinc (NZ2500ARG0), the control feed with 1% arginine (ZN0ARG1) and the control feed with both supplements (ZN2500ARG1).

Piglets and uneaten feed were weighed daily, they said. Blood samples were collected for analysis from a selection of piglets on each diet on day 0, 8 and 15.

Feed samples also were analyzed for energy content, nitrogen content and mineral levels, the researchers said.

Results​

Adding zinc to piglet diets improved growth performance and lowered serum levels of haptoglobin while boosting ADG, G:F and ADFI, the researchers said. Adding supplemental arginine tended to lower ADG and decreased ADFI, but did not significantly influence G:F.

“The zinc supplement improved piglet growth performance (ADG and ADFI) and oxidative status (based on malondialdehyde concentration),” ​they said. “The arginine supplement had a limited effect on growth performance and oxidative status under these conditions.”​

It is possible that the elevated levels of dietary arginine also increased the requirement for lysine, generating a lysine deficiency for piglets, they said. That potential deficiency may explain how the supplement improved oxidative status but did not improve growth performance.  

When averaged across all diets, total antioxidant capacity (TAC) increased throughout the trial as did the TAC: Total oxidant status (TOS) ratio, they said. Piglets on the combined diet also had an increased TAC:TOS ratio.

“The average concentration of plasma malondialdehyde was reduced from 4.37 to 3.91 μmol/L by zinc and from 4.38 to 3.89 μmol/L by arginine, as measured on d 8 and 15,” ​the researchers said. “In contrast, neither supplement had any effect on plasma TAC or TOS during the same period.”​

Zinc levels in plasma increased for piglets on the zinc-supplemented diets, but the increase was higher when arginine was also supplemented, they said. Piglets receiving the combined supplement diet also saw increased GSH on day 8 but not day 15 of the feeding trial.

Source: Animal Nutrition​

Authors: N. Bergeron, F. Guay