Plant feed additives (PFA) such as essential oils, extracts, and by-products from plant processing can be included in poultry diets. A total of 39 peer-reviewed articles were selected from the literature published in the last 20 years (2000–2020) comparing PFA antioxidant effects with synthetic antioxidant vitamins (mainly vitamin E) in poultry nutrition. The PFA can be used as an effective nutritional strategy to face poultry’s oxidative stress with positive impact also on their productivity and efficiency. They can partially or completely replace antioxidant synthetic vitamins (the latter administered at doses between 150 and 500 mg/kg) in animal diets, sometimes affecting important physiological functions or expressing synergistic effect with the synthetic antioxidants. It is crucial to take into consideration the issues related to the absorption and the metabolism of these additives and their interaction with gut microbiota. However, some form- and dose-dependent negative effects on growth performances are observed.

In the last two decades, the interest in natural plant feed additives (PFA) as alternatives to synthetic vitamins in livestock nutrition has increased. After a systematic review, a total of 19 peer-reviewed papers published between 2000 and 2020 were retained to evaluate the antioxidant effects of PFA compared to synthetic antioxidant vitamins (mainly vitamin E; VitE) in livestock nutrition. These studies demonstrated that PFAs could be as efficient as VitE in counteracting oxidative stress in pigs, rabbits, and ruminants. However, PFAs only positively affected animals’ growth performance and feed efficiency in some monogastric studies. The PFA can affect antioxidant enzyme activity in a dose- and method of administration-dependent manner. The antioxidant capacity of both PFA and VitE were depressed in cows fed with diets rich in polyunsaturated fatty acids. Variability among studies could be related to species differences. Despite the interest of the feed industry sector in PFA, there are still very few studies evaluating their antioxidant effect in species other than poultry.

The interest for safe and natural foods of animal origin is currently increasing the use of plant feed additives (PFA) as antioxidants in animal nutrition. However, studies with livestock animals dealing with PFA as antioxidants are scarce. The aim of the present review was to evaluate the antioxidant impact of PFA compared with synthetic vitamins on animal food product yield and quality. For this purpose, peer-reviewed studies published between 2000 and 2020 were collected. Most papers were carried out on ruminants (n = 13), but PFA were also tested in swine (n = 6) and rabbits (n = 2). The inclusion of PFA in the diets of pigs, rabbits, and ruminants improved the products’ quality (including organoleptic characteristics and fatty acids profile), oxidative stability, and shelf life, with some impacts also on their yields. The effects of PFA are diverse but often comparable to those of the synthetic antioxidant vitamin E, suggesting their potential as an alternative to this vitamin within the diet.

There is limited information on the impact of dietary supplementation with separate rumen-protected (RP) amino acids (AA), or with their combination, on ewes’ oxidative status. Sixty ewes were divided into five groups; C: basal diet (control); M: basal diet + 6 g/ewe RP methionine; L: basal diet + 5 g/ewe RP lysine; LML: basal diet + 6 g methionine and 5 g lysine/ewe; and HML: basal diet + 12 g methionine + 5 g lysine/ewe. Milk’s fat content increased in RP-AA fed ewes, while that of protein in M and L only. In blood plasma, the malondialdehyde (MDA) content was reduced in the M, LML, and HML compared to C-fed ewes. An increase in glutathione transferase activity in the blood plasma of the M and LML compared to the C and HML-fed ewes were found. In milk, lower values of the ferric reducing ability of plasma (FRAP) in the LML and HML-fed ewes and of 2,2′-Azino-bis 3-ethylbenzthiazoline-6-sulfonic acid (ABTS) in LML only, were found. Lysine increased milk’s FRAP values and MDA content. Both L and HML diets increased milk’s protein carbonyls content. Methionine improves the organism’s oxidative status, without adversely affecting milk’s oxidative stability. Lysine dietary inclusion affects negatively the oxidative stability of milk.

Scientific evidence demonstrates that plant feed additives (PFA) can be a viable alternative to synthetic antioxidant vitamins in poultry nutrition. PFA are represented by plants, essential oils, plant extracts, and by-products from herbal or crop processing. The use of PFA in the feed industry has increased in recent years as their biologically active compounds (polyphenols) have demonstrated antimicrobial and antioxidant effects in food-producing animals. However, few trials have directly compared the effects of PFA with synthetic vitamins. After a systematic literature review of studies comparing the effects of PFA and synthetic vitamins on poultry products in the last 20 years (2000–2020), a total of 44 peer-reviewed articles were included in the present work. A positive effect of PFA on poultry products’ oxidative stability during storage, organoleptic characteristics, and fatty acids profile has been observed without a specific impact on their performances. The effects of PFA are variable but often similar to those of vitamin E, suggesting the opportunity for a partial substitution of the latter in poultry diets.

Several studies have reported gross composition differences between organic and conventional milk; however, most studies have not considered other factors such as breed and diet ingredients, which are known to influence milk composition. Thus, this study aimed to provide a detailed characterization of Holstein-Friesian cow milk from organic (ORG) and conventional (CONV) herds with similar diet ingredients and in the same geographic area. Bulk milk samples (n = 225) of 12 ORG and 12 CONV farms were collected from September 2019 to August 2020. Farms were located in Northern Italy, included corn (meal, silage, or both) in the lactating diets, and had similar management conditions, but ORG herds spent a period on pasture. Factors affecting milk composition were tested using a linear mixed model, which included calendar month, farming system (ORG and CONV), and their interactions as fixed effects, and farm nested within farming system as random effect. Results showed that total fat, lactose, vitamin E, and AA did not significantly differ between farming systems. Total protein and casein contents were significantly lower in ORG than CONV herds, and somatic cell score (SCS) was greater in ORG than CONV. Among minerals, differences were observed for Fe, K, Mg, and S in some months, being lower in ORG than CONV for K, Mg, and S and greater or lower for Fe depending on the month. Among fatty acid (FA) groups, index, and ratios, only polyunsaturated FA and n-3 FA tended to be greater in ORG than CONV, and cis-FA were greater in ORG than CONV during October. Among the most abundant individual FA, only C16:1n-9 differed, being lower in ORG than CONV. The calendar month (and hence seasonal feed ration) was significant for milk gross composition, SCS, vitamin E, mineral profile (except for Mo, Sr, and Zn), AA profile, FA groups (except for medium-chain FA), FA index and ratios, and individual FA (except C16:0). We conclude that the overall milk composition was quite similar between the 2 farming systems. This could be related to the similarity of the selected farms, the Holstein-Friesian breed, and generally high level of intensity in both farming systems.