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Peer reviewed

Effect of a phytogenic feed additive on weaning-to-estrus interval and farrowing rate in sows

Robert K. Kis, PhD; Gabor Bilkei, DVM, PhD

RKK, GB: Bilkei Consulting, Raubbühlstrasse 4, 8600 Dübendorf, Switzerland; Tel.: 0041 1 820 02 26. Corresponding author: G. Bilkei, Bilkei Consulting, Raubbühlstrasse 4, 8600 Dübendorf, Switzerland.

Cite as: Kis RK, Bilkei G. Effect of a phytogenic feed additive on weaning-to-estrus interval and farrowing rate in sows. J Swine Health Prod. 2003;11(5):296-299. Also available as a PDF.


Primiparous and multiparous sows were supplemented during lactation and until the first standing estrus with oregano, chlortetracycline, or no supplement. Weaning-to-estrus interval was shorter in sows supplemented with oregano compared to other treatments, and farrowing rate was greater in sows supplemented with either chlortetracycline or oregano compared to untreated sows.

Keywords: swine, oregano, weaning-to-estrus interval, farrowing rate, total born litter size
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Received: August 27, 2002
Accepted: December 11, 2002

Weaning-to-estrus interval (WEI) is a major contributor to sow nonproductive days.1 Shortening WEI may be achieved by zootechnical methods (eg, feeding management, flushing, breeding management practices) or biotechnical methods (eg, use of exogenous gonadotropins).2

Oregano feed supplementation exerts positive effects against various gastrointestinal infectious or multifactorial diseases.1,3-16 Khajarern and Khajarern8 found that when essential oils of the plant Origanum vulgare (commonly called oregano) were fed to sows, there was a significant positive effect on live born litter weights, weaning weights, preweaning mortality, and sow feed intake during lactation. There have been no previously published reports on the effect on WEI, farrowing rate (FR), and subsequent total born litter size when oregano essential oils are fed to a large number of sows under field conditions.

Material and methods


This trial was conducted between April and August 2002, in a 1600-sow, indoor production unit in Alföld, Hungary. A total of 132 primiparous and 138 multiparous sows (Landrace x Duroc, F1 generation) were used in the study. The herd was of high health status, with minimal signs of respiratory disease in finishing pigs. Sows were vaccinated against erysipelas during the second trimester of pregnancy, and against pseudorabies, leptospirosis, and Escherichia coli (with a commercial killed E coli vaccine to prevent diarrhea in neonatal piglets) during the third trimester.

Study groups and study design

Sows were assigned at parturition to one of three treatment groups, with 44 primiparous and 46 multiparous animals in each. The animals were identified with ear tags of different colors for each treatment group. During lactation, and from weaning to first standing estrus, Group 1 received supplementation with oregano in the feed, Group 2 received no feed supplementation or treatment (controls), and Group 3 were treated with in-feed chlortetracycline (subtherapeutic dose). A body condition (BC) score,1 as defined in Table 1, was determined for all sows at parturition and at weaning. The degree of fat cover was estimated visually and by palpation over the ischium, ribs, vertebrae, and tailhead. Weight loss and loss of back fat during lactation were not recorded.

During lactation, sows were housed in identical large farrowing barns, each with 30 identical individual farrowing crates. Assignment of sows to crates was randomized so that sows in the same treatment group were not necessarily housed next to each other. Caretakers were not blinded to the treatments. Piglets were cross-fostered within 24 hours of birth to provide an even litter size of 10 piglets. Litters were weaned at 22.1 +/- 2.1 (SD) days of lactation.

At weaning, all sows were transferred to a single breeding area in an adjacent barn, consisting of 20 identical breeding sub-complexes, where they were housed in identical crates arranged so that they had continuous nose-to-nose contact with boars and sows in adjacent crates.1 Sows were checked twice daily for estrus, beginning on Day 3 postweaning. Because of individual variation in the time of ovulation, all sows were bred by artificial insemination at detection of estrus and again 24 hours later.1 Artificial insemination was performed using commercial pooled semen with 3 x 109 spermatozoa per dose. Three weeks post insemination, sows were rehoused in groups of eight in large pens (14 m2).


Sows in all treatment groups were fed the same commercial lactation diet (digestible energy [DE], 12.6 MJ per kg; crude protein, 180 g per kg; lysine, 12 g per kg; calcium, 8.5 g per kg; and phosphorus, 6.5 g per kg). During the last 4 days prior to farrowing, sows were fed 2 to 3 kg of this ration daily. Feed was withdrawn on the day of farrowing. Beginning the day after parturition and continuing until the day of weaning,the lactation ration was provided ad libitum. In the period between weaning and standing heat, the lactation diet for all three groups was provided ad libitum and was top dressed with vitamin E, 300 IU per kg feed. For the first 12 days after insemination,the lactation ration was fed at 2 kg per sow per day.1 Between days 12 and 90 of gestation, sows in all treatment groups were fed, according to their body condition, 2 to 2.5 kg daily of a commercial gestation diet1 (DE, 12.2 MJ per kg; crude protein, 125 g per kg; lysine, 6.5 g per kg; calcium, 8.5 g per kg; and phosphorus, 4 g per kg).

The lactation diet for Group 1 was supplemented with Oregpig (Feed Additives, Pecs, Hungary), 1000 mg per kg of feed. Oregpig contains the dried leaf and flower of Origanum vulgare, enriched with 500 g per kg cold-pressed essential oils of the leaf and flower of Origanum vulgare, and also contains 60 mg per kg carvacrol and 55 mg per kg thymol. The lactation diet for Group 3 contained 100 mg chlortetracycline per kg. The lactation diet for Group 2 contained no supplement.

The amounts of lactation diet required for Groups 1 and 3 for the entire trial were mixed in the same mixer at the beginning of the study. The feed mixer was flushed between rations to ensure that there was no residue in the next feed mixed. The diets for the three treatment groups were stored in bags of different colors.

In each farrowing crate, a plastic container with a capacity of 50 kg delivered feed into a deep trough (depth 30 cm). Average daily feed disappearance was interpreted as average daily feed intake. Feed disappearance for each sow was calculated during lactation by weighing the feed given to the sow and the unconsumed feed. Because of the depth of the trough, no feed wastage was expected, and feed wastage was not recorded.

Estrus detection

Signs regarded as indicative of impending estrus included sow activity, vocalization, nibbling and nosing with the boar and sows standing in adjacent crates, and reddening and swelling of the vulva (not always present in older sows).2 A positive "riding test" and slight sticky discharge (positive thumb test) were considered final confirmation of estrus.2

Calculations and statistical analysis

Statistical analyses were performed using the GLM procedures of SAS (SAS Institute, Cary, North Carolina) to derive least squares means and SE. Differences between calculated parameters of the groups (average voluntary daily feed intake, WEI, and subsequent total born litter size) were compared.When marked deviations from normality were present (verified by Levene's test significance), data were transformed to homogenize such variations. Covariate included in the model was parity, and the dependent variables were WEI and subsequent total born litter size. The month of weaning was found significant (P = .04) and was therefore included as a covariate. Full lactation length, full litter size suckled, number of piglets removed, and number of piglets remaining with the sow had no significant effects on WEI or subsequent total born litter size and were not included as covariates. Only sows detected as estrous by 18 days after weaning were included in the analyses. For the purposes of this study, the remaining sows were designated as "anestrus." Farrowing rates were compared by c2 analysis. Body condition score and number of anestrous sows in each treatment group were not statistically analyzed.


All sows remained healthy, without excessive post-mating or postparturient discharges. Average BC score was 3.3 +/- 0.2 at parturition and 3.0 +/- 0.2 at weaning for primiparous sows, and 3.2 +/- 0.2 at parturition and 3.0 +/- 0.3 at weaning for multiparous sows.

Among primiparous sows, one sow in each of Groups 1 and 3 (2.8%), and two sows in Group 2 (4.5%) failed to exhibit estrus by 18 days after weaning. Among multiparous sows, one sow in Group 1 (2.2%), two in Group 2 (4.3%), and three in Group 3 (6.5%) were anestrous.

Feed wastage was not observed. Primiparous sows had an average voluntary daily feed intake of 5.6 +/- 0.84 kg, with 5.5 +/- 0.81 kg in Group 1, 5.5 +/- 0.89 kg in Group 2, and 5.7 +/- 0.17 kg in Group 3. Daily feed intake of primiparous sows did not differ among treatment groups (P > .05).

Multiparous sows had an average voluntary daily feed intake of 7.2 +/- 0.63 kg, with 7.5 +/- 0.11 kg in Group 1, 7.0 +/- 0.39 kg in Group 2, and 7.2 +/- 0.14 kg in Group 3. Mean feed intake of multiparous sows was greater in Group 1 than in Group 2 (P = .05), but did not differ between Groups 1 and 3 and Groups 2 and 3 (P > .05).

Effects on WEI and FR of treatment with oregano (Group 1) or chlortetracycline (Group 3) compared to no treatment (Group 2) are shown in Table 2. The mean WEI of primiparous sows (5.8 +/- 0.2 days) was greater (P = .03) than that of multiparous sows (5.1 +/- 0.2 days). In both primiparous and multiparous sows, WEI was shorter in Group 1 compared to Groups 2 and 3 (Table 2). Farrowing rates were higher in Groups 1 and 3 compared to Group 2, both for primiparous and multiparous sows (Table 2).

Subsequent total born litter size did not differ among treatment groups (P > .05). Mean total born litter size for primiparous sows was 10.1+/- 0.4 in Group 1, 10.1 +/- 0.5 in Group 2, and 10.2 +/- 0.6 in Group 3. Mean total born litter size for multiparous sows was 10.8 +/- 0.5 in Group 1, 10.7 +/- 0.6 in Group 2, and 10.8 +/- 0.4 in Group 3.


Especially in Europe, social pressure for less antimicrobial usage in pig production is forcing researchers to identify environmentally friendly natural alternatives that exert therapeutic effects similar to in-feed antimicrobials.1,3-16 In this study, chlortetracycline did not influence anestrus, but WEI and FR were significantly better for sows treated with in-feed chlortetracycline compared to the untreated controls. The subtherapeutic dose of chlortetracycline might have exerted a protein-sparing effect and resulted in acceleration of milk production and uterine involution.1

Phytogenic feed additives are not new in veterinary medicine. Studies have shown that essential oils derived from the plant Origanum vulgare have in vitro antimicrobial activities against various bacteria7-16 and, in addition, have antioxidant properties.3 Effectiveness of origanum oils has been reported for postweaning diarrhea caused by Escherichia coli,6,7,14 growth retardation of growing pigs,5 and porcine proliferative enteropathy.6 It has been reported thatOriganum vulgare stimulates organic and microbiotic digestion.7,13 Oregano supports digestion and absorption of nutrients and regulation of gastrointestinal metabolism, and exerts antibacterial properties in the digestive tract of the pig by hindering dysbiotic processes.7,11-16 It was reported that supplementation of pigs with oregano at 1000 ppm in the feed during the postweaning period significantly improved weight gain and health.7 In a recently published study, Khajarern and Khajarern8 reported a significant (P < .05) positive effect of oregano essential oils on total litter birth weights, total litter weaning weights, preweaning mortality, and sow feed intake during lactation, stating that Origanum vulgare essential oils in sow feed stimulated appetite and digestion. In contrast, average voluntary feed intake in this study was not significantly greater in primiparous sows treated with oregano, but was significantly greater in multiparous sows treated with oregano, compared to the control animals.

Khajarern and Khajarern8 concluded that carvacrol and thymol accelerate renewal rate of mature enterocytes on intestinal villi, and that Origanum essential oils not only act as alternative antibacterial performance promoters, digestion aids, and appetite enhancers in sows, but also enhance growth and reproductive performance.

The effect of oregano on sow fertility may only be speculated. If Origanum vulgare stabilizes gut microflora,13 decreases populations of undesirable microorganisms,10-15 and increases the digestibility of the feed,13 the sows' general health may be improved, and postparturient immune system activation might be positively influenced (ie, the delayed immune response and reduced leukocyte activity of the postparturient uterus may be diminished).1 Such an effect may improve uterine involution and protect the sow from postpartum urogenital infections. In this study, improved WEI and FR might have been the result of an additive effect between Origanum vulgare and Vitamin E, which plays a role in normal leukocyte function.17

The results of this study show that feeding oregano to lactating and postweaning sows does improve some reproductive parameters. Oregano is a feed additive of natural origin that may be preferred because it is perceived as more consumer and environmentally friendly. Where it is available in Europe, it is more cost effective than antibiotics. It is important to note that the natural origin of a feed additive does not make it better or safer than other additives. Many antibiotics are of natural origin, originating from molds. There is no evidence that oregano is more user friendly to producers and safer for consumers than antibiotics, particularly if it exerts antimicrobial effects. Therefore, basic research is needed both to describe the precise effects of essential oils of Origanum vulgare on the gastrointestinal, immune, and urogenital systems, and to discover possible problems with residues in meat.


  • Supplementation with Origanum vulgare in the feed during the first 22 days of lactation, and from weaning to mating, may improve the reproductive performance of sows fed ad libitum.

References - refereed

3. Aeschbach R, Loliger J, Scott BC, Murcia A, Butler J, Halliwell B, Aruoma OI. Antioxidant actions of thymol, carvacrol, 6-gingerol, zingerone and hydroxytyrosol. Food Chem Toxicol. 1994;32:31-36.

4. Baumann B, Bilkei G. Effect of dietary Origanum vulgare extract on the development of swine dysentery in a pure-culture challenge model. Biol Tiermed. In press.

5. Bilkei G, Gertenbach W. Retrospektive Untersuchung des Kombinationseffektes hoher Vitamin E- und pflanzlicher Oregano-Futterzusätze auf die Entwicklung von verzögert wachsenden Mastschweinen [A retrospective evaluation of the combined effect of Origanum vulgare feed additives on the production of growth retarded fattening pigs]. Biol Tiermed. 2001;3:83-87.

6. Bilkei G, Biro O, Bölcskei A, Clavadetscher E, Orban P, Waller C. Practice related management strategies on post-weaning E. coli problems in the intensive pig production. Hung Vet J. 1995;10:776-777.

7. Gertenbach W, Bilkei G. Der Einfluss von pflanzlichen Futterzusatzstoffen in Kombination mit Linolensäure auf die immuninduzierte Wachstumsverzögerung nach dem Absetzen [The effects of phytogenic feed additives and linolenic acid on immune induced growth retardation of weaned pigs]. Biol Tiermed. 2001;3:88-92.

8. Khajarern J, Khajarern S. The efficacy of origanum essential oils in sow feed. Int Pig Top. 2002;17(4):17.

9. Kinvanc M, Akgul A, Dogan A. Inhibitory and stimulatory effects of cumin, oregano, and their essential oils on growth and acid production of Lactobacillus plantarum and Leuconostoc mesenteroides. Int J Food Microbiol 1991;13:81-85.

10. Lis-Balchin M, Deans SG. Bioactivity of selected plant essential oils against Listeria monocytogenes. J Appl Microbiol. 1997;82:759-762.

11. Sivropoulou A, Papanikolaou E, Nikolaou C, Kokkini S, Lanaras T, Arsenakis M. Antimicrobial and cytotoxic activities of Origanum essential oils. J Agr Food Chem. 1996;44:1202-1205.

12. Didry N, Dubreuil L, Pinkas M. Activity of thymol, carvacrol, cinnamaldehyd and eugenol on oral bacteria. Pharm Acta Helv. 1994;69(1):25-28.

16. De Koning WH, Biao DH, Fu WX, Yi R. Chinese Herbs in Animal Nutrition. London, England: Nottingham University Press. 1993:31-74.

17. Elmore RG, Martin CE. Mammary glands. In: Leman AD, Straw B, Glock RD, Mengeling WL, Penny RHC, Scholl E, eds. Disease of Swine. 6th ed. Ames, Iowa: Iowa State University Press; 1986:168-182.

References - non refereed

1. Bilkei G. Herd health strategy for improving the reproductive performance of pigs. Hung Vet J. 1995;10:766-768.

2. Britt JH. Biology and management of the early weaned sow. Proc. AASP. Nashville, Tennessee. 1996;417-426.

13. Günter KD, Bossow H. The effect of etheric oil from Origanum vulgaris (Ropadiar) in the feed ration of weaned pigs on their daily feed intake, daily gains and food utilization. Proc. 15th IPVS Cong. Vol 3. Birmingham, England. 1998;223.

14. Kyriakis SC, Sarris M, Lekkas S, Tsinas AC, Giannakopoulos CG, Alexopoulos C, Saoulidis K. Control of postweaning diarrhoea syndrome of piglets by in-feed application of Origanum essential oils. Proc. 15th IPVS Cong. Vol 3. Birmingham, England. 1998;218.

15. Tsinas AC, Giannakopoulos CG, Papasteriades A, Alexopoulos C, Mavromatis J, Kyriakis SC. Use of oreganum essential oils as growth promoters in pigs. Proc. 15th IPVS Cong. Vol 3. Birmingham, England. 1998;221.