J. Anim Sci. 2008. 86:333-338. doi:10.2527/jas.2007-0153
© 2008 American Society of Animal Science
A regional evaluation of injections of high levels of vitamin A on reproductive performance of sows1,2
M. D. Lindemann*,
,3,
J. H. Brendemuhl*,
,
L. I. Chiba*,
,
C. S. Darroch*,#,
C. R. Dove*,||,
M. J. Estienne*,¶ and
A. F. Harper*,¶
* S-145 Regional Research Committee on Nutrition and Management of Swine for Increased Reproduction Efficiency;
and
Department of Animal and Food Sciences, University of Kentucky, Lexington 40546;
and
Department of Animal Sciences, University of Florida, Gainesville 32611;
and
Department of Animal Sciences, Auburn University, Auburn, AL 36849;
and
# Department of Agriculture and Natural Resources, University of Tennessee, Martin 38238;
and
|| Department of Animal Science, University of Georgia, Tifton 30602; and
¶ Department of Animal and Poultry Sciences, Virginia Tech, Blacksburg 24061
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Abstract
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A regional study involving 443 litters from 182 sows was conducted at 5 cooperating experiment stations to determine the effects of an i.m. injection of vitamin A at weaning and breeding on subsequent litter size of sows. Sows were assigned to 1 of 3 treatments given at weaning and again at breeding: 1) a placebo i.m. injection (2 mL of corn oil), 2) i.m. injection with 250,000 IU of vitamin A (1 mL of vitamin A palmitate in oil), and 3) i.m. injection with 500,000 IU of vitamin A (2 mL of vitamin A palmitate in oil). Corn-soybean meal diets in gestation were formulated to contain 13% CP and 0.60% total Lys. Lactation diets were formulated to contain 17% CP and 0.90% Lys. A common vitamin-mineral premix that supplied 11,000 IU of vitamin A/kg of diet (as-fed) was used by all stations. As expected, station effects were noted for many response measures. Analysis of the data also revealed both treatment x station and treatment x parity interactions for litter size responses. The treatment x parity interactions were stronger than the treatment x station effects, and when the litter size response was separated into early parity sows (parity 1 and 2) and late-parity sows (parity 3 to 6), the treatment x station interactions were no longer present in either subgroup. For sows of parity 1 and 2, litter sizes were increased linearly (P 
0.003) for treatment 1 to 3, respectively, for the total (10.15, 12.14, and 13.18), live born (9.70, 11.14, and 12.16), and weaned (8.92, 10.12, and 10.60) piglets. For sows of parity 3 to 6, litter sizes were not affected for treatment 1 to 3, respectively, for the total (11.82, 11.71, and 11.46), live born (10.82, 10.64, and 10.23), and weaned (8.65, 9.01, 8.79) piglets. Piglet BW were affected (P < 0.001) by station and were associated with station differences (P < 0.05) in lactation length. Piglet BW decreased due to vitamin A treatment in parity 1 and 2 sows (linear, P 0.026) and was likely due to the differences observed in litter size. The results of this regional project demonstrated that injection of high doses of vitamin A in young sows at weaning and breeding improves the subsequent number of pigs born and weaned per litter, indicating that vitamin A requirements for maximal performance may vary with age.
Key Words: injection • litter size • reproductive performance • sow • vitamin A
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INTRODUCTION
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Vitamin A is important as a dietary supplement for swine, and its deficiency in the sow may result in a failure of estrus, resorption of fetuses, and stillbirths (McDowell, 1989
). Brief and Chew (1985) examined the effects of feeding vitamin A or injecting vitamin A or β-carotene on reproductive performance of primiparous sows that were depleted of vitamin A. Gilts injected with either β-carotene or vitamin A in early gestation had more pigs per litter at birth and at weaning. The potential for enhancing reproductive performance by vitamin therapy in multiparous sows or sows receiving sufficient dietary vitamin A has not been adequately studied. Coffey and Britt (1993) reported that treatment with β-carotene did not affect reproduction in primiparous sows, but treated multiparous sows had more pigs born alive in their subsequent litter. In a second experiment, in which vitamin A was supplemented at a rate of 11,000 IU/kg of diet, injection of sows with either β-carotene or vitamin A increased (P < 0.10) the number of pigs born alive in the subsequent litter.
These results indicate potential opportunity to increase sow performance by acute delivery of vitamins at critical stages of the reproductive process. The study of Coffey and Britt (1993), in which sows were receiving dietary supplementation well above NRC (1988) requirements, indicates that greater levels of certain vitamins may be required during critical periods of embryonic development to enhance embryo survival. Such levels may be considerably greater than those required to avoid overt deficiency signs. Thus, the objective of this study, conducted at several research stations, was to examine the effect of 2 levels of vitamin A injection on reproductive performance of sows over consecutive parities.
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MATERIALS AND METHODS
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Research in individual stations followed the guidelines stated in the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching (http://www.fass.org/page.asp?pageID=216).
A regional study involving 443 litters from 182 sows was conducted at 5 cooperating experiment stations. Participating experiment stations were Alabama, Georgia, Kentucky, Tennessee, and Virginia. Number of females allotted by each station and station differences in several other areas are given in Table 1.
A common diet formulation was used (Table 2). Corn was used as the grain source and soybean meal as the protein source in both gestation and lactation diets, and individual stations could use either regular or dehulled soybean meal. The diets were formulated to meet or exceed NRC (1988) requirement estimates for all nutrients. A common source of vitamins and trace minerals (DSM Nutritional Products Inc., Parsippany, NJ) was used at each station.
The premixed injection treatments were made centrally and distributed to participating stations. Bottles of injectable vitamin A palmitate (100 mL, 250,000 IU/mL) were prepared from sterile, sealed 100-g vials (1,600,000 IU of USP vitamin A palmitate/g, Sigma Chemical Company, St. Louis, MO) and diluted to appropriate concentration using corn oil as a carrier. Cooperators kept the bottles of injectable vitamin A refrigerated below 6°C. Before injection, the bottles were brought to room temperature in warm water.
Sows were allotted to treatment on the day of weaning, with care given to balance the allotment relative to parity, BW, and genetic background. At 1 station, estrus was induced in prepubertal gilts (n = 10) with PG 600 (Intervet America Inc., Millsboro, DE) to synchronize these young females with a sow group being weaned. The treatments imposed were the injection of 0 (2 mL), 250,000 (1 mL), or 500,000 (2 mL) IU of vitamin A palmitate or corn oil carrier i.m. into the neck behind an ear on the day of weaning for sows (and on that same day for PG 600-injected gilts being synchronized with that particular sow group) and on the day of breeding.
During gestation, sows were fed 1.82 kg/d during the months of March to November and 2.27 kg/d during the months of December to February for those stations that determined that sows needed greater feed intake during that time of year. Feed was provided on an ad libitum basis during lactation. Animals were on deworming and vaccination schedules particular to the individual stations. Newborn pigs were processed according to standard procedures at each station.
Data recorded were parity (actual parity as well as study parity) and sow BW at breeding, d 110 of gestation, farrowing (within 24 h postpartum), d 21 postpartum, and weaning. Feed consumption of sows was recorded from farrowing to d 21 and from d 21 to weaning. Number and BW of pigs at birth (total and live), d 21, and weaning were recorded. The number of days to return to estrus was recorded. No sows were removed from the study for failing to exhibit estrus. The data were submitted on standardized forms for collective analysis.
Results from sows greater than an actual parity 6 and from sows completing more than 3 parities were removed from the data analysis because of imbalance across treatments; further, with the low number of gilts assigned, by parity 3 there was only 1 observation on 1 of the treatments, and so the third-parity observations for all of these were removed. This reduced the data set to 411 litters from 175 sows. The data were subjected to ANOVA using the GLM procedure (SAS Inst. Inc., Cary, NC) as a randomized block design, with the sow or litter serving as the experimental unit. The model included terms for station, treatment, parity on study (or actual parity in preliminary analyses), and all possible interactions. Linear and quadratic contrast coefficients were used to evaluate treatment effects. Because of the unbalanced contribution of data from each station, least squares means are presented.
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RESULTS AND DISCUSSION
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Animal, management, and facility characteristics of the research stations participating in this regional project are provided in Tables 1
and 3 and illustrate the value of cooperative research studies for evaluation of reproductive responses in sows. Aaron and Hays (2001) stated that progress in sow nutrition and management research is hampered by the large variation among sows in the economically important reproductive traits. With normal variation, the number of replications needed to detect a 10% difference in litter size at birth with an 80% chance of detecting that difference and a 10% probability level is 112 sows per treatment. None of the 5 participating research stations could dedicate that many sows to the experiment individually, but collectively, over 130 litters/treatment were generated. It was expected that there would be differences in animal performance among stations, and those are evident in Table 3 with regard to sow BW, feed intake, and the postweaning return to estrus, as well as pig BW. Many performance differences (e.g., pig weaning weight) are the result of differences in lactation length. There were, however, no differences among stations in litter size at birth.
The effects of the vitamin A injections for the total study are provided in Table 4. Linear increases in litter size, the primary response of interest in the study, were observed for total pigs born/litter (P = 0.050) and in pigs weaned/litter (P = 0.026) with increasing amount of vitamin A injected. Treatment effects for other responses were largely absent. There was a linear increase in feed intake during lactation (P = 0.056) in response to vitamin A injection, which was expected given the differences in numbers of pigs nursed. There were many main effects of study parity (sows could remain on the study for 3 parities), but these were normal changes in performance or BW associated with advancing parity, and, thus, the results are not presented.
The results of the current experiment are in accordance with previous studies (Brief and Chew, 1985; Coffey and Britt, 1993). Brief and Chew (1985) fed gilts a diet deficient in vitamin A for 5 wk and reported that subsequent weekly injections of vitamin A (12,300 IU) and β-carotene (32.6 mg), beginning at the first estrus after the depletion period, increased the number of pigs born alive and the number of pigs weaned. Coffey and Britt (1993) injected sows with 50,000 IU of vitamin A at weaning, on the day of first mating, and on d 7 after first mating and observed a 0.6 pig increase (P < 0.10) in litter size.
In contrast to the current study and previous reports (Brief and Chew, 1985; Coffey and Britt, 1993), Pusateri et al. (1999) failed to increase litter size with vitamin A injections in sows. In that study, however, only a single injection of vitamin A (100,000 IU) was administered on d 0, 2, 6, 10, 13, 19, 30, 70, or 110 after breeding. Perhaps the equivocal results can be explained by a requirement for more prolonged exposure to vitamin A achieved by multiple injections in the current study and in the reports of Brief and Chew (1985) and Coffey and Britt (1993).
Initial analysis of the data revealed a weak tendency (P 
0.15) for a few station x treatment interactions in litter size. Further analyses were conducted to assess interactions of treatment with either actual physiological parity or with parity on study (e.g., a sow may have began the study after weaning its second litter, which would mean an actual parity of 3 and a study parity of 1). These analyses revealed that there were interactions of treatment with actual parity of the sows (P = 0.049 to 0.071) but essentially no interaction of treatment with study parity for any litter size responses (no interactions at P < 0.15). The decision was then made to divide the data set into responsive parities and nonresponsive parities. After the determination that interactions did not exist for station x treatment or for study parity x treatment (no litter size responses had interactions with P < 0.15) when the data set was split into older (i.e., parity 3 and greater) and younger sows, the data set was split into 2 subsets, and the interaction terms were removed from the statistical model for the computation of least squares means.
The effects of the vitamin A injections for parity 1 and 2 females are provided in Table 5. It is apparent that these younger females were responsible for the significant effects evident in the total data set. Large linear increases were observed in total pigs born/litter, pigs born live/litter, and pigs weaned/litter (P 0.003) with increasing amount of vitamin A injected. These effects on litter size were associated with linear effects (P 0.035) on piglet BW and sow feed intake that are consistent with changes in litter size. Additionally, there was a linear increase in time to return to estrus (P = 0.016) with the increasing litter size, but it was less than 1 d. Using a split-weaning strategy, Stevenson and Britt (1981) demonstrated that sows nursing smaller litters, and thus exposed to reduced suckling intensity, had a more rapid return to estrus postweaning. Moreover, Koketsu et al. (1996) showed an increase in feed intake with increasing litter size for small and medium size litters. There were no study parity differences in this data subset other than time to return to estrus postweaning (P = 0.051), in which the values for parity 1 and 2 females were 5.14 and 3.87 d, respectively.
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Table 5. Least squares means of supplemental vitamin A effects on sow and litter performance (actual parity 1 to 2)1
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The effects of the vitamin A injections for parity 3 to 6 females are provided in Table 6. In this group of older sows, there were no treatment effects on litter size, sow BW changes, or feed intake. And there were also no effects on piglet BW other than a spurious quadratic effect in weaning weight that probably has little, if any, biological significance. In this data subset, which includes females of 4 parities, there were occasional study parity differences.
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Table 6. Least squares means of supplemental vitamin A effects on sow and litter performance (actual parity 3 to 6)1
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Thus, in the current experiment, beneficial effects of vitamin A injections were most evident in gilts and primiparous sows. Coffey and Britt (1993), however, reported a positive effect of vitamin A or β-carotene injections on litter size but no vitamin A or β-carotene x parity interaction in an initial experiment, indicating that the treatments were equally effective in both young and old sows. Coffey and Britt (1993) then reported a second experiment during which sows received an i.m. injection of a sustained release form of β-carotene (0, 50, 100, or 200 mg) on the day of weaning. In contrast, a dose response to β-carotene was noted in multiparous, but not in primiparous, sows for number of pigs born alive, with the largest litter size reported at the greatest dose. The lack of response in primiparous sows could be explained by the fact that in the second experiment, the younger females had a much longer weaning-to-estrus interval (12 d) compared with older counterparts (6.7 d) and may have been bred after the time when β-carotene exhibits positive effects on litter size. It is not clear whether the positive effects of β-carotene injections on performance in sows is due to a unique role of the substance in reproduction or its function as a natural precursor of vitamin A.
Although a growing body of evidence is consistent with the concept that vitamin A or β-carotene treatment of weaned sows increases litter size, mechanisms by which these effects are manifested are not completely resolved. Presumably, vitamin A and β-carotene may increase litter size by exerting positive effects on 1 or more critical reproductive processes, including oocyte maturation, ovulation, fertilization, and early embryonic survival and development. Because fertilization rates are typically high (>95%; Pope, 1994) in swine, it is doubtful that increased litter size attributed to vitamin A or β-carotene treatment is a consequence of effects on this particular stage of reproduction. Moreover, treatment with vitamin A failed to alter the number of ova shed during ovulation in gilts (Brief and Chew, 1985; Whaley et al., 1997, 2000).
To evaluate potential mechanisms by which vitamin A might influence litter size, Whaley et al. (1997) used an experimental model in which gilts were intentionally fed a high-energy diet to reduce embryo survival. Gilts were fed high-energy or control diets from 7 d after second estrus until 11 to 12 d after third estrus and were injected i.m. with vitamin A (100,000 IU) or vehicle within each dietary treatment on d 15 after second estrus and mated at third estrus. The high-energy diet decreased the number of embryos and percentage of embryo survival and increased variation in embryo diameter. In contrast, vitamin A exerted a positive influence on embryo number and percentage of survival, decreased variation in embryo diameter, and increased average diameter.
Using the same high-energy-fed gilt model, Whaley et al. (2000) subsequently reported that treatment with vitamin A (100,000 IU) stimulated an earlier resumption of meiosis and altered development of oocytes before ovulation, resulting in more uniform and advanced oocytes and early embryos. In swine, asynchrony of development is associated with increased embryonic mortality (Pope et al., 1990).
In summary, injections of vitamin A at weaning and mating increased litter size in sows with the positive effects evident in young females. Thus, vitamin A requirements for maximal sow performance may vary with age. Although the mechanism by which these effects were manifested in the current study cannot be ascertained, it likely involves a decrease in early embryonic mortality.
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Footnotes
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1 This manuscript is based on research supported in part by the Kentucky Agricultural Experiment Station and is published by the Kentucky Agricultural Experiment Station as paper no. 07-07-030. 
2 Special appreciation is expressed to DSM Nutritional Products Inc. (Parsippany, NJ) for providing the vitamin-trace mineral premix used in the study.
3 Corresponding author: mdlind1{at}uky.edu
Received for publication March 9, 2007.
Accepted for publication October 25, 2007.
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LITERATURE CITED
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Aaron, D. K., and V. W. Hays. 2001. Statistical techniques for the design and analysis of swine nutrition experiments. Pages 605–622 in Swine Nutrition. 2nd ed. A. J. Lewis and L. L. Southern, ed. CRC Press Inc, Boca Raton, FL.
Brief, S., and B. P. Chew. 1985. Effects of vitamin A and β-carotene on reproductive performance in gilts. J. Anim. Sci. 60:998–1004.[Abstract/Free Full Text]
Coffey, M. T., and J. H. Britt. 1993. Enhancement of sow reproductive performance by β-carotene or vitamin A. J. Anim. Sci. 71:1198–1202.[Abstract]
Koketsu, Y., G. D. Dial, J. E. Pettigrew, W. E. Marsh, and V. L. King. 1996. Characterization of feed intake patterns during lactation in commercial swine herds. J. Anim. Sci. 74:1202–1210.[Abstract]
McDowell, L. R. 1989. Vitamins in Animal Nutrition. Academic Press Inc., San Diego, CA.
NRC. 1988. Nutrient Requirements of Swine. 9th rev. ed. Natl. Acad. Press, Washington, DC.
Pope, W. F. 1994. Embryonic mortality in swine. Pages 53–77 in Embryonic Mortality in Domestic Species. M. T. Zavy and R. D. Geisert, ed. CRC Press Inc., Boca Raton, FL.
Pope, W. F., S. Xie, D. M. Broermann, and K. P. Nephew. 1990. Causes and consequences of early embryonic diversity in pigs. J. Reprod. Fertil. Suppl. 40:251–260.[Medline]
Pusateri, A. E., M. A. Diekman, and W. L. Singleton. 1999. Failure of vitamin A to increase litter size in sows receiving injections at various stages of gestation. J. Anim. Sci. 77:1532–1535.[Abstract/Free Full Text]
Stevenson, J. S., and J. H. Britt. 1981. Interval to estrus in sows and performance of pigs after alteration of litter size during late lactation. J. Anim. Sci. 53:177–181.[Abstract/Free Full Text]
Whaley, S. L., V. S. Hedgpeth, and J. H. Britt. 1997. Evidence that injection of vitamin A before mating may improve embryo survival in gilts fed normal or high-energy diets. J. Anim. Sci. 75:1071–1077.[Abstract/Free Full Text]
Whaley, S. L., V. S. Hedgpeth, C. E. Farin, N. S. Martus, F. C. L. Jayes, and J. H. Britt. 2000. Influence of vitamin A injection before mating on oocyte development, follicular hormones, and ovulation in gilts fed high-energy diets. J. Anim. Sci. 78:1598–1607.[Abstract/Free Full Text]
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Abstract
INTRODUCTION
