NCSU Extension Swine Husbandry 2002
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March, 2002 . Volume 25, Number 02

The Science of Odor




A large portion of the current swine artificial insemina- tion (AI) research is focused on a means to reduce the number of sperm required per service (i.e. estrus) without compromising sow farrowing rate or litter size. There are two basic strategies to achieve this goal - either reduce the number of sperm per insemination dose or reduce the number of inseminations per service. Several recent experiments have attempted to do both by bypassing areas where sperm are lost through intrauterine (i.e. transcervical) insemination and by hormonally synchronizing the inherently variable processes of estrus and ovulation to allow one fixed-time insemination [6, 7, 8, 9]. The outer (vaginal) end of the cervix is the normal site of semen deposition during natural mating and conventional AI (figure 1). Within 2.5 h of a typical conventional AI approximately 70% of the volume and 25% of the sperm inseminated are lost as they flow back out of the sow's reproductive tract [11]. Several different instruments have been developed to transverse the entire length of the sow's cervix ( 6 in.) and deposit semen in the uterine body (intrauterine insemination, IUI) or anterior portion of a uterine horn (deep intrauterine artificial insemination, DIUI). The potential advantages of these techniques are that they may allow fertilization results comparable to conventional AI with fewer sperm and could also bring other technologies like embryo transfer [4] and sexed semen [5] closer to commercial application. The potential disadvantages of these techniques are that they may increase the chance of causing or aggravating an existing cervical or uterine injury (post- insemination bleeding) and introducing a uterine infection. In addition, intrauterine catheter placement is more difficult (especially in gilts) and requires more time compared to conventional AI, although the deposition of the semen is quicker because uptake is not depen- dent on sow uterine contractions. A gonadotropin preparation (P.G. 600 , Intervet, Inc.) is currently available for estrus synchronization of swine, but since the more effective and versatile progestagen, GnRH, eCG, and hCG products necessary to achieve a high degree of ovulation synchrony are not approved for swine use, intrauterine insemination protocols that do not require fixed-time AI [13] will likely be adopted first.

Figure 1. Site of semen deposition for conventional, intrauterine, and deep intrauterine insemination in the sow reporductive tract.

Review of the Available Data

During the 1950's and 60's, research on the transport of sperm in gilts and sows inseminated with doses differing in volume and number of sperm suggested that approximately 5 to 10 x 109 sperm in 100 mL was neces- sary to achieve optimal fertility [1, 12]. Since then, the number of sperm per insemination dose has decreased primarily due to improvements in semen extender. A recent review of the swine AI industry in the US suggests that AI accounts for an estimated 60% of all matings and that on average a sow receives 2.2 insemi- nation doses per service each containing 2.5 to 4 x 109 sperm in a 70 to 100 mL volume [13]. These numbers suggest that on average a sow mated by AI receives 7.2 x 109 sperm per service (2.2 inseminations x 3.25 x 109 sperm per dose). If an average boar ejaculate contains 70 x 109 sperm then only 8 or 9 sows could be inseminated 2.2 times each. This review also estimated that on average AI boars are collected 4.7 times per month and that 100 doses per boar per month is a common production goal [13]. There would be an obvious increase in economic and genetic efficiency even if the number of sperm per insemination dose could only be reduced a few fold.

A recent study found that as few as 10 x 106 sperm (in 0.5 mL) surgically deposited near the utero-tubal junction (UTJ) of each uterine horn in synchronized gilts were sufficient to provide fertility comparable to one conventional AI with 3 x 109 sperm (a 150-fold reduction) [7]. A similar study with synchronized sows using the same surgical DIUI technique confirmed this finding [6]. The authors concluded that when a non-surgical catheter was developed to deliver semen near the UTJ this technology could be applied in the field [6, 7]. Some of the earliest non-surgical intrauterine insemination experiments in swine found a greater proportion of cleaved ova recovered 3 to 4 days post-insemination when semen was deposited in the uterus compared to the cervical canal [2, 3]. More recently, semen has been non-surgically deposited at the anterior third of one uterine horn (near the UTJ) by inserting an expensive, flexible, fiber optic endoscope [9] or a less expensive, flexible, secondary catheter without an endoscope [8] through a modified AI catheter. Results from these non-surgical DIUI experiments are summarized in Table 1.

It is important to note that in both studies DIUI sows were inseminated once at a fixed-time after hormonal synchronization and that the conventional AI sows received two inseminations but were synchronized only by their common 4-day weaning-to-estrus interval. Both studies appear to suggest that one non-surgical DIUI of synchronized sows with as few as 150.0 to 200.0 x 106 sperm can produce a farrowing rate and litter size comparable to two conventional inseminations with 3 x 109 sperm in non- synchronized sows (a 15- to 20-fold reduction). It was possible to successfully pass the long, flexible, intrauterine catheter through the cervix in 95% of the sows with an average time of approximately 3.7 minutes [8].

Unlike the two DIUI studies [8, 9], the third set of data represents a commercial-based study that utilized non- synchronized sows, a commercially available intrauterine catheter, and trained farm employees to perform the insemi- nations [13]. In addition, the semen was deposited in the uterine body (IUI) instead of two thirds of the way up a uterine horn (DIUI) and the IUI and conventional AI (control) sows were all inseminated on the same schedule. Only when the insemination dose was reduced to 1.0 x 109 sperm did the conventional AI sows have reduced fertility compared to the IUI sows (Table 1). Even though this study was intended to demonstrate the benefits of IUI it also demonstrates that we may be able to moderately reduce the number of sperm per insemination dose with conventional AI without affecting reproductive performance. Field reports of herds that achieve a high level of reproductive perfor- mance (>85% farrowing rate and >10 pigs born alive) with only 1.5 to 2.0 x 109 sperm per insemination dose are becoming more common. However, management may view 3.0 to 4.0 x 109 sperm per insemination dose as a relatively cheap form of insurance to cover potential deficiencies in semen quality from the boar stud or insemination timing, technique, or quality at the sow farm.


Improvements in semen evaluation, semen extender, detection of estrus, prediction of ovulation, and sow management will continue to allow moderate reduction in the number of sperm required per service with conventional AI. The adoption of intrauterine and fixed-time insemination techniques may allow a much larger decrease in the number of sperm required per service but would also require increased training of breeding technicians and the use of hormones for synchronization. Since few effective products for estrus and ovulation synchronization are currently approved for use in swine, protocols that utilize multiple intrauterine inseminations would likely be implemented first. Due to the lack of published data there is currently considerable controversy over the ideal intrauterine insemination device, optimal insemination dose (number of sperm and volume), and site of semen deposition (uterine body vs. uterine horn). One thing that is certain is that if a substantial reduction of the number of sperm required per service is made, it will increase the need for accurate evaluation of semen quality and a high level of sow breeding management to maintain fertility.


[1] Baker, R.D., P.J. Dziuk, and H.W. Norton. 1968. J. Anim. Sci. 27:88-93.
[2] Hancock, J.L. and G.J.R. Hovell. 1961. Anim. Prod. 3:153-161.
[3] Hancock, J.L. 1959. Vet. Rec. 71:527.
[4] Hazeleger, W. and B. Kemp. 2001. Therio. 56:1321-1331.
[5] Johnson, L.A. 2000. Anim. Reprod. Sci. 60-61:93-107.
[6] Krueger, C. and D. Rath. 2000. Reprod. Fertil. Dev. 17:113-117.
[7] Krueger, C., D. Rath, and L.A. Johnson. 1999. Therio. 52:1363-1373.
[8] Martinez, E.A., J.M. Vazquez, J. Roca, X. Lucas, M.A. Gil, I. Parrilla, J.L. Vazquez, and B.N. Day. 2002. Reprod.      123:163-170.
[9] Martinez, E.A., J.M. Vazquez, J. Roca, X. Lucas, M.A. Gil, I. Parrilla, J.L. Vazquez, and B.N. Day. 2001. Reprod.      122:289-296.
[10] Singleton, W.L. 2001. Therio. 56:1305-1310.
[11] Steverink, D.W.B., N.M. Soede, E.G. Bouwman, and B. Kemp. 1998. Anim. Reprod. Sci. 54:109-119.
[12] Stratman, F.W. and H.L. Self. 1960. J. Anim. Sci. 19:1081-1088.
[13] Watson, P.F., J. Behan, G. Decuadro-Hansen, and B. Cassou. 2001. VIth Int. Conf. on Pig Reprod., Univ. of      Missouri-Columbia. pp. 135.

—Brad Belstra



North Carolina House Bill 515 required the state Environ- mental Management Commission (EMC) to adopt temporary odor rules by March 1999. The permanent rules were adopted on October 14, 1999. The enforcement of these rules falls under the N.C. Department of Environment and Natural Resources (DENR) Division of Air Quality (DAQ). A complete copy of these rules can be found at Here is how these rules have been implemented.

Current Status

As of January 2002, the DAQ had received 415 odor complaints from 255 complainants. To date, DENR inspectors have verified that 6 locations, involving 10 farms, are producing objectionable odors.

The Rules

The EMC determined that the rules would be complaint driven and, based on the language of House Bill 515, would focus solely on animal operations using liquid animal waste management systems. This confines the effect of these rules largely to the lagoons and sprayfields associated with the swine industry. The rules also provide regulatory guidelines for the determination of objectionable odors and the requirements for the implementation and revision of odor control best management plans (BMPs) on existing, new, and modified animal operation. The rules establish required odor control management practices that must be implemented on all animal operations within the state and require certain animal operations, based on size, to submit odor management plans. The rules set regulatory requirements for the implementation of odorous emission control technology on those animal operations that fail to control their objectionable odors through the use of BMPs.

Required Management Practices

  1. Dead animal disposal within 24 hours.
  2. Waste from spray systems to be applied in a manner and under conditions to prevent drift from the irrigation field beyond the boundary of the animal operation. (Exception for emergencies with prior notification).
  3. Wastewater spray system intakes to be located near the liquid surface of the lagoon.
  4. Ventilation fans to be maintained to manufacturers' specifications.
  5. Animal feed storage containers outside the building to be covered except to remove or add feed.

Objectionable Odors

These rules define an "objectionable odor" as "any odor present in the ambient air that by itself, or in combination with other odors is or may be harmful or injurious to human health or welfare, or may unreasonably interfere with the comfortable use and enjoyment of life or property." "Harmful or injurious odors" are further defined as those odors that lessen human food and water intake, interfere with sleep, upset appetite, produce irritation of upper respiratory tract, cause symptoms of nausea, or have a chemical or physical nature that is detrimental or dangerous to human health.

What Causes Odors From Animal Operations?

Objectionable livestock odors are often caused by animal wastes, but problems can be aggravated by improper handling of dust from barns and feed storage areas and by dead animals. Dust, in particular, can magnify the intensity of odors. Weather conditions also contribute to problems, with odors often more pronounced in the evening and early morning hours, when winds are lighter. Other factors that can contribute to the magnitude of odors include the size of the facility, type of animals, proximity to residential areas, and management practices at the facility.

Complaints and Investigations

To register odor complaints, citizens first contact their local DAQ regional office. DAQ staff members will fill out detailed complaint forms to help determine the source of the odors and respond to problems. Citizens provide information, if possible, on the sources of odors and the locations and operators of offending facilities. Citizens are encouraged to keep accurate logbooks to record odor events. These logbooks should include information that will help document and describe odor events, including dates, times, temperatures, wind direction, duration and intensity of odors, and suspected farm and operation (barn, lagoon, sprayfield) causing the problem.

DENR inspectors will determine whether a facility has objectionable odors based on various factors, including personal observations, complaints from nearby residents, and health studies. Other factors to be considered include the nature, intensity, frequency, pervasiveness, and duration of odors. Inspectors will consider the potential of an animal operation to emit odor-causing compounds, such as ammonia, hydrogen sulfide, and total volatile organics. Farms found to be producing an objectionable odor are required to develop an Odor Management Plan. If objectionable odors persist, facilities will have to submit modified plans and eventually could be required to install economically feasible equipment for controlling odors-such as lagoon covers or "wash walls" that filter odors from barn ventilation systems.

—M. Todd See

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Last modified March 22, 2002.