August, 2000 . Volume 23, Number 7 
NCSU Extension Swine Husbandry
August, 2000 . Volume 23, Number 7
Introduction
I've recently had numerous conversations with individuals concerned with results they have
been achieving with their artificial insemination (AI) program, specifically, number of
piglets born alive (~10-10.5). The Catch-22 of these conversations is that most of the
producers that I have spoken with are achieving very good farrowing rates that range from
87 to 92 percent on an annual basis. Both of these measurements would put these operations
in the top 1/3 percentile, according to Iowa Swine Business Record summary. Ironically,
the very fact that their farrowing rates are this high may be the direct cause for
lower-than-desirable average litter sizes. Most of the time achieving a large litter size
and conception rate are unrelated, whereas only a few oocytes need to be fertilized for
pregnancy to actually occur. This number unfortunately is far short of many producers
expectations of an ideal litter size, which is likely closer to 12 to 13 pigs born alive.
As in the case of these previously mentioned operations, they are likely doing such
a good job with their breeding program that sows and gilts that normally wouldn't conceive
in many operations are conceiving with a minimum number of fetuses (three to four),
consequently, lowering average litter size. The question that producers need to ask
themselves is whether they would like to sacrifice above-average conception rates to
achieve a higher average litter size. Nevertheless, it is not unreasonable to achieve
success in both of these categories. The focal point of this article is to describe the
factors which influence these fertility parameters and to review methods to achieve high
targets in both litter size and conception and farrowing rates, in herds that are
relatively disease free.
Timing, Frequency and Quality of Insemination
The use of artificial insemination (AI) allows for a higher degree of quality control than
natural service. In addition to having control of semen quality, AI users can also ensure
that fertile semen is deposited into the uterus. Accurately timing multiple inseminations
can be difficult but is fundamental to the success of AI. Mistimed inseminations lead to
lower fertility and many of the problems associated with farrowing rates. Occasionally
litter size can be attributed to poorly timed and performed inseminations. The major
limiting factor for the number of piglets farrowed is ovulation rate. Most females ovulate
between 15 and 20 oocytes approximately 40 hours after the onset of estrus. However, both
number and timing of ovulations can vary considerably between females, genetic lines,
environments, nutritional programs and management components such as short versus long
lactation lengths. It's true that multiple inseminations that are routinely performed
throughout estrus increase the chances that one insemination will be performed at an
optimal time relative to ovulation (<24 h) to optimize fertilization rates; this
procedure does not necessarily assure a large litter size. Provided that a large number
of oocytes are ovulated, the next most limiting factor is ensuring that a viable population
of sperm is present in the oviducts at the time of ovulation. There are four factors: sperm
and oocyte longevity in the female reproductive tract, estrus detection frequency, and
projected estrus length for determining when and how often to breed to accomplish this is
determined.
The fertile life span of a spermatozoa population in the female with the ability to produce
a pregnancy is estimated to be from 12 to 36 hours, even though motile sperm have been
recovered 10 days following insemination. The fertile life span of the ovulated egg is
approximately eight hours. Therefore, once ovulation occurs, it is necessary for a viable
population of spermatozoa to be present in the oviducts at this time because of the
relatively short lifespans of the egg, coupled with a four to six hour period of time after
insemination when sperm cannot fertilize an egg. Good fertilization rates (> 90 percent)
can be achieved when a single insemination is performed during a 24-hour period before
ovulation (Soede et al., 1995). This optimal "AI time" is assuming that 1) an
adequate number of sperm are inseminated and retained (> 1 billion and less than 20 ml
of back flow; Steverink et al., 1998), and (2) semen is relatively fresh (less than 38 h
old; Waberski et al., 1994). This interesting finding would suggest that all producers need
to do is determine when ovulation is going to occur and inseminate the sow. It is
unfortunate however that, on average, ovulation takes place 35 to 45 hours after onset of
oestrus (standing response in presence of a boar) but the variability between sows
is extremely large, thus making it difficult to accurately time a single insemination.
Therefore, performing multiple inseminations throughout estrus is an easy answer to
increase the chances that one insemination will be performed at an
"optimal time." Although it is difficult to predict ovulation, research has
shown that sows generally ovulate sometime during the last half of their estrus
period. Thus, if a sow or gilt's estrus length is known, then we have a pretty good idea
when ovulation will occur and can then time our inseminations accordingly.
The goal in most swine operations should be to ensure that at least one AI is performed
within 24 hours of ovulation. What we don't know is if two or more inseminations performed
during this time have an additive effect. Nevertheless, regardless of the interval between
inseminations, the length of time that the female "stands to be mounted" by
a boar will determine how many times to inseminate. Perhaps the most important consideration
to remember is that when estrus length increases, reproductive performance will improve with
an increase in insemination frequency (i.e., from two to three inseminations per estrus
period; Flowers and Esbenshade, 1993). Generally, females that are in strong estrus for
three days will receive three inseminations or one insemination per day while
in estrus. However, one should also consider that shortening the interval between the
second and third insemination (i.e., from 24 to 12 hours) should in theory, help reduce the
negative consequences of mistiming the last AI, which has been shown to reduce both litter
size and farrowing rate (Rozeboom et al., 1997).
There is no ideal number or insemination interval. The ideal frequency and intervals
between each insemination on each farm is influenced by semen age at AI, semen storage
conditions, individual boar fertility and the composition of the AI dose (percentage of
seminal plasma). Conservatively speaking, when freshly extended (< 72 hours old) semen
(3-4 billion motile cells) containing 10-12 percent seminal plasma is inseminated by an
experienced technician at 24-hour intervals, a viable population of spermatozoa should be
in the female at all times. However, research suggests that spermatozoa viability and
fertility in the female tract decrease when any of these factors are reduced or changed
(Flowers, 1994; Waberski et al., 1997; Rozeboom et al., 1999). Therefore, it is
reasonable to presume that when semen conditions fall outside these criteria, intervals
should be reduced to 12 to 18 hours. Finally, it's important to consider that gilt estrus
behavior patterns differ from sows. Estrus lengths are generally shorter and often
less pronounced in gilts and therefore, the first insemination should occur immediately
following detection of estrus. A follow-up insemination 24 hours later should be conducted
provided the gilt is still in standing estrus.
Increasing the frequency of estrus detection will provide for a more accurate determination
of the true beginning and end of estrus. Estrus detection is very labor-intensive and
time-consuming, and consequently, most operations do not check heat more than once per day.
However, it may be of benefit to heat check sows twice a day for three to four breeding
periods in order to get a better idea of the average herd estrus lengths. This information
may be useful in determining if the first AI can be delayed after the female is first
detected in estrus (i.e., wait 12 to 24 hours before first AI because of extremely long
estrus lengths such three or four days). Although 2x/day estrus detection provides a more
accurate assessment of the true onset of estrus, it may be too impractical on most
operations, and thus delaying the first insemination is probably not justified on most
farms with limited labor resources. Because of the variation that exists between farms, it
is important to set realistic targets and evaluate reproductive performance after
approximately 75 to 100 matings. Readjustments can then be made to optimize your AI
schedule.
Last, consider the quality of inseminations. In a recent study, we investigated the
influence of insemination quality on a single AI performed < 24 hour prior to ovulation.
The results show that when females exhibit a strong standing heat reflex, have a tight
cervical lock on the spirette, and very little semen back flow occurs, that a higher
conception rate will occur. Females that received a high quality AI (n = 44; strong heat,
tight lock, and little or no back flow), had a 25 percent advantage in conception rate
compared to females that received a poor quality AI (n = 52; restless, poor cervical
lock and some to moderate back flow).
Summary
Ensuring that a viable population of sperm is present in the oviducts at the time of
ovulation is the most significant factor that influences fertilization rates. This factor
is largely influenced by AI timing relative to ovulation and the efficiency of
sperm transport to the site of fertilization. Litter size, however, is a much more complex
process and, as a result, troubleshooting suboptimal numbers of piglets born alive on farms
can be a more frustrating task. Litter size to a larger degree than conception rate is
influenced by ovulation rates, the quality of semen that reaches the oviducts
(fertilization rates) and embryo survivability (embryo quality, uterine environment,
external conditions, and inherent fertility). Use these guidelines for establishing
an AI schedule and simultaneously optimizing farrowing rate and litter size. But remember
if your system isn't broken, don't fix it.
Suggested Readings
Flowers, W. L. and K. L. Esbenshade. "Optimizing management of natural and artificial matings in swine." J. Reprod. Fertil. 1993. (Suppl 48):217-228.
Rozeboom K. J., M. H. T. Troedsson, G. C. Shurson, J. D. Hawton and B. G. Crabo. "Late estrus or metestrus insemination subsequent to estrual inseminations decreases farrowing rate and litter size in swine." J. Anim. Sci. 1997. 75:2323-2327.
Soede, N. M., C. C. H. Wetzels, W. Zondag, M. A. I. de Koning, and B. Kemp. "Effects of time of insemination relative to ovulation, as determined by ultrasonography, on fertilization rate and accessory sperm count in sows. " J. Reprod. Fert. 1995a. 104:99-106.
Steverink, D.W.B., Soede, N.M., Bouwman, E.G. and B. Kemp. "Semen backflow after insemination and its effect on fertilisation results in sows." Anim. Reprod. Sci., 1998. 54: 109-119.
Waberski, D., K. F. Weitze, T. Gleumes, M. Schwarz, T. Willmen, and R. Petzoldt. " Effect of time of insemination relative to ovulation on fertility with liquid and frozen boar semen." Theriogenology. 1994a. 42:831-840.
Waberski, D. "Effects of semen components on ovulation and fertilization." J.
Reprod. Fertil. Supple. 1997. 52:105-109.
Kevin J. Rozeboom
| Breeder | Address | Breeds |
| Bob Ivey* | 314 N.C. 111 S, Goldsboro 27530 | L, D, H, Y, CW, X |
| Wesley Looper* | 4695 Petra Mill Rd., Granite Falls 28630 | L, D, H, Y, X |
| Thad Sharp, Jr., & Sons | 5171 N.C. 581 Hwy., Sims 2788030 | D, Y, X |
| Tommy Spruill | Rt. 1, Box 149, Columbia 27925 | L, X |
| Swan Acre Farm | 1060 Main Street, Swan Quarter 27885 | X |
| Thomas Farms | 8251 Oxford Rd., Timberlake 27583 | X |
| UCPRS (Swine Dev. Center) | Rt. 2, Box 400, Rocky Mount 27801 | X |
| *Real-Time Ultrasound | ||
Frank Hollowell
David Lee
| August |
| 16th Hands-On Land Application Training Class-Training Option 3 6.0 credit hours as course number AB02049911 Contact Karl Schaffer, 919-515-7538 |
| 17th Hands-On Land Application Training Class-Training Option 1 6.0 credit hours as course number AB02049909 Contact Karl Schaffer, 919-515-7538 |
| September |
| 19th Hands-On Land Application Training Class - Training
Option 4 6.0 credit hours as course number AB02049912 Contact Karl Schaffer, 919-515-7538 |
| 21st ands-On Land Application Training Class - Training
Option 2 6.0 credit hours as course number AB02049910 Contact Karl Schaffer, 919-515-7538 |
| 27-29th Extension Swine Educators Conference Des Moines, IA |
| October |
| 5th Hands-on Land Application Training Class - Training
Option 5 6.0 credit hours as course number AB02049913 Contact Karl Schaffer, 919-515-7538 |