[t]Boar Exposure Linked to AI Success University of Illinois researchers report that frequency of boar exposure to newly weaned sows can improve timing inseminations, increasing the chance of sows being inseminated within the preferred 24-hour period prior to ovulation.

Illinois research was aimed at evaluating whether increasing the frequency of boar exposure would affect the accuracy of determining the onset of estrus, therefore, the accuracy of predicting ovulation in weaned sows.

Between January and August 2000, sows of mixed parity were weaned 18 days after farrowing and then randomly allotted to boar exposure treatment by genotype, parity and lactation length. Sows were weaned into gestation crates. Boar exposure was initiated three days after weaning by moving boars through the alleyway at the front of the crate. Individual sow exposure lasted two to five minutes.

The three treatment regimes included 186 sows exposed to boars once daily (1X), twice daily every 12 hours (2X), or three times daily every eight hours (3X). Once estrus was detected, transrectal ultrasound was performed every eight hours to visualize the ovaries and determine time of ovulation. Sows in the 1X group were bred by artificial insemination at zero and 24 hours after first detected estrus. Sows in the 2X group were bred at 12 and 24 hours. And, sows in the 3X groups were inseminated at 16 and 32 hours after first detected estrus.

Researchers learned that wean-to-estrus was not influenced by frequency of boar exposure and averaged 4.5 days. Ninety to 100% of sows expressed estrus within eight days and were unaffected by treatment or month.

Treatment did, however, influence the percentage of sows ovulating. Sows exposed to a boar two or three times had an ovulation rate of 85%, while 98% of the sows exposed a single time ovulated.

The wean-to-ovulation interval was not influenced by treatment and averaged 6.5 days. The length of estrus averaged 58.5 hours and was influenced by both treatment and month, but no interaction was noted.

Estrus lasted longer in the 3X exposure sows (62-hour avg.) compared to the 2X exposure group (53-hour avg.) and the 1X group (42-hour avg.).

Researchers also reported the shortest average estrus length occurred in August, February and March (40-49 hours), while the longest lengths were recorded in April and June (75-58 hours).

The estrus-to-ovulation period was not influenced by treatment or month and averaged 45 hours.

The occurrence of ovulation to the end of standing estrus was influenced by month, with the shortest interval from ovulation-to-estrus in the February and March replicates (11 hours), intermediate intervals in late March and August (23 hours), while longest intervals were recorded in April and June (39 hours).

Researchers note that more frequent boar exposure improved the percent of inseminations that occurred 24 hours before ovulation. The increased exposure frequency improved the percent of first inseminations occurring within 24 hours from 10% in the 1X group to 29% in the 2X group, and to 46% in the 3X exposure group.

The higher exposure frequency also slightly improved the percentage of second services administered 24 hours before ovulation from 81% in the 1X group to 82% in the 2X group, and to 85% in the 3X group. But these were not statistically different.

The results of this experiment indicate that the frequency of boar exposure for weaned sows can improve the precision for timing inseminations and the frequency of first and second services administered within 24 hours before ovulation,the researchers say.

Researchers: Robert Knox, Gina Miller, Kilby Willenburg, and Sandra Rodriguez-Zas, University of Illinois-Urbana. Phone Knox at (217) 244-5177 or e-mail at rknox@uiuc.edu.

[t]Genotype Affects Response to Stress Though relatively equal in muscle growth ability, different genotypes can respond differently to early postmortem stress and may contain inherently different capacities to develop quality pork.

This means progressive seed-stock suppliers must consider the quality characteristics of a genotype along with rate of gain, feed efficiency and cutability in their selection programs, say researchers at Purdue University.

They conducted a study for the National Pork Producers Council to determine the effects of stress (simulated by early postmortem electrical stimulation) and genotype on pork quality traits in halothane-negative pigs.

In the experiment, 150 pork carcasses from three genetic lines virtually identical in muscling and composition were electrically stimulated at various times postmortem to investigate how muscle of various genotypes responds to varying stress.

The first genetic line consisted of pigs from terminal cross sires mated to Landrace females. The second line was from Duroc-Large White sires mated to Yorkshire-Landrace females, and the third genotype consisted of pigs from U.S. Duroc sires mated to Yorkshire by Duroc-Landrace dams.

Treatments consisted of one of four postmortem treatments of electrical stimulation (13 pulses): 100 volts at 15 minutes, 100 volts at 25 minutes, 200 volts at 15 minutes or 200 volts at 25 minutes or controls (no stimulation).

Pork chops were taken from the 10th rib at 24-hours postmortem and used to evaluate drip loss, color (Hunter and NPPC), firmness and marbling scores.

Genotypes responded differently to electrical stimulation, which altered muscle pH decline and meat quality characteristics, the researchers report. Differences were observed in pH at 20, 30, 40, 50 and 60 minutes postmortem between carcasses stimulated at 15 minutes and those stimulated at 25 minutes.

Animals stimulated with greater voltages tended to have lower pH values. In addition to affecting pH, electrical stimulation also affected muscle temperature.

Researchers say the differences in pH and temperature declines of these three lines of superior muscled animals indicate that some genotypes respond more dramatically (metabolize energy and dissipate heat) to an insult or stress. They conclude that some lines of heavy muscled animals have inherent muscle differences that make them more susceptible to adverse meat development. Other lines, they say, are less vulnerable to stress and trepidation, such as aggressive live animal or carcass handling procedures.

In addition, researchers say this finding shows that during the conversion of muscle to meat, some genotypes are more sensitive to electrical stimulation, and that calls into question the widely used electrical stunning methods in most U.S. pork slaughtering facilities.

More research is needed to pinpoint exactly what is causing these differences across highly selected genotypes.

Researcher: David E. Gerrard, Purdue Research Foundation. Phone Gerrard at (765) 494-8280 or e-mail dgerrard @purdue.edu.