Genetics/Reproduction

Boosting Lysine Levels Spurs Gilt Development When Given PG600

Ensuring that developing gilts have adequate lysine:metabolizable energy levels improves body growth, muscle and reproductive response when gilts are given PG600.

University of Illinois researchers studied three diets with different amino acid levels to determine whether diet could affect the introduction of replacement gilts into the breeding herd.

The one-year study involved PIC C-22 terminal line gilts at the University of Illinois swine research center.

The diets were formulated for two phases — from 100 to 145 days of age and for over 145 days of age. The diets provided high, medium or low standardized digestible lysine:metabolizable energy.

Gilts were housed and fed individually in an environmentally controlled area. Feed was restricted to match the amount required for gilts from the genetic line to maximize growth when group-housed. Feeding was adjusted so that total daily energy intake was equalized across treatments.

Gilts were weighed weekly and body composition determined at 115, 145 and 175 days of age. Blood was collected and tested for insulin at Day 145.

At 175 days of age, gilts were injected with PG600 (Intervet Inc.). During this time, gilts were exposed to a mature boar and checked for estrus once daily using fenceline contact for seven days. Reproductive tracts were collected 20 days after PG600 injection and assessed for ovarian structures.

The experiment showed that the high and medium diets increased body weight by Week 8, and that average gilt body weight remained above those gilts from the low diet until the end of the study (Table 1).

Insulin and backfat were not influenced by diet; however, loineye area was increased by diet from the onset of the trial (Table 1).

As Table 2 illustrates, the expression of estrus increased as the lysine ratio increased, while other measures of estrus were unaffected.

Also, the percentage of gilts ovulating remained unchanged between treatments and exceeded 85%, and there was no effect on the number of corpora lutea (Table 2).

Overall, this experiment indicated that increasing the lysine-to-energy ratio during gilt development impacts body weight, loin muscle area and estrus expression.

But diet enhancement had little effect on other body measures and ovulation characteristics.

The response to PG600 in this study reflected a high level of gilt fertility, with an average of 80% estrus expression, 89% ovulation and 19 eggs ovulated.

Study results cannot be extrapolated to predict the impact of increased amino acid levels on long-term gilt reproductive performance, researchers said.

Table 1. Impact of Dietary Lysine Levels on Reproductive Responses to PG600
Item High Medium Low
Number 34 36 36
Week 0 weight (lb.) 109.3 108.7 110.2
Week 5 weight (lb.) 174 176.7 169.6
Week 10 weight (lb.) 251.2 253.7 230.3
Insulin (IU/ml.)* 6.9 8.2 8.6
Backfat Day 100 (in.) 0.45 0.46 0.46
Loineye Area Day 115 (sq. in.) 4.2 4 3.9
Backfat Day 145 (in.) 0.5 0.52 0.52
Loineye Area Day 145 (sq. in.) 5.82 5.7 5.1
Backfat Day 175 (in.) 0.64 0.63 0.66
Loineye Area Day 175 (sq. in.) 7.3 6.83 6.32
*IU = International Units

Researchers: R. Knox, K. Soltwedel, J. Pettigrew, K. Farris, M. Hon, S. Breen, A. Jackson, S. Bensen and M. Ellis, University of Illinois. Contact Knox by phone (217) 244-5177; fax (217) 333-8286; or e-mail rknox@uiuc.edu.

Table 2. Estrus Expression in Response to Increases in Lysine Ratio
Item High Medium Low
Estrus in 7 days (%) 90.9 83 72.2
PG600 to estrus (hours) 118 116 108
Duration of estrus (hours) 47 56 52
Ovulating (%) 91.9 89.5 86.4
Number of corpora lutea 16.4 18.5 21.4