By Eduardo Beltranena and William Flowers, North Carolina State University

Altrenogest (Matrix, ChronoMate, SwineMate) is a synthetic progestogen approved for the synchronization of the time of heat in sexually mature gilts that have shown at least one estrous cycle (~21 days).

A meta-analysis of 26 studies (Wang et al. 2018) showed that feeding altrenogest to cyclic gilts for at least 14 days vs. untreated gilts increased

To reduce labor some production systems are implementing feeding altrenogest to nonresponding, noncyclic gilts that have had a short period of boar stimulation with mixed results and disregard for costs.

The objective of this analysis was to evaluate the feasibility of the off label feeding of altrenogest to nonresponding gilts on potential reproductive performance vs. product, feed, housing and labor costs.

Scenarios

Results

Discussion

Tables 1, 2 and 3 (top) show the cost of EARLY, INTERMEDIATE and LATE responding replacement gilts to 7, 14 or 23d boar stimulation, respectively. If old enough, gilts generally respond to boar stimulation within ~10d. Late responding gilts are more likely to have lower retention in the herd and reduced longevity (culled after 1st or 2nd parity; Patterson and Foxcroft 2019).

Tables 1, 2 and 3 (bottom) show that if these gilts fail to show 2nd heat after their 1st heat-no-serve estrus (puberty), the producer may still earn sufficient revenue by selling them as market (meat) gilts.

Table 4 (top) shows nearly one-third greater cost for a gilt that after not responding to boar stimulation for 14d is fed altrenogest for 14d and bred at her 1st heat vs. an intermediate responding gilt with equivalent boar exposure (Table 3 top). Nonresponding gilts treated with altrenogest may have unpredictable heat and reduced fertility. If only 50% respond, the cost would double per bred gilt.

Table 4 (bottom) shows that cost triples for a gilt that after not responding to boar stimulation for 14 days is fed altrenogest for 14 days and shows no heat after vs. a late responding gilt. Treated nonresponding gilts must remain in the barn for at least 21d before slaughter to satisfy the product withdrawal requirement. By then, nonresponding gilts are so heavy that the producer would certainly lose money selling them as discounted heavy hogs or culled sows.

Recommendations

Reducing labor by checking gilts is what producers wrongly focus on. Labor (only ~5%), feed and housing to provide up to 23d boar stimulation would be cheaper than the cost of feeding altrenogest to noncyclic gilts because of their unpredictable response. Treated non-responders must remain in the barn for ≥21d to meet the product withdrawal requirement. The potential of an extra 0.5 piglet born (~$20), slightly greater farrowing rate and heat synchrony would not likely mitigate drug, extra labor, feed and housing costs.

Producers should systematically expose gilts to different boars for at least 15 min/d, track the progression of heat signs, tag and record their first heat-no-serve. Regroup gilts that have shown first heat-no-serve to separate pens weekly. Reinitiate boar exposure ~5d before expected 2nd heat to confirm. Ovulation rate naturally increases from 1st to 2nd but not to 3rd heat thus expect larger litter size delaying breeding to 2nd heat.

Weekly mix gilts that have not responded and continue boar stimulation for up to 23d. By then, most likely they are anestrous, or you missed their 1st heat (puberty) and should be shipped to slaughter. The older your start boar stimulation, the more likely you are to reduce days to onset of 1st heat and the more uniform the response will be thus reducing labor input, but feed and housing costs, and nonproductive days would increase disproportionally.

References

Patterson, J., and G. Foxcroft. 2019. Gilt management for fertility and longevity. Animals 9:434. https://doi.org/10.3390%2Fani9070434

Wang, Z., B. S Liu, X. Y. Wang, Q. H. Wei, H. Tian, and L. Q. Wang. 2018. Effects of altrenogest on reproductive performance of gilts and sows: A meta-analysis. Anim. Reprod. Sci. 197:10-21. https://doi.org/10.1016/j.anireprosci.2018.08.035