Onset of Luteal Activity in Non-Foaling Mares during the Early Breeding Season in Finland

Abstract

The luteal activity in mares was studied in the Equine Research Station (ERS) and in trotting stables (TS) in South-Finland. The mares were Standardbreeds in the TS and mainly Finnhorses in the ERS. Between January and June blood was collected once a week for serum progesterone determinations. The mares in the ERS were distributed in 1 of 3 groups: three-years old not yet in training (N = 38), brood mares (N = 21) and mares in training (N = 47). A 4th group was the mares in training in the trotting stables (N = 73).

Every 5 th mare in the ERS and every 4th mare in the trotting stables were cycling already at the beginning of the year. Onset of luteal activity in anoestrous mares was most common in the middle of May. Over 95 % of the mares were cycling at the beginning of June.

In the ERS 40 % of the Finnhorse mares in training were cycling through the winter. The three-years old and the brood mares were all anoestrous during winter. They started to cycle on average before the middle of May. Anoestrous training mares started before the middle of April.

Anoestrous Finnhorse mares began to cycle later than warm blooded mares in all of the groups studied. Mares which had foaled the previous year were more often anoestrous during the winter than dry mares.

The time of year when cycling began in a particular mare tended to be the same from year to year (p < 0.01).

Sammanfattning

Lutealfunktionen hos ston undersöktes vid Hästforskningsstationen (HF) samt vid någon travcentral i södra Finland (TC). Stona vid TC utgjordes av varmblodiga travhästar och vid HF av finnhästar. Progesteron i serum bestämdes en gång i veckan under tiden januari-juni. Stona vid HF indelades i 3 grupper: treåriga ston som ännu inte börjat tränas (N = 38), fölston (N = 21) och ston i träning (N = 47). Den 4. gruppen utgjordes av ston i träning vid TC (N = 73).

Brunstcykeln var igång hos vart femte sto i HF-gruppen och hos vart fjärde sto i TC-gruppen redan i början av året. Lutealfasen hos de anöstrala stona började oftast i mitten av maj. Brunstcykeln var igång hos mer än 95 % av stona i början av juni.

Fyrtio procent av de finnhäststona i träning hade brunstcykel under hela vintern, medan stona i de 2 andra grupperna vid HF var anöstrala hela vintern. Deras brunstcykel började i medeltal före mitten av maj, medan första brunstcykeln hos de anöstrala stona i träning inleddes före mitten av april.

Av de olika grupper var de anöstrala finnhäststona sist med igångsättningen av sin brunstcykel. Vin-teranöstrus forekom oftare hos ston som hade fölat under foregående år än hos sådana som inte fölat.

Tidpunkten på årstiden då brunstcykeln började tenderade att vara den samma hos de individuella stona under flera år (p < 0.01).