Abstract
Sixty-four mares (27 foaling, 37 barren or maiden), mainly Finnhorses, were subjected to treatment with 14.5 h of light and 9.5 h of darkness, starting at the beginning of December. The onset of cycling in non-foaling mares was estimated by weekly serum progesterone determinations. All of the non-foaling mares cycled in the middle of March. They started to cycle on average in the middle of February, 11.1 weeks after the beginning of the trial. There were statistically significant differences in relation to breed (Finnhorses started to cycle 2 weeks later than warm blooded, p < 0.02) and in relation to age (brood mares with mean age 10 years, started to cycle 10 days later than those 3 years old, p < 0.03). However, there was no statistical significant relation to previous lactation, although lactating mares lactating up to the previous autumn started to cycle 7 days later than dry mares (p < 0.15).
Artificial insemination of 14 mares in the 2nd oestrus of the year, in March, resulted in 12 foalings in the subsequent year (86 %).
The following winter, all pregnant mares (N = 27) were exposed to the same kind of light treatment, starting on 1st December. The 1st mare foaled at the end of January. The time from foaling to 1st post partum ovulation was significantly longer (17.0 days) in foalings taking place within 10 weeks from the beginning of the light treatment period, than in foalings occurring after more than 10 weeks of lighting (12.1 days)(p < 0.01).
Keywords: light treatment, progesterone determination, horses
Sammanfattning
Sextiofyra ston (huvudsakligen finnhästar) av vilka 27 var fölston och 37 subfertila eller virginella ston, utsattes dagligen för 14,5 timmars artificiellt ljus åtföljt av 9,5 timmars mörker – behandlingen inleddes i början av december. Initieringen av brunstcykeln hos de icke-fölande stona fastställdes med hjälp av progesteronhalten i blodprover tagna en gång per vecka. I mitten av mars var alla icke-fölande ston igång med sin brunstcykel; igångsättningen skedde i genomsnitt i mitten av februari, dvs. 11.1 veckor efter det att studien påbörjades. Följande signifikanta skillnader påvisades: 1) ras: finnhästarna visade brunst 2 veckor senare än varmblodiga ston (p < 0.02); 2 ålder: ston som fölat (genomsnittsålder 10 år) inledde ovulationscykeln 10 dygn senare än treåriga ston (p < 0.03). Ingen signifikans påvisades däremot i relation till tidigare laktation, utom hos ston som hade lakterat under foregående höst. Dessa ston inledde brunstcykeln 7 dygn senare än de övriga stona (p < 0.15). Artificiell insemination av 14 ston under deras andra brunst för året (i mars) resulterade i 12 fölningar (86 %) under det följande året.
Följande vinter utsattes dräktiga ston (N = 27) för samma ljusbehandling med början 1 december. Det första stoet fölade i slutet av januari. Intervallet melian fölning och den första Ovulationen var signifikant längre (17.0 dygn) hos de ston som fölat inom 10 veckor efter påbörjad ljusbehandling jämfört med ston som fölat senare an 10 veckor efter inledd ljusbehandling (17.0 vs. 12.1 dygn, p < 0.01).
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