A 15-year survey of reproductive efficiency of Standardbred and Finnhorse trotters in Finland--descriptive results.

Background: The major horse breeds in Finland are the Finnhorse (FH) and the American Standardbred (SB). The foaling rates of the FH have consistently been lower than those of the SB. During the last years, a decreasing trend in foaling rates of both breeds has been observed. The purpose of this study was to describe and compare the structure of these two mare populations for age, reproductive history and mating type. In addition, changes over the years were studied that could explain the decline in foaling rates.

Methods: In Finland, the mating statistics and foaling rates per stallion are published yearly by Suomen Hippos, which is the Finnish trotting and breeding association authorized by the EU. The studied material was the electronic breeding data of Suomen Hippos in 1991-2005 which contained 69 180 cases (one mare bred in one year with one stallion), 20 168 mares, 2 230 stallions and 5 397 stud managers. The effect of mare age and type, mating type and changes during the study period were examined separately for FH and SB using SAS 9.1 for descriptive statistical analyses (frequencies, percentages, means, standard deviations and confidence intervals). The outcome of the last mating per season (foal or not) was used in the calculation of the foaling rates.

Results: The FH mares were on average one year older and belonged to the older age groups more often than the SB mares. Ageing decreased foaling rates and even more in FH; the foaling rates were the following: young FH 68.6 and SB 72.1%, middle-aged FH 66.1 and SB 71.9%, ageing FH 61.2 and SB 68.4%, and very old FH 52.8 and SB 61.8%. The foaled mares were more frequent in the SB (45%) than in the FH (37%), but the barren and rested mares were more common in the FH. Natural mating was more commonly practiced in the FH as compared to the SB. The foaling rates decreased from 1991 to 2005 in SB from 75.1 to 65.9% and in FH from 66.5 to 60.8%. For both breeds, the proportion of young mares decreased and the proportion of very old mares increased over the years. Similarly, the proportion of foaled mares in both breeds decreased and the proportion of barren mares increased during the study period. In both breeds, insemination (AI) by transported cooled semen increased, diminishing the on-site AI in the SB and the natural mating in the FH.

Conclusions: The results of this study suggest that mare age and type and mating type all affect foaling rates and that the structural differences in the mare populations can explain differences in the foaling rates between the horse breeds and between the time periods.