A retrospective cohort study on fertility in the Norwegian Coldblooded trotter after artificial insemination with cooled, shipped versus fresh extended semen

Abstract

BackgroundPregnancy rates with cooled equine semen can be unsatisfactory and show great variation. Information about first cycle pregnancy rates and pregnancy rates per cycle are often lacking from publicly available records. This retrospective cohort study was performed to evaluate the fertility of the Norwegian Coldblooded trotter. The aim of the study was to compare the breeding results after insemination with fresh, extended with those of cooled, shipped semen among Norwegian Coldblooded trotter mares. First cycle pregnancy rate was the main parameter used to measure fertility. Stud-books were collected from four studs from the years 2006–2010. Statistical analyses were done in Stata using Chi square test and multivariable analyses where different models were compared based on Akaike’s information criterion.ResultsFirst cycle pregnancy rate, seasonal pregnancy rate and foaling rate all showed significant differences (P < 0.0001) when comparing mares inseminated at stud with mares inseminated with cooled, shipped semen, favoring artificial insemination (AI) at stud. First cycle pregnancy rate was 55.1 % for mares inseminated at stud with fresh extended semen and 42.2 % for mares inseminated with cooled shipped semen. The overall pregnancy rate per cycle was 84.4 % for AI at stud and 66.9 % for cooled, shipped semen. The parameters stud, mare age, number of inseminations within an estrus cycle and individual stallion were also investigated for influence on fertility.ConclusionsFew retrospective studies include the parameter of first cycle pregnancy rates. Our study does not differ dramatically when comparing seasonal pregnancy rates and foaling rates with similar studies. Fertility parameters for the Norwegian Coldblooded trotter do not differ significantly from most other studies of Coldblooded mares and other mare breeds around the world. But the difference in fertility parameters between AI at stud to AI with cooled semen between our study and others, indicates that higher pregnancy rates in Norwegian Coldblooded trotter may be possible.

Reproductive performance of a cohort of Standardbred mares under a commercial breeding system

“…10 A study on the fertility of Norwegian Coldblood trotters under AI conditions reported an FCPR of 51.2%. 22 A study incorporating 11 farms in Victoria, Australia reported a FCPR of 65.3%-75% in Thoroughbreds (7 farms) and 57.1%-74.0% in Standardbreds (4 farms). 1 Our current study showed considerably greater variability in FCPR for mares inseminated both on-farm (range 52.7%-72.5%) and off-farm (range 49.7%-67.3%) and we contend that this may reflect the differences in mare age and semen type.…”

Analysis of factors affecting the pregnancy rate of mares after inseminations with cooled transported stallion semen

“…Also in the present study, the FH mares were about one year older than the SB mares. The negative effect of ageing on mare fertility has been reported in all studies where mare age has been included as a factor [1,[21][22][23][24][25][26][27]. Age affects many aspects of reproduction, such as uterine function (uterine contractility, intrauterine fluid accumulation, endometrial inflammation and fibrosis), PR and pregnancy loss [22].…”

Predicting the Outcome of Equine Artificial Inseminations Using Chilled Semen

“…These selection methods, although undeniably producing champions, have consequently led to a decline in fertility [ 1 , 2 ]. While limited information is available for the per cycle conception rates in standardbred horses alone, other breeds, which also utilize artificial insemination (AI), have indicated pregnancy rates per cycle range from 76% to 83% [ 3 , 4 , 5 ] after AI using fresh semen and pregnancy rates of 44–69% after AI using chilled semen [ 5 , 6 , 7 , 8 ]. Several factors have been observed to impact reproductive efficiency, including the age of the stallion and mare, the mare’s reproductive history (e.g., maiden, barren, foal heat), the month of breeding, genotype, frequency of mating, and endocrine levels [ 9 , 10 , 11 , 12 , 13 ].…”