Abstract
Declining reproductive performance is a serious breeding concern in many countries. To reveal the situation in Norwegian cattle, trends in reproductive performance were studied using insemination reports from 1985 to 2005 and data based on herd recording files from 1989 to 2005. The total number of first services was 469.765 in 1985 declining to 335.712 in 2005. The number of recorded herds and animals declined from 21.588 to 14.718 and 360.289 to 309.452 from 1989 to 2005, respectively. Sixty days non-return rate after single inseminations (NR60) increased from 68.1 in 1985 to 72.7% in 2005 (p < 0.001) and the number of services per inseminated animal (NIA) decreased from 1.8 to 1.6 (p < 0.001) from 1985 to 2005. However, return rates 0–3 days post insemination (RR0-3) increased from 6 to 12% in the same period (p < 0.001). NR60 was higher and the RR0-3 was lower in the summer season compared to the winter season during the whole period. A fertility index (FS), has been calculated from the herd recording files each year from 1989 to 2005. The average FS-index did not show a significant trend and the calving interval was also fairly constant between 12.4 and 12.6 months during this period. The average interval from calving to first and last insemination, respectively, increased from a low of 79 and 102 days in 1990 to a high of 86 and 108 days in 2005. Both intervals were consistently longer for cows in first lactation than for cows in later lactations. The percentage of inseminated animals reported culled because of poor fertility decreased from 6.0% in 1989 to 4.6% in 1996 and thereafter again increased to 6% in 2005. In conclusion, most fertility measures, mainly comprising the Norwegian Red (NRF) breed, show a relatively high level of reproductive performance with a positive or a relatively constant trend during the last two decades.
Highlights
In many countries there has been a decline in reproductive performance in dairy cattle
Sixty days non return rates after single inseminations (NR60), return rates 0–3 days post insemination (RR0-3), average number of inseminations per animal inseminated (NIA) and seasonality are based on all inseminations performed in the country during the period, irrespective of membership in the milk recording system
The major part of the inseminations is performed with semen from the Norwegian Red (NRF) breed, varying from a high of 97.8% in TFibnroisgeeteuamdlrinen(uᮀa1mt)iobenevsreproyef r5ffirothsrtymeinaesrdefmwroitnmhats1ieo9mn8s5en(t■ofr)2oa0mn0d5bpuellrscoefntahgeeNs oRfF Total number of first inseminations (■) and percentages of inseminations performed with semen from bulls of the NRF breed (ᮀ) every 5th year from 1985 to 2005
Summary
In many countries there has been a decline in reproductive performance in dairy cattle. Several studies show increasing number of days from calving to first service and decreasing pregnancy rates, e.g. The number of inseminations per inseminated cow, days from calving to conception and calving intervals have increased. To improve fertility and save labour, various pharmaceuticals to control the oestrous cycle and to treat reproductive disorders are extensively used in many herds, e.g. During the last decades the productivity of dairy cattle has increased considerably in many countries, not least because of progress due to genetic improvement. A serious breeding concern is that estimates from a number of studies present unfavourable genetic correlations, on average near 0.3, between various fertility (page number not for citation purposes)
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