Reproductive performance of Norwegian cattle from 1985 to 2005: trends and seasonality

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. [1-5]. As a result, 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. [6,7]. During the last decades the productivity of dairy cattle has increased considerably in many countries, not least because of progress due to genetic improvement. However, a serious breeding concern is that estimates from a number of studies present unfavourable genetic correlations, on average near 0.3, between various fertility measures and production [8]. In contrast to many other countries, Norway has a long tradition of including fertility in the Total Merit Index (TMI). Viewed against this background, the primary objective of the present study was to describe the trends in some reproductive measures in Norway the last two decades. Seasonal variations in reproductive performance are also revealed.The results obtained in the present study are based on insemination reports and herd recording files in Norway comprising 66.8% of the herds in 1985 increasing to 94.2% in 2005 [9]. AI-technicians and veterinarians report all inseminations into the AI-database, and they are only paid when the inseminations are registered. From 1985 to 2005, the part of inseminations performed by veterinarians has increased from 45.8% to 59.7%. The rest of the inseminations was performed by technicians, but from 2002 also a small part by herdsmen, increasing from 0.3% to 0.7% in 2005. After attending an AI-course the herdsmen have to sign an agreement to report inseminations to the AI-database. Sixty days non return rates after single inseminations (NR60), return rates 0–3 days pos