RAPESEED PRODUCTS FROM DOUBLE-LOW CULTIVARS AS FEED FOR DAIRY-COWS - EFFECTS OF LONG-TERM FEEDING ON THYROID-FUNCTION, FERTILITY AND ANIMALHEALTH

Eighty-five dairy cows of the Swedish Red and White Breed (SRB) were i ncluded in a long-term experiment during 3 consecutive lactations. The cows were divided into 3 different dietary groups that received no ra peseed (NR), up to 1.2 kg dry matter (DM) 00-rapeseed meal plus 0.2 kg DM full-fat 00-rapeseed (MR), and up to 2.5 kg DM 00-rapeseed meal pl us 0.9 kg DM full-fat 00-rapeseed (HR) per day. No significant differe nces in culling rates or disease rates were found between the feeding groups at any time during the experiment. The interval from calving to conception among the primiparous cows was longer for the HR-group (12 5 days) than for the NR-group (100 days). The response to a thyrotroph releasing hormone around 90 days postpartum during the first lactatio n was significantly higher for the HR-group (86.7 mu/L/h) than for the NR-group (55.2 mug/L/h). This indicates that at the highest level of rapeseed feeding, glucosinolates had a very mild, suppressive influenc e on thyroid hormone release, apparently compensated for by an increas ed activity along the hypothalamic-pituitary-thyroid axis. No signific ant differences in fertility or thyroid function were found among the pluriparous cows. During 2nd lactation the concentration of serum urea was higher in the NR-group (7.31 mmol/L) than in the HR-group (6.83 m ol/L). The effects of independent environmental factors influenced fer tility and thyroid function to a much greater extent than the rapeseed feeding. It was concluded that the feeding of rapeseed products from certified double low varieties of B. napus to adult dairy cows in amou nts up to 3 kg rapeseed meal per cow and day would not have any negati ve effects on animal health or fertility.