The aim of this study was to evaluate how red and blue LED light during the daytime affects dry matter intake, feed selection, and milk yield in dairy cows. Ten multipa-rous pregnant Swedish Red cows in post-peak lactation were used. Cows were housed in a tie stall barn. They were subjected to a 33-day red or blue LED light treatment during a long day photoperiod with 16 hours day and 8 hours night. Cows were fed silage and concentrates separately. Silage was fed three times a day ensuring ad libi-tum intake with 5-10% orts. Concentrate was fed four times per day. Samples of si-lage were collected thrice a day and individual orts were collected at the end of the day and at the end of the night. Data for eating behaviour and milk yield was collected five days before and five days after the treatment period. Eating behaviour was de-termined using the difference in distribution of fractions of different straw length in the silage that was fed and orts during daytime and night time. A 2-screen Penn State Particle Separator (PSPS) (19mm and 8mm) with a solid bottom pan was used to determine distribution of large, medium and short silage fractions. Treatments did not affect total DMI. Overall, cows sorted for the large fractions, against the medium and short fractions. During the LED period there was a difference (P<0.001) in sort-ing between Red and Blue cows during the daytime. Cows on the Red LED light sorted for the short fractions during daytime. Blue cows showed different sorting (P<0.05) during day and night. Their sorting for the large fractions was more pro-nounced during daytime than night. Milk yield did not change during the trial and did not differ between the Red and Blue groups. In conclusion, sorting activity was greater during the daytime in the LED period, which could have been influenced by the LED light. Interestingly cows seem to have better vision in red than blue LED light. Furthermore, it also possible that the LED light maintains milk yield, since no change was observed during the four-week trial in post peak lactation.Syftet med studien var att utvärdera hur rött och blått LED-ljus påverkar foderintag,
foderselektion och mjölkmängd hos mjölkkor. Tio dräktiga kora v rasen Svensk Röd
Boskap i andra eller högre laktation ingick i studien. Korna inhystes i en stallavdelning
för uppbundna kor. Behandlingarna var 33 dagar med rött eller blått LED-ljus
under 16 timmar dag och svagt ljus från lysrör under åtta timmar på natten. Korna
utfodrades med ensilage i fri tillgång med 5-10 % rester. Ensilagegivan fördelades på
tre utfodringstillfällen och koncentrat på fyra tillfällen. Ensilageprover togs tre
gånger per dag och individuella foderrester vägdes och provtogs i slutet av dagen och
i slutet av natten under fem dagar innan och fem dagar efter behandlingsperioden.
Ätbeteende beskrevs som skillnaden i strålängdsfraktioner mellan utfodrat ensilage
och foderrester. Ensilagets strålängd separerades i fraktionerna kort, medium och
lång med en Penn State partikelseparator (19 och 8 mm). Det var ingen skillnad mellan
behandlingarna i torrsubstansintag. Korna sorterade för lång strålängd, emot medium
och korta strån. Under LED-ljusperioden sorterade kor som behandlades med
rött ljus för korta strålängd under dagen (P<0.001). Korna som behandlades med blått
ljus visade mer omfattande selektion för den långa strålängden på dagen än på natten
(P<0.05). Mjölkmängden förändrades inte under försöksperioden och skiljde heller
inte mellan grupperna. Sammanfattningsvis sorterade korna mer uttalat under dagen
än natten under LED-perioden. Det verkar som att korna såg bättre i rött än blått
dagsljus. Det är möjligt att LED-ljuset stimulerade mjölkmängd eftersom mjölkmängden
inte förändrades under försöket trots att korna hade passerat topplaktation
