Abstract
Effects on reproduction in a total of 135 dairy cows managed for calving intervals of 12, 15 or 18 months (72, 38 and 25 cows respectively) were studied. The cows were of the Swedish Red and White Breed (SRB) and the Swedish Freisian Breed (SLB) and were housed in 2 different herds with 3 different management systems (tied, loose, and tied but milked in a milking parlour; mixed). The cows in one of the herds (48 cows) were assigned for milking either 2 times or 3 times a day. When comparing conception rate at 1st insemination (AI) and the percentage of cows finally pregnant, we found no significant differences between the 3 calving interval groups, however, a tendency for a higher conception rate with a 15 months' interval compared with a 12 months' interval was found in one of the herds (50% vs 41.5%). The percentage of finally pregnant animals varied between 81% and 100%, but this variation was mainly attributed to the herd rather than calving interval group. A significantly higher percentage of cows was treated for anoestrous in the 12-month group than in the 15-month group in one of the herds (28.6% vs. 5.3%).
The frequency of ovulations with external heat signs increased with ovulation number up to the 4th ovulation and thereafter remained stable. No significant difference was found in number of AIs required per conception with respect to calving intervals, breeds, or milking frequency groups. However, cows milked 3 times a day had a significantly longer interval from the 1 st AI to conception compared with cows milked 2 times a day (45.8 days vs 17.6 days, p<.01). Cows kept loose exhibited 1st ovulatory oestrous, approximately 2 weeks earlier (55.9 days vs 69.7 days, p<.05) than their herd mates kept tied.
In conclusion, our study shows that lengthening the calving interval to 15 or 18 months may have a positive influence on reproduction in terms of less need for treatments of ovarian disorders and higher conception rates. Our results also indicate that milking 3 times a day may have negative effects, and keeping cows in a loose-housing management system may have positive effects on ovarian function. kw|Keywords|k]reproduction; k]extended calving intervals; k]cattle; k]milking frequency
Sammanfattning
Med gradvis ökande mjölproduktion per ko och ett bibehållet mål på ca 12 månaders kalvningsintervall ökar risken för störningar i kornas hälsa och fruktsamhet. Därmed ökar kraven på intensiv övervakning av kornas könsfunktioner under postpartum perioden samtidigt som man riskerar en ökad behandlingsfrekvens och därmed en ökad användning av exempelvis hormoner. Detta medför kostnader för djurägaren samt negativa effekter på djurens välbefinnande som därmed kan ge negativa konsumentreaktioner. Med en medvetet förlängd period till första inseminition finns möjligheten att en större andel av korna spontant skulle återfå normal cyklicitet efter kalvning, att behovet av vissa behandlingar skulle minska samtidigt som dräktighetsprocenten per insemination (AI) ökar. Samtidigt kan risken öka för andra störningar i form av äggstockscystor och svag brunst. Motivet för föreliggande undersökning var därför att studera effekten på fruktsamheten hos mjölkkor som medvetet styrdes till kalvningsintervall på ca 12, 15 eller 18 månader.
Sammanlagt 135 mjölkkor av SRB- och SLB-ras styrdes medvetet till att insemineras första gången 50, 140 eller 230 dagar efter kalvning. Korna hölls i 2 olika besättningar och i 3 olika uppstallningssytem; uppbundna på båspall, lösdrift eller uppbundna men mjölkade i mjölkgrop. Korna i den ena besättningen var dessutom uppdelade i 2 grupper som mjölkades 2 respektive 3 gånger per dygn. Ingen signifikant skillnad sågs beträffande dräktighetsprocenten vid första AI mellan kalvningsintervallsgrupperna. I en besättning sågs dock en högre dräktighetsprocent i 15-månaders gruppen än i 12-månaders gruppen (50% resp. 41.5%). Andelen slutligt dräktiga varierade mellan 81% och 100%, men denna skillnad var mera kopplad till besättning än till kalvningsintervall. En större andel kor behandlades för anöstrus i 12-månaders gruppen än i 15-månaders gruppen i en av besättningarna (28.6% respektive 5.3%). Inga tendenser sågs till sämre brunstsymtom med ökat avstånd från kalvning. Vid den första ägglossningen efter kalvning var andelen kor som uppfattades som brunstiga låg, (<10%). Andelen kor där brunst registrerades ökade sedan med ovulationsnummer fram till 4:e ovulationen (50%–70%) för att sedan förbli stabil på denna nivå. Korna i lösdriftsystemet visade första brunst i samband med ägglossning ca 14 dagar tidigare än uppbundna kor. Sammantaget sågs således tendenser till gynnsamma effekter på fruktsamheten hos kor med kalvningsintervall på 15 månader jämfört med 12 månader samt hos kor i lösdrift jämfört med bundna kor.
Full Text
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Acknowledgments
This study was supported by the Swedish Farmers Research Council and the World Bank through ARP/SL grant CR 1776-CE. The authors gratefully acknowledge Agr. Gudrun Tengroth and Assoc. Prof. Birgitta Larsson for valuable help in providing data from herd 1.
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