Abstract
The number of offspring sired by individual bulls in multisired beef herds was determined by blood grouping. Six series of tests, each having from 3 to 18 bulls as possible sires,, yielded from 35 to 114 dam-offspring pairs. The paternity was established for 45 to 90 % of the calves tested in each series. The rest were cases with either more than 1 bull not being excluded as the possible sire, or all bulls excluded from being the sire. The causes for the non-established paternities are discussed. Highly significant differences were found in the number of offspring sired by each bull. In each series, bulls ranking in the top third of the siring order sired 65–100 % of the calves with established paternities. Since a minority of the bulls sired the majority of the calf-crop, the generally recomended number of bulls for herds on the range can perhaps be reduced.
Keywords: paternity tests, beef herds, blood grouping, sire prolificacy.
Sammendrag
Med henblik på at bestemme de enkelte tyres andel i antallet af kalve i større besætninger med løsdrift og naturlig bedækning, er der udført blodtypeundersøgelse i fem besætninger. I en besætning omfatter undersøgelsen to avlssæsoner. Herved er der udført ialt seks serier ai faderskabsundersøgelser, hver omfattende fra 34 til 114 moder-afkom par og med ira tre til 18 tyre som mulige fædre.
Ved blodtypeundersøgelse kunne faderskabet fastlægges for mellem 45 og 90 % ai de undersøgte kalve i de enkelte serier. For de resterende kalve kunne faderskabet ikke afgøres, idet der enten var mere end én tyr, der ikke kunne udelukkes som mulig fader, eller ingen af tyrene kunne være fader. De mulige årsager hertil er diskuteret.
Ved sammenligning af de enkelte tyres andel i antallet af kalve fandtes statistisk sikre forskelle mellem tyre inden for besætning. Den bedste trediedel af tyrene med hensyn til antal kalve fandtes at være fader til mellem 65 og 100 % af kalvene med fastlagt faderskab i de enkelte besætninger. Det synes derfor muligt at reducere det almindeligt anbefalede antal tyre pr. besætning under løsdriitiorhold med naturlig bedækning.
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Acknowledgements
Blood sampling was carried out by the veterinarians and technicians of the Governmental Veterinary Services, Afula and Ramla districts. The cooperation and help of the herdsmen in Kibbutz Sha’alvim and at the Newe Ya’ar Agricultural Experiment Station are gratefully acknowledged.
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