Evaluation and definition of reference lactation length in Chios dairy sheep

Z Basdagianni*, G Banos, Z Abas, G Arsenos, E Sinapis, D Zygoyiannis

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Prediction of milk yield at a fixed reference lactation length allows objective comparison between animals and facilitates herd management. A widely accepted 305-day lactation length has been established in dairy cattle. In this study, various lactation lengths were evaluated as reference for the Chios sheep. Data included 42 675 test-day milk records of 7 121 ewes, in their first three lactations, from 75 flocks, collected between 1998 and 2000. Data were analyzed with a random regression model that included a 4(th)-order Legendre polynomial for the fixed and random (animal) effect. Each lactation was analyzed separately. (Co)variance components were calculated for both individual test-day and total lactation milk yield, and were estimated with Gibbs sampling. Thirteen different lactation lengths were evaluated, ranging from 120 to 240 days, defined at 10-day intervals. Evaluation criteria included:

animal genetic correlation of reference lactation milk yield with actual lactation yield (CORL) and yield at first test (CORT);

ratio of animal genetic to total phenotypic variance of reference lactation yield (VRT); and

predicted con-elated response in reference lactation milk yield to selection based on the first test-day yield (CRSP). Estimates of CORL were very high, ranging from 0.95 to 0.98, the highest being for reference length of 180-210 days.

Estimates of CORT were inversely linear to the reference length, ranging from 0.87 for the longest (240 days) to 0.99 for the shortest (120 days) length. Estimates of VRT were 0.70-0.74, the highest being for a lactation length of 180-210 days. Finally, CRSP increased linearly from reference length 120 to 200 by about 0.7% per day, and then much slower by approximately 0.1% per day for greater reference length. Results from this study suggest that the desirable reference lactation length for the Chios sheep is between 190-200 days.

Original languageEnglish
Title of host publicationPERFORMANCE RECORDING OF ANIMALS: STATE OF THE ART, 2004
EditorsM Guellouz, A Dimitriadou, C Mosconi
Place of PublicationWAGENINGEN
PublisherWageningen, The Netherlands: Wageningen Academic Publishers
Pages121-125
Number of pages5
ISBN (Print)90-76998-54-X
Publication statusPublished - 2005
Event34th Biennial Session of the International-Committee-for-Animal-Recording - Sousse, Tunisia
Duration: 28 May 20043 Jun 2004

Publication series

NameEAAP EUROPEAN ASSOCIATION FOR ANIMAL PRODUCTION PUBLICATION
PublisherWAGENINGEN ACADEMIC PUBLISHERS
ISSN (Print)0071-2477

Conference

Conference34th Biennial Session of the International-Committee-for-Animal-Recording
Country/TerritoryTunisia
CitySousse
Period28/05/043/06/04

Keywords

  • dairy sheep
  • random regression model
  • LEGENDRE POLYNOMIALS
  • Chios breed
  • GROWTH
  • GENETIC-PARAMETERS
  • reference lactation

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