HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Lee, A. J. Search for Related Content PubMed Articles by Lee, A. J.

Month, Year, and Herd Effects on Age Adjustment of First Lactation Milk Yield¹

Animal Research Institute, Research Brand, Canada Agriculture, Ottawa, Canada

ABSTRACT

First lactation Record of Performance records on 59,778 Canadian Holsteins calving over 4 yr were studied. Within each 6 mo year-season, least squares constants were derived for combined effects of month of age and calendar month of calving (age-month) on milk yield with herd effects eliminated. Herd by age-month interaction accounted for 2.8% of the total variance compared to 3.6% for age-months, 41.5% for herds, and 52.1% for error by method III of Henderson. Within season, month of calving affected age-month constants, and those effects were similar for all years. A quadratic curve described the relationship between age-month constants and age at calving better than a linear one. Quadratic curves differed across years, months, and month by years; however, differences were small, erratic, and of little practical importance. The quadratic curve pooled within mcnth and year of calving was similar to comparable estimates from New York and to previous results from regression analyses within herd-year-season. This curve allows for 213.2 ± 21.8 kg milk/mo and –2.7 ± .4 kg milk/mo² for age at first calving and is recommended for age adjustment of first lactation milk yield.

¹ Contribution No. 503 of the Animal Research Institute.

² Present address: Dairy Science Department, University of Illinois, Urbana 61801.