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Genetic and non-genetic factors associated with lactation length in seasonal-calving dairy cow pasture-based systems.

M. Williams

Events

06-24-2020

Abstract:

326
Genetic and non-genetic factors associated with lactation length in seasonal-calving dairy cow pasture-based systems.
M. Williams*1,2, C. P. Murphy2, R. D. Sleator2, M. M. Judge1, S. C. Ring3, D. P. Berry1. 1Department of Animal Bioscience, Animal and Grassland Research and Innovation Centre, Teagasc Moorepark, Fermoy, Co. Cork, Ireland, 2Department of Biological Sciences, Cork Institute of Technology Bishopstown, Co. Cork, Ireland, 3Irish Cattle Breeding Federation Bandon, Co. Cork, Ireland.

Lactation yield estimates standardized to common lactation lengths of 270-d or 305-d equivalents are commonly used in management decision-support tools and dairy cow genetic evaluations. The use of such measurements to quantify the (genetic) merit of individual cows fails to penalize cows that do not reach the standardized lactation length, or indeed reward cows that lactate for more than 270 or 305 d. The objective of this study was to identify the genetic and non-genetic factors associated with lactation length in seasonal-calving pasture-based dairy cows. A total of 616,350 lactation length records, from 285,598 cows, were used. Linear mixed models were used to investigate the associations between lactation length and calving month, calving day, parity, age at calving, dry period length, calving difficulty score, herd size, heterosis, recombination loss, and breed, as well as to estimate the variance components of lactation length. The median lactation length was 288 d, with 27% of cows achieving lactations > 305 d. Relative to cows calving in January, the lactation of a cow calving in February, March, or April was 4.2, 12.7, and 21.9 d shorter, respectively. The lactation length of a first-parity cow was 7.8, 8.6, and 8.4 d shorter than that of second, third, and fourth parity cows, respectively. Norwegian Red and Montb�liarde cows had, on average, a 4.7 and 1.6-d shorter lactation than Holstein-Friesian cows, respectively. The heritability estimate and coefficient of genetic variation for lactation length were 0.02 and 1.2%, respectively. When ranked on their genetic merit for lactation length, there was a 9.2-d phenotypic difference in lactation length between cows in the top and bottom 20%; demonstrating exploitable genetic variability. Given the vast array of genetic and non-genetic factors associated with lactation length; an approach which combines improved management practices and selective breeding may be the most efficient way to lengthen lactations.

Keywords: lactation length, genetic merit, non-genetic factors.

Biography: I am a second year PhD student working with Teagasc Moorepark and Cork Institute of Technology in Ireland. The focus of my PhD is on improving efficiency in pasture-based dairy cow production systems.