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The effect of growth rate on reproductive outcomes in replacement dairy heifers in seasonally calving, pasture-based systems
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The effect of growth rate on reproductive outcomes in replacement dairy heifers in seasonally calving, pasture-based systems - JDS 2019.pdf | 597.29 KB |
Date Issued
01 June 2019
Date Available
08T08:20:18Z May 2019
Abstract
The effect of average daily gain (ADG) on reproductive outcomes in replacement dairy heifers was investigated. All heifers were managed in the typical Irish spring calving, pasture-based system, where the herd calves in 1 block between January and April and the majority of the diet comprises grazed grass. Heifer calves (n = 399) from 7 herds were weighed at birth and at the beginning of the breeding season, and ADG was calculated. Service dates and pregnancy diagnosis results were recorded, and conception dates were calculated. Days open (DO) was defined as the number of days between the beginning of the breeding season and conception. Genetic data were retrieved from the Irish Cattle Breeding Federation database. A Cox proportional hazard model was constructed to identify variables with a significant effect on DO. An accelerated failure time model was used to predict survival curves and median survival times for different combinations of the significant variables. The ADG ranged from 0.41 to 0.91 kg/d, with a median of 0.70 kg/d. Frailty effect of farm within year, maintenance subindex of the economic breeding index, and ADG had a significant effect on DO. Derived from the final accelerated failure time model, the predicted median DO for a heifer with an ADG of 0.40, 0.70, or 0.90 kg/d aged 443 d at the beginning of the breeding season and with a maintenance subindex in the second tercile were 27, 16, and 11 d, respectively.
Type of Material
Journal Article
Publisher
American Dairy Science Association
Journal
Journal of Dairy Science
Volume
102
Issue
6
Start Page
5599
End Page
5611
Copyright (Published Version)
2019 American Dairy Science Association
Language
English
Status of Item
Peer reviewed
ISSN
0022-0302
This item is made available under a Creative Commons License
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