Rearing Strategies for Dairy Heifers

Costigan, Hazel (2021) Rearing Strategies for Dairy Heifers. Doctoral thesis, Waterford Institute of Technology.

Text Hazel Costigan Rearing Strategies for Dairy Heifers thesis FINAL.pdf Download (5MB)

Abstract

Replacement heifer rearing is one of the most important tasks on a dairy farm due to the cost it incurs and the potential benefits that may arise in terms of heifer growth and performance thereafter. A successful heifer rearing strategy prioritizes DMI, BW, and frame size of the heifer; however, consideration must also be given to the way in which a heifer is managed. Therefore, the aim of this thesis was to establish the effect of different heifer rearing strategies on aspects of pasture-based heifer growth. An experimental field study was carried out to investigate the effect of weaning age (eight or 12 weeks) and post-weaning feeding regime (high or low) on the DMI, growth performance, and reproductive efficiency of pasture-based heifers of different breed groups. Results in Chapters 3, 4, 5, and 6 indicated that although heifer DMI, BW, and frame size differed with breed group, they were highly susceptible to the post-weaning feeding regime, irrespective of weaning age. This finding has positive practical significance for pasture-based dairy farmers as it indicates that post-weaning feed management can be manipulated to ensure that weight-for-age targets are achieved. Pasture-based heifer DMI throughout the rearing period was quantified in Chapter 3, and the resulting data were used to create an equation to predict the DMI of HF and JE using BW as a proxy. An accurate DMI prediction equation will assist pasture-based dairy farmers in optimizing pasture allowances and thus increasing the efficacy of pasture utilization. In Chapter 4, an equation was created to determine the growth trajectory of pasture-based HF and JE; this equation showed that pasture-based heifer growth was sigmoidal in shape. Furthermore, the use of this equation to create additional weight-for-age targets for pasture-based heifers will optimize heifer growth prior to the commencement of the breeding season. A separate equation was created in Chapter 6 to predict heifer BW using a series of LBM; this facilitates the monitoring of heifer growth in the absence of a weighing scale. Findings in Chapter 5 suggested that growth pattern throughout the rearing period is an important determinant of reproductive performance, the efficiency of which was impeded when feed allowance fluctuated between the pre and post-weaning periods and when heifers were ahead of target BW at breeding. Furthermore, by using an external dataset of 1,323 heifers across 2,924 parity one to three calving events, the associations between AFC and BW at first calving of pasture-based heifers were quantified. Findings indicated that BW at first calving had a greater impact on performance in the lactating herd than that of age. Moreover, BW at first 109 calving has the potential to negate the suboptimal performance that is often associated with a younger AFC. The findings in this thesis highlight the importance of management decisions on the performance of dairy heifers.

Item Type:	Thesis (Doctoral)
Uncontrolled Keywords:	Dairy farming
Departments or Groups:	*NONE OF THESE*
Divisions:	School of Science > Department of Chemical and Life Sciences
Depositing User:	Derek Langford
Date Deposited:	03 Jun 2022 09:19
Last Modified:	03 Jun 2022 09:19
URI:	https://repository.wit.ie/id/eprint/3528

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