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Feed and production efficiency of young crossbred beef cattle stratified on a terminal total merit index1
Kelly, David N Conroy, Stephen B Murphy, Craig P Sleator, Roy D Berry, Donagh
Kelly, David N
Conroy, Stephen B
Murphy, Craig P
Sleator, Roy D
Berry, Donagh
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2020-07-01
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D N Kelly, S B Conroy, C P Murphy, R D Sleator, D P Berry, Feed and production efficiency of young crossbred beef cattle stratified on a terminal total merit index, Translational Animal Science, Volume 4, Issue 3, July 2020, txaa106, https://doi.org/10.1093/tas/txaa106
Abstract
Few studies have attempted to
quantify the association between a terminal total
merit index with phenotypic feed and production
efficiency in beef cattle, particularly when feed
efficiency is itself explicitly absent as a goal trait
in the index. The objective of the present study
was to quantify the differences in phenotypic performance for feed intake, feed efficiency, and carcass traits of crossbred bulls, steers, and heifers
differing in a terminal total merit index. A validation population of 614 bulls, steers, and heifers
that were evaluated for feed intake and efficiency
in the same feedlot and subsequently slaughtered
at the end of their test period was constructed.
The Irish national genetic evaluations for a terminal index of calving performance, docility,
feed intake, and carcass traits were undertaken
with the phenotypic records of animals present
in the validation population masked. The validation population animals were subsequently
stratified into four groups, within sex, according
to their terminal index value. Mixed models
were used to quantify the association between
terminal genetic merit and phenotypic performance; whether the associations differed by sex
were also investigated. The regression coefficient
of phenotypic feed intake, carcass weight, carcass conformation, or carcass fat on its respective estimated breeding values was 0.86 kg
dry matter 0.91 kg, 1.01 units, and 1.29 units,
respectively, which are close to the expectation
of one. On average, cattle in the very high terminal index stratum had a 0.63 kg DM/d lower
feed intake, a 25.05 kg heavier carcass, a 1.82 unit
better carcass conformation (scale 1 to 15), and
a 1.24 unit less carcass fat score (scale 1 to 15),
relative to cattle in the very low terminal index
stratum. Cattle of superior total genetic merit
were also more feed efficient (i.e., had a lower energy conversion ratio, lower residual feed intake,
and greater residual gain), had a greater proportion of their live-weight as carcass weight (i.e.,
better dressing percentage) and were slaughtered
at a younger age relative to their inferior total
genetic merit counterparts. This study provides
validation of an all-encompassing total merit
index and demonstrates the benefits of selection
on a total merit index for feed and production efficiency, which should impart confidence among
stakeholders in the contribution of genetic selection to simultaneous improvements in individual
animal performance and efficiency.