<p>The
objective of this study was to evaluate the long-term effects that early life
events have on heifer growth up to 400 d of age, heifer conception rate,
survivability through first lactation, and first lactation milk production of
calves raised in automatic calf feeders. Chapter one evaluates possible early
life variables that would affect heifer growth and lifetime production as well
as research that has been done to predict future growth. The major points
discussed include pre-weaning feeding strategies, automatic calf feeding
systems, respiratory disease and ways to diagnose cattle with this disease, and
the impact of early
life growth on the future productivity of the dairy cow.<br></p>
<p>The
second chapter discusses in detail the process of creating a predictive
equation using significant early life variables that affect Holstein heifer
growth up to 400 d of age. Variables collected for the growth analysis included
sixty d cumulative milk consumption (MC), serum total protein values, respiratory
disease and scours incidences, genetic body size, birthweights, and incremental
body weight variables on a commercial dairy farm from October 1, 2015 to
January 1, 2019. Calves were fed pasteurized whole milk through an automated
calf feeding system (feeders = 8) for 60 d (range: 48 – 126d), with a 30% Crude Protein (CP)
and 5% Crude Fat enhancer added at 20 g/L of milk. Calves were
weighed at birth and several other times prior to calving. Average birth weight
of calves was 40.6 ± 4.9 kg (mean ± SD), serum total protein was 6.7 ± 0.63
g/dL, and cumulative 60 d MC was 508.1 ± 67.3 L with a range of 179.9 to 785.1 L. Daily body weights were predicted for individual animals using a third
order orthogonal polynomial to model growth curves. The linear and quadratic
effects of cumulative 60 d milk consumption, birthweight, feeder, yr born,
season born, respiratory incidence, and genetic body size score were
significant (<i>P</i><0.0001) when
predicting heifer body weight at 400 d (pBW<sub>400</sub>) of age (R<sup>2</sup>=0.31). There was
up to a 263 kg difference in pBW<sub>400 </sub>between the heaviest and
lightest animal. Birthweight had a significant effect on predicted weights up
to 400 d (<i>P</i><0.0001), and for every
1 kg increase in birthweight, there was a 2.5 kg increase in pBW<sub>400</sub>.
The quadratic effect of cumulative 60 d MC was significant for pBW<sub>400</sub>
(<i>P</i><0.0001). When 60 d MC was
divided into quartiles, heifers had the highest pBW<sub>400 </sub>in the third
quartile, when 60 d MC was between 507.8 and 552.5 L. Body size composite
(genomic index) showed a
21.5 kg difference in pBW<sub>400</sub> between the top and bottom 25<sup>th</sup>
percentile of heifers. Heifers were 4.2 kg lighter at 400 d if treated for
respiratory disease 3+ times during the first 60 d of life, compared to heifers
not treated for respiratory disease.</p>
<p>The third
chapter utilizes the data described in chapter two and followed those heifers
through breeding and first lactation. Heifer conception age and 280 d first
lactation milk production (280M) were collected. Average age at conception was 437.5 ± 45.0 d;
range of 308 to 631 d (n=5,193), and average 280M was 9,305 ± 1,371.8 kg; range
of 712-13,358 kg (n=1,324). Heifer conception age was
impacted by season, yr, and the quadratic effects of predicted bodyweight at
300 d of age (pBW<sub>300</sub>) and ADG (0-400; all <i>P</i> < 0.05; total model R<sup>2</sup>
= 0.08). Season
born, ADG (0 - 400 d), genomic milk, and the linear effect of heifer conception
age had a significant impact on 280M (all <i>P</i>
< 0.05; R<sup>2</sup> = 0.28). For every 1 kg increase in genomic milk value
there is 1.42 kg increase in first lactation 280M. Calves not diagnosed
with bovine respiratory disease (BRD) from 60-120 d old had a significantly
higher chance for survival to first lactation than animals treated three or
more times for BRD (hazard ratio = 0.71, 95% CI = 0.574
to 0.886, <i>P </i>= 0.0023, Table 3.3).
Heifers treated twice or more for BRD had reduced likelihood to become pregnant
than heifers not treated for BRD from 60-120 d (twice <i>P </i>= 0.02; three or more <i>P </i>=
0.05). </p>
<p>In
conclusion, the results from this thesis support that early life events in
Holstein heifers continue to influence future growth and productivity. Future
research aims to validate the predictive equation generated in chapter two on
farm as well as adapt the equation to other farms allowing them to utilize it
as well. The goal is to have farms utilize this tool to aid in their
replacement heifer management decisions and to select the most productive
heifers for the future of their herds. </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/12732908 |
| Date | 29 July 2020 |
| Creators | Tabitha S Steckler (8876651) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/EARLY_LIFE_EVENTS_ALTER_FUTURE_HOLSTEIN_HEIFER_GROWTH_SURVIVABILITY_REPRODUCTION_AND_FIRST_LACTATION_MILK_PRODUCTION/12732908 |
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