Download NUTRITIONAL REGULATION OF PREPUBERTAL MAMMARY GLAND GENE EXPRESSION IN HOLSTEIN HEIFER CALVES

NUTRITIONAL REGULATION OF PREPUBERTAL
MAMMARY GLAND GENE EXPRESSION
IN HOLSTEIN HEIFER CALVES
Paola Piantoni, Juan J. Loor, Michael Akers, Kristy M. Daniels,
Robin E. Everts, Sandra L. Rodriguez-Zas, and Harris A. Lewin
TAKE HOME MESSAGES
•
Microarray technology is a powerful tool that allows the analysis of thousands of genes in
a particular tissue at a particular physiological stage.
•
Optimal mammary development is crucial for future profit.
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Mammary gland development and weight is increased by greater dietary protein and fat
in milk replacer.
•
The identification of nutrient-regulated genes related to mammary development in dairy
heifer calves could be used to improve the nutritional management from birth to weaning
to increase the profitability of dairy enterprises.
INTRODUCTION
Microarray technology is a powerful tool for the simultaneous analysis of the expression of
thousands of genes in a tissue. This high-throughput technology assesses the expression level of
“messenger RNA” (mRNA), which is the molecule that encodes and carries information from
DNA during several steps that result in the production of a gene product or protein. These
proteins can perform one or more important biological functions. Nutrition is an important
environmental stimulus that can affect the expression of mRNA in animal tissues.
Alterations in gene expression patterns underlie many tissue regulatory mechanisms and
determine various physiological effects, especially those involving long-term responses such as
the synthesis of a particular hormone. Identifying and defining roles for expressed genes will
improve our understanding of how groups of genes interact in a particular tissue across different
physiological stages. Grouping genes according to expression patterns into “clusters” is an
approach that allows for the discovery of potential relationships among genes. In the end, the
information generated through gene expression analysis could be integrated with whole-animal
data such as level of milk production and growth rate to allow for the integration of knowledge
with regards to animal physiology and pathology.
It is well established in a number of species that gene expression can be modified by nutrients
(e.g., fatty acids or amino acids), thus, genomic technologies may be useful in identifying
regulatory mechanisms in the bovine mammary gland that are susceptible to different plane of
nutrition. Increasing energy and protein intake during the pre-weaning period in dairy heifers
may increase body growth rates and mammary parenchymal mass without causing excessive fat
tissue deposition. An increase in mammary parenchymal mass during this growth period would
be suggestive of an enhanced rate of parenchymal development, which might be crucial in the
long term for future profit.
Our hypothesis is that level of dietary energy and protein in pre-weaning diets alter the
expression of genes associated with various aspects of mammary development such as cellular
growth, lipid synthesis, and protein synthesis. These coordinated global changes in gene
expression are responsible in large part for enhanced development of the entire mammary gland.
We are currently using microarray technology developed at the University of Illinois to
determine the effect of intake level and concentration of dietary protein and fat in pre-weaning
heifer diets on gene expression profiles in mammary parenchyma and mammary fat pad tissue.
Our objectives, therefore, are:
1) To determine global gene expression patterns in mammary parenchyma and fat pad tissue for
more than 13,000 genes during the pre-weaning period using a bovine-specific oligonucleotide
microarray.
2) To determine how overfeeding protein and fat during the pre-weaning period alter gene
expression and mammary gland development.
3) To relate mammary gene expression profiles with other physiological measurements such as
blood leptin, growth hormone, insulin, and IGF-I. We will develop integrative models of wholeanimal tissue function using gene expression data and other physiological measurements
available.
The ultimate benefit of this research might be the identification of nutrient-regulated genes in
the developing mammary gland. That information could be used to improve the nutritional
management from birth to weaning of heifer calves, and consequently increase the potential for
profitability of dairy enterprises in Illinois and beyond.
EXPERIMENTAL DESIGN
Twenty two Holstein heifer calves were used in this study. Calves were blocked and fed one of 4
milk replacer treatments to test the effects of different levels and intakes of dietary protein and
fat as shown in Table 1. Calf starter (ad libitum) and milk replacer were fed from day 0 to day
63 of life to achieve the desired average daily gain, based on NRC (2001) recommendations. All
calves were slaughtered after 63 days on experiment. Mammary tissue weights were recorded,
and parenchyma and fat pad dissected. Data that will be available in the future include:
mammary chemical composition, blood serum hormones (insulin-like growth factor-1 and
growth hormone), nutrient intakes, and growth parameters. Mammary composition data, such as
gland weight, was obtained by gross dissection of the right side of the udder of each heifer after
its slaughter. A portion of tissue was frozen in liquid nitrogen and stored until gene expression
analysis.
PRELIMINARY RESULTS
Results showed that increasing dietary protein alone (28:20 vs. 20:20) might be sufficient to
enhance mammary gland development. In addition, there appeared to be some benefit in feeding
additional fat to the high-protein milk replacer (28:20 vs. 28:28). Further studies with larger
numbers of animals might be needed to fully elucidate the effect of additional fat when protein
intake is high. It was evident, however, that mammary growth was not maximized and
responded to additional intake of the high-protein and high-fat milk replacer (28:28+), resulting
in increases of ~300% or 96% compared to the control or both the 28:20 and 28:28 treatments.
The physiological changes observed in mammary gland weight due to dietary protein and fat
might have been driven through changes in gene expression. We are currently elucidating that
possibility.
Table 1. Nutrient intake and mammary gland weight.
Ratio of dietary protein to fat
N° calves
Target milk replacer intake1, kg DM/d
Actual intake, kg DM/d
Total (milk replacer + starter) DMI,
Predicted gain, kg/d
Total mammary gland weight, g
20:20
(control)
5
0.45
0.35
1.25
0.16
87a
28:20
28:28
28:28+
5
0.97
0.76
1.31
0.93
143b*
6
0.97
0.78
1.18
0.94
203b
6
1.46
1.18
1.50
1.5
339b
SEM
1.6
28
Composition of calf starter (20% crude protein): corn grain (40%), soybean meal (40%), and
cottonseed hulls (20%).
1
Intake based on NRC (2001) requirements for calves gaining as indicated.
20:20 (control) vs. other treatments, P < 0.005
*Comparison of 28:20 vs. 28:28, P = 0.14; and 28:20 vs. 20:20, P = 0.19
a