Date of Award
Master of Science
Animal Breeding and Genetics
Long-term selection for increased milk production in the US dairy industry has contributed to a decline in fitness traits of high producing cows. To achieve the increase in milk yield, cows must provide sufficient energy through their diet and/or tissue mobilization to support the energy demands of lactation. The objectives of this study were to evaluate indicators of energy mobilization in cows selected for high versus average production of milk components, to define the relationships between these indicators and production traits, and to evaluate mRNA abundance of selected genes that play a significant role in regulating energy utilization in adipose tissue. Cows were chosen to represent selection lines at the Iowa State University dairy research herd, that have been selected for high (HFP) versus breed average (AFP) fat plus protein PTA since 1986. Experimental group 1 had 28 HFP and 22 AFP cows. Blood samples were taken weekly at weeks 1-12 post parturition, and monthly through week 24. Experimental group 2 consisted of 8 cows (n = 4 per line) representing extreme phenotypic differences. Blood samples were taken -4 weeks and +4 weeks relative to parturition. Blood samples were used for metabolite profiles. Body condition scores (BCS) and body weights (BW) were recorded at each blood collection. Adipose tissue biopsies were collected 5, 21, and 139 days post calving on experimental group 2. Analysis of BCS showed HFP cows had significantly less body condition than did AFP cows at weeks 12 and 16 (p<0.05). Serum creatinine levels for AFP cows were significantly less than HFP cows at weeks 2, 3, and 4 (p<0.05). Significant positive correlations between NEFA and cumulative weekly milk production occurred for samples taken during weeks 5-12 of lactation (p<0.05). Leptin mRNA abundance significantly dropped from day 5 to day 21 and returned to levels above day 5 at day 139 post partum (p<0.05). Adiponectin receptor 2 mRNA abundance was significantly higher in HFP cows than AFP cows (p<0.05). In this study, we did not see statistical evidence between adipose tissue indicators (NEFA, glycerol, triglycerides) between lines. Leptin mRNA abundance may indicate changes in energy balance.
Megan Marie Westall
Westall, Megan Marie, "Characterization of Iowa State University dairy cattle selection lines for indicators of tissue mobilization" (2006). Retrospective Theses and Dissertations. 19081.