Variation in plasma growth hormone during first parity in lactating cows

Area of Science:

• Animal Genetics
• Dairy Science
• Endocrinology

Background:

• Plasma growth hormone (GH) concentrations vary significantly during lactation in dairy cows.
• Understanding genetic and phenotypic variation in GH is crucial for improving dairy cow productivity and health.
• Previous studies have not fully clarified the impact of basal versus peak GH concentrations on genetic and phenotypic analyses.

Purpose of the Study:

• To analyze genetic and phenotypic variation in plasma GH during lactation in first-parity dairy cows.
• To evaluate the effectiveness of excluding peak GH concentrations to obtain basal GH levels for analysis.
• To determine heritability and repeatability of GH concentrations under different dietary energy levels and genetic groups.

Main Methods:

• Blood samples were collected 17 times from Holstein, Red Dane, and Jersey cows (n=214) during first parity.
• Plasma GH concentrations were assayed, and an algorithm was used to separate basal and peak GH levels.
• Heritability and repeatability were estimated using log-transformed GH data, considering genetic groups and dietary energy concentrations.

Main Results:

• The separation algorithm identified only 4.0% of plasma GH concentrations as peaks.
• Excluding peak concentrations improved the repeatability of GH during lactation.
• Log-transformed GH concentrations showed heritability ranging from 0.08 to 0.14 and repeatability from 0.24 to 0.61.
• Heritability was lower in mid and late lactation compared to early lactation.

Conclusions:

• Excluding peak GH values to obtain basal concentrations was not effective in clarifying phenotypic or genetic effects in infrequently sampled lactating cows.
• The study highlights the complexity of GH dynamics and the challenges in analyzing genetic parameters from basal concentrations alone.
• Further research may be needed to develop more effective methods for analyzing GH variation in dairy cattle.