Protein yield in early lactation is linked to protein production in late lactation
Take Home Message: If you wish to have extended lactations above 305 days then select bulls with a high genetic merit for milk and milk protein yield that produce a high proportion of milk in the first few months of lactation
Protein yield early in lactation – the first two months – has a genetic correlation of about 0.8 with protein yield produced after 300 days of lactation.
That was the key finding of a study, carried out by researchers in Australia, to determine the genetic and environmental relationship with milk protein yield in the first 300 days and after 300 days of lactation.
“More specifically, we estimated heritability, genetic and phenotypic correlations between milk yields at different stages of lactation, including 300 to 600 days after calving,” explained Mekonnen Haile-Mariam, from Victoria’s ‘Animal Genetic and Genomics’.
The work looked at test-day milk yield and somatic cell count data over extended lactations (540–600 days in milk). Test-day data from about 100,000 cows, which calved between 1998 and 2005, were used for this study. And in all analyses, a sire model was used.
“And we also found that the genetic correlations between lactation stages that are adjacent to each other were high – 0.9 or more – within parity,” said Mr Haile-Mariam.
“Across parities, genetic correlations were high for both protein and milk yield if they are within the same stage of lactation. Phenotypic correlations were lower than genetic correlations.”
The team also noted that heritability of milk-yield traits varied from 0.15 at the beginning of the lactation to as high as 0.37 by the fourth month of lactation. And all genetic correlations between different days in milk were positive, with the highest correlations between adjacent days in milk and decreasing correlations with increasing time-span.
“The pattern of genetic correlations between milk yield in the second 300 days (301 to 600 days) of lactation do not significantly differ from the pattern in the first 300 days of lactation,” added Mr Haile-Mariam. “The lowest estimated genetic correlation was 0.15 between milk yield on days 45 and 525 of lactation.”
The result from this study also show that progeny of bulls with high estimated breeding values for yield traits, and those that produce at a relatively high level in the first few months, are the most likely candidates for use in herds favouring extended lactations.
Full_paper (pdf)
Full details: Haile-Mariam M and Goddard M: “Genetic and phenotypic parameters of lactations longer than 305 days (extended lactations).” Animal 2: 325-335.
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