Juvenile predictors could aid selection of best dairy animals
Take Home Message: Decisions on which dairy animals to breed from could be made at just 6 months old
Selection of the best dairy animals for breeding could be made on the basis of juvenile predictors through the use of genotyping coupled with phenotypic profiling of type traits and metabolic parameters.
Just one of the conclusions of a study, carried out by UK scientists, to determine factors influencing heifer survival and fertility on commercial dairy farms.
The average dairy cow survives only three lactations, reducing the availability of replacement heifers. Prenatal losses occur due to early embryonic mortality, later embryo loss or abortion.
A recent survey of 19 UK herds showed that 7.9% of calves were born dead and 3.4% died within a month. During the rearing phase, 6.7% of animals were lost before reaching first service at 15 months due to disease or accident and another 2.3% failed to conceive.
“Many potential replacements therefore never enter the milking herd. This severely limits opportunities for on-farm selection of breeding cows in addition to presenting a welfare issue and causing economic loss,” said Claire Wathes, from the Royal Veterinary College, explaining the rationale behind her team’s work.
“We have investigated some possible juvenile predictors of future performance. Low-birth-weight calves were more likely to come from either primiparous mothers or older dams with higher peak milk yields, suggesting that the uterine environment may limit prenatal calf growth due to competition for nutrients with maternal growth or milk production.”
The team also found that linear trait classification scores for frame size show genetic correlations with longevity. The skeletal measures of height and crown rump length in one-month-old calves was correlated to subsequent stature, and frame size was correlated to weight at 15 months.
“It may, therefore, be possible to predict performance from simple size measurements as juveniles,” said Professor Wathes.
She added that high lifetime milk production is achieved by a combination of reasonable yields with good fertility and longevity. “Single nucleotide polymorphisms (SNPs) are being identified, which have marked effects on milk production and will almost certainly also affect longevity.
“Size and growth rate measurements made from birth until first breeding at 15 months of age predict aspects of both fertility and milk production. And our results suggest that cows with a high potential to partition energy into milk in early lactation may suffer reduced longevity and that it may be possible to predict this at six months of age.”
Full details: Wathes DC, Brickell JS, Bourne NE, Swali A and Cheng Z: “Factors influencing heifer survival and fertility on commercial dairy farms.” Animal 2, 1135-1143
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