Increased early heifer growth reduces age at first calving and offers fertility benefits
Take Home Message: A target growth rate of 0.6-0.8 kg/d during the first 6 months of the rearing period is optimal in relation to rearing costs, first lactation milk yield and fertility.
An increased average daily gain during the first six months of life significantly reduces the age at first calving in dairy heifers. And after their first calving a larger proportion of these heifers were pregnant 200 days into their lactation.
“Increasing average daily gain (ADG), often through high planes of nutrition, does presumably increase rearing costs,” the Royal Veterinary College’s Jessica Brickell told delegates at this year’s British Society of Animal Science annual conference.
“But a low ADG will lengthen the non-productive period. So we would suggest rearing heifers at a moderate growth rate of between 0.6kg/day and 0.8kg/day during the first six months of life. And more effort should be made within the industry to ensure that all heifers reach this target,” she added.
Rearing heifer replacements that reach first calving at an age and body weight to achieve their full lifetime potential, in terms of both yield and profitability, is a key factor in ensuring dairy business efficiency.
The aim of Dr Brickell’s study was to determine the effect of growth rate during the first six months of life on AFC, and subsequent fertility and milk production during first lactation of Holstein-Friesian heifers in UK dairy herds.
A total of 17 dairy farms across southern England milking Holstein-Friesian cows were recruited during 2003 and 2004 to provide a range of management practices representative of those commonly encountered in the UK. For heifer calves recruited, body weight was measured at one and six months of age, to calculate the ADG from one to six months. Heart girth and height at withers were measured at one to two weeks before first calving.
After calving, measures of fertility – AFC, days to commencement of luteal activity, days to conception, and services per conception – were recorded, as were milk production parameters including days in milk, milk yield per day, the 305-day lactation yield and total milk yield.
“The ADG from one to six months was 0.76kg/day and the mean AFC was 26 months. Heifers with an ADG of less than 0.6kg/day were smaller and, on average, three months older at first calving compared to those with an ADG of more than 0.8kg/day,” said Dr Brickell.
“After calving, these smaller but older animals tended to have a longer interval to the commencement of luteal activity (CLA). Heifers with the shortest interval to the CLA had an ADG of between 0.6kg/day and 0.8kg/day.
“There was no significant difference in the number of days to conception and services per conception between the three groups, but a larger proportion of animals with an ADG of between 0.6kg/day and 0.8kg/day and more than 0.8kg/day were pregnant 200 days into their lactation.
“First-lactation milk production was not significantly different between the three groups, although heifers with an ADG of more than 0.8kg/day tended to produce less milk,” she added.
Presented to the British Society of Animal Science Annual Meeting, March 30 to April 1, 2009, Southport, UK.
Full details: Brickell JS, Wathes DC: “The effect of growth rate on age at first calving, fertility and milk production during the first lactation of Holstein-Friesian heifers on UK dairy farms.”
Summary (pdf) Presentation_013brickell (pdf)
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