But Brit work begs
BRITISH scientists are warning dairy farmers against growing heifers too quickly pre-puberty, despite US research which suggests it is not necessary to restrict growth to puberty.
Bridget Drew, dairy director of ADAS Bridgets, Hants, where MDC/BOCM Pauls funded research on heifer rearing is underway, is concerned that UK producers may heed USadvice and suffer milk production potential losses.
"It may be that the European Holstein responds differently to that in the US, but all our evidence shows that growing too quickly pre-puberty compromises performance later on."
Dr Drew questions the logic of the heifer rearing in the US trial. "They push them on when all other evidence suggests it is best not to do so, and then knock them back at a time when there is no evidence of any risk in growing them more quickly."
Early work on rapid rearing to get Friesian heifers to calve at 21 months was a disaster in a trial at Compton, Berks, she explain.
"Heifers grown at 1kg a day between three and 12 months gave 800kg less milk in their first and second lactations and 1200kg less in the third lactation. All my work with Friesian and Holstein heifers since suggests that this is the case.
"But as heifers which are heavier at calving give more milk, it does make sense to push them on during the service period and pregnancy, when it is cost effective to do so, pregnancy rates are higher, and good for rumen development.
At ADAS Bridgets Holstein calves are grown at 0.9kg a day for about four months, until 150kg. Growth is then pegged at 0.65kg a day from five to 10 months until 280kg liveweight, moving up to 0.9kg from 11 to 13 months or 350kg liveweight. After service, heifers are grown at 0.9kg or up to 1.2kg as necessary to achieve the optimum calving weight of 630-650kg at 24 months. In the last month of pregnancy growth rates are reduced to minimise calving difficulties, adds Dr Drew.
"I suggest dairy farmers wait for the results of the MDC/BOCM Pauls funded studies before making any changes. It will not be long before we have some really good data on both the effect of growth rate and protein."
Research at Bridgets is examining effects of heifer growth rates on performance. "If we are looking for heavier animals at calving, we must limit the period of restricted growth to when it is most beneficial." Research is also looking at whether increasing protein level can reduce risks associated with growing faster pre-puberty.
First results will be available later this year. Until then Dr Drew advises producers to stick to current rearing targets.
"It may be that in Holsteins growth does not necessarily have to be restricted to 0.65kg a day; it is possible we could go up to 0.75kg without trouble. But, for now, do not go up to the 0.9-1kg a day suggested by the US data."
Dr Drews views are echoed by heifer rearing expert Kris Sejrsen of the Danish Institute of Agricultural Sciences.
"I am worried that farmers increasing heifer growth rates pre-puberty will compromise milk production and fertility."
Dr Sejrsen advises against changing heifer rearing plans on the back of US advice, which, he suggests, is based on limited trial data.
He dismisses as premature suggestions that raising the protein content of the diet will allow higher daily lw gains pre-puberty without compromising future milk yields.
"US research on raising protein levels is too limited and inconclusive." He is adamant that in all his work he has found no benefit in altering protein level or source.
He advises growing heifers at 0.65-0.7kg a day pre-puberty, or at 0.8kg a day for a fast growing Holstein if prepared to accept a small cut in milk yield. This stage is when the heifer is 90-300kg or from about three to 12 months.
"Grow heifers any faster than 0.8kg a day during this period and you will see a dramatic reduction in milk yield." That was the case in the US study, he says, when increasing growth rates from 0.68kg a day to 0.94kg a day reduced first lactation yields by 450kg.
All our research suggests that milk production potential suffers when heifers are grown too quickly pre-puberty, says Dr Bridget Drew.
HEIFER REARING POINTERS
• Treat US research with caution.
• UK data available later in year.
• Maximum 0.75kg/day pre-puberty.