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Monitoring out-wintered dairy heifers


Does it pay to out-winter heifers?

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It is generally thought heifers perform better when out-wintered, rather than housed, but there is little information on actual on-farm performance.

Out-wintering replacement dairy heifers on grass, kale or fodder beet is common in low input spring-calving herds. However, forage crops can be low in trace minerals and there is little information on animal performance when out-wintered on different systems.

To provide more detail on the topic, Harper Adams University, with funding from AHDB Dairy, carried out a study of nine spring-calving dairy herds to investigate the health and performance of replacement dairy heifers, before calving and during their first lactation when out-wintered on grass, kale or fodder beet, with or without trace mineral supplementation.

Three of the herds were due to out-winter replacement heifers on grass, three on kale, and three on fodder beet. A group of 40 cross-bred heifers from each farm were selected and managed with the rest of the herd. Half the heifers were supplied with a trace mineral bolus supplementation containing cobalt, selenium, iodine and copper at the start of out-wintering, and half had no mineral supplementation.

Heifer health and performance was monitored over the winter period, as was first lactation performance and fertility.

The study found during the out-wintering period, growth and body condition of heifers was variable between farms.

Harper Adams animal science expert Prof Liam Sinclair, one of the study authors, says: “Heifers in some herds gained weight while other herds lost weight. One of the anecdotal comments was the farmers who weighed their heifers regularly using accurate scales met their liveweight targets, whereas those who did not were the ones with the most variable weights and did not meet their targets.”

Forage type and mineral bolus supplementation had no effect on heifer performance, although body condition prior to calving was slightly higher in heifers provided with a trace mineral bolus.


First lactation milk performance was not affected by the choice of winter forage. The provision of a trace mineral bolus increased milk fat content and tended to increase fat corrected milk yield in early lactation, especially when out-wintered on kale.

Health and reproductive performance was not affected by the treatments, although farms using fodder beet had a higher in-calf rate and heifers which grazed kale and received no mineral bolus were more likely to receive a fertility treatment.

Prof Sinclair says: “There was more variation in heifer performance between individual farms than due to the out-wintered forage. Therefore, decisions on the most appropriate forage should be made on soil type and potential crop yield.

“Supplementing with a mineral bolus improved heifer mineral status but had only a marginal effect on body condition, although milk fat content was increased in early lactation, particularly in herds which grazed kale.”

The study's results


  • Forage type and mineral bolus supplementation had no effect on heifer liveweight change prior to calving
  • Body condition was unaffected by forage type. However the research did find the heifers which received the mineral bolus had a slightly higher body condition score prior to calving, compared to those given no mineral bolus


  • Milk yield, milk fat, milk protein and somatic cell count were unaffected by forage type. In week 10 of lactation, heifers supplemented with the mineral bolus had a milk fat content which was 1.9g/kg higher than those receiving no bolus, and fat corrected milk yield tended to be higher too. The difference was greater for heifers provided with the mineral bolus and out-wintered on kale. By week 19 of lactation there was no effect of the bolus on milk fat content
  • Heifers out-wintered on fodder beet had a higher in-calf rate
  • Heifers which grazed kale without receiving the mineral bolus were more likely to receive fertility treatment
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