Why age is not necessarily the main issue affecting fertility in replacement heifers

Catherine Hurley

Catherine Hurley

There is not one single issue fundamental to achieving reproduction targets when rearing replacement heifers, according to Senior Researcher at Teagasc, Moorepark, Emer Kennedy.

“Age is not necessarily the biggest issue when getting heifers to calve down in time, it’s actually the weight and body condition score of the heifer at breeding,” according to Emer.

This was found by research carried out in Moorepark on 800 replacement heifers from over 50 commercial farms.

Poor fertility in replacement heifers is often due to heifers being underweight at mating start date (MSD), according to Teagasc research.

Once the mature weight of the herd is known, target weights can be calculated by using a proportion of mature bodyweight. Targets are as follows; 30pc mature body weight at 6 months, 60pc mature body weight at 15 months or breeding and 90pc mature BW at calving.

In relation to this year, some farmers may have struggled to meet target weights, but if this is the case, it’s not too late,according to Emer.

“Most farmers are starting to weigh their heifers now,” said Emer, adding that “there is a good response to feed at this time of year, while the heifers are still at grass.”

Problems regarding weight can be avoided if weight and weight gain of the heifers is regularly monitored, according to Teagasc research. Heifers can be weighed individually on a weighing scales or a representative proportion of heifers brought to a weigh bridge to get an indication of their weight.

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Prior to the first winter, heifers should be weighed, ideally in August at six months of age, to ensure that they are on target to achieve the desired body weight at the start of the breeding.

“Most farmers are weighing their heifers now [at this time of year], and can address any weight issues before the housing period,” explained Emer.

Generally higher weight gains are achieved from pasture than from winter diets, weight gains of more than 1kg/day are achievable in early spring at pasture, according to Teagasc research.

If replacement heifers are not a uniform group, the lighter animals should be prioritised and turned out to pasture earliest and offered concentrates if necessary, the research shows.

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