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Liveweight at first mating and calving will have an impact on the reproductive performance and milk production potential of heifers.

Liveweight at first mating and calving will have an impact on the reproductive performance and milk production potential of heifers.

Heifers must be reared to achieve their liveweight targets otherwise their first calving will be delayed, liveweight at calving will be too low and fertility during the next mating period reduced. Well-grown heifers will produce more milk in the first lactation, compete better with mature cows and survive longer in the herd.

Having targets offers a measure of performance and indicates well grown stock.  Targets also establish an agreed position for farmers involved in a contract grazing relationship. 

Heifer liveweight targets

  • 30% of mature weight at 6 months of age
  • 60% of mature weight at 15 months (mating)
  • 90% of mature weight at 22 months (pre-calving)

Because body weight is the key driver of puberty it is important that heifers reach key liveweight targets if they are going to reach puberty at 12 months and get in-calf at 15 months.

Achieving the 30-60-90 percentage targets is more important than the pattern of growth.

Estimating mature liveweight

There are three methods to estimate average mature liveweights for a group of heifers: liveweight breeding value, weighing a selection of mature cows (6-8 years of age), and using a breed based average mature weight.

  • Liveweight breeding value (Lwt BV)

    Obtain a 'breeding value trait report' from your herd recording provider (e.g. CRV, LIC). From this report calculate the average Lwt BV using the following equation:

    Mature liveweight = 503kg ± Lwt BV

    • If the BV is +20, then the average mature target liveweight for a group of heifers will be 503kg + 20 = 523kg
    • If the BV is -15, then the average mature target liveweight for a group of heifers will be 503kg - 15 = 488kg

    Strengths

    Weaknesses

    • Objective measure
    • Best prediction based on an animal’s genetics
    • Based on actual data from sire proving herds
    • Accounts for current breeding program targets
    • Majority of animals will have a Lwt BV
    • An on farm study showed that 30% of animals were not matched to the correct mother
    • Genes are randomly inherited
    • Normal variation is -5% to +5% of the prediction
    • Liveweight is 35% heritable so management has more influence on the final result
    • Currently only available through MINDA software
    • Data will not be available for herds with a high proportion of overseas genetics
  • Mature herd average weight

    Average herd liveweight can be determined by weighing a cross section of the mature herd. Weighing guidelines to establish the target are:

    • 20–50 cows (the more you weigh the more accurate)
    • 6-8 years of age
    • 100-200 days in milk
    • BCS 4.5 (add or subtract weight if above or below)
    • After the morning milking

    This information can be used to validate Lwt BVs and will be most accurate for herds with consistent breeding strategies and limited breed variation within the herd.

    Strengths

    Weaknesses

    • Representative of actual herd
    • Data will not be available for herds with a high proportion of overseas genetics
    • Improves information for the herd (e.g. stocking rates, drench rates, mineral dosing)
    • Captures management and environmental conditions of the farm system
    • Time required
    • Not every animal will represent “average”
    • Does not capture recent changes in breeding policies (e.g. increasing crossbreeding)
    • Will set targets too low if mature stock were poorly grown
  • National breed average mature liveweight

    Estimate the likely average mature weight from an assessment of the breed composition of the group of heifers using the table below 

    Jersey 423 kg
    Crossbred 467 kg
    Friesian 499 kg

    Source: National Dairy Statistics (2014)

    As these mature weights are the average of the population, groups of heifers of a comparative breed can have targets above the average mature weight. Weight gain records and physical observations should also be used to evaluate the average mature weight when applied to a group of heifers. Based on base cow liveweight of 503kg.

Monitoring performance

Most dairy farmers and farm advisers can recognise whether heifers are in good or poor condition, but few can judge whether heifers have actually achieved target liveweights for their particular age.

Weighing heifers on a regular basis provides an 'accurate' assessment of how well heifers are growing compared to targets. It also allows for proactive management - if heifers are under target at weighing, remedial action can be taken to get them back on track. Find out more about heifer feeding and nutrition.

There is no strict rule about how often heifers should be weighed (InCalf recommends every 3 months). The more frequently heifers are weighed the more quickly a problem will be detected. Find out more about heifer weights and weighing.


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