Young Stock - Dairy NZ

The below factsheet is from the Dairy NZ website and is looking at the growth weights for dairy heifers. The numbers are based on research carried out by scientists at Dairy NZ and I have included in other blog posts some of the reference material.

The growth targets affect mating success as the heifer will reach puberty at around 250kg liveweight. Later on, heifers that enter the milking herd underweight will be negatively affected as they will be partitioning energy into growth rather than production so their yields will be lower than their genetic potential.

Most heifer growth targets are based on a linear weight gain across the period - but it questionable on whether this is achievable on a pasture diet? Can the heifer achieve compensatory growth after periods of sub optimal growth? Should the growth targets take into account the pastoral growth and climate challenges? Does it actually suit the heifer better to have stepped periods of growth bursts to reach targets?

I've found these weight targets are treated as stretch targets and from the reading I have done I'm currently regarding these as minimum growth standards. However I do believe the growth is unlikely to be linear.

Dairy NZ (2015) Feed Requirements for Grazing Dairy Heifers. Retrieved from http://www.dairynz.co.nz/animal/calves-and-young-stock/young-stock/

Target weights for your young stock should be relative to the weight that they will grow to as mature cows: 30% of mature liveweight at six months of age, and 40% at nine months; 60% of mature liveweight at 15 months (mating); 90% of mature liveweight at 22 months.

Benefits of achieving liveweight targets

• Production
  
• At a $4 payout, each additional kg of LW at 22 months between 80-90% of mature liveweight will return around $1 in the first lactation.


• Reproduction
  
• Achieving the 15 month liveweight target will help minimise the incidence of non-cycling heifers at mating.

To estimate mature liveweight for a line of heifers either:

• Use the average liveweight breeding value (BV) of the line of heifers using the following equation:

Liveweight at maturity (kg) = 500 kg + (Average BV Liveweight for the line of heifers)

or

• Weigh the 6-8 year old cows in the herd in December

Liveweight measurements taken in early lactation can underestimate mature liveweight as cows are generally at their thinnest. Liveweight measurements taken in the dry period will overestimate mature liveweight as a proportion of the weight consists of the foetus and foetal components.
The average mature liveweight of Jerseys was 407 kg, and 528 kg for Friesians in the 2004/5 LIC Sire Proving Herds.
For further information refer to:

• Feed demand requirements of young stock (Farmfact 3-21)