Effect of heifer live weight on calving pattern and milk production

This paper looks at the lost opportunity of an undergrown heifer and the cost of her not making her live weight target at first calving. If she enters the lactation with significant growth to make up then the feed conversion into milk will be lower than what it could have been as energy will be partitioned into her own growth. Her voluntary feed intake will also be limited by her size. If a 9% milk solids test is assumed, the expected response is about two kilograms of milk solids per lactation for every one percent increase in target live weight attained. For a heifer with a pre-calving target of 500 kg, five kilograms is equal to one percent of live weight.

The report found that regular monitoring is required as accurate live weight gain information is required to plan the feed intakes for the heifers. I have found this to be true in my own experience as calves with a very low ADG have been thought by the grazier to be doing very well and in fact they have been going backwards. Regular monitoring can pick this up before the condition scoring perception was able to.

LR McNaughton* and T Lopdell (2013) Effect of heifer live weight on calving pattern and milk production, Proceedings of the New Zealand Society of Animal Production, 73, 103-107

Abstract

Many heifers on New Zealand dairy farms fail to reach their target live weight. This failure leads to lost milk production and poorer reproductive performance. This study investigated effects of breed and region on heifer live weight and also effects of pre-calving heifer live weight (18–21 months) on milk production. Less Friesian heifers reached their target live weight than Jerseys, or Crossbreds (85.3 versus 89.3 versus 88.1%; P <0.001). Heifers born in Otago (91.9%) and Taranaki (91.8%) were the closest to achieving their target live weight, whilst those born on the West Coast (85.6%) and Northland (86.0%) had the greatest number of heifers not reaching their target. Heifers that had only one calving recorded on the database were a significantly lower percentage of target live weight than those heifers that had two calvings recorded (83.5% versus 87.1%; P <0.001). In heifers with a live weight record between 18 and 21 months of age, every 1% increase in the percentage of target live weight attained was associated with an increase in milk volume of 23 ± 0.6 litres in the first lactation and 24 ± 0.9 litres in the second lactation. Further work is required on the economics of feeding heifers to achieve their target live weight.