But animal nutritionist Natalie Chrystal told this year’s Zoetis Dairy Vet conference that despite that level of investment, heifer management was often overlooked until the animals returned to the milking herd.
In her review of both local and international research on the impact of heifer body weights on long term survival and fertility, Chrystal identified data from a study carried out last year in New Zealand which showed a significant effect of weight between 15 and 17 months on the likelihood a heifer would calve, and subsequently survive for a second lactation.
Earlier research, also carried out in this country, had shown 80% of heifers with an 18-month liveweight of 315kg would make it to the end of their first lactation, compared with 100% of heifers weighing 385kg. By the end of the fourth lactation only 55% of the lighter heifers remained, compared with 70% of their heavier herd mates.
“Body weight at first calving also has a significant effect on a heifer’s lifetime performance. Simply put the heavier a heifer is at calving, the higher her milk yield for that and following lactations.”
There were two key drivers for this.
“The heavier heifers will have more reserves which can be utilised to produce milk early in lactation, when their energy intake is less than the energy required for milk production.”
The second reason relates to the heifer’s nutrient requirements for growth. The heavier the heifer is at calving, the closer she is to her mature body mass and consequently over her first lactation, less energy needs to be directed to growth in order for her to reach her mature body weight. This energy can be used for milk production.
The effect of additional liveweight on milk production in the first lactation is affected by the mature body mass of the animal and her genetic potential, and typically an additional 0.1-2kg milksolids (MS) is gained in production for every 1kg of liveweight gain at first calving.
A review of LIC data carried out by McNaughton and Lopdell in 2012 found that only 36% of NZ heifers achieved their target body weight at 22 months old.
“Those authors suggest that calf rearers are doing a good job of meeting body weight targets pre-weaning as only 2% of calves didn’t achieve their body weight targets at three months. But that gap increased after weaning with 5% of calves behind target after six months and 14% at 12 months. By 22 months the average calf weight was 11% under the target.”
“On average NZ heifers are 50kg lighter at first calving than they should be, meaning they will produce about 6.5kg MS less in the first lactation.”
The onset of puberty is more closely related to body weight than age, so growth rates from weaning to 10 months play a key role in determining the onset of puberty. Chrystal outlined some key steps to ensuring better gains during this period.
Good rumen development through the use of grain-based feeds before weaning helps increase the animal’s ability to effectively use forages after weaning and helps to reduce weaning stress.
Chrystal highlighted the importance of allowing free access to clean water during the rearing period to aid rumen development. Other ways of reducing stress at weaning, including gradual rather than abrupt withdrawal of milk supply, would also help.
After weaning Chrystal highlighted the importance of proactive disease control, particularly against bovine viral diarrhoea, worms and coccidiosis. All three of these can have a dramatic effect on the ability of the animal to use feed effectively and result in poor post-weaning weight gains.
Immediately after weaning offering high-quality feed was vital.
“A 10% drop in pasture quality will require a 15-20% increase in intake, and that is not always achievable.”
Strategies such as rotational grazing should be used to maximise pasture quality. Where pasture quality is limited the use of other high quality supplements should be considered.
Simply throwing heifers some poorer quality feed not considered suitable for the milkers was not good enough. Poor quality silage would only depress feed intake and utilisation further and impede growth progress.
Chrystal emphasised the importance of providing sufficient protein for lean tissue development. She said while pasture typically provided sufficient protein, it was important to consider protein supply over summer when protein levels in pasture were low, or when heifers were fed other low protein supplements.
The last two months before calving can be a particularly challenging time for heifers as the nutrient demand of the growing foetus increases rapidly at the same time as the heifers feed intake is decreasing and NZ data suggests that heifers are often not consuming enough energy during this period. .
Chrystal said where practical similar feeds to those which will be introduced after calving should be presented before calving. For example, feeding a proportion of the diet as whole crop or maize silage was a useful way of introducing starch into the diet of heifers which will be fed grain once they entered the milking herd. Overall, any spending on good heifer rearing should be considered an investment in the herd’s future.
“Establishing target body weights and monitoring regularly is important, and will maximise the return on the investment made in genetic progress and calf rearing.”
