Calf And Heifer Performance

There are several advantages in maximising heifers weights.

Several studies have been done showing that heifer weights relate to milk production.

Increasing calving liveweights for Fresians from 360 to 460 kg increased milk production during the first lactation by ~30kgMS (Freeman 1993). This production benefit extended into the second and third lactation ~63kgMS/yr. Obviously you must be able to feed them enough energy to get these benefits.

At what size are calves too big? The Creator's plan was for calves to develop with full access to their mother's milk and "ad lib" on pasture for as long as they wanted. An inbuilt regulation mechanism was implanted into each individual telling them when to wean themselves off milk. When your calves get bigger than this benchmark, then maybe they are too big.

The onset of puberty, and the commencement of cycling is related to Live weight more than to age. Puberty occurs at 35-45% of mature weight, while conception occurs at 45-50% of mature weight. Calving problems depend more on heifer LW at mating rather than on LW at calving. Dairy cows will attain their mature LW by the fourth lactation and the objective of rearing heifers is to produce 80-85% of mature LW by first calving. Frame size is determined early, so there is doubtful merit in the practice of feeding older heifers to make up for poor growth earlier in life.

Heifers calving 100kg heavier can increase their peak production by ~0.38kgMS/day in their first lactation.
Fresian heifers mated below 260kg had 34% conception to first insemination compared to 58% for heifers mated weighing 300kg or more. Last year one of our Drummond clients heifers were mated at 400kg with only 2-3 out of 200 being empty at first lactation.
Of the smaller heifers below 260kg 24% had difficulty calving. This declined to 8% in heifers mated at 260-280kg and was lowest in 340-360kg heifers.

Poorly, grown heifers do not last long in the milking herd. They are more likely to be culled for poor milk production or poor fertility during their first lactation. Total herd costs can be greatly increased by this high wastage.

Post weaning heifers must receive feed with a minimum energy level of 11MJME/kg.

A Southland pasture trial in March 2007 saw Pasture Plus Formula 2 produced grass with 11.6MJME/kg vs Urea 9.7. Calves feed on Urea treated pasture will always struggling to achieve optimum weights.

Extracts from article by John Moran. Department of Primary Industries 2005
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