AgResearch Deer Growth Study

Post-weaning growth rates in deer during autumn are variable and a number of fawns have a considerable live weight check at and/or after weaning, which may be due to their underdeveloped rumen. Deer researchers at Invermay are examining the relative intake by fawns of pasture and milk at this time, which may be influenced by pasture management during lactation. This is research work in progress, and results are not yet available, so this item is showing the application of R&D money on behalf of deer farmers.

Reductions in growth rates immediately after weaning may result from fawns having an underdeveloped rumen. While the fawn initially relies on the intake of milk to meet its energy requirements for maintenance and growth, post-weaning it must rely on the intake of pasture and rumen digestion. This means that the stomach must develop from a monogastric at birth to a ruminant at weaning. This transition generally occurs when milk production declines and the fawn begins to graze pasture to compensate for the loss of energy from the hinds milk. The length of time required for the rumen to completely develop may be dependent on the relative intake of pasture to milk. This is influenced by the amount of milk supplied by the hind, and the quantity and/or quality of the feed on offer to both the hind and fawn.

Therefore, a fawn's relative intake of pasture to milk may be influenced by pasture management during lactation. If pasture availability is limited, the fawn may be more reliant on the milk supplied by their dam than the intake of pasture. In addition, if pasture availability is abundant, the hind may have greater milk production, which may reduce the fawns voluntary intake of pasture. An inadequate intake of pasture may therefore lead to an underdeveloped rumen reducing post-weaning growth rates.

With support from Deer Industry New Zealand levies on deer farmers, Invermay researchers are examining the relative intakes of pasture and milk, with a view to making pasture management recommendations to farmers, so as to avoid the check of the fawn at weaning and afterwards and optimize growth rates. Growth rates at this time of the year are important for commercial deer farmers to able to attain slaughter weights and mating weights in deer progeny.

The objective to alter the relative intake of milk-to-pasture of fawns by using three contrasting grazing management strategies over the lactation period and to measure the resulting impact on post-weaning growth. Fifty-four mixed-age pregnant hinds have been randomly assigned into three grazing treatments for over the lactation period November 2009 to February 2010:

1. Hind and calf grazing on a low pasture cover of 800-1200 kg DM/ha, resulting in calves having a low intake of both milk and pasture (LH-LC).

2. Hind grazing on a low pasture cover, while calf will have access to both low and high pasture cover paddocks via a creep feed gate system. The aim of this treatment is to have a low calf milk intake, while allowing the calf to have a high pasture intake (LH-HC).

3. Hind and calf grazing on a high pasture cover of 1800-2200 kg DM/ha, resulting in calves having high intakes of milk and potentially low intakes of pasture (HH-LC).

The Red hinds were selected using pregnancy scanning records to achieve a condensed calving period. Hinds were also be balanced for live weight and genotype across treatment groups. During calving in early November the hinds were set-stocked as a single mob in a paddock adjacent to the main trial site. Over this period the birth weight and birth date of calves was recorded. Once all of the hinds have given birth they were placed in their respective trial paddocks. In grazing treatment two (LH-HC) the young calves were taught to use the creep feeding gates by having openings wide enough to initially allow the dams also to pass through. However, after four weeks of mean calf age (late November) extra bars were added to the creep feeding gate limiting its use to only the fawns. The hinds and fawns will remain in their grazing treatment groups up until weaning (12 weeks of mean calf age), around late February, when the hinds will be removed from the trial and the calves will be grouped into one mob and grazed on an unrestricted pasture allowance until early June 2010.

The live weight of both the hinds and fawns were measured weekly from four weeks of mean calf age, along with body condition scoring of the hinds, up until weaning. After weaning the live weight of the calves will continue to be measured weekly until early June 2010.

Red hinds produce two to two-and-a-half litres a day of milk in early lactation, reducing to half-litre to one litre nearing weaning. The ratio of the major components in the milk, lactose, fat and protein, is similar to that of cows milk, but with less water, being a 22% milk solids composition.