Abstract:
Animal Production in Australia 1998 Vol. 22 BENEFITS OF REARING DAIRY HEIFERS TO ACHIEVE HIGH TARGET WEIGHTS AT CALVING R.F. PITMAN Macalister Research Farm Co-operative Ltd, Maffra 3860 Numerous trials, as summarised by Moran (1996), have indicated substantial production benefits could result from better growth rates in dairy heifer replacements. In December 1993, the Macalister Research Farm (MRF) commenced a four year demonstration to promote the adoption of improved systems of heifer rearing on dairy farms. The main aim of the project was to compare the performances of two comparable groups of heifers, which were reared to reach different liveweights at calving. Of the 77 heifer calves born at MRF in August/September 1993, all were numbered in chronological order and reared together. Shortly after weaning in late November 1993 the calves were split into two groups with even numbers in one group and odd numbers in the other. One group was sent away to be reared under contract to reach a minimum mean liveweight of 480 kg at calving, at about two years of age. The control group was reared at home as in previous years and was expected to average 450 kg a head at calving. Both groups joined the herd at MRF at calving and were managed identically from then on. Growth rates of both groups of heifers were monitored regularly up to calving. Since then, their productive and reproductive performances as milking cows have been monitored over two full lactations. The average liveweight at weaning of both groups of calves was 101 kg. The well reared group then grew steadily at close to the targeted rate to a mean liveweight of 496 kg at calving. Growth of the control group was irregular to a mean 414 kg at calving. Subsequent performances of both groups are presented in Tables 1 and 2. Table 1. Average production of milk (L) and fat and protein (kg) of well reared and less well reared heifers in their first and second lactations First lactation (95/96) Milk Well reared Less well rd. 4,691 4,245 Fat 203 184 Protein 149 136 Second lactation (96/97) Milk 4,805 4,568 Fat 202 195 Protein 160 149 Lifetime performance (to date) Milk 9,496 8,813 Fat 405 379 Protein 309 285 Table 2. Survival of well reared and less well reared heifers in their first three years Number of heifers/cows in group Dec 93 Well reared Less well rd. 37 40 Aug 95 31 37 Jun 96 27 35 Jun 97 23 29 Oct 97 23 26 Average calving date 1996 Aug 29 Aug 31 1997 Sept 7 Sept 5 After two lactations, the heavier heifers had outproduced their lighter counterparts by 683 litres per cow. This represented a response of 8.3 litres to each additional kg liveweight at calving, which was lower than had been anticipated. The value of the additional milk was $188.50, at 1996/97 prices, and was still sufficient to have justified more attention to the rearing of the lighter group. The survival rate of animals in both groups was disappointing. Most culling was caused by failure to get in calf or poor production in early lactation. While numbers were too small for firm conclusions, the results do not indicate any tendency for lighter heifers to be poorer survivors or less fertile. MORAN, J.B. (1996). Proc. Aust. Soc. Anim. Prod. 21, 71-81. 376