Abstract:
Proc. Aust. Soc. Anim. Prod. I996 Vol. 21 LIVE WEIGHT, AGE AND PRODUCTIVITY RELATIONSHIPS FOR DAIRY HERDS IN SOUTH-EAST QUEENSLAND R.J. MOSS, D.R. MILLER and I.K. BUCHANAN Dept of Primary Industries, Mutdapilly Research Station, MS 825, Ipswich, Qld 4306 Moss (1993) proposed a theoretical relationship between herd productivity and liveweight of cows, and suggested that replacement heifers calve at 85% of mature live weight. To test this relationship data were obtained for 2100 animals on 14 commercial dairy farms in the West Moreton region of south-east Queensland. Farms with production levels from 3500 to 8700 litres(L)/cow were selected, and all animals above 12 months of age were weighed immediately after morning milking during a 4-week period in summer 1994. Mature liveweight of cows at calving Y (kg) increased from 560 to 730 kg with increasing production X (L/cow) (Figure l):For lactating cows this relationship was less precise with cows at v&ious stages of lactation. As herd productivity increased, cows lost more weight, using body condition to support milk production:Liveweight of heifers at 2 years varied from 340 to 500 kg while pi-calving liveweight ranged from 400 to 620 kg with a mean of 536 (+ 16) kg for herds above 5500 L (Figure 1). Average age of heifers at calving was 29.8 (+ 2.5) months (range 25 to 34 months), with higher production farms calving younger - 24 days per 1000 L increase in yield. Farms in the range 4500 to 6500 L calved heifers close to 85% of the liveweight of mature cows in the herd and produced 82% of the milk in first lactation, 96% in second lactation and >lOO% in third lactation (Figure 2). In contrast, farms averaging ~4500 or > 6500 L calved heifers at 78% of mature weight and production in the first lactation was 69 and 79% of mature cows respectively. In both groups mature levels of production were reached at the fourth or later lactations. Figure 1. Predicted (-) and observed (----) relationships between herd productivity and live weight of cows and heifers at calving Figure 2. Milk yield by heifers and young cows relative to mature production at various farm production levels Heifers which calved close to 85% of their mature weight can be as productive as mature cows by their third lactation. As herd productivity is increased, liveweight targets for heifers should also be increased, and pre-calving liveweight of 85% of mature size is recommended. MOSS, R.J. (1993). Trop. Grassl. 27: 238-49. 452
