Setting targets

The target within any heifer rearing program is to produce well developed heifers, capable of expressing their full genetic potential, cost effectively. The targets set for rearing high genetic heifers at Greenmount Campus are to calf heifers at two years of age at a pre calving weight of 600 KG.

The optimum age at first calving is two years (see COSTS OF REARING DAIRY HEIFERS). A significant number of farmers calve their heifer replacements at 2.5 - 3 years of age. However rearing heifers to calve at 2.5 years or older means that there will be significantly more stock carried on the farm. For example, increasing age at first calving for a 100 cow dairy herd with 30 replacements per year from two to three years will increase the number of replacements on the farm by up to 50 percent (Table 2). This in turn leads to an increase in rearing costs.

(100 cow herd with 30 heifer replacements each year)

Benefits of calving at two years include:

Rear heifers to calve down at two years

(100 cow herd with 30 heifer replacements each year)

Studies carried out in the United States (Cornell University) have shown that the weight of heifers at calving has an impact on subsequent milk production. Target weight at calving will vary according to genetic merit. Dairy farmers using Friesian type cows should calve down their heifer replacements at a lower weight than dairy farmers using Holstein type stock. Recommendations for medium (Friesian type) and high (Holstein) genetic merit animals are given in Table 4. While the management principles involved in rearing medium and high merit stock are similar this booklet will deal primarily with the management skills required to rear Holstein type dairy heifer replacements.

Recent research work at ARINI, Hillsborough has shown that there is an acceptable range in pre calving weights. The important factor is that weight is not dictated by body condition. The results indicated that fat, overweight heifers did not perform as anticipated while lighter heifers, calving in fit condition, were easier to manage and gave acceptable levels of performance. As a compromise between rearing costs and heifer performance and to satisfy the requirements for the range of milk production systems at Greenmount Campus, a pre calving weight target of 600 kg at a condition score of 3.0 has been set.

To achieve the pre calving liveweight targets it is important to monitor weight changes through the rearing period. Liveweight can be monitored using a weighbridge or a weighband (see MONITORING HEIFER PERFORMANCE). Particular emphasis should be placed on the pre pubertal period (4 - 10 months). Experiments have shown that calves which undergo accelerated growth at this stage do not produce as much milk in their first or subsequent lactations compared to calves where growth rates are controlled during the same period (see Table 5). Recent studies carried out at ARINI, Hillsborough would suggest that there is less requirement to check pre pubertal growth rates with Holstein heifers. The target growth rate for Friesian type heifer calves at this stage is 0.60 KG/day. The target growth rates set for Holstein calves aged 4 - 10 months at Greenmount Campus is 0.80 KG/day.

Source: Pennsylvania State University, USA

The body condition score of heifers at calving will also have a bearing on their subsequent performance. Ideally heifer replacements should calve down at condition score 3.0. Work carried out at ARINI, Hillsborough has shown that heifers in condition score 3.5 – 4.0 at calving (typical of many autumn calving herds) eat less and loose excessive weight after calving resulting in poorer conception rates at first service.

Aim to calve heifers down at condition score 3.0