Why should you weigh heifers?
At Grasslands, we have a saying: ‘Measure to Monitor’. We try to implement this philosophy across every single aspect of the business from grass to fertility, milk production to calf rearing. Outlined below are the methods we like to use when weighing our heifers and why we choose to do so.
Rearing Dairy Heifers
Rearing replacement dairy heifers has numerous health and genetic benefits. However, this can be a costly process with current estimates of around £1200 from birth to calving. The heifer only starts to return her rearing costs halfway through her second lactation. Subsequently, the sooner she calves and the more we can aid her longevity within the herd, the more cost effective the process becomes and ultimately, the more profit we can make.
Emma Kennedy from Teasgasc Moore Park in Ireland, reports that heifers at target weight on MSD are shown to produce more milk solids in their first and subsequent lactations compared to those which are lighter. Producing more milk is obviously directly linked to increased profits across the lifetime. Calving at 2 years old is thus preferable to 3.
Target Weights of Heifers
Regular weighing is needed to monitor growth rates to check that they’re on target to achieve optimum weights at weaning, bulling and calving. Our target weights are derived from the cows mature weight. They are 60% at bulling and 95% at calving. Our third calvers are typically 550-575kg so we are aiming for 330kg minimum bulling and 525kg minimum calving.
These marked targets are broken down into monthly and even daily target weights to help us micro-manage our way to ensuring these broader life stage targets are achieved. We weigh our heifers at fortnight intervals up until weaving and then monthly thereafter to coincide with other stock jobs. These include TB testing, worming and blousing. The more often we weigh them, the more opportunities we have to alter the outcome.
Grouping Heifers According To Weight
On a weigh day, any smaller heifers (either under their target weight or under performing in their current grouping/feeding regime) are re-grouped with others of a similar weight. This helps to minimise competition between the heaviest and the lightest in the group, allowing us to target the preferential treatment towards the lighter animals only. Preferential treatment can be provided through alteration of the type of covers grazed, the residuals achieved or by introducing concentrates. One of the most economically efficient and performance effective methods, the lighter animals soon catch up.
It is important to take advantage of the high feed conversion efficiency that a young calf has. We put real focus on increasing growth rates at this time as the heifer accelerates towards her first target, weaning. It is during this time that 75% of frame growth occurs. Average daily gain can be influenced by the quantity and quality of milk and corn, as well as the cleanliness of the rearing environment and push them along to weaning weight. Study work by Emma Kennedy shows that calves which are heavier at weaning have higher post weaning weight gains. Therefore they produce stronger, healthier calves. Our weaning weight is thus 90kg.
During a weighing session, it is important to assess each animal individually and not just look at the average weight and gain for the group. This can easily mislead you into thinking that the whole group is performing well when there are some individuals that require particular attention to improve their performance well when in fact that there are some individuals that require a greater degree of attention.
Weight range within a group heavily influences the performance of lighter heifers within it. Even when grass is abundant there is still, believe or not, competition for feed. Growth rates of any smaller individuals will suffer if mixed with others that are considerably heavier and eat more DM.
Next Steps After Weighing
After each weighing session we review the feeding history of the group since the last weighing and the resulting ADG. We also check that they are achieving the results we desire and see if any costs can be cut or better focused on those individuals which need it. After a few years of weighing we begin to build a large data set and develop a template of what feed and management practices produce the most significant weight gains and which have proved ineffective.
Health Benefits of Weighing
Weighing is not only a good indicator of the quality and quantity of feed we give heifers but also their health status. Ill animals, such as those suffering from BVD virus, intestinal parasites or respiratory infection, often have decreased weight gains. A heifer may start to slow down growing before she physically looks ill. Identifying these individuals allows us to detect and treat problems sooner before they become damaging and are both harder and more expensive to cure.
Live weight is a greater determinant of oestrous cycling and the onset of puberty than age, therefore checking that their performance is sufficient to meet these demands it vital. Animals at target weight during bulling and calving are more likely to have well developed reproductive organs. This ensures that they have higher conception rates and calve sooner meaning that they last longer in the herd. Overall, the heifer becomes a worthwhile investment. Additionally, animals at target weight have wider, well-structured pelvises making the calving process easier. This lowers the chance of injury and problems with conceiving in the future. They are also easier to get in calf as second calvers and are more likely to maintain their body condition and continue growing after entering the milking herd.