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Wednesday 7 December 2016

Time and management essential for maiden heifers to achieve targeted mating weights

Mary Kinston

Published 22/02/2011 | 05:00

March 1 is less than a week away, which means that there is only about 45-65 days left before the maiden heifers will be mated. For some, the measurements have already been taken and appropriate management strategies adopted to deal with any lighter maiden heifers.

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The target we are striving for here is 60pc of mature liveweight by the start of mating. Table 1 (right) shows the target mating liveweights for herds of differing mature liveweights.

Liveweight and body condition score of the maiden heifer have far more influence than age on calving date, survivability and subsequent milk production. Therefore, achieving these liveweight targets with animals with good body condition scores (BCS) should be a priority in spring. This equates to a BCS of 3. With this target in mind, the critical questions at this stage are:

1. How heavy are your maiden heifers on average and, in particular, what are the weights of the lightest 25pc?

2. Are all your maiden heifers going to hit target liveweight at mating with your present management? Are they better indoors on silage or outdoors on grass?

3. How much liveweight does each heifer, either as individuals or in batches, need to gain to achieve this target and what daily liveweight gain per day is required to do so?

4. Can you get your heifers, especially the lighter ones, out to grass? Is supplementary feed required?

5. Do your heifers need to be divided into smaller groups, with small, lighter heifers fed supplements in order to achieve the required target?

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6. Are some of your lightest heifers ever going to make the target in the time left? For example, should you consider carrying over or selling heifers that are, for example, 80kg behind target?

7. Are there any other factors, such as mineral deficiencies, worm or fluke burdens, that need to be mitigated against in order to promote growth?

If considered simply, daily liveweight gains of 0.5kg/day, 0.8kg/day and 1kg/day will result in overall liveweight gains of 22.5-32.5kg, 36-52kg, and 45-65kg/head respectively between now and the second half of April. Considering this, what level of daily liveweight gain needs to be achieved by your heifers and by what management strategy will it be achieved?

Keeping animals indoors on silage is likely to result in liveweight gains closer to 0.5kg/day, which may result in your heifers being lighter than the desired target at mating. This will result in a higher number of non-cycling heifers, that will calve down later and produce less milk.

Late calving heifers generally become late calving cows and therefore they are also more likely to fall out of the herd sooner. In comparison, turning heifers out to grass will be more likely to achieve daily liveweight gains closer to 1kg per day, so getting maiden heifers out to grass may be a priority for you at this stage. You may also consider feeding a small batch of light heifers supplements in order to guarantee a higher daily liveweight gain during this critical time.

A lot of farmers have realised the value in being able to weigh heifers at critical times and the benefits of having the certainty that heifers are on target or not. As a result, weigh scales are becoming a common feature on many farms. However, for those who do not have access to scales, the girth and height measurements table (2, left) will aid you in estimating heifer liveweights. While the degree of accuracy of this system is sometimes questioned, it is better than the 'eye-o-meter' of "she's grand". Weighing or measuring will also highlight the variability and range in the liveweights of a group of animals, which may alter management decisions accordingly.

Mary Kinston is a dairy consultant based in Kerry mary.kinston@gmail.com

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