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Bull selection: There is increased interest in using sexed semen. At a Eurogene/LIC meeting last week, it was stated that the best time to AI an animal with sexed semen is 16 hours after the onset of heat. In the case of maiden heifers, those seen bulling after 3pm in the afternoon should not be served until the following morning. The best time to AI heifers that come into heat in the morning is late at night, which isn’t very practical. Therefore, it’s best to stick a conventional straw in these, either in the morning or afternoon.
It won’t be practical to use sexed semen on all heifers, so you should be willing to use conventional straws also; otherwise conception rates will suffer. Cows for sexed semen should be handpicked based on BCS and time since calving and should be free from lameness, mastitis and have had more than one cycle. According to Stephen Butler of Teagasc, there is no issue with using synchronisation with sexed semen, provided the correct protocol is followed.
Updates to EBI were made last week and the new Active Bull List has just been published. Take the time now before things get really busy at calving to pick the bulls for the coming season. Decide what your herd is lacking and choose bulls that will improve that area, without negatively affecting other areas. The sire advice programme on the Herdplus website is useful for choosing bulls. Make sure to pick a large team of bulls and use them equally across the herd.
Calving: As calving kicks off, do all you can to reduce sickness in the herd. Make sure dry cows are getting enough pre-calving minerals. The minimum amount of magnesium a cow should be supplemented with per day is 25g. The amount of magnesium in dry cow minerals will be stated on the bag, eg 23%. This means that if 110g/head of minerals is being fed, the cow will be getting 25g. However, for cows at high risk of metabolic disorders, such as over fat cows, high yielders, cows fed high potash silage or Jersey cows, extra magnesium should be fed in the runup to calving. Up to 40g per day should be fed where there is a high risk or a history of milk fever. Other milk prevention aids are available, such as liquid feeds and boluses after calving, but increasing magnesium intake before calving will probably be a cheaper option so should be tried first.
Heifers: The target liveweight for a 12-month-old heifer on 1 February is to be 50% of her mature liveweight. For a 550kg mature cow, this is a target weight of 275kg now. If the mature liveweight is heavier, at say 600kg, the target liveweight of the heifer should be 300kg now, or 250kg for a 500kg cow. If heifers can be turned out to grass over the next few weeks, target the below- and on-target-weight heifers first. If heifers are going to be kept in for another month or more, then they must be split up and managed separately. The below-target-weight heifers should get good-quality silage and 3kg of meal per day. The heifers that are on target should get good-quality silage and 1.5kg of meal and those that are above target will suffice on good-quality silage only.
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