PHOTO: CHRIS MCCULLOUGH
Energy corrected milk (kg)
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(months in milk) and a decrease of 0.225 kg/day of daily ( energy corrected) milk production. These results clearly highlight that calving at 24 months of age does not negatively affect future performance; rather, it improves overall lifetime milk production performance by up to 13%.
Inseminating heifers For dairy heifers to calve at the goal of 24 months, they obvi- ously have to be inseminated at 15 months old. Some dairy farmers opt for an easy calving beef breed to use on heifers for the first time, but most will choose to inseminate with an easy calving dairy sire with a good Economic Breeding Index (EBI), to help increase the expected profitability per lactation of the progeny of the sire. Using AI on heifers works is efficient, as they are very fertile and are usually high genetic merit animals. Using AI can also help with good management of the herd, ensuring a more compact calving period compared to using a bull. An animal with an EBI of € 200 means the progeny of that animal, on average, will yield € 200 more profit per lacta- tion than the average progeny of an individual of EBI € 0, producing in a similar environment. Similarly, the progeny of the € 200 individual will yield € 50 more profit per lactation than the progeny of an individual with an EBI of € 150. To achieve a successful pregnancy, heifers must be well
16 ▶ DAIRY GLOBAL | Volume 9, No. 2, 2022
grown in order to cycle two to three times before they need to be inseminated at 15 months. The first few heats may be erratic and ovulation may not occur, after which, heifers should come into season every 21days (range 18–24 days). Just like cows, heifers are more fertile if they have shown a heat before they need to be inseminated, compared to those that are inseminated at their first heat. Puberty for a heifer begins when it is around 40% of its mature body weight. This weight must be reached by about nine months of age so that heifers have two to three normal oestrus cycles before breeding at 55% of mature body weight.
Herd introduction Experts say that it is best to introduce newly calved heifers into the main herd in the evening time after milking as the older cows are calmer at this time and are fed. This means there should be less competition for feeding space, and heifers get a chance to become familiar with their new surroundings.
Figure 2 – Energy corrected milk (kg) produced over lifetime. 32000
30000 28000 26000
Calving at 24 months of age does not negatively affect future perfor- mance; rather, it improves overall lifetime milk production per- formance by up to 13%.
Low
Middle Age at first calving level
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