Nutritional Management of Heifers
Mismanagement through over or under feeding during the critical phases of pregnancy can adversely affect lifetime productivity. Energy intake beyond needs for structural and muscular growth in heifers may cause dystocia as will heifers that have their energy intake restricted suffer with dystocia due to smaller frame size, reducing pelvic area and reduced energy levels at calving.
The nutritional requirement for a pregnant heifer (due to calve at two years of age) reflected as a daily weight gain is 0.5 – 0.7 kg/day with peak energy required later in the preg- nancy. Preferably, heifers should maintain their body condition score for the last trimester (50 – 60 days) of pregnancy. You are better to supplement the heifers from weaning to joining to make sure they are a minimum joining weight of 300 kg and a condition score of 3 rather than playing catch up after conception.
Pasture management for pregnant heifers is important, as Hypocalcaemia, more commonly known as ‘milk fever’, will cause dystocia. At the point of calving heifers experience an increase in demand for nutrients to produce colostrum, milk and energy to physically calve. The increase in essential nutrients required to adopt these changes within their body can create an imbalance, usually calcium deficiency. Calcium is amongst the most critical in the 14-21 days leading up to calving and it is common for most heifers (and cows) at this time to experience some level of calcium deficiency.
Heifers and cows undergo metabolic and physiological changes in the period leading up to calving that restrict
their ability to absorb and mobilise (release from the bones) calcium when it is required the most. Calcium is vital for the contractile strength of muscles, namely the uterus and at calving low available calcium within the body will result in weak contraction or ‘lazy calvers’.
Furthermore, pastures higher in nitrogen and potassium are counterproductive to the requirements of the calving heifer, particularly during the last 3-4 months of pregnancy, as they cause nutrient imbalance and affect the release of calcium.
Feeding magnesium and calcium to heifers pre-calving will help with the release of calcium from the bones. Many feedstuffs are detrimental to magnesium bioavailability and therefore calcium availability, which can include excessive levels of urea, legume silages/hay, molasses, salt and lush green feed. The irony is that many of these things are recommended pre-calving.
Between 14-21 days prior to calving the reduction in the heif- ers availability to counterproductive feed, as outlined above, and the introduction of low nitrogen and potassium feed, such as cereal or grass hay, grains and the availability of calcium and magnesium will help decrease dystocia. For cost effec- tiveness and management, only fed in calving groups 2 weeks out from calving. The benefits of smaller management groups will be; more calves born, less heifer deaths, better growth rates from more milk, better re-conception rates and ease of management.
Once the heifer has calved she should be moved onto higher energy pasture. A heifer needs to regain pre –calving weight and condition quickly if high re-joining conception rates are to be achieved.
Lienert Supplamins HiMag is used at Manchee Ag during our spring calving of heifers.