For cow-calf operations, a major component of profitability is reproductive efficiency or the number of calves weaned per cow exposed. When open rates are higher than expected, it can be difficult to pinpoint the cause; there may be many factors that contributed. Dry conditions over the past several years have impacted many aspects of beef operations, including those that contribute to open rates.
The quantity and quality of forage available to many cow herds has been reduced due to dry conditions. Pasture may be unable to supply the energy needed for cows to maintain their body condition. Cows in lower body condition at calving will be slower to resume cycling following calving, conceive later in the breeding season and calve later the next year or remain open if unable to conceive before bulls are pulled.
To maintain herd size, more replacement heifers may be kept to compensate for an increase in open cows. If yearling heifers haven’t reached 55 to 65 per cent of their mature body weight by breeding time, their fertility may also be reduced. Over two to three years, the result is higher than expected open rates at pregnancy checking, or fewer than expected calves on the ground at calving. Whether developing or purchasing, bringing new animals into the herd is an expensive endeavour. It takes several years for those animals to start paying for themselves.
Trace minerals, specifically copper, manganese and zinc are necessary for reproductive processes in both cows and bulls. Trace mineral deficiency can occur due to low levels of minerals in forage or insufficient intake of mineral supplements. Components present in feed or water which bind trace minerals and decrease their availability to the animal will also lead to a trace mineral deficiency. Water quality in dugouts tends to decrease during dry conditions. When evaporation is high and recharge of surface water sources is low, dissolved solids like sulfates increase in concentration. Sulfates bind copper and other minerals in the animal’s digestive system rendering them unavailable to the animal. Over time, this contributes to deficiencies in cows, which can result in lower conception rates.
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