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Discipline: hypocalcaemia; Key words: oral calcium bolus, subclinical hypocalcaemia, transition cow.
Dairy cows have many metabolic adaptations around calving, one of which is meeting the increased demand for calcium (Ca) that occurs at the beginning of colostrum and milk production. Even with many physiological adaptations to maintain normal Ca levels, many cows fail to meet this demand without affecting their internal Ca status. As a result, these cows can experience clinical Ca shortage (hypocalcaemia) or at least subclinical hypocalcaemia (SCH). Cows with SCH often suffer severe negative energy balance and metabolic diseases as well as increased susceptibility to metritis in the early post-calving period. Subclinical hypocalcaemia may also result in early lactation culling and poor reproductive performance. In an effort to relieve some of the consequences for cows that experience SCH, Ca can be provided by injection of readily available Ca into the blood or oral administration of Ca salts in the form of pastes or boluses. Whereas injection of Ca is necessary for cows showing clinical signs of hypocalcaemia, oral Ca supplements in the form of boluses may be more appropriate for suspected cases of SCH and have been demonstrated to provide a more moderate but sustained increase in blood Ca concentration. The efficacy of boluses versus injection of Ca was further investigated by Dr B. M. Leno and colleagues, the results of which they published in the Journal of Dairy Science, Volume 101 of 2018. Page 3285 to 3302. The title of their paper is: Differential effects of a single dose of oral calcium based on postpartum plasma calcium concentration in Holstein cows.
The objectives of their study were (1) to determine the effect of a single dose of an oral Ca bolus within 24 hours after calving on plasma Ca concentration, (2) to determine the response of first-calf cows and multi-lactation cows to this supplementation strategy, and (3) to observe the different responses of the cows based on initial plasma Ca levels. For objective 1, fifty cows from a commercial dairy farm were allocated within 19 hours after calving and randomized within lactation group (first, second, and third or more) to a Control which received no Ca, or a dose bolus treatment, supplying three oral Ca boluses of 54 to 64 gram of Ca. Plasma Ca was measured repeatedly between one and 24 hours following treatment. For objectives 2 and 3, cows on six commercial farms were assigned to treatment as for objective 1 (Control, 1973 cows; Bolus, 1976 cows). Herd records for health, reproduction and Dairy Herd Improvement Association test day milk production were collected. Multivariate models were developed to analyse the data. Objective 2 analyses also considered treatment with shortly after calving risk factors, whereas objective 3 analyses also considered Ca status.
No difference was observed for plasma Ca between one and 24 hours after treatment. First- calf cows which received boluses and calving at more than 712 days old showed a decreased risk of one or more health disorders and those with body condition score of more than 3.5 responded to the boluses with increased milk production (Control = 31.7kg per day; Bolus 35.1kg per day), as did those with days-carried-calf of more than 277 (Control = 31.9Kg per day; Bolus = 34.7kg per day). A reduced risk of one or more health disorders (retained placenta, displaced abomasum etc) was observed in cows with equal or more than three lactations and multiple-lactation cows with body condition score of more than 3.5, or that were lame. Variable responses for first-calf cows by Ca status were minimal. For multiple-lactation cows with low plasma Ca, bolus supplementation decreased the need for additional Ca treatment as well as the risk of experiencing one or more health disorders.
It was concluded that supplementation with a single oral dose of Ca could be used for shortly after calving risk groups to improve health. Calcium status did not really have an effect in the response of first-calf cows, but multiple-lactation cows with low Ca at calving had improved health status when supplemented.