Effect of Thermal Stress, Cistern Size and Milking Frequency on Plasma Mineral Concentrations in Holstein Dairy Cows

Rim Ben Younes¹, Moez Ayadi², Taha Najar¹, Margherita Caccamo³, Iris Schadt³, Moncef Ben M′Rad¹

1. Ressources Animales, Halieutiques et Technologie Alimentaire, Institut National Agronomique de Tunisie, Tunis 1082, Tunisie
2. Production Animale, Institut Supérieur de Biologie Appliquée de Médenine, 4100 Médenine, Tunisie
3. CoRFiLaC, Regione Siciliana, 97100 Ragusa, Italy

This study was designed to evaluate heat stress and cistern size as well as milking frequency effect under heat stress on plasma minerals in dairy cows. This study was carried out in 2006, in North Tunisia using 28 Holstein cows in midlactation. Cows had either large (47 cm² ± 17) or small cisterns (23 cm² ± 8). The experiment was performed in spring (April 5) and summer (July 19, August 19, and September 19). On each test day, temperature-humidity index (THI) was determined and cows’ blood was sampled from the jugular vein to determine serum concentrations of P, Fe, Ca, Mg, K, Na, Cl. In April and July, cows were  milked twice a day. Immediately after July, within each cistern size group, cows were randomly assigned to equal groups of either two or three times milking. Mean THI were 62, 79, 84, and 77 in April, July, August and September, respectively. All minerals concentrations were affected by test day (P < 0.05), but not by cistern size. Under heat stress, with exception of K, all blood minerals, increased when cows were milked three times compared to two times (P < 0.05). Increasing milking frequency could attenuate lowered mineral levels under heat stress.

Keywords: Heat stress, Plasma minerals, Milking frequency, Temperature-humidity index[/vc_column_text]

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