The effect of slow-release selenium and cobalt bolus on milk production and composition, reproductive performance and some blood parameters of Lari Bakhtiari's ewes

In mammals, the need for minerals increases during the pregnancy period for the growth and development of the fetus and reaches to its maximum level at the end of the pregnancy period. Therefore, it is vital to supplement pregnant ewes with sufficient quantity of micro-minerals to preserve the fetus and improve the growth of the newborn lambs. Selenium and cobalt are two essential elements for ruminants, which play a major role in animal performance. Selenium is necessary to maintain the normal physiological functions of the body, it also plays an important role in the production of thyroid hormones and the conversion of thyroxine to triiodothyronine. Cobalt is one of the essential elements that presents in the structure of vitamin B12. Therefore, the present study aimed to investigate the effects of using slow-release bolus of selenium and cobalt on milk production and composition, reproductive performance and some blood parameters of Lori Bakhtiari's ewes.

One hundred Lori-Bakhtiari ewes with an average age of three to four years and an average weight of 47.55 ± 5.44 kg were used in a completely randomized design. Experimental treatments included: 1) control ewes without receiving slow-release bolus, 2) ewes receiving slow-release selenium bolus with a release rate of 0.3 mg per day, 3) ewes receiving slow-release cobalt bolus with a release rate of 0.3 mg per day and 4) the ewes receiving slow release bolus containing selenium and cobalt with a release rate of 0.3 mg of selenium and cobalt per day. Blood samples were collected at 76 days post-breeding (mid-gestation) and 30 days postpartum from all ewes, and analyzed for serum concentrations of selenium, zinc, iron, triiodothyronine, thyroxine and creatine-phospho-kinase activity. The number and percentage of pregnant ewes, number and percentage of healthy lambs born, number and percentage of twining, number and percentage of lambs with white muscle disease and number and percentage of lambs survived after 70 d were also recorded.

Supplementing ewes with slow-release boluses of selenium and cobalt had no effect on the number of pregnant ewes, lambs born healthy, twins, lambs with clinical symptoms of white muscle and the number of live lambs up to the age of 70 days (P<0.05). Milk production was higher in ewes receiving slow-release cobalt and selenium-cobalt tablets compared to other treatments (P<0.05). Milk fat percentage in the ewes receiving slow-release cobalt and selenium-cobalt bolus was significantly lower than other treatments (P<0.05). The percentage of milk protein in the treatment receiving slow-release selenium-cobalt bolus was significantly higher than the control treatment (P<0.05), but there was no significant difference with the other treatments (P<0.05). Serum concentration of selenium in ewes receiving slow-release selenium and selenium-cobalt boluses was significantly higher than other treatments (P<0.05). Serum concentrations of zinc, iron and serum creatine phosphokinase activity were not affected by the experimental treatments (P<0.05). Serum concentration of vitamin B12 in ewes receiving slow-release cobalt and selenium-cobalt boluses was significantly higher than the other treatments (P<0.05). Serum concentrations of triiodothyronine and thyroxine were not affected by the experimental treatments, but the ratio of thyroxine to triiodothyronine was significantly lower in ewes receiving selenium and selenium-cobalt than the other ewes (P<0.05).

The results showed that supplementing ewes with slow-release boluses containing selenium and cobalt at the time of estrus synchronization increased serum concentrations of selenium and vitamin B12 before and after parturition, and increased milk production and milk protein content.