Effect of increasing dietary energy and lasalocid treatment on gonadotrophin secretion in rams

In the mature ram, supplementary feeding, for example with lupin grain, stimulates gonadotrophin secretion. To test whether this effect is reproducible with alternative diets not containing lupin grain, rams were fed either a basal diet (1kg of oat hay containing 10% lupin grain and 2.5% minerals) or a high energy diet (50% lucerne chaff, 27.5% hammer-milled oat hay, 20% rolled barley and 2.5% minerals) at the daily rate of 2.5% of live weight for 7 days. After this period, half of the first group received 750 g/head daily whereas half of the second group received a daily drench of an ionophore, lasalocid (45 mg/kg of food) for 10 days. The other rams remained on their respective diets. Blood was sampled every 20 min for 24 h on days 0, 7 and 17 relative to the start of treatments for the study of plasma LH pulse profiles. Plasma samples taken every other hour were assayed for FSH (days 0, 7 and 17), insulin and glucose (days 7 and 17). Rumen fluid samples taken, from rams fed the high energy diet, on days 7 and 17 were analysed for volatile fatty acid content. It is concluded that feeding either lupins grain or a high energy diet stimulates LH and FSH secretion. These effects are associated with increased plasma concentrations of glucose and insulin.