Effects of supplements of phosphorus or phosphorus and protein on the ovarian activity of cows fed native pasture hay

Abstract

Eight cows with calves in pens were fed native tropical pasture hay harvested at intervals throughout the wet season. Four of the cows were supplemented with phosphorus. When pastures matured and declined in quality, calves were weaned and their dams were firstly group-fed hay in yards and later allowed to graze native pasture. One group continued to receive phosphorus supplement and both groups were supplied with protein supplement to offset possible deficiency. During the pen feeding period, none of the cows exhibited oestrus and plasma progesterone declined as the quality of the hay fell; the cows were refractory to treatment with luteolytic prostaglandin. Some four months after the commencement of protein supplementation, two cows from the group receiving phosphorus supplement exhibited oestrus. Three cows from each group had elevated plasma progesterone levels, and these animals all exhibited oestrus following treatment with prostaglandin. Phosphorus supplementation had no significant effect on feed intake, liveweight change or milk production. Blood inorganic phosphorus was significantly increased by treatment but bone phosphorus was not. It was concluded that phosphorus supplementation alone had no significant effect on reproductive activity. If cows received adequate protein, however, oestrus activity was markedly increased whether phosphorus was supplemented or not.