Milk yield and lactose synthetase activity in the mammary glands of superovulated ewes

Abstract

Twenty-four lactating ewes were used to study the effects of superovulation prior to mating on milk and lactose yields during lactation, and the activity of lactose synthetase of the mammary glands at the end of lactation (91 days post-partum). Ten ewes were injected with 700 IU pregnant mare serum gonadotropin (PMSG) and the other 14 with saline as a control. During pregnancy and lactation, half of the experimental ewes (3 superovulated [all gave birth to a single lamb] and 9 non-superovulated ewes [6 and 3 ewes gave birth to a single and twin lambs, respectively]) were fed with standard protein and TDN diet (12% CP and 65% TDN) and the others (7 superovulaled [3 and 4 ewes gave birth to a single and twin lambs, respectively] and 5 non-superovulated ewes [4 and 1 ewes gave birth to a single and twin lambs, respectively]) were fed with high protein and TDN diet (15% CP and 75% TDN). The results of the experiment indicated that superovulated ewes had higher milk (55%) and lactose yields (54%) ( p < 0.01) during lactation as compared to non-superovulated ewes. At the end of lactation period, superovulated ewes had higher wet mammary weight (31%) and lactose synthetase activity per gram mammary glands (20%) ( p < 0.01). In this experiment, ration quality and litter size did not significantly affect milk and lactose yields during lactation, and mammary wet weight and lactose synthetase activity at the end of lactation. Lactose synthetase in the secretory cells of the mammary glands operated at glucose concentration around 0.250 mM, which was far below serum glucose concentrations (1.94–3.03 mM). The data suggested that glucose entry into the secretory cells was the limiting factor in lactose synthesis. It was concluded that superovulation in the ewes prior to mating increased milk and lactose yields during lactation. Increased milk and lactose yields in the superovulated ewes was contributed by the increased synthetic activity of the mammary glands during lactation.