Artificial induction of lactation in cattle: Effect of modified treatments on milk yield, fertility, and hormones in blood plasma and milk

Abstract

Holsteins were divided into groups CON and IL, each with six dry cows and six heifers. Group CON calved in mid-summer when group IL was treated (kg body weight per day) with (a) progesterone (P; .25 mg) and estradiol-17β (Eβ), either .05 mg or .10 mg, for 7 days; (b) continued Eβ at one-third the initial rate until udders were engorged; (c) then 12 injections (8-hr intervals) of TRH (each 200 μg) or saline; and (d) GnRH during lactation. Milk yield was not affected by Eβ dose rate, TRH or GnRH. GnRH luteinized the persistent ovarian follicles in group IL, and pregnancy rates were 80% and 83% in groups IL and CON, respectively. Large differences ( P < .01) between groups IL and CON were observed in plasma prolactin (IL-low), insulin (IL-high) and growth hormone (IL-low) wherein insulin was correlated ( P < .01) negatively with milk yield between days 7 to 49 of lactation. Milk concentrations of P, Eβ, estrone and estradiol-17α in group IL were no higher ( P > .10) 14 days after the last injection of P or Eβ than in group CON or in milk from the herd's bulk tank. The steroids were lowest in milk and plasma from ovariectomized cows. It was hypothesized that high insulin, as well as low prolactin and growth hormone, may contribute to inferior induced lactations.