PARENT SESSION
Gene Regulation & Function

EFFECTS OF BOVINE SOMATOTROPIN ON OVIDUCTAL AND UTERINE GENES ENCODING COMPONENTS OF THE IGF SYSTEM IN LACTATING DAIRY COWS.

Pershing, Randi¹, Thatcher, William¹, Badinga, Lokenga¹, ¹

ABSTRACT- Bovine somatotropin (bST) treatment at timed insemination increases pregnancy rates in lactating dairy cows when heat detection is eliminated from the reproductive management system. The objective of this study was to examine the effect of exogenous bST on oviductal and uterine genes encoding components of the IGF system when given at 16 h after the second GnRH injection in an Ovsynch/TAI protocol. Twenty-one lactating, cyclic Holstein cows averaging 80 days (D) in milk were synchronized to estrus using the Ovsynch program and then randomly assigned to receive bST (Posilac, 500 mg; n=11) or serve as untreated control (n=10). Within each treatment group, cows were assigned to be sacrificed on D 3 or 7 post-ovulation. Samples of oviductal and endometrial tissues were collected from the oviduct and uterine horn ipsilateral to the corpus luteum and frozen at -80°C until subsequent analysis of IGF-I, IGF-II, IGFBP-2, IGFBP-3 and growth hormone receptor (GHR) mRNA contents. Northern blots revealed mRNAs for IGF-I, IGF-II, IGFBP-2 and IGFBP-3 in all oviductal and endometrial tissue samples. Significant amounts of GHR mRNA were detected in the uterus but not in the oviduct. Concentrations of IGF-I transcripts did not differ between control and bST-treated cows. Levels of IGF-II mRNA were higher (+ 250%; P<0.05) in oviducts but lower (- 60%; P<0.05) in uteri collected from bST-treated cows than control cows. Irrespective of the site or stage of the estrous cycle, IGFBP-3 mRNA levels were higher (+ 125%; P<0.05) in bST-treated cows than the control cows. IGFBP-2 transcript levels did not differ between treatments or stages of the estrous cycle. The GHR mRNA was decreased (- 30%; P<0.05) in bST-treated cows by D 7 of the estrous cycle. Results suggest that bST effects on fertility responses in lactating dairy cows are likely to involve complex and tissue specific regulation of IGFs and IGFBPs within the uterus.

KEY WORDS: bST, uterus, gene, cattle