title: Reproductive responses to daily injections with porcine somatotropin before mating in gilts.
abstract: Litter size and progeny birth weights are lower in gilts than in sows. Somatotropin (ST) is an important regulator of ovulation, fetal growth and survival. We therefore investigated effects of pST treatment of gilts for two to four weeks before mating on ovulation rate, behavioural estrus, fetal growth and survival, litter size and birth weights. In Experiment One, gilts were injected with 0, 30, 60 or 90 µg pST/kg/day for 14 days commencing 7 days after first estrus. Reproductive tracts were collected and corpora lutea and follicle numbers counted 5.5 days after second estrus. Ovulation rate (P=0.031) and number of medium-sized follicles (P=0.059) correlated positively with pST dose. In Experiment Two, gilts were injected with 0, 12.5, 25 or 50 µg pST/kg/day for 21 days from first estrus, and mated at second estrus. Numbers of corpora lutea, follicles and fetuses were counted at day 31 of pregnancy. Numbers of medium follicles and ovary weights were positively related to pST dose. In Experiment Three, 31 week old (1(st) replicate) or 27 week old (2(nd) replicate) gilts were injected daily with 0 or 12.5 µg pST/kg/day until mating 25.9 ± 0.6 days later, and delivered at term. Pre-mating pST increased total litter size in younger gilts in the 2(nd) replicate only (P<0.05). In conclusion, injecting gilts with pST before mating does not consistently alter ovulation rate, increases the number of medium follicles available for recruitment at the second mating after treatment and increases subsequent litter size in younger gilts.
authors.affiliation: Discipline of Obstetrics and Gynaecology, School of Paediatrics and Reproductive Health, University of Adelaide, SA.
authors.forename: Kathryn L
authors.initials: KL
authors.lastname: GATFORD
authors.forename: Christopher G
authors.initials: CG
authors.lastname: GRUPEN
authors.forename: Roger G
authors.initials: RG
authors.lastname: CAMPBELL
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Luxford
authors.forename: Robert J
authors.initials: RJ
authors.lastname: SMITS
authors.forename: Phillip C
authors.initials: PC
authors.lastname: OWENS
authors.forename: Mark B
authors.initials: MB
authors.lastname: NOTTLE
mesh_terms: D000818:Animals; D004971:Estrus / Q000502:physiology; D005260:Female; D013006:Growth Hormone / Q000494:pharmacology*; D008098:Litter Size / Q000187:drug effects / Q000502:physiology; D008297:Male; D006080:Ovarian Follicle / Q000187:drug effects / Q000254:growth & development / Q000502:physiology; D010060:Ovulation / Q000187:drug effects* / Q000502:physiology; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000187:drug effects* / Q000502:physiology; D012098:Reproduction / Q000187:drug effects* / Q000502:physiology; D034421:Sus scrofa / Q000502:physiology*
chemical_list: D013006:Growth Hormone