Effect of Presence or Absence of Corpora Lutea on Milk Production in East Friesian Dairy Ewes

¹ Department of Animal Sciences, University of Wisconsin, Madison 53706
² Department Dairy Science, University of Wisconsin, Madison 53706
³ Institut National de la Recherche Agronomique, UMR production du lait 35042 Rennes, France

The potential luteal effects on milk production were examined in dairy ewes that were not superovulated in contrast to studies using superovulated ewes. Lactating East Friesian crossbred ewes (n = 24) were synchronized using intravaginal progesterone (controlled intravaginal drug-releasing device), PGF₂, and gonadotropins. After ovulation, corpora lutea (CL) were counted via laparoscopy on d 4 and 11. On d 5, ewes received either saline (CLYES, n = 12) or PGF_2alpha; (CLNO, n = 12) to allow CL persistence (2.4 ± 0.3 CL on d 11) or regression (0 CL on d 11), respectively. Each ewe received two CIDR d 5 to 18 to maintain high concentrations of plasma progesterone (P₄) and to suppress estradiol (E₂). Each ewe received PGF₂ on d 18. Data were collected during three periods (pretreatment: d 0 to 5; treatment: d 6 to 18; posttreatment: d 19 to 25). Milk yield and milking time were recorded daily, milk samples were obtained for analyses of fat and protein, and blood samples were collected for P₄ and E₂ immunoassay. During treatment, CLYES ewes had higher milk yield (1.56 vs. 1.44 ± 0.01 kg/d), milk fat (92.2 vs. 81.1 ± 1.3 g/d), and milk protein (83.7 vs. 77.5 ± 0.8 g/d) compared with CLNO ewes, respectively. Differences were maintained posttreatment, despite luteolysis in CLYES ewes. Estradiol concentrations did not differ between treatments and were low after d 5. Milk production was increased in East Friesian ewes in the presence of an average of 2.4 corpora lutea, an effect independent of estradiol.

Key Words: corpus luteum • East Friesian • estradiol • milk yield

Submitted on August 16, 2001
Accepted on November 19, 2001

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