Effectiveness of intravaginal progesterone inserts and FSH for inducing synchronized estrus and increasing lambing rate in anestrous ewes

The objectives of this study were to determine whether a new progesterone ( P-4)-releasing intravaginal insert would induce fertile estrus and whether FSH combined with the insert would increase prolificacy in anestrous ewes i ntroduced to rams. Ewes of mixed breeding on six farms were assigned to fou r randomized; treatments: control (C), n = 73; 12 d P-4 (polycapralactone [ PCL] insert with 0.82 g P-4), (P12), n = 73; 12 d P-4 plus i.m. FSH (Folltr opin, 55 mg NIHFSH-PI equivalent) in propylene glycol, 24 h before insert r emoval, (P12F), n = 71; and 5 d P-4 plus FSH (P5F), n = 77. Growth and ovul ation of follicles were observed ultrasonographically in 20 ewes at four fa rms (five/treatment) at insert removal and 36, 48, 72, and 96 h later; Inta ct rams (1:15 ewes in multiple-sire groups) were joined at insert removal, and raddle marks were observed every 12 h for 5 d. On d 26 to 30, rams were removed; ewes were examined for pregnancy then and 20:d later. Percentage of ewes marked by rams was greater in P-4-treated (66 to 79%) than in C (12 %; P < 0.01) ewes and in P5F (79%) than in P12F (66%; P < 0.05). Diameters of largest follicles at insert removal were greater (P < 0.05) in P-4-treat ed (5.5 +/- 0.2) than in C ewes (4.8 +/- 0.2). Progesterone increased numbe rs of follicles > 3 mm (P < 0.01) or ovulated (P < 0.05; 2.6 +/- 0.6 vs 1.3 +/- 0.6 in C ewes) and FSH increased number of follicles > 3 mm (P < 0.05) . In FSH-treated ewes, ovulation rate tended to be greater after treatment with P-4 for 5 than for 12 d (P = 0.09, 3.3 +/- 0.6 and 2.2 +/- 0.4, respec tively). More P-4-treated than C eu es lambed (P < 0.01) to the first (38 t o 45 vs 0%) or both (63 to 66 vs 41%) service periods. Prolificacy (first; service) did not differ between FSH-treated ewes (P12F + P5F; 1.8 +/- 0.1) and ewes treated with P-4 only (P12; 1.6 +/- 0.1). However, FSH increased p rolificacy to first service (1.8 +/- 0.1) over prolificacy to second servic e (C ewes 1.5 +/- 0.1; P < 0.05, and all ewes 1.4 +/- 0.1; P < 0.01). Pregn ancy retention did not differ among treatments but was greater (P < 0.01) i n ewes that conceived at the first (90.9 +/- 3.7) than at the second (72.5 +/- 3.3) service period. In conclusion, a PCL insert in combination with ra m introduction at insert removal was more effective than ram introduction a lone to induce synchronized estrus and ovulation and to yield pregnancy aft er one or two service periods. Treatment with P-4 for 5 d was as effective as for 12 d to induce fertile estrus in FSH-treated anestrous ewes.