Veterinarija ir Zootechnika

The current study aimed to determine the reproductive performance and progesterone profile in East Friesian sheep after GnRH administration on day 4 post artificial insemination (AI). The experiment was carried out with 67 sheep subjected to estrus synchronization and artificial insemination. The animals were divided in two groups: I (control group, n = 30) and II (GnRH group, n = 37), treated by GnRH on day 4 after AI. Rams were introduced on day 12 and removed on day 20 after AI. Ultrasound pregnancy check was on days 20 and 60 after AI, and sheep were separated on the basis of their reproductive status (RS). Blood progesterone (P4) concentrations were measured by ELFA on days 4, 12 and 20 after AI, and a likehood for early embryonic mortality was estimated. The percentages of non-pregnant and pregnant sheep in both groups on day 20 were close; however, there were significantly (P < 0.05) more pregnant sheep in the GnRH group on day 60 compared with day 20. The investigated factors affected the P4 concentrations independently of each other. Analysis of the main effects of GnRH and RS showed a significant (P < 0.005) influence on the progesterone profile. The day after AI had a strong positive effect on the P4 concentration, with significant (P < 0.001) differences between mean P4 values measured during the different days. The estimated likehoods of early embryonic mortality (EEM) for both groups was 25.4%. In conclusion, GnRH injection on day 4 after artificial insemination and the introduction of ram on day 12 did not have a direct effect on the pregnancy rate, but led to improvement of the reproductive performance at the flock level. Gonadotropin releasing hormone treatment, reproductive status and day after AI affected the progesterone concentrations in East Friesian sheep irrespective of each other, and had a significant (P < 0.005) effect on the hormonal profile. The treatment by GnRH on day 4 after AI tended to reduce early embryo mortality, but future investigations are needed to clarify this effect.

Milkability is defined as the ability of an animal to give a regular, complete, and rapid milk secretion by the mammary gland in response to a proper milking technique. Indicators of milk production and milkability of ewes were determined in 359–370 ewes of 9 genotypes. For each ewe, the milk flow was recorded during the individual control measurements. The amount of milked milk was measured in individual time intervals after the attachment of milking cups to teats on udder of the ewe (10 indicators). We processed the obtained data using the REML methodology, with the MIXED procedure of the SAS statistical package. All indicators characterizing milk production and milkability of ewes were statistically significantly influenced by the genotype and the control year factors (p < 0.001). The order and stage of lactation were also significant factors in some cases. The machine milk yield of the monitored population of ewes was 318.26 mL on average. The total milk yield was 436.58 mL and the machine stripping ratio was 27.73% on average, ranging from 0 to 95%. The highest machine stripping ratio was determined in the Lacaune breed (37.69%), which had the highest total milk yield (524.69 mL) and one of the highest machine milk yield (332.70 mL). Compared with purebred Tsigai ewes and ewes of the Improved Valachian breed, crossbreeds with specialized dairy breeds (Lacaune and East Friesian) had better milk production and, in some indicators, also better milkability.