Effect of sire, age at first calving, season and year of calving and parity on reproductive performance of Friesian cows under semiarid conditions in Egypt.

SUMMARY The objective of this paper was to study some factors affecting reproductive performance of a locally-born Friesian herd in Egypt. Data of 2096 reproductive records representing 482 Friesian cows daughters of 38 sires raised at the Dairy Unit of Milk and Meat Project of Faculty of Agriculture, Alexandria University, Egypt (located at the northern western part of the Nile Delta) between 1985-2002 were utilized to study the effects of sire of the cow, age at first calving (AFC), season and year of calving/birth and parity on period from parturition to first service (FSP), days open (DO), calving interval (CI), number of services per conception (NSC), AFC and breeding efficiency (BE). The least squares mixed model analysis by SAS (1999) indicated that the overall least squares means (± standard error) of FSP, DO, CI, NSC, AFC and BE were 88.4 ± 1.1, 130.7 ± 1.9, 403.1 ± 1.9 days, 2.1 ± 0.1 services, 30.7 ± 0.1 months and 90.1 ± 0.6 %, respectively. Sire had highly significant (P<0.01) effect on DO, CI, NSC and AFC, but had insignificant effect on FSP and BE. The influence of AFC on FSP was highly significant (P<0.01) and not significant on DO CI, NSC and BE. Cows had AFC more than 36 months had the longest FSP (92.6±4.5) and cows had AFC less than 29 months of age had 87.8±2.7 days FSP. Season of calving had significant effect on FSP (P<0.01), DO and CI (P<0.05), but had insignificant effect on NSC. Season of birth had no significant effect on both AFC and BE. Cows calving in autumn had the shortest CI (394.3±4.7 days) comparing with those calved in other seasons (ranged between 404.8±6.5 and 409.4±5.2 days). Cows calving in autumn also had the shortest DO (122.6±4.8 days). Year of calving/birth had significant (P<0.05 or P<0.01) effect on all traits studied. A decreasing efficiency in reproductive performance of cows was observed over time. The shortest FSP and DO were in the period 1988 to 1990 (64.3±5.3 and 98.1±8.9 days, respectively) and the longest were in the period 2000 to 2002 (107.5±5.2 and 188.1±8.8 days, respectively). Calving interval increased from 371 days in [1988][1989][1990] to 450 days † Corresponding autho

Supplemental progesterone increases pregnancy rates and embryo survival in lactating dairy cows

Administering progesterone to lactating dairy cows has sometimes proven effective in increasing pregnancy rates. In this study, cows were treated with the Ovsynch protocol in addition to supplemental progesterone given for 7 days between the first gonadotropin- releasing hormone (GnRH) injection and the prostaglandin F2á (PGF2á) injection. Conception rates were greater in lactating Holstein dairy cows receiving exogenous progesterone (62.5%) than in controls treated with only the Ovsynch protocol (35.5%). In addition, progesterone supplementation increased embryo survival between 28 and 56 days of pregnancy

Pregnancy rates in dairy cattle after three different, timed, breeding protocols

Synchronizing ovulation enables dairy producers to inseminate cows by appointment rather than after detected estrus. Three different, timed artificial insemination protocols using different combinations of prostaglandin F2alpha and gonadotropin-releasing hormone were used to synchronize ovulation in 702 lactating Holstein cows. Cyclicity, pregnancy rate, and embryonic survival rate from each treatment were compared. Our results indicate that all three treatments produced acceptable pregnancy rates in first lactation cows. However, for cows in their second or greater lactation, the treatment using prostaglandin F2alpha 12 days before the Ovsynch protocol improved pregnancy rates more than the other two

Increasing pregnancy rates at first service in dairy cows exposed to high ambient temperatures before and after calving

Cows exposed to heat stress before or after calving or both are prone to reduced fertility because of reduced expression of estrus and less embryonic survival if pregnant. Cows calving on three dairy farms during the summer of 1998 were studied. First inseminations were programmed to occur between 50 and 70 days in milk using the Ovsynch protocol, which included a timed artificial insemination. Control cows were treated similarly but did not receive the second injection of gonadotropin-releasing hormone and were inseminated only after estrus was detected (Select Synch). The Ovsynch protocol increased pregnancy rates from 17.6 to 31.3%, because AI submission rates were 100% and conception rates were not different from those of control (Select Synch) cows