Study of the Effect of some environmental factors on Reproductive Traits of Friesian Cows in Libya

Abstract

This study aims to analyze the effect of milk production levels and other environmental factors represented by years and seasons on lactation length, calving interval, days open, number of Service per conception, and fertility rate. Data were collected from 1199 production and reproduction records of Friesian cows at the dairy cattle station of the Al-Nasr Production Project, spanning the period from 1999 to 2004. Records were divided into four groups based on milk production level, with groups defined according to total milk yield: Level 1 low production (less than 2500 kg), Level 2 medium production (2500-4000 kg), Level 3 high production (4000-5500 kg), and Level 4 very high production (more than 5500 kg). The effect of these levels, as well as the influence of year and season differences, on the mentioned traits was analyzed. The results showed that the overall means for total milk production, lactation length, calving interval, days open, number of Service per conception, and fertility rate were 4883.76±47.75 kg, 337.52±2.94 days, 442.74±3.31 days, 160.7±2.71 days, 2.04±0.05 inseminations, and 71.94±1.04% respectively. Analysis of variance results also indicated that differences in years and milk production level had a highly significant effect (P<0.05) on all studied traits; however, differences in seasons had a significant effect only on days open. Furthermore, a positive correlation was observed between milk production and lactation length, while a clear negative relationship existed between milk production and reproductive parameters, implying that increased production may lead to deterioration in reproductive efficiency. Therefore, the study recommends improving feeding programs, enhancing early estrus detection, determining optimal insemination timing, and regularly monitoring cow health.