ABSTRACT
This review describes the oestrus-to-ovulation interval, the possibility of predicting the time of ovulation, and the optimum time for insemination relative to oestrus in dairy cows. The duration of oestrus in dairy cows is approximately 8-20 h, with differences possibly related to the methods of oestrus detection and the frequency of observations. Most cows ovulate approximately 24-33 h after the onset of oestrus and 15-22 h after the end of oestrus. The interval from the preovulatory luteinising hormone (LH) surge to ovulation is approximately 4-30 h. Ovulation occurs when follicle diameter averages 18-20 mm. When it is possible to correctly determine the beginning of oestrus, artificial insemination can be performed utilizing the "a.m.-p.m. rule", and only one insemination may be applied. In cows with too long or too short oestrus-to-ovulation intervals, fertility can be compromised. One important factor that can alter the oestrus-to-ovulation interval is acute or chronic heat stress during the warm season. When there is a risk that insemination may occur too early or too late with respect to the time of ovulation, GnRH administration can be considered.
ABSTRACT
Intestinal disorders can affect pigs of any age, especially when animals are young and more susceptible to infections and environmental stressors. For instance, pathogenic E. coli can alter intestinal functions, thus leading to altered nutrient adsorption by interacting with local cells through lipopolysaccharide (LPS). Among several compounds studied to counteract the negative effects on the intestine, short-chain fatty acids (SCFA) were demonstrated to exert beneficial effects on gut epithelial cells and resident immune cells. In this study, acetate and propionate were tested for their beneficial effects in a co-culture model of IPEC-J2 and porcine PBMC pre-stimulated with LPS from E. coli 0111:B4 aimed at mimicking the interaction between intestinal cells and immune cells in an inflammatory/activated status. IPEC-J2 viability was partially reduced when co-cultured with activated PBMC and nitric oxide concentration increased. IPEC-J2 up-regulated innate and inflammatory markers, namely BD-1, TLR-4, IL-8, TNF-α, NF-κB, and TGF-ß. Acetate and propionate positively modulated the inflammatory condition by sustaining cell viability, reducing the oxidative stress, and down-regulating the expression of inflammatory mediators. TNF-α expression and secretion showed an opposite effect in IPEC-J2 depending on the extent of LPS stimulation of PBMC and TGF-ß modulation. Therefore, SCFA proved to mediate a differential effect depending on the degree and duration of inflammation. The expression of the tight junction proteins (TJp) claudin-4 and zonula occludens-1 was up-regulated by LPS while SCFA influenced TJp with a different kinetics depending on PBMC stimulation. The co-culture model of IPEC-J2 and LPS-activated PBMC proved to be feasible to address the modulation of markers related to anti-bacterial immunity and inflammation, and intestinal epithelial barrier integrity, which are involved in the in vivo responsiveness and plasticity to infections.