Date Published: April 17, 2012
Publisher: BioMed Central
Author(s): Kristina Nordéus, Renée Båge, Hans Gustafsson, Patrice Humblot, Lennart Söderquist.
Declining fertility is a major concern for dairy farmers today. One explanation is shorter and weaker expression of oestrus in dairy cows making it difficult to determine optimal time for artificial insemination (AI). Chemical communication is of interest in the search for tools to detect oestrus or to synchronise or enhance oestrous periods. Pheromones, used in chemical communication within species, can influence reproduction in different ways. The aim here was to investigate whether oestrous cycle length, and duration and intensity of oestrous expression in dairy heifers could be manipulated through exposure to pheromones in oestrual substances from other females.
Beginning on day 16 of two consecutive control oestrous cycles, ten heifers of the Swedish Red Breed (SRB) were exposed to water. During the two following cycles the heifers were exposed to urine and vaginal mucus, obtained from cows in oestrus. Cyclicity parameters were monitored through hormone measurements, oestrus detection and ultrasonographic examination.
We found no difference in cycle length or in duration of standing oestrus between control and treatment. We did, however, find a tendency of interaction between type of exposure (control or treatment) and cycle number within type of exposure for cycle length (p = 0.068), with the length differing less between the treatment cycles. We also found a tendency of effect of type of exposure on maximal concentration (p = 0.073) and sum of concentrations (p = 0.063) of LH during the LH surge, with values being higher for the control cycles. There were also significant differences in when the different signs of oestrus occurred and in the intensity of oestrous expression. The score for oedema and hyperaemia of external genitalia was significantly higher (p = 0.004) for the control cycles and there was also a significant interaction between type of exposure and time period for restlessness (p = 0.011), with maximum score occurring earlier for treatment cycles.
No evidence of altered oestrous cycle length or duration of oestrus after exposure of females to oestrous substances from other females was found. Expression of oestrus, and maybe also LH secretion, however, seemed influenced by the exposure, with the effect of treatment being suppressive rather than enhancing.
Through breeding programs and improved management, the dairy cow milk yield has increased substantially since the 1950s. At the same time the dairy cow reproductive performance is deteriorating worldwide, which is partly attributable to the negative genetic correlation between milk yield and fertility . One explanation for the poor reproductive results may be that the expression of standing oestrus is growing weaker and shorter , resulting in faltering oestrus detection [3,4] and, consequently, poorly timed artificial insemination (AI). This decline in fertility brings substantial economic losses to farmers .
There is anecdotal evidence from farmers that cyclic animals grouped together tend to synchronise their oestrous cycles and the study of Izard and Vandenbergh  supports this. However, no study has ever provided indisputable proof of inter-female primer pheromones causing synchronisation of oestrous cycles in cattle. This could be because there is no such pheromone or because the complexity of large mammals makes it difficult to design and carry out the necessary experiments. In the present study, unique in that it was performed on animals in isolation, we found no effect of oestrous urine and vaginal mucus on the cycle length, neither when measured as the interval between LH surges nor as the interval between ovulations.
Exposing heifers to oestrous urine and vaginal mucus caused no effect on the length of the oestrous cycle. However, the length of the two treatment cycles was very similar, while it differed significantly between the two control cycles. We did also see an effect on the expression of oestrus, which may have been caused by an inter-female pheromone. Furthermore, a tendency for an effect on the maximal LH concentration and the sum of concentrations of LH during the preovulatory LH surge was seen, which further support our previous findings regarding the LH pulsatility pattern preceding the preovulatory LH surge . We believe that further studies, focusing on the LH secretion, on a larger number of animals would be of great interest for future research on bovine inter-female pheromones.
AI: Artificial insemination; ANOVA: Analysis of variance; CV: Coefficient of variation; GLM: General linear model; LH: Luteinising hormone; PGF2α: Prostaglandin F2α; RIA: Radioimmunoassay; SLU: Swedish University of Agricultural Sciences.
The authors declare that they have no competing interests.
KN participated in the design of the study, carried out all experimental procedures and drafted the manuscript. RB participated in the design of the study and helped to draft the manuscript. HG participated in the design of the study and helped to draft the manuscript. PH performed the statistical analyses, except for the oestrus scoring scale data, and commented on the manuscript. LS participated in the design of the experiment and helped to draft the manuscript. All authors read and approved the final version of the manuscript.