Threshold values of acoustic features to assess estrous cycle phases in water buffaloes (Bubalus bubalis)
Introduction
Water buffaloes contribute substantially to the economy of many countries in tropical and subtropical regions including Indian sub-continent, China, South-East Asia, South and Central America, Africa, Australia etc. Riverine buffalo (Bubalus bubalis) finds an important rank in livestock production system particularly in Indian economy in terms of milk (49%), meat (23%) and draught power (DAHD&F report, 2017-18). Due to rapid and large-scale commercialization in dairy sector, management is substantial. Due to large animal number and labor issues estrus detection has become cumbersome more particularly in buffaloes due to their silent estrus behavior. This is perhaps the most important factor leading to poor reproductive efficiency in these animals (Kanai and Shimizu, 1983; Madan and Prakash, 2007). Buffalo shows behavioral estrus signs mostly during cool hours of day, so there may be chances of ignorance of important estrus events in buffaloes as farmer/attendant are less active during night time (Reddy et al., 1999; El-Wardani and El-Asheeri, 2000) or extra labour should be employed for the night time. Single missed estrus could cost around Rupees 4000–4500 to farmers which includes cost of feeding, maintenance and losses from milk production for around 21 days (Srivastava et al., 2013). So, there is need of an automated and accurate system which may give some clues about estrus phase especially in large commercial farms where animals are more (>15-20) in number so that it becomes difficult to monitor individual animal.
In recent years, use of animal’s voice as a mean to express their state has attracted many researchers. Voice produced by animal is multidimensional and can be related to variety of behavioral and physiological signs including reproductive stage and status. A few studies have tried to describe vocalization subjectively (Laube et al., 1988; Liebenberg et al., 1977) and classify methodically (Ikeda and Ishii, 2001; Jahns et al., 1997). Some studies have tried to correlate voice articulated by animals with their various physiological expressions and states like dominancy (Koene, 1997), gender or age (Hall et al., 1988), class of animal (Hinch et al., 1982), individual identity (Blackshaw et al., 1996; Singh et al., 2013), need (Weary and Fraser, 1995), pain (Weary et al., 1998), isolation (Watts et al., 1998) and changes in vocal response owing to stress (Hudson and Mullord, 1977), but literature relating vocalization with respect to estrus phases is less, except a few that have tried to relate changes in vocal behavioral expression with estrus phase (Chung et al., 2013; Dreschel et al., 2014; Schon et al., 2007; Yeon et al., 2006) in dairy animals. As only frequency of bellowing can’t be relied upon in buffaloes for estrus detection, so attention may be paid on other acoustic features of vocal signals which are altered during estrous cycle. It is hypothesized that along with other factors reproductive hormones elicit hormone dependent morphological changes in organs responsible for voice production, like vocal cords (Gerritsma et al., 1994) and larynx, tissues known to contain receptors for sex steroids (Newman et al., 2000; Schneider et al., 2007; Voelter et al., 2008). Besides being non-invasive and easy to handle, bioacoustics technique/tools can be used to detect estrus both economically and accurately (Chung et al., 2013; Hamel, 2009; Lee et al., 2014). The aim of present study was to find out threshold values or cut off points of various acoustic features which may be utilized in developing algorithms to differentiate different phases of estrous cycle in order to identify estrus phase at right time in water buffaloes.
Section snippets
Location of study
Location of experiment was Livestock Research Centre (LRC) of Indian Council of Agricultural Research (ICAR’s) deemed university - National Dairy Research Institute, Karnal, Haryana, India (MSL-253 m; 29.69 °N latitude; and 76.99 °E longitude). The mean annual rainfall is about 860 mm, most of which is received during monsoon season (June and August). Relative humidity ranges from 41 to 85 percent. Karnal has a sub-tropical climate and experiences extremes of temperature in winter (2℃) and
Mean values of voice acoustic features during estrous cycle in Murrah buffaloes
The data extracted for various bioacoustics features from voice samples were subjected to least squares analysis in order to examine the significant differences during four phases of estrous cycle because comparable alterations in voice parameters occur in response to physiological changes (Watts and Stookey, 2000; Manteuffel et al., 2004) and hormonal changes (Schneider et al., 2007; Bryant and Haselton, 2009) in animals. The least squares mean values for various acoustic features during
Discussion
Along with other factors, reproductive hormones elicit hormone dependent morphological changes in vocal cords (Gerritsma et al., 1994) and larynx, tissues known to contain receptors for sex steroids (Newman et al., 2000; Schneider et al., 2007; Voelter et al., 2008) and thereby influencing changes in acoustic parameters (Yeon et al., 2006). Mean Call duration (sec.) and average mean intensity (dB) of vocal signals during estrus phase was significantly (p < 0.05) longer than other phases. During
Conclusions
The acoustic features viz. call duration (sec.); mean intensity (dB); formants (Hz): F1, F2, F3, F4, F5; mean pitch (Hz) and mean noise to harmonic ratio (%) from vocalizations of water buffaloes can effectively be used for discrimination of estrus phase from other phases of estrous cycle i.e. proestrus, metestrus and diestrus phase. Moreover, calculation/estimation of threshold values for these features may enhance their efficacy of differentiation and may further be utilized in developing
Declaration of Competing Interest
We have no conflicts of interest to disclose regarding this study.
Acknowledgements
The authors gratefully acknowledge the facilities and financial support from ICAR-National Dairy Research Institute, Karnal, Haryana, India, for carrying out this research work for Ph.D. thesis.
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