Can accelerometry and proximity loggers determine the onset of puberty in sheep? : a thesis presented in partial fulfilment of the requirements for the degree of Masters in Animal Science at Massey University, Palmerston North, New Zealand
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2024
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Massey University
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The global demand for sheep products has increased over the past decade, which presents both opportunities and challenges in sheep production. One strategy to enhance productivity is to mate ewes as lambs, reducing the generational interval and increasing the number of lambs weaned per year. However, this approach requires the accurate detection of puberty attainment, a crucial period marked by physiological and behavioural changes. Puberty can be defined as the first oestrus followed by elevated blood progesterone concentrations above 1.0 ng/mL. Traditional methods for detecting the first ovulatory oestrus of ewe lambs include teaser rams, hormonal analysis and ultrasound examinations. This thesis explored the potential of collar-mounted accelerometers as a novel, non-invasive method for detecting behavioural and activity changes associated with puberty in ewe lambs. Eight prepubertal ewe lambs (seven Dorset Down x Romney crosses and one Wiltshire x Romney cross) sourced as orphans or mismothered lambs from Massey University’s sheep farms were used for this study. The ewe lambs were fitted with ActiGraph® accelerometers and continuous (30 Hz) acceleration and proximity data were collected throughout the trial. Two teaser rams were alternated every 7 – 10 days within the flock. Live weight was recorded and blood samples were collected twice weekly. Ultrasound examinations were conducted weekly to measure follicular growth and the presence of a corpus luteum. Over the 73 day study period, multiple measures of puberty attainment were assessed, including serum progesterone and oestradiol concentrations, tupping data, proximity data, ultrasound examinations and activity data. Ewe lambs were removed from the study after receiving a Grade 3 tup mark or when the presence of a corpus luteum was confirmed. While hormonal analysis and ultrasound examinations were reliable methods for the accurate detection of puberty attainment in the ewe lambs, their high costs and the need for experienced professionals to perform them make them impractical for routine farm management. Tupping was not a reliable method for determining puberty attainment, as the ewe lambs were marked weeks before their first ovulation. The early tupping was likely associated with anovulatory prepubertal follicular growth. The results from this study revealed that as lambs approach puberty, there was an increase in the time spent in close proximity to the ram. This was likely related to oestrus and mating behaviours by the increase in oestradiol concentrations. There was also a consistent decline in the daily activity of the ewe lambs following their first ovulation, which was correlated with the development of their first CL and elevated progesterone concentration. Thus, these accelerometer devices show potential for the detection of a ewe lamb’s first ovulatory oestrus and subsequent luteal phase. However, further research is required to validate their reliability and accuracy for detecting the onset of puberty in ewe lambs.
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Figures 2.1 (=Bartlewski et al., 2011 Fig 2) and 2.2 (=Gonzalez-Bulnes et al., 2010 Fig 2) were removed for copyright reasons.